1521-0081/72/4/829–861$35.00 https://doi.org/10.1124/pr.120.

019398
PHARMACOLOGICAL REVIEWS Pharmacol Rev 72:829–861, October 2020
Copyright © 2020 by The Author(s)
This is an open access article distributed under the CC BY-NC Attribution 4.0 International license.

ASSOCIATE EDITOR: ROBERT DANTZER

Is Oxytocin “Nature’s Medicine”?

C. Sue Carter, William M. Kenkel, Evan L. MacLean, Steven R. Wilson, Allison M. Perkeybile, Jason R. Yee, Craig F. Ferris,
Hossein P. Nazarloo, Stephen W. Porges, John M. Davis, Jessica J. Connelly, and Marcy A. Kingsbury
Kinsey Institute, Indiana University, Bloomington, Indiana (C.S.C., W.M.K., A.M.P., H.P.N., S.W.P.); School of Anthropology, Department
of Psychology, and College of Veterinary Medicine, University of Arizona, Tucson, Arizona (E.L.M.); Department of Chemistry, University of
Oslo, Oslo, Norway (S.R.W.); Institute of Animal Welfare Science, University of Veterinary Medicine, Vienna, Austria (J.R.Y.); Departments
of Psychology and Pharmaceutical Sciences, Northeastern University, Boston, Massachusetts (C.F.F.); Department of Psychiatry, University
of Illinois at Chicago, Chicago, Illinois (J.M.D.); Department of Psychology, University of Virginia, Charlottesville, Virginia (J.J.C.); and
Department of Pediatrics, Massachusetts General Hospital and Harvard Medical School, Charleston, Massachusetts (M.A.K.)

Abstract. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
Significance Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
I. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
II. Overview and Challenges. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 831
A. Oxytocin and Vasopressin: an Integrated System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 832
III. Discovery of Oxytocin and Vasopressin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833

Downloaded from by guest on September 12, 2020

IV. Evolution as an Organizing Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 833
V. Oxytocin-Like Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
VI. Precursors and Fragments of Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
A. Precursors and Extended Forms of Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
B. Fragments of Oxytocin May Be Biologically Active . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 835
VII. Processes Regulating Oxytocin and Vasopressin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
A. Oxytocin and Vasopressin Are an Integrated System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
B. The Structure of These Peptides Identifies Some of the Challenges They Present . . . . . . 836
C. Feedback Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
D. Patterns of Peptide Release Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 836
E. Individual Differences Are to Be Expected . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
F. Effects of Other Molecules on the Oxytocin-Vasopressin System . . . . . . . . . . . . . . . . . . . . . . . 837
VIII. Measurement of Oxytocin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
A. Oxytocin Is Difficult to Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
B. Controversy Was Generated by Divergent Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 837
C. Disulfide Bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
D. Salivary Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
E. Can Endogenous Hormone Levels in Bodily Fluids Be Useful in Predicting
Responses to Exogenous Oxytocin Treatments? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
F. Exogenous Peptides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 838
G. Other Measures May Index Receptor Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
IX. Receptors for Oxytocin and Vasopressin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
A. The Oxytocin Receptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
B. Measuring the Oxytocin Receptor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
C. Vasopressin Receptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
D. Receptor Distributions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
X. Subcellular Signaling Specifies the Functions of Oxytocin and Vasopressin . . . . . . . . . . . . . . . . 840
XI. Genetics and Epigenetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840
XII. Early Experience and Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840

Address correspondence to: C. Sue Carter, 428 Lindley Hall, Indiana University, Bloomington, IN 47405. E-mail: suecarterporges@
gmail.com
This work was supported by the Eunice Kennedy Shriver National Institute of Child Health and Human Development of National Institutes
of Health [Grants F32-HD092051, R21-HD095217, R01-HD098117, and P01-HD075750]. The content is solely the responsibility of the authors
and does not necessarily represent the official views of the National Institutes of Health.
https://doi.org/10.1124/pr.120.019398.

829
830 Carter et al.

A. Emotional Context Matters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 840

B. Adversity Versus High Nurture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
C. Vasopressin Systems as Likely Targets for Adversity and Stress in Early Life . . . . . . . . . 841
D. Early Exposure to Peptides May Modulate Perceived Context . . . . . . . . . . . . . . . . . . . . . . . . . 841
E. Birth and Epigenetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 841
XIII. The Autonomic Nervous System as a Target for Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
A. Neural and Peptide Interactions Allow a Wide Range of Adaptive Responses . . . . . . . . . . 842
B. The Autonomic Nervous System Consists of Sympathetic and Parasympathetic
Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
C. The Polyvagal Hypothesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 842
D. The Hypothalamus as a Site for Coordination of Vagal-Peptide Interactions . . . . . . . . . . . 842
E. Social Communication and Myelinated Ventral-Vagal Pathways . . . . . . . . . . . . . . . . . . . . . . . 842
F. Cortical Integration of Peptide-Autonomic Interactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
XIV. Oxytocin and “Stress Coping” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
A. Acute Stress Responses. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
B. Chronic or Traumatic Stress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
C. Myelinated Ventral-Vagal Pathways and Passive Coping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 843
XV. Immunologic and Anti-Inflammatory Effects of Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
A. Oxytocin and Neuroinflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
B. Early Experience and Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
C. Microglia and Macrophage. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 844
D. Oxytocin Protects against Inflammation Associated with Birth . . . . . . . . . . . . . . . . . . . . . . . . 846
E. Oxytocin, Oxidative Stress, and Mitochondria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846
F. Oxytocin and Gastrointestinal Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
G. Oxytocin Is Protective to the Developing Gut . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
H. Oxytocin and Breast Milk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 847
I. Oxytocin and the Healing of Damaged Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
J. Oxytocin and Developmentally Induced Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 848
K. Oxytocin, CD38, Immune Function, and Social Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
L. Oxytocin Regulates Probiotic Bacteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
M. Vasopressin and Inflammation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
N. Sex Differences in the Immune System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 849
XVI. Sex Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
A. Sex Differences in Vasopressin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
B. Developmental Effects of Oxytocin and Vasopressin Are Often Sexually Dimorphic . . . . 850
C. Sex Differences in Response to Stress and Trauma. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
D. Sex Differences in Strategies Used to Manage Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 850
E. Females and Vasopressin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
F. Sex Differences in Response to Exogenous Peptides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
G. The Stress of Birth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
H. Gonadal Steroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
XVII. Implications for Oxytocin in Mental and Physical Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
A. Social Support and Perceived Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
B. Oxytocin in Psychologic Functioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 851
XVIII. Examples of the Complexity Encountered in Treating Disease with Oxytocin-Like Drugs . . . 852
A. Postpartum Depression. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 852
B. Oxytocin and Cancer: a Complex Relationship . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
XIX. Pharmacology and Oxytocin: Issues in Therapeutic Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
A. The Effects of Oxytocin Are Dose-Dependent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853

ABBREVIATIONS: AVP, arginine vasopressin; AVPR, AVP receptor; cADPR, cyclic ADP-ribose; CNS, central nervous system; CRH, cor-
ticotropin-releasing hormone; DMX, dorsal motor nucleus of the vagus; Ga, guanine nucleotide–binding protein-a; GPCR, G-protein–coupled
receptor; HPA, hypothalamic-pituitary-adrenal; IL, interleukin; iNOS, inducible nitric oxide synthase; IRAP, insulin-regulated aminopepti-
dase; LPS, lipopolysaccharide; MIF-1, melanocyte-inhibiting factor-1; MOR, m-opioid receptor; MS, mass spectrometry; NF-kB, nuclear factor-
kB; OT-X, precursor or extended forms of oxytocin; OXT, oxytocin; OXTR, OXT receptor; PVN, paraventricular nucleus; RAGE, receptor
for advanced glycation end products; TNF-a, tumor necrosis factor-a; UPR, unfolded protein response; UPRER, UPR in the endoplasmic
reticulum.
 Oxytocin As Medicine 831

B. Individual and Sex Differences Are to Be Expected in Both the Production of and
Response to Oxytocin. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
C. The Basic Biochemistry of Oxytocin, Including Its Capacity to Bond to Other
Molecules, Creates Special Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 853
XX. Methods for Administering Oxytocin or Stimulating the Oxytocin System. . . . . . . . . . . . . . . . . . 854
A. Does Peripherally Administered Oxytocin Reach the Brain? . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
B. Placental Transport of Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
C. Oral Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 854
D. Increasing the Bioavailability of Oxytocin . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
XXI. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 855

Abstract——Oxytocin is a pleiotropic, peptide hor- more ancient peptide molecule, vasopressin, and
mone with broad implications for general health, ad- the vasopressin receptors. In addition, oxytocin
aptation, development, reproduction, and social behavior. receptor(s) are epigenetically tuned by experience,
Endogenous oxytocin and stimulation of the oxytocin especially in early life. Stimulation of G-protein–coupled
receptor support patterns of growth, resilience, and receptors triggers subcellular cascades allowing
healing. Oxytocin can function as a stress-coping these neuropeptides to have multiple functions. The
molecule, an anti-inflammatory, and an antioxidant, adaptive properties of oxytocin make this ancient
with protective effects especially in the face of adversity molecule of special importance to human evolution
or trauma. Oxytocin influences the autonomic nervous as well as modern medicine and health; these same
system and the immune system. These properties of characteristics also present challenges to the use of
oxytocin may help explain the benefits of positive social oxytocin-like molecules as drugs that are only now
experiences and have drawn attention to this molecule as being recognized.
a possible therapeutic in a host of disorders. However, as
detailed here, the unique chemical properties of oxytocin, Significance Statement——Oxytocin is an ancient
including active disulfide bonds, and its capacity to shift molecule with a major role in mammalian behavior
chemical forms and bind to other molecules make and health. Although oxytocin has the capacity to act
this molecule difficult to work with and to measure. as a “natural medicine” protecting against stress
The effects of oxytocin also are context-dependent, and illness, the unique characteristics of the oxytocin
sexually dimorphic, and altered by experience. molecule and its receptors and its relationship to a re-
In part, this is because many of the actions of lated hormone, vasopressin, have created challenges
oxytocin rely on its capacity to interact with the for its use as a therapeutic drug.

I. Introduction post-traumatic stress disorders, borderline personal-

ity, addiction, pain, metabolic and digestive disorders,
Oxytocin was the first peptide hormone to be
diabetes, cardiovascular diseases, cancer, and infec-
biochemically described and synthesized. This com-
tious diseases (to name only a few) (Hurlemann and
paratively simple nine–amino acid molecule has been
Grinevich, 2018). Our intent is not to duplicate the
called the “best understood neuropeptide” (Jurek and
massive literature in this field. Rather, from this
Neumann, 2018). There is abundant evidence for
literature we have attempted to extract basic mecha-
diverse functions and health benefits for the molecule
nisms of action of the endogenous oxytocin system and
known as oxytocin. Here we examine the hypothesis
to highlight gaps in knowledge. Awareness of the basic
that oxytocin and oxytocin-like molecules are compo- biology of oxytocin actions can help guide the future
nents of a “natural medicine” capable of both prevent- development of drugs based on this system as well as
ing and treating various disorders and influencing behavioral interventions for regulating the production
a broad range of diseases. and release of endogenous peptides.
As background for the current review, it is helpful to
recall that the word “medicine” is commonly used in at
least two ways, including “the science or practice of the II. Overview and Challenges
diagnosis, prevention and treatment of disease” or a “com- In June of 2020, a Pubmed search for “oxytocin”
pound or drug used for the prevention or treatment of yielded over 27,700 articles, most of which were
disease.” This review addresses the potential of both published within the last two decades. Among these
endogenous and exogenous oxytocin to serve as medicine articles are thousands of empirical studies and hun-
in both senses of the word. dreds of recent reviews (Grinevich et al., 2016; Carter,
Oxytocin has been tested in the treatment of 2017; Carter and Perkeybile, 2018; Hurlemann and
conditions as apparently diverse as autism spectrum Grinevich, 2018; Jurek and Neumann, 2018), with
disorders, schizophrenia, postpartum depression, anxiety, many examining the therapeutic properties of oxytocin
832 Carter et al.

or oxytocin-like molecules for physical and behavioral peptide receptors in the nervous system influence the
disorders. In theory, with so much information it should entire body but also often differ in abundance and
have been easy to create effective drugs based on the localization among individuals and species (Witt et al.,
oxytocin system. However, as summarized here, attempts 1991; Freeman and Young, 2016; Freeman et al., 2018).
to use oxytocin or oxytocin-like molecules as drugs have Of particular importance to oxytocin’s capacity to
faced a variety of obstacles. promote health and influence behavior is the growing
evidence for actions of oxytocin throughout the immune
A. Oxytocin and Vasopressin: an Integrated System system and its major role as an anti-inflammatory and
As summarized below, at least part of the confusion antioxidant (Szeto et al., 2011; Bordt et al., 2019;
associated with understanding oxytocin arises be- Kingsbury and Bilbo, 2019). Effects on immunity and
cause this molecule is a component of an ancient and inflammation suggest another source of apparently
evolved system that includes the related peptide, “non-specific” effects of oxytocin. Components of the
vasopressin, and its receptors (Carter, 2014, 2017; immune system also control the production (CD38)
Carter and Perkeybile, 2018) (Fig. 1; Table 1). Aware- and act as a binding protein regulating the capacity
ness of the characteristics of oxytocin-vasopressin of oxytocin to cross membranes (Yamamoto and Higashida,
interactions is necessary to address the challenges 2020).
associated with creating therapeutics based on this The oxytocin-vasopressin system is “plastic,” and its
system. The oxytocin-vasopressin system interacts receptors are sensitive to epigenetic modification across
with the hypothalamic-pituitary-adrenal (HPA) axis the lifespan, but especially in early life (Kenkel et al.,
as well as acetylcholine, GABA, glutamate, opioids, 2019; Perkeybile et al., 2019). Functions of this system
cannabinoids, catecholamines, indoleamines, and ste- are context-dependent and changed by experience,
roids (Hurlemann and Grinevich, 2018; Jurek and including a history of stress and trauma (Fig. 2).
Neumann, 2018). Although they are beyond the scope Furthermore, there is evidence, especially in the face
of this review, these interactions have broad func- of psychologic or physical challenges, that males and
tional consequences that can affect the usefulness of females may differ in their response to oxytocin and
oxytocin-based molecules as “drugs.” vasopressin (Carter and Perkeybile, 2018; Jirikowski
Oxytocin and vasopressin have acute and lasting et al., 2018).
effects on both the central (Carter, 2014) and autonomic Taken together these factors help to explain why
nervous system (Porges, 2012; Quintana et al., 2019). responses to oxytocin-vasopressin pathways may vary
This, in turn, creates another source of complexity, since among species, among individuals, and by sex. To truly

Fig. 1. The descent of the neuropeptide ligand and receptor systems through evolutionary time, adapted from Grinevich et al. (2016). Beginning
approximately 700 million years ago (MYA), the ancestral peptide and its receptor predate mammals and indeed vertebrates. Both peptide and
receptor underwent two rounds of genome duplication approximately 550 MYA. These systems eventually consisted of mesotocin (MS), the mesotocin
receptor (MSR), vasotocin (VT), and three vasotocin receptors (VTRs). At the emergence of mammals approximately 200 MYA, the vasotocin peptide
and receptor evolved into their modern forms, consisting of AVP and its three receptors (AVPR1A, AVPR1B, and AVPR2). Modern mammalian
oxytocin (OXT) and its receptor (OXTR) first evolved approximately 100 MYA.
 Oxytocin As Medicine 833
TABLE 1
Comparative adaptive functions of vasopressin and oxytocin
Individual and species differences are commonly observed. These differences are adaptive and context-dependent. Early life experiences can epigenetically tune these
systems (see text and Fig. 3).

Hypothesized Functions Vasopressin – or AVPR Activation Oxytocin – or OXTR Activation

Life history strategies and reproductive More primitive – faster More modern – slower
investment Lower parental investment and more Greater parental investment and fewer
offspring offspring
Responses to challenges defense strategies Mobilization (fight-flight) Immobilization without fear
Amplifying stress and fear Stress coping and resilience
Reduced cooperation Social cooperation
Mobilization Activation Approach
Reactive aggression Positive social behaviors
Immobility with fear Immobilization without fear
Freezing or subordination? Parental and sexual behavior
Anxiety Anxiogenic Anxiolytic
Mild stress Release of vasopressin Inhibition of oxytocin?
Extreme acute stress Release of vasopressin Release of oxytocin
Chronic stress Release of vasopressin? Inhibition (males?); release of oxytocin
(females)
Autonomic nervous systema Sympathoadrenal Parasympathetic (vagalb)
Inflammation Proinflammatory (primarily) Anti-inflammatory
Pain Increasing or reducing? Prevention or reducing
a
Interactions between AVP and OXT and the autonomic nervous system support flexibility in behavioral, emotional states and allow different strategies for dealing with
challenges with effects that may differ between males and females.
b
The vagus nerve has more than one branch arising from different source nuclei in the brainstem. The more modern branch arises in the ventral-vagal complex and
supports social behaviors and features that are unique to mammals, such as facial expression, social engagement, and language. The more primitive branch arises in DMX
(i.e., 10th cranial nerve) and is associated with conservation of energy in response to extreme stressors or trauma (Porges, 2011).

appreciate oxytocin’s potential as a medicine for a broad with no known consequences for males may have slowed
range of human disorders, it is useful to recognize these initial interest in this molecule.
sources of diversity and to briefly review the history of Studies by de Wied in the 1970s (Kovacs et al., 1979)
knowledge in this field and the evolution of the oxytocin- showed that learning behavior, especially active avoid-
vasopressin system. ance, could be affected by oxytocin and vasopressin. In
1979, Pedersen and Prange (1979) demonstrated the
ability of oxytocin to facilitate maternal behavior in
III. Discovery of Oxytocin and Vasopressin
reproductively naïve female rats. In the 1980s, Keverne
The pressor function of the pituitary gland was and Kendrick (Kendrick et al., 1987) showed that
discovered in the late 19th century. In the early 1900s, maternal bonding in sheep also depended on oxytocin.
it was shown that pituitary gland extracts could be used A decade later, our own research using the highly social
to induce uterine contractions (Dale, 1906), and that prairie vole revealed a role for oxytocin in adult social
milk ejection could be stimulated by pituitary extracts behaviors (Witt et al., 1990) in the formation of adult
(Mackenzie, 1911). In 1928, Ernst and Berta Scharrer social bonds in both sexes (Williams et al., 1994) and
identified the largest cells in the hypothalamus, showed for the first time that prairie voles had a novel
calling these the “magnocellular neurons” (Scharrer pattern of distribution of the oxytocin receptors (Witt
and Scharrer, 1939). However, the behaviorally active et al., 1991). Since that time, socially monogamous
chemicals that were secreted by the magnocellular voles, with many behavioral and physiologic parallels
neurons were not identified until Vincent du Vigneaud to humans, have become particularly useful for the
synthesized oxytocin in 1953 (du Vigneaud et al., analysis of the neural, genetic, and epigenetic actions of
1954) and vasopressin in 1954 (du Vigneaud et al., oxytocin and its receptors (Gobrogge and Wang, 2016;
1958). Du Vigneaud received the 1955 Nobel Prize in Carter and Perkeybile, 2018; Perkeybile et al., 2019).
Chemistry for the “first synthesis of a polypeptide
hormone.” His Nobel lecture titled “A Trail of Sulfa
IV. Evolution as an Organizing Concept
Research: From Insulin to Oxytocin” set the stage for
the understanding that physiologically active hor- Understanding the functional versatility of oxytocin
mones were produced not just in the pituitary or requires recognition of the long evolutionary history of
peripheral endocrine organs but also in the nervous the genes that code for vasopressin, oxytocin, and their
system. The field of neuroendocrinology arose in part receptors. More than 600 million years ago, oxytocin-
from these discoveries. However, early investigations vasopressin–like molecules appeared in the shared
focused on oxytocin as a “female reproductive hormone” ancestors of modern vertebrates and invertebrates
that was involved mainly in birth and lactation. The (Acher et al., 1995; Knobloch and Grinevich, 2014).
mistaken notion that oxytocin was only important to one Vertebrates emerged approximately 500 million years
sex (female) and in one context (female reproduction) ago. The signaling properties of the class of molecules
834 Carter et al.

Fig. 2. Processing of the oxytocin molecule and its targets. After conversion from the prohormone form, oxytocin exists in an extended form with three
extra amino acids. The conversion from extended OXT to oxytocin consisting of nine amino acids occurs with maturation of the hypothalamus in
neurotypical individuals. It is not known how this extended form interacts with receptors. In their canonical nine–amino acid forms, both oxytocin and
vasopressin bind and act as agonists to both OXTR and AVPR1A, although oxytocin has a higher affinity for OXTR than the AVPR1A, as denoted by
the thicker arrow. Oxytocin also acts as an agonist to the pain-sensing transient receptor potential vanilloid-1 (TRPV1) receptor and as a positive
allosteric modulator at the MOR. After degradation by IRAP, the C-terminal tail is cleaved from oxytocin to form MIF-1, which can both inhibit MOR
and act as an allosteric modulator on the D2 subtype of dopamine receptors (D2R). Oxytocin can also be degraded by other as of yet unspecified
peptidase activity into a linear form that stimulates activity of the a-2 type adrenoreceptors (a2ARs). Conventional arrow = agonist; circle-tipped arrow
= positive allosteric modulator; block-tipped arrow = antagonist.

to which the oxytocin and vasopressin receptors belong arose through duplication from a common ancestral
appeared in this period, and the genes for these receptors molecule presumed to be vasotocin (Acher et al., 1995;
are associated with behavioral phenotypes that are con- Goodson, 2013). The vasopressin gene currently found in
sistent among divergent species (Yamashita and Kitano, vertebrates appeared over 200 million years ago, and the
2013). oxytocin gene appeared over 100 million years ago
It is interesting to note that aspects of the behavioral (Knobloch and Grinevich, 2014; Grinevich et al., 2016).
patterns elicited by oxytocin-like peptides in modern- It is estimated that mammalian evolution began around
day nematodes appear remarkably similar to those 200 million years ago. Three separate modern receptors
found in mammals, suggesting that these peptides are for arginine vasopressin (AVP) [AVP receptor (AVPR)
both genetically and functionally conserved (Lockard 1A, AVPR1B, and AVPR2] and the receptor for oxytocin
et al., 2017). Even in nematodes, oxytocin-like mole- (OXTR) evolved during the period of mammalian global
cules regulate a series of behavioral patterns and social radiation and expansion (Fig. 1) (Ocampo Daza et al.,
interactions necessary for successful mating (Garrison 2012). The original genes responsible for oxytocin- and
et al., 2012). Moreover, the peptide-stimulated behav- vasopressin-like peptides and their receptors are associ-
iors described in nematodes appeared strikingly similar ated with the evolution of behavioral adaptations in
to those seen in vertebrates. modern mammals, including lactation and maternal
Vasopressin is more ancient than oxytocin, and vaso- behavior.
pressin receptors are sensitive to and regulated by both Evolutionarily, more modern functions, including
peptides (Carter, 2017). Both oxytocin and vasopressin social behavior patterns and reproductive strategies
 Oxytocin As Medicine 835

found in mammals, may be especially dependent on the challenges (Neumann and Slattery, 2016) possibly
effects of oxytocin or related molecules on the oxytocin facilitating coping.
receptor rather than through actions on the vasopres- Early work on oxytocin and vasopressin suggested
sin receptor (Table 1). Among these is the uniquely that high concentrations of the receptors for these
mammalian function of milk ejection (Caldwell, 2017). peptides were located in brain regions that were distant
Behaviors associated with selective social memories, from the source nuclei. This led to the hypothesis that
high levels of sociality, and social reward necessary for within the nervous system, oxytocin and vasopressin
mammalian as well as avian parenting emerged in were transported by passive diffusion or “volume trans-
conjunction with the evolutionary appearance of the mission” (Landgraf and Neumann, 2004). More recently,
oxytocin receptor (Goodson et al., 2012; Kelly and fine peptide-containing processes have been described
Goodson, 2014). Taken together, the appearance of throughout the nervous system; these findings support
oxytocin and its receptor set the stage for human the hypothesis that the peptides are released locally, but
evolution (Carter, 2014). peptide also is detected within fibers that reach some
distance from the cells of origin (Grinevich et al., 2016;
Chini et al., 2017).
V. Oxytocin-Like Molecules
Oxytocin and vasopressin are small peptides with VI. Precursors and Fragments of Oxytocin
similar chemical structures (Fig. 2). Classic vertebrate
versions of these peptides consist of nine amino acids in A. Precursors and Extended Forms of Oxytocin
a six–amino acid ring formed by cysteine bonds and Precursors, from which the nine–amino acid form of
a three–amino acid tail with a terminal amine. Vaso- oxytocin is produced, have been shown to be biologically
pressin differs in structure from oxytocin by two amino active. The precursors or extended forms of oxytocin,
acids. Both oxytocin and vasopressin are synthesized sometimes called OT-X (Fig. 2), consist of 10, 11, or 12
in conjunction with carrier proteins (neurophysin 1 amino acids. Cleavage of the extended form of oxytocin
and 2, respectively). The gene for oxytocin is located creates the nine–amino acid molecule classically known
on human chromosome 20, adjacent to the gene for as oxytocin (Fig. 2). The extended forms of oxytocin
vasopressin. These genes lie on opposite strands and likely have many unidentified functions both in adults
have opposite transcriptional orientations (toward and during development (de Wied et al., 1991; Gainer,
one another) (Gainer, 2012). 2012). For example, the extended form of oxytocin is
Oxytocin and vasopressin are synthesized in brain found in mammalian fetuses (Gainer, 2012). Studies in
regions that are critical to behavioral and physiologic mice also suggest that both oxytocin and the extended
homeostasis. Different cells in specific brain regions form have a critical role in tissue differentiation in the
produce these two peptides, including the supraoptic heart and in survival or restoration of heart tissue after
nucleus and paraventricular nucleus (PVN) of the damage (such as hypoxia) or disease (such as diabetes)
hypothalamus (Sannino et al., 2017). The neurons of (Gutkowska et al., 2014; Jankowski et al., 2016).
the PVN, termed magnocellular neurons, which syn- There is one report that the extended form of oxytocin
thesize oxytocin and vasopressin, extend processes to may be elevated in autistic individuals in conjunction
the posterior pituitary gland where these peptides are with lower-than-normal amounts of the nine–amino
released into the systemic circulation. acid form of oxytocin (Green et al., 2001), suggesting
The primary cells of origin of oxytocin also produce that a failure to modify the oxytocin precursor could
networks of neural projections reaching throughout produce a less-active form of the molecule. However, the
the brain and spinal cord (Grinevich et al., 2016). For characteristics and functions of extended forms of
example, oxytocin from the PVN can reach the central oxytocin remain at present poorly understood (Uvnäs
amygdala with the capacity to quickly modulate Moberg et al., 2019).
emotional functions of the amygdala and brainstem
(Stoop, 2012). The PVN is a major site of convergence B. Fragments of Oxytocin May Be Biologically Active
and integration for neural communication relating to The nine–amino acid oxytocin molecule also can be
stress with effects on the HPA axis and autonomic further cleaved into other biologically active forms
functions (Ulrich-Lai and Herman, 2009). Oxytocin is (Fig. 2). As one example, in mouse models of autism,
colocalized in at least some of its cells of origin with the oxytocin metabolite OT 4–9 has been shown to
corticotropin-releasing hormone (CRH), which in turn produce a dose-dependent increase in prosocial behav-
regulates the HPA axis (Sawchenko and Swanson, iors without a change in measures of anxiety (Moy et al.,
1985). CRH or CRH-vasopressin actions also have 2019). This effect was seen 24 hours after the termina-
been implicated in some of the detrimental effects of tion of a subchronic regimen (2.0 mg/kg of OT 4–9) and
chronic stress (Elkabir et al., 1990; Aguilera et al., persisted for 12 days, suggesting an effect that outlives
2008). Oxytocin may be coreleased with CRH or the presence of the OT 4–9 molecule. Interestingly, OT
vasopressin as an adaptive response to a variety of 5–9 did not affect social behavior.
836 Carter et al.

As originally identified by Kastin (Kheterpal et al., B. The Structure of These Peptides Identifies Some of
2009), the N-terminal fragment of oxytocin, proline- the Challenges They Present
leucine-glycine-NH2 (OT 7-9), is also known as The disulfide bonds in oxytocin and vasopressin are
melanocyte-inhibiting factor-1 (MIF-1). Among the important in explaining the broad biologic consequen-
functions of MIF-1 is the regulation of pain through ces of these molecules. These bonds also help to explain
interactions with the opioid receptors (Khan et al., the challenges and apparent discrepancies in the mea-
2010). MIF-1 differs from oxytocin in that it is more surement of oxytocin and vasopressin (MacLean et al.,
resistant to degradation and easily passes through the 2019). Another consideration for understanding and
blood-brain barrier. Animal and human research sup- interpreting oxytocin’s effects is the fact that acute
ported the notion that MIF-1 could function as an versus chronic patterns of oxytocin release can have
antidepressant and “endogenous naloxone.” Specifi- biologic consequences that also differ. The speed at
cally, MIF-1 decreases the analgesic effect of morphine which these peptides degrade or bind to other mole-
(Galina and Kastin, 1986; Bocheva and Dzambazova- cules is critical to their function. Moreover, the
Maximova, 2004) and acts as a positive allosteric pharmacodynamics of these peptides at their recep-
modulator of the D2 and D4 dopamine receptor sub- tors is another essential element in determining their
types (Vartak et al., 2007; Mann et al., 2010). Oxytocin availability (Jurek and Neumann, 2018). In addition,
also can be degraded by aminopeptidase activity into oxytocin and vasopressin differ in their effects on
a so-called “linear” form (Fig. 2) (Burbach et al., 1980, receptor-transduced subcellular signaling cascades
1983), and this linear form acts to stimulate a-2 adrenor- (Gulliver et al., 2019).
eceptors (Uvnäs Moberg et al., 2019). The oxytocin system
and adrenoreceptors interact in a variety of ways with C. Feedback Loops
potential functions that are at present only partially
understood (Saniger et al., 2011; Wrzal et al., 2012a,b). Oxytocin-producing cells and OXTR also are sensitive
The original use patent for MIF-1 was filed by to the oxytocin peptide. Under some conditions, a form
Abbott Laboratories in the late 1960s, and in 1991, of autocrine feedback regulates the functions of
a patentable analog was developed by another com- oxytocin-producing cells. Stimulation of the oxytocin
pany. Although these efforts did not result in medi- system, especially in early life, can “feed forward” to
cations for reasons described by Ehrensing (2015), in release more oxytocin (Bowen et al., 2011; Suraev et al.,
conjunction with more recent animal research, they do 2014; Kenkel et al., 2019). Genetic deletion of Oxtr
offer proof of concept for the functions of oxytocin results in lifelong, region-specific changes in oxytocin
fragments (Uvnäs Moberg et al., 2019). The creation of peptide expression, which speaks to oxytocin’s autor-
MIF-1 from oxytocin is accomplished by insulin- egulation (Vaidyanathan and Hammock, 2020). In
regulated aminopeptidase (IRAP), which thereby reg- some cases, the administration of oxytocin enhances
ulates the persistence of extracellular oxytocin levels. the synthesis of endogenous oxytocin in the central
Thus, when conceiving of oxytocin-signaling equilibria, nervous system (Grippo et al., 2012). As described
we must account for not only the relative contributions of below, the expression of Oxtr in adulthood also is
ligand and receptor but also degradation via peptidases, regulated by oxytocin’s actions in early life (Kenkel
such as IRAP. For example, when IRAP is knocked out in et al., 2019; Perkeybile et al., 2019). Moreover, avail-
male mice, approach to stranger conspecifics is more ability of OXTRs can be dynamically modulated by
frequent, suggesting increased oxytocin action (Burns increasing exogenous oxytocin administration (Plested
et al., 2019). and Bernal, 2001; Robinson et al., 2003).

D. Patterns of Peptide Release Matter

VII. Processes Regulating Oxytocin
and Vasopressin The availability and actions of endogenous oxytocin
and vasopressin differ by patterns of release or admin-
A. Oxytocin and Vasopressin Are an istration. The hypothalamic neurons synthesizing oxy-
Integrated System tocin exhibit the capacity for pulsatile release. This may
The effect of endogenous oxytocin signaling as well as be related to a unique morphologic and functional
vasopressin and related molecules depends on many plasticity of these cells, which can change in minutes
factors. These include variation in genetics and epige- (Theodosis, 2002; Hatton and Wang, 2008). In adult
netics of the peptides and their various receptors, which rats, oxytocin-synthesizing neurons undergo physical
may differ across and within species (reviewed by transformations in response to hormonal and social
Feldman et al. (2016), Carter and Perkeybile (2018)). stimulation. During pregnancy, birth, and lactation
Although oxytocin and vasopressin are often studied and under other physiologic conditions (such as
separately, they function as an integrated system, dehydration or sexual stimulation), glial processes
creating additional levels of complexity (Caldwell and extending from pituicytes (the resident astrocytes of
Albers, 2016; Carter, 2017). the posterior pituitary) that normally separate the
 Oxytocin As Medicine 837

oxytocin-containing neurons may be retracted, allow- (Dolen, 2015), GABA (Ben-Ari, 2018), and opioids
ing electrical coupling and subsequent stimulus- (Meguro et al., 2018), interact with these peptides to
driven or endogenous pulsatile release of oxytocin. influence behavior and other functions. Use of drugs,
These dynamic neuronal-glial interactions allow for such as opiates, stimulants, and selective serotonin
remarkable plasticity that is intricately tuned to reuptake inhibitors, and diet, can affect both endoge-
hormonal demand for oxytocin (Hatton et al., 1984). nous oxytocin and its receptors with effects that are
Interestingly, vasopressin-containing neurons typi- largely unknown. In addition, sex differences in oxyto-
cally do not show this form of dramatic plasticity and cin and vasopressin are common, and it is likely that
pulsatile release. In the context of labor, this pulsa- steroids, including estrogens, androgens (Carter and
tile release of oxytocin coordinates the intermittent Perkeybile, 2018; Jirikowski et al., 2018), and glucocor-
smooth muscle contractions of the uterus that occur ticoids (Liberzon and Young, 1997), play a major role in
by oxytocin binding to OXTRs and the subsequent the regulation of the actions of oxytocin and availability
influx of extracellular calcium (Batra, 1986). Pretreat- of receptors for oxytocin across the lifecycle. As de-
ment with oxytocin or the clinical use of Pitocin (syn- scribed below, stress and experiences across the life
thetic oxytocin) can cause uterine OXTR desensitization, cycle also have major consequences for the release and
receptor internalization, and a decreased responsiveness actions of oxytocin and vasopressin.
to further oxytocin exposure (Robinson et al., 2003;
Gottlieb, 2016). Moreover, compared with continuous VIII. Measurement of Oxytocin
exogenous oxytocin exposure, intermittent exposure has
been shown to maintain oxytocin-induced uterine A. Oxytocin Is Difficult to Assay
contractility and uterine responsiveness, highlighting Important to the study of oxytocin, even when consid-
the importance of oxytocin’s pulsatile release (Talati ering only the classic form, is the capacity to measure this
et al., 2019). It seems likely that oxytocin’s evolution- molecule. Initial measurements of oxytocin-using bio-
arily conserved role in smooth muscle contractility assays and radioimmunoassay suggested that oxytocin
during labor (Batra, 1986), milk lactation (Hatton and was typically present in human blood at low concen-
Wang, 2008), and ejaculation (Filippi et al., 2003; trations of approximately 5 pg/ml (Leng and Ludwig,
Viveiros et al., 2003) was coadapted for social behav- 2016), with small pulses in oxytocin release (;15 pg/ml)
ioral functions, such as enhanced mother-infant bond- being sufficient to induce lactation and facilitate uterine
ing during birth (Nissen et al., 1995) and lactation as contractions in mammals (Saameli, 1963; Leng and
well as selective partner preference formation during Ludwig, 2016). Studies using immunoassay or mass
sexual intercourse (Carter, 2017). It is possible that spectrometry (MS) preceded by an extraction procedure
the capacity for pulsatile release allows oxytocin to continued to detect concentrations in the 5–30 pg/ml
stimulate different receptors and even override some range (Szeto et al., 2011; Kagerbauer et al., 2013).
of the actions of vasopressin. Thus, dynamic interac- However, other methods, including MS, have indicated
tions of oxytocin and vasopressin are important for that endogenous oxytocin may occur in blood at much
both the acute and chronic effects of these molecules. higher concentrations greater than 500–1000 pg/ml
(Kramer et al., 2004; Brandtzaeg et al., 2016; MacLean
E. Individual Differences Are to Be Expected et al., 2017b).
In describing individual differences in the actions of In addition, local tissue concentrations of oxytocin
oxytocin in humans, it will be important to keep in may give results of particular relevance to understand-
mind that oxytocin and vasopressin and their recep- ing the beneficial effects of this peptide. For example,
tors are genetically variable, epigenetically regulated, within the microenvironment of ovarian tumors, oxyto-
and sensitive to stressors and diet across the lifespan. cin levels were measured at 200 times higher than those
As one example, salt releases vasopressin and also in plasma (Cuneo et al., 2019). These high levels of
oxytocin (Leng and Russell, 2019). In addition, nico- oxytocin may reflect a response to the tumor with
tine is a potent regulator of vasopressin; thus, smok- apparent benefits to reducing inflammation. But they
ing, including prenatal exposure of a fetus, holds the also could be related to the absence within the tumor
potential to adjust this system with effects that likely (compared with blood) of peptide binding molecules,
differ between males and females and that may be which, in turn, might affect the concentrations of oxyto-
transgenerational. cin detected by antibody-based methods (MacLean et al.,
2019; Yamamoto and Higashida, 2020).
F. Effects of Other Molecules on the
Oxytocin-Vasopressin System B. Controversy Was Generated by Divergent Findings
Beyond the scope of this review but important to It was initially suggested that high levels detected by
understanding oxytocin and vasopressin is the fact that immunoassay were measurement artifacts due to the
many other molecules, including dopamine (Wang and binding of antibodies to nonhormonal components
Aragona, 2004; Gobrogge and Wang, 2016), serotonin of blood (Szeto et al., 2011; McCullough et al., 2013).
838 Carter et al.

However, recent work indicates that oxytocin readily et al., 2019). These dynamics may explain at least some
engages in complexes at its disulfide bridge (Avanti et al., of the unique properties of oxytocin and vasopressin but
2013) and that the vast majority of oxytocin in biosamples also account for problems associated with in vivo mea-
evades detection using conventional approaches to mea- surement of oxytocin and vasopressin. For example,
surement (Brandtzaeg et al., 2016). Importantly, these common approaches to sample preparation, such as
findings have been confirmed using MS—which is highly solid-phase extraction, likely discard the majority of
specific compared with immunoassay—suggesting that oxytocin in blood (Brandtzaeg et al., 2016; MacLean
earlier critiques of the high oxytocin concentrations et al., 2019). Thus, measurements in blood in particular
detected by immunoassay (which were within concen- introduce many other factors that can affect peptide
tration ranges deemed implausible) may have been determinations.
misguided. However, despite its advantages regarding
specificity, MS-based methods for measuring oxytocin D. Salivary Oxytocin
are still in active development, and many researchers Salivary measurements, possibly with fewer sources
have faced substantial challenges for reliable detection of of variation, offer an alternative for the assessment of
oxytocin using this approach. For example, Brandtzaeg changes in oxytocin (Carter et al., 2007; White-Traut
et al. (2016) struggled to reproduce earlier MS-based et al., 2009; Bernhard et al., 2018; MacLean et al.,
methods for measurement of unbound oxytocin. Further- 2018). Several studies have revealed reliable varia-
more, Franke et al. (2019) have argued that Brandtzæg tions in oxytocin concentration, especially in rapid
et al.’s method may have been significantly affected by response to specific experiences, such as anticipation
the lower resolution MS instrument used. Hence, it is of breast feeding (White-Traut et al., 2009), sexual
important to keep in mind that although MS is a very stimulation, exercise, affiliative social contact, and psy-
sophisticated approach, the verdict on the optimal chologic stress (Jong et al., 2015; MacLean et al., 2017a).
measurement method is still being debated. Addi- However, the relationships between concentrations of
tional areas in which MS measurement of oxytocin peptides in saliva, blood, and peptide concentrations
can be improved include the removal of interferents in the source brain nuclei are not yet well-understood
(e.g., phospholipids, which can suppress signals, result- (Quintana et al., 2018).
ing in vast underestimation of oxytocin concentrations),
automation (including sample preparation) for higher E. Can Endogenous Hormone Levels in Bodily Fluids
throughput, and further development/maturation of Be Useful in Predicting Responses to Exogenous
high-sensitivity microfluidic separation systems (e.g., Oxytocin Treatments?
nano liquid chromatography). Knowledge of endogenous oxytocin or vasopressin
The dynamic factors that affect the measurement of concentrations is important to predicting the consequen-
oxytocin and vasopressin also can influence attempts to ces of exogenous oxytocin exposure. Such assessments are
create a pharmacology based on oxytocin. At present, rarely made, in part because of the difficulties associated
measurements of peptides have suffered from poor with the measurement of oxytocin (MacLean et al., 2019).
specification regarding the forms in which researchers However, at least in autism spectrum disorders, meas-
intend to detect oxytocin; this is, in part, because urements of endogenous oxytocin (Parker et al., 2017) and
the biologic significance of different states of oxytocin especially vasopressin (Carson et al., 2015; Oztan et al.,
remains poorly understood. Current work suggests that 2018a) did predict behavioral sensitivity to exogenous
oxytocin and vasopressin are dynamically changing in hormone treatments. Comparatively low levels of vaso-
biologic matrices, such as blood. In addition, detecting pressin (but not oxytocin) measured in neonatal cerebro-
the presence of binding molecules will be critical to spinal fluid have been associated with a subsequent
accurate representations of the availability of these diagnosis of autism (Oztan et al., 2020). In another recent
elusive molecules (Yamamoto and Higashida, 2020). example, relative concentrations of endogenous oxytocin
and vasopressin in plasma were associated with sex, age,
C. Disulfide Bonds anxiety, attachment behaviors, and cognition (Plasencia
Disulfide bonds in the cysteines of both oxytocin and et al., 2019). These studies support the usefulness of
vasopressin allow these molecules to be highly reactive, measurements of both oxytocin and vasopressin but
forming relatively temporary unions with other mole- leave many empirical questions unresolved.
cules. Furthermore, oxytocin may be quickly seques-
tered by binding to other abundant thiol-containing F. Exogenous Peptides
molecules, such as glutathione as well as phospholipids One of the most remarkable aspects of pharmacological
and cellular elements, such as blood cells that are studies of the effects of exogenous oxytocin or related drugs
discarded in the creation of plasma. This binding of is the fact that these compounds are being given to humans
nonapeptides to other molecules could be influenced by —with a few notable exceptions—without attempts to
temperature, pH, availability of oxygen, other factors in measure either endogenous oxytocin or vasopressin. The
the medium being studied, or methods in use (MacLean measurement of endogenous oxytocin has indeed proven
 Oxytocin As Medicine 839

difficult and contentious but is not impossible (MacLean identifying, stimulating, or blocking receptors for oxy-
et al., 2019). Doses of exogenous oxytocin have the tocin and vasopressin may not be sufficiently selective
potential to either be ineffectively low or nonspecifically to allow easy identification or manipulations of these
high (see oxytocin’s ability to act on the AVPR1A, below), receptors, especially in vivo (Busnelli and Chini, 2018).
particularly when these doses are not informed by endog- Cell culture or other in vitro methods do not necessarily
enous concentrations and release patterns. reflect the functional availability of these peptides,
especially since the binding that occurs in vivo, including
G. Other Measures May Index Receptor Sensitivity in blood or tissues, could be influenced by competing
Most studies of receptors are limited to genetic markers molecules that differ from one test condition to another
or in rare circumstances made in postmortem tissues (Yamamoto et al., 2019). For example, as described below,
(Bao and Swaab, 2018). For example, age-related reduc- microglial OXTR has been difficult to detect in vivo but
tions in receptors for oxytocin have been detected in appears to be significantly upregulated after immune
postmortem brain tissues from individuals with autism challenges/stressors, especially when microglia and mac-
(Freeman et al., 2018). However, as described below, rophages are challenged in vitro (Yuan et al., 2016; Szeto
proxies for the status of oxytocin and vasopressin et al., 2017).
receptors, including measures of methylation levels
in receptor genes, also may predict reactions to C. Vasopressin Receptors
endogenous or exogenous oxytocin (Lancaster et al., The three vasopressin receptor subtypes respond to
2015; Ebner et al., 2019). Thus, there is usefulness in oxytocin to varying degrees. These are expressed in
measuring both the availability of oxytocin and the different tissues, and their genes are located on sepa-
sensitivity of receptors that are capable of responding rate chromosomes. AVPR1A is found in the nervous
to this molecule (see below). system and throughout the cardiovascular system with
a broad set of behavioral functions. AVPR1B is found in
IX. Receptors for Oxytocin and Vasopressin the pituitary but also in brain areas with a role in the
management of stress and aggression (Vaccari et al.,
A. The Oxytocin Receptor 1998; Stevenson and Caldwell, 2012). AVPR2 is local-
Only one oxytocin receptor has been described ized primarily to the kidney with a classic role in fluid
(OXTR), the gene for which is located in humans on balance. Functional effects of oxytocin and vasopressin
chromosome 3p24–26 (Gimpl and Fahrenholz, 2001; depend on interactions with both OXTR and AVPR1A
Jurek and Neumann, 2018). The OXTR gene encodes (Song et al., 2014; Hicks et al., 2015; Carter, 2017; Chini
a G-protein–coupled receptor (GPCR) with a seven- et al., 2017; Song and Albers, 2018).
transmembrane domain. The same oxytocin receptor
is present in neural tissue and in other parts of the body, D. Receptor Distributions
such as the uterus, breast, and gastrointestinal tract. Receptors for both oxytocin and vasopressin are
Although there is technically only one OXTR, it is now localized in areas of the nervous system that regulate
understood that oxytocin affects numerous different social, emotional, and adaptive behaviors, including the
GPCRs (Fig. 2). Oxytocin can bind to receptors that amygdala, the HPA axis, and the autonomic nervous
were identified in vitro, such as OXTR, but also to system (Quintana and Guastella, 2020). Based on work
vasopressin receptors (AVPR1A, AVPR1B, AVPR2) (de primarily in rodents and birds, among the regions with
Wied et al., 1991; Peter et al., 1995; Ragnauth et al., especially high levels of OXTR are various parts of
2004; Manning et al., 2008; Ocampo Daza et al., 2012). the amygdala, the bed nucleus of the stria terminalis,
In general, oxytocin (vs. vasopressin) has its highest the nucleus accumbens, brainstem source nuclei for the
affinity for OXTR. However, oxytocin also readily binds autonomic nervous system, and in systems that regu-
to AVPR1A (reviewed in Song and Albers (2018)). late the HPA axis as well as in brainstem tissues
Outside these two neuropeptide systems, recent re- involved in pain and social attention (Stoop et al.,
search has found several other targets for oxytocin’s 2015; Freeman and Young, 2016; Wilson et al., 2016;
effects. For example, oxytocin acts as an agonist on the Gobrogge et al., 2017; Poisbeau et al., 2018). OXTR is
pain-sensing transient receptor potential vanilloid-1 also found in various cortical areas and the hippocam-
receptor, where it attenuates nociception and drives pus, brain areas that are especially variable among
nocifensive behavior (Nersesyan et al., 2017; Wee et al., species and individuals, with possible consequences for
2019). Oxytocin also acts as a positive allosteric modu- behavioral plasticity (Witt et al., 1991; Grunewald et al.,
lator of the m-opioid receptor (MOR) (Meguro et al., 2012; Seelke et al., 2016a,b; Duchemin et al., 2017).
2018), where it likely furthers antinociception. Both individual and species differences in OXTR and
AVPR1A distributions are commonly identified and pre-
B. Measuring the Oxytocin Receptor sumably adaptive (Witt et al., 1991; Hammock and
The measurement of peptide receptors is problematic Young, 2005; Freeman and Young, 2016; Okhovat et al.,
because the pharmacological tools that are available for 2017; Ophir, 2017; Carter and Perkeybile, 2018; Okhovat
840 Carter et al.

et al., 2018). Species variation is likely important in the XI. Genetics and Epigenetics
evolution of different patterns of sociality, including
A reduction or upregulation in the availability of
those that differentiate socially monogamous from non-
the oxytocin or vasopressin receptors can reflect both
monogamous rodent species (Carter and Perkeybile,
heritable genetic variation (King et al., 2016; Baker
2018) and affiliative versus nonaffiliative avian species
et al., 2017) and/or epigenetic tuning (Okhovat et al.,
(Goodson et al., 2006; Wilson et al., 2016). However,
2015; Baker et al., 2017; Okhovat et al., 2018; Towers
regional distributions of CNS OXTR in primates, in-
et al., 2018; Perkeybile et al., 2019) of this system. The
cluding humans, have proven challenging to identify
variable expression in tissues of OXTR is also epigenet-
and interpret (Freeman and Young, 2016).
ically tuned by early life experience (Baker et al., 2017;
Krol et al., 2019a; Perkeybile et al., 2019), increasing
X. Subcellular Signaling Specifies the Functions the capacity of peptides to have complex adaptive
of Oxytocin and Vasopressin functions. Evidence in humans for the functional
importance of the oxytocin genetic-epigenetic systems
Oxytocin acts via GPCRs to activate subcellular
at present comes primarily from correlations among
cascades with eventual effects on transcription fac-
genetic and epigenetic variations in the OXTR gene
tors (Busnelli and Chini, 2018; Jurek and Neumann,
and individual differences in behavior, physiology, and
2018). Knowledge of the subcellular signaling path-
brain anatomy (Rodrigues et al., 2009; Tost et al., 2010;
ways that respond to the stimulation of oxytocin or
Jack et al., 2012; Puglia et al., 2015; Lancaster et al.,
vasopressin receptors are among the next generation
2018b).
of approaches to the creation of medicines based on
Genetic variations in the OXTR, indexed by single-
oxytocin pathways (Lerman et al., 2018; Gulliver
nucleotide polymorphisms, were originally related to
et al., 2019; Kingsbury and Bilbo, 2019). Genes for
autism spectrum disorders (for example, variant
OXTR and the three vasopressin receptors code for
rs2254298 G.A and rs53676 G.A) (Jacob et al.,
separate GPCRs, each with a seven-transmembrane
2007). The OXTR gene can be silenced via DNA meth-
domain. The subcellular signaling pathways vary
ylation, thus reducing the expression of the oxytocin
among receptors. In addition, the capacity of oxytocin
receptor (Kusui et al., 2001). Functional relationships
and vasopressin to activate a given receptor sub-
between methylation of the oxytocin receptor gene and
cellular signaling pathway may differ according to
behavior were first detected in autism (Gregory et al.,
the concentrations of the peptides and based on
2009) and recently validated (Andari et al., 2020). Such
variations in the regional location of receptors in
relationships have also been found in other conditions,
the nervous system (Stoop et al., 2015; Chini et al.,
including postpartum depression (Bell et al., 2015) and
2017; Busnelli and Chini, 2018; Song and Albers,
schizophrenia (Rubin et al., 2014). In neurotypical
2018). Differences in subcellular signaling could help
humans, methylation status of the OXTR also has been
to explain the capacity of oxytocin and vasopressin to
shown to strongly predict measures of social perception
have different functions in various tissues, such as
in both college-aged adults and infants (Jack et al., 2012;
those regulating birth (Arrowsmith and Wray, 2014),
Puglia et al., 2015, 2018; Krol et al., 2019b). Specific
social behavior (Caldwell and Albers, 2016; Song et al.,
single-nucleotide polymorphisms could be implicated in
2016), reactivity to stressors (Murgatroyd and Nephew,
a variety of functions through epigenetic and intergen-
2013; Stoop et al., 2015; Neumann and Slattery, 2016),
erational effects on the expression of OXTR (Bell et al.,
cancer (Lerman et al., 2018), and cardiovascular disease
2015; Chagnon et al., 2015). Below, we discuss how
(Reiss et al., 2019).
experiences in early life, including parental care and
When given as an exogenous treatment, the behav-
oxytocin administration in the context of obstetric care,
ioral consequences of oxytocin are dose-dependent but
can program epigenetically the OXTR system to produce
not typically linear (Ceanga et al., 2010; Klein et al.,
lifelong changes in this system.
2011, 2013; Borland et al., 2019). As with other peptide-
based treatments acting on GPCRs, more is rarely
better. This may explain several of the unexpected or XII. Early Experience and Context
paradoxical findings reported when oxytocin is given as
an exogenous treatment (Carter, 2017; Song and Albers, A. Emotional Context Matters
2018). The lack of a full understanding of the subcellular This is in part because context can influence physiol-
pathways through which oxytocin and vasopressin ogy, helping to create individual differences in the
function is at present a barrier to using these non- capacity to react to environmental events. As one
apeptides as medicines. Furthermore, as mentioned example, behavioral changes induced by early experi-
above, the oxytocin and vasopressin-like molecules exist ence may reflect changes in the oxytocin system.
in several endogenous forms, and the signaling func- Human research, especially studies conducted in indi-
tions of precursors or fragments of these peptides have viduals with a history of personal adversity, suggest
only begun to be described. that in some contexts, exogenous oxytocin can have
 Oxytocin As Medicine 841

asocial or negative consequences (Bartz et al., 2010), represent, in part, the capacity of oxytocin to stimulate
including the increased perception of threat in the pres- AVPR1A and AVPR1B (Fig. 3) (Caldwell, 2017; Carter,
ence of individuals from other social groups (De Dreu, 2017). This may be of particular importance in individ-
2012). In terms of early experience, positive parenting (vs. uals primed by negative experience. For example, even
neglect) has lasting beneficial consequences for behavior small amounts of oxytocin might be capable of acti-
and health in the offspring, possibly also through retuning vating vasopressin receptors, with effects that involve
of the oxytocin/vasopressin pathways. mobilization and potentially defensive emotional or
behavioral responses. Based on data from oxytocin
B. Adversity Versus High Nurture knockout mice, in which the vasopressin system is
Animal research also suggests that the nature of early sensitized (Ragnauth et al., 2004), we can also hypoth-
experience can influence the development of oxytocin/ esize that individuals with low concentrations of
vasopressin pathways and subsequent long-term behav- endogenous oxytocin might be more likely to experi-
ioral outcomes. For instance, adversity in early life has ence increased vasopressin-like activities when given
the capacity to sensitize the vasopressin system and, in oxytocin (Carter, 2017).
some cases, upregulate AVPR1A in brain regions in-
volved with defensive behaviors (Carter, 2017). Alterna- E. Birth and Epigenetics
tively, early life exposure to highly nurturant parenting Data from animal models and human epidemiol-
or as little as a single exposure to exogenous oxytocin ogy indicate that widely used medical interventions
produces epigenetic changes in Oxtr (Kenkel et al., 2019; (i.e., exogenous oxytocin, such as Pitocin given to facilitate
Krol et al., 2019a; Perkeybile et al., 2019). Receptor labor, opioid medications that block the oxytocin system,
changes such as these can have long-lasting consequen- or cesarean sections that alter exposure to endogenous
ces for the capacity for sociality and emotional regulation oxytocin), have lasting consequences for the offspring
(Carter, 2003; Carter et al., 2009; Kenkel et al., 2019). and/or mother (Hayes and Weinstein, 2008; Kroll-
Desrosiers et al., 2017; Kingsbury and Bilbo, 2019).
C. Vasopressin Systems as Likely Targets for Such exposures hold the potential to have epigenetic
Adversity and Stress in Early Life effects on the oxytocin systems, including changes in
Expression of vasopressin or the vasopressin recep- DNA methylation (Kenkel et al., 2019). These changes
tors also are likely to be affected by negative social in turn would have lasting effects on the expression of
experiences, including neglect or maltreatment in early receptors for oxytocin, leaving individuals differentially
life (Bunck et al., 2009; Hernandez et al., 2016). Under able to respond to oxytocin and also possibly to the
conditions in which the vasopressin system is sensi- effects of vasopressin. For instance, in a recent study
tized, especially in a context of fear or danger, we can intended to model labor induction, voles exposed in-
hypothesize that oxytocin could stimulate the vasopres- directly to oxytocin at birth (via maternal administra-
sin receptor. Thus, early adversity or maltreatment tion) show changes in Oxtr methylation patterns in the
might dysregulate or upregulate vasopressin, the vaso- fetal brain, a gregarious phenotype of social behavior,
pressin receptor, or other factors regulating this system, and sex- and region-specific changes in OXTR and
including catecholamines. This switch from oxytociner- AVPR1A densities in the brain as adults (Kenkel
gic to vasopressinergic stimulation in turn would alter
the ability to cope with a challenge. In later life, it could
encourage either a more active or mobilized defensive or
aggressive behavioral strategy possibly accompanied by
anxiety. In cases of severe traumatic stress, a more
energetically conservative “shut-down” strategy might
emerge, characterized by immobility due to fear rather
than mobilization. It is likely that dynamic interactions
between oxytocin and vasopressin allow behavioral,
autonomic, and emotional-state shifts between anxiety
and depression, such as those that characterize a history
of trauma (see below).

D. Early Exposure to Peptides May Modulate

Perceived Context
In individuals with a history of adversity or trauma, Fig. 3. The effects of oxytocin and vasopressin can be context-dependent.
the effects of exogenous oxytocin may appear to be Sensitivity of the AVPR1A or OXTR to either oxytocin or vasopressin may
detrimental [for example, Walsh et al. (2018)]. Once be altered by a history of adversity or by positive experiences, especially
during early life. For example, as illustrated here, arousal or stress may
more, we can hypothesize that the apparently paradox- increase the release of oxytocin and/or increase sensitivity of AVPR1A to
ical effects of oxytocin in responses to extreme stressors oxytocin [reviewed Carter (2017)].
842 Carter et al.

et al., 2019). Deconstructing the developmental benefits C. The Polyvagal Hypothesis

of endogenous oxytocin and the implications of exoge- The autonomic nervous system supports the physio-
nous exposure to this peptide has much to teach us logic and metabolic demands of the cerebral cortex and
about the biology of health versus disease. is necessary for social behavior (Porges, 2009, 2012).
Embedded within the mammalian parasympathetic
XIII. The Autonomic Nervous System as a Target nervous system/vagus nerve are two systems: a more
for Oxytocin ancient unmyelinated branch of the vagus with cells
that originate within the brainstem region known as the
A. Neural and Peptide Interactions Allow a Wide dorsal vagal complex and with pathways to subdiaph-
Range of Adaptive Responses ramatic organs but also innervating the heart. In
Understanding the complex actions of oxytocin addition, encased within the vagus nerve, as it exits
requires awareness that oxytocin regulates not only the brainstem, is a more evolutionarily modern myelin-
the brain and reproductive system but also the immune ated vagal system; cells for this branch originate in the
(see below) and autonomic nervous systems. Effects on ventral-vagal complex, with pathways to the heart and
the autonomic nervous system include shifts in state bronchi. The ventral-vagal pathways interact with the
and emotional regulation and can be seen as acute brainstem nuclei that innervate the striated muscles
changes as well as chronic adjustments that affect the regulating the face and head; these may be of particu-
entire body. For example, evidence supporting the lar relevance to social communication as well as the
coordinated effects of acetylcholine (the major neuro- anti-inflammatory actions of oxytocin (Dantzer, 2018,
transmitter in the parasympathetic nervous system) Kingsbury and Bilbo, 2019).
and oxytocin comes from colocalization of these mole- Oxytocin receptors are especially abundant in brain-
cules and their receptors in tissues, including hypotha- stem regions, including the dorsal vagal complex or
lamic and brainstem areas, that regulate the autonomic dorsal motor nucleus of the vagus (DMX) that regulates
nervous system (Freeman and Young, 2016; Quintana subdiaphramatic organs. Stimulation of the DMX slows
et al., 2019). Interactions between oxytocin and the the heart. Vagal regulation is also implicated in sexual
autonomic nervous system are also relevant under and social behaviors and is linked with motivation and
conditions in which the system is manipulated phar- reward circuitry (Han et al., 2018). Oxytocin may act on
macologically. For example, treatment with exogenous these ancient and highly conserved brainstem regions
oxytocin induces increases in vagal activity as mea- to permit mammalian patterns of maternal and sexual
sured by respiratory sinus arrhythmia (Quintana et al., behavior that require immobility without fear (Porges,
2013). 1998; Kenkel et al., 2013).

B. The Autonomic Nervous System Consists of D. The Hypothalamus as a Site for Coordination of
Sympathetic and Parasympathetic Components Vagal-Peptide Interactions

The sympathoadrenal axis is associated with flight- The PVN of the hypothalamus is both a major site of
fight responses. Under extreme stress or life-threatening oxytocin synthesis and a key area that responds to
situations, both oxytocin and vasopressin activate sym- oxytocin, presumably via input from oxytocin recep-
pathetic and parasympathetic pathways, with a more tors (Quintana et al., 2019). Furthermore, the PVN is
variable autonomic response in the face of milder stressors a regulatory center for autonomic functions, particu-
(Porges, 2012; Yee et al., 2016). larly vagal functions (Herman et al., 2012). The visceral
The parasympathetic nervous system and specifically target organs of the autonomic nervous system, such
vagal pathways have important consequences for brain as the heart, digestive, and immune systems, also
and cognitive function. The vagus also plays a particu- contain abundant receptors for oxytocin (Welch et al.,
larly important role in the neural regulation of the 2005; Gutkowska and Jankowski, 2012; Jurek and
mammalian immune system (Dantzer, 2018). It is likely Neumann, 2018; Wang et al., 2019). Thus, it is not
that these peptides integrate the activity of different surprising that in the face of stress oxytocin can
branches of the autonomic nervous system, which helps protect the functions of the digestive system (Yang
to explain the importance of social attachment in et al., 2019), heart (Gutkowska and Jankowski, 2012;
protecting against or modulating different forms of Buemann and Uvnas-Moberg, 2020), and immune
emotion dysregulation. These same peptides, together system (Kingsbury and Bilbo, 2019).
with the vagus nerve, have effects on the immune and
metabolic systems across the lifespan, which also helps E. Social Communication and Myelinated
to explain the lasting effects of early emotional experi- Ventral-Vagal Pathways
ences on physical health and well-being (Hammock, The muscles of the mammalian face and head are
2015; Amini-Khoei et al., 2017; Kingsbury and Bilbo, regulated by the same brainstem area that also regu-
2019). lates the myelinated vagal pathway, thus linking
 Oxytocin As Medicine 843

through bidirectional communication the heart with (Pournajafi-Nazarloo et al., 2011; Bosch and Young,
facial expressions and intonation of vocalizations. This 2018). In many cases reactions to acute stressors
integrated social engagement system provides mecha- include the release of oxytocin, possibly in anticipa-
nisms through which emotional experience and physi- tion of more chronic situations that may follow (Lang
ologic states are involved in social communication. et al., 1983; Gibbs, 1986; Engert et al., 2016). These
Autonomic actions of oxytocin as well as vasopressin anticipatory responses also may include increases in
also influence the capacity for and expression of social social behavior and transient changes in other organ
bonds that arise in response to challenge or adversity systems, including the heart (Grippo et al., 2012;
(DeVries et al., 1996; Cho et al., 1999). Kemp et al., 2012).
Oxytocin acting via the autonomic nervous system
and acting on the cortex and brainstem has been B. Chronic or Traumatic Stress
repeatedly implicated in human social engagement,
Oxytocin has particular importance in the face of
facially expressed emotions, and eye gaze (Kemp
chronic stress when “stress-coping” effects may take
et al., 2012; Quintana et al., 2013; Freeman and
precedent. Oxytocin can facilitate passive forms of
Young, 2016). Evidence from rodents indicates that
coping and protect against shutting down or “immobi-
the oxytocin receptor plays an important role in
lization with fear” (Porges, 1998). Behavioral, physio-
cortical functions necessary for social cognition
logic, and anatomic data from rodents (Grippo et al.,
(Ophir, 2017), social reward (Song et al., 2014), and
2009) and humans (Grewen and Light, 2011) suggest
social affective behavior (Rogers-Carter et al., 2018;
that chronic, antistress effects of social support can
Rogers-Carter and Christianson, 2019). At least some
downregulate the sympathetic nervous system, allow-
of these effects also involve interactions between oxyto-
ing the expression of protective and restorative func-
cin and dopamine (Quintana et al., 2019; Martins et al.,
tions of the vagal systems (Thompson et al., 2008; Yee
2020). Moreover, the modulation of social approach
et al., 2016).
behavior by PVN oxytocin release onto ventral tegmen-
tal area dopaminergic neurons is dependent on gut-
brain signaling via the vagus nerve (Sgritta et al., 2019). C. Myelinated Ventral-Vagal Pathways and
Passive Coping
F. Cortical Integration of Studies in prairie voles have revealed that oxytocin
Peptide-Autonomic Interactions has protective actions on the autonomic functions of the
The insular cortex, a multisensory processing region ventral, myelinated vagus, as measured by changes in
that also contains a rich population of OXTRs, functions neutrally regulated heart rate variability (respiratory
to integrate external sensory stimuli with internal sinus arrhythmia) (Grippo et al., 2009). Oxytocin also
visceral, emotional, and motivational states (Rogers- may directly co-opt the older unmyelinated vagus
Carter and Christianson, 2019). Specifically, the “vis- through receptors in the dorsal vagal complex, protect-
ceral insular cortex,” which receives input from gastric ing mammals from responding to threat with a more
mechanoreceptors, arterial chemoreceptors, and car- primitive “reptile-like” freezing pattern and evacuation
diovascular baroreceptors, respiratory centers, and of the lower bowel (Porges, 2012).
the vagus nerve, plays a central role in interoception Immobility with fear or freezing, associated with
(Barnabi and Cechetto, 2001). This region of cortex is traumatic experiences, can be a component of despair
able to detect changes in internal state, influencing and depression. This response is adaptive in conserving
appropriate social responses, such as approach versus energy. But freezing in fear is not optimal for other
avoidance behavior with a stressed conspecific (Rogers- functions, such as active social behaviors that rely on
Carter et al., 2018). mobilization and high levels of metabolic activity
(Porges, 2012). The capacity of oxytocin to protect this
system is critical to the types of social engagements that
XIV. Oxytocin and “Stress Coping”
characterize mammalian social behavior, including
Many of the emotional, visceral, and immune effects birth and parenting.
of oxytocin and vasopressin rely on interactive actions of Mammals, with their comparatively large brains,
these molecules on the autonomic pathways. These are particularly vulnerable to the need for oxygen.
effects are adaptive in the face of stressful experiences, Under traumatic conditions, the functions of oxytocin
although the functions of these peptides as well as may allow a shift to those necessary for protection of
hormones of the HPA axis are different under condi- the survival of cortical processing. However, when
tions of acute versus chronic stress (Table 1). oxygen is insufficient, psychologic dissociation (Li
et al., 2020) or even loss of consciousness can occur
A. Acute Stress Responses (Carter, 2014). As one example, oxytocin levels were
Adaptive responses to acute stressors have a dis- exceptionally high in women with a history of trauma
tinct physiology from those elicited by chronic stress who showed a pattern of dissociation, supporting the
844 Carter et al.

hypothesis that elevations in oxytocin can be adap- proinflammatory cytokines TNF-a and IL-1b, and the
tive in trauma (Seng et al., 2013). levels of proinflammatory mediators cyclooxygenase-2
As described below, oxytocin, in part through effects and iNOS. These effects were detected in the prefrontal
on the vagus nerve, has direct and indirect effects on cortex of LPS-treated adult male mice, as compared with
the immune and metabolic systems across the life- LPS-treated males that received intranasal vehicle
span. These actions also help to explain the lasting (Yuan et al., 2016). Interestingly, oxytocin has no effect
effects of early emotional experiences on physical health on these inflammatory measures in the absence of LPS
and well-being (Hammock, 2015; Engert et al., 2016; Amini- exposure, suggesting that oxytocin’s anti-inflammatory
Khoei et al., 2017; Quintana et al., 2017; Kingsbury and actions require the presence of a stressor. Remarkably
Bilbo, 2019). similar effects of oxytocin were observed in healthy men
subjected to an immune challenge (Clodi et al., 2008).
Compared with men administered LPS alone, men who
XV. Immunologic and Anti-Inflammatory Effects
received intravenous infusion of LPS plus oxytocin had
of Oxytocin
an attenuated endocrine, cytokine, and chemokine re-
Oxytocin has central roles in immune surveillance sponse to the immune challenge. Taken together, these
and immunologic homeostasis and supports resistance findings demonstrate that oxytocin can lessen the in-
to a whole host of immune challenges, stressors, and flammatory response induced by LPS across species.
insults across a range of body tissues (Li et al., 2017b;
Buemann and Uvnas-Moberg, 2020). Many of the pro- B. Early Experience and Inflammation
tective effects of oxytocin observed across the lifespan In animals subjected to early life adversity, oxytocin
appear to be mediated through the OXTR and occur in also has protective effects (i.e., boosts resilience) later in
response to both normal adaptive stressors during life against subsequent stressors or immune challenges
development (e.g., birth, gut microbial colonization) through a reduction in brain inflammatory processes
and in response to injury and trauma (Kingsbury and (Amini-Khoei et al., 2017; Mairesse et al., 2019) (Fig. 4).
Bilbo, 2019). Furthermore, although oxytocin can in- For instance, male mice subjected to maternal separa-
fluence immune-system development (Geenen, 2006; tion stress during the first 2 weeks of life are character-
Murgatroyd et al., 2016; Rotondo et al., 2016; Li et al., ized by a depressive-like phenotype in adulthood during
2017b), such as being highly concentrated in the a forced swim test, sucrose preference test, and grooming
thymus and playing a role in the “education” of thymic assay. This depressive phenotype is accompanied by
cells for self-tolerance (Geenen, 2006), we focus here impaired mitochondrial function, reduced antioxidant
on oxytocin’s anti-inflammatory roles in the context activity, increased oxidative stress, and increased gene
of immune-system function and homeostatic cellular expression for immune-proinflammatory markers, all
processes. within the hippocampus (Amini-Khoei et al., 2017).
Importantly, the depressive-like phenotype and the
A. Oxytocin and Neuroinflammation accompanying inflammation were attenuated if male
The role of oxytocin as an important regulator of the mice were injected intracerebroventricularly with oxy-
mammalian immune system (Li et al., 2017b; tocin in adulthood but not if the OXTR antagonist,
Kingsbury and Bilbo, 2019) that ties social behavior atosiban, was administered alongside oxytocin. Simi-
and experiences with the capacity to heal in the face of lar findings were observed for mice subjected to a low-
stress or trauma is especially evident within the protein diet during gestation to simulate fetal growth
nervous system (Fig. 4). In an adult animal model of restriction, a condition associated with the develop-
ischemic stroke, animals subjected to focal cerebral ment of cerebral palsy, cognitive, and behavior deficits.
ischemia have reduced tissue damage, increased anti- In this model, subsequent postnatal injections of the
oxidant activity, and decreased oxidative stress if they inflammatory cytokine IL-1b cause increased expres-
are socially housed during the recovery period, as sion of classic and nonclassic proinflammatory genes
opposed to animals that recover in social isolation within microglia, decreased myelination, decreased
(Karelina et al., 2011). These effects of social housing brain connectivity, and increased anxiety-like behav-
are mediated by oxytocin, as the administration of ior (Mairesse et al., 2019). When carbetocin, a long-
exogenous oxytocin to experimental animals recovering lasting OXTR agonist, was administered postnatally
in social isolation recapitulates the neuroprotective alongside IL-1b, it attenuated the microglial proin-
effects; OXTR antagonism blocks this protection in both flammatory gene expression, reversed the myelination
socially housed and socially isolated animals (Karelina and connectivity deficits, and normalized anxiety-like
et al., 2011). Similarly, in a model of acute brain behavior.
inflammation induced by a systemic injection of the
bacterial endotoxin lipopolysaccharide (LPS), intrana- C. Microglia and Macrophage
sal administration of oxytocin 1 hour prior to the LPS Many of oxytocin’s anti-inflammatory actions appear
injection reduces microglial activation, the levels of to be, at least in part, through the attenuation of
 Oxytocin As Medicine 845

Fig. 4. Oxytocin acts as an anti-inflammatory molecule for the nervous system in the presence of stressors. For the developing brain, oxytocin confers
neuroprotection in the presence of a stressor by inhibiting the release of proinflammatory cytokines by microglia by decreasing oxidative stress
exposure and by protecting mitochondrial function. For the adult brain, oxytocin confers similar neuroprotection in the presence of a stressor by
inhibiting the release of proinflammatory cytokines by microglia, by decreasing oxidative stress exposure, by protecting mitochondrial function, and by
increasing antioxidant capacity. Moreover, similar to its inhibition of microglia-mediated inflammatory cascades, oxytocin inhibits macrophage-
mediated proinflammatory cascades outside of the central nervous system during an immune challenge with LPS. Although oxytocin mediates many
aspects of social behavior and cognition, the known social and cognitive functions that oxytocin protects in the presence of inflammation are shown here
for the developing and adult brain. Inflammatory cascades are shown in purple and oxytocin signaling is shown in red. All of oxytocin’s protective
effects shown here are believed to be mediated by oxytocin binding to the OXTR. COX-2, cyclooxygenase-2; GPx, glutathione peroxidase; GSH, reduced
glutathione; GSSG, oxidized glutathione; HMGB1, high-mobility group box 1.

inflammatory processes mediated by microglia and isolated from both animals exposed to an inflammatory
macrophages (Karelina et al., 2011; Yuan et al., 2016; low-protein diet during gestation and control animals
Li et al., 2017b; Szeto et al., 2017; Mairesse et al., 2019) injected with IL-1b and interferon a (proinflammatory
(Fig. 4). OXTR is present on the cell surface of microglia mediators), the oxytocin agonist carbetocin reduces the
as well as neurons and astrocytes; the addition of morphologic changes associated with microglia activa-
oxytocin to microglia cultures stimulated with LPS tion as well the expression of proinflammatory media-
dampens the expression of major histocompatibility tors IL-6, TNF-a, and iNOS (Mairesse et al., 2019).
complex class II, a gene that is induced within activated These effects are mediated through OXTR, as addition
microglia (Karelina et al., 2011). Similarly, both Oxtr of an OXTR antagonist (L-368899) prevents the micro-
mRNA and OXTR protein are enriched in primary glial morphologic changes and the attenuation of IL-6,
microglia stimulated with LPS, and treatment of these TNF-a, and iNOS expression. Given the ancient con-
microglial cultures with oxytocin suppresses the LPS- served functions of oxytocin, it is perhaps not surprising
induced production of TNF-a and IL-1b (Yuan et al., that carbetocin has similar immune suppressive effects
2016). After an LPS immune challenge in vivo, oxytocin on microglia morphology and cytokine release in zebra-
also reduces the expression and production of proin- fish in vivo after an inflammatory stimulus (Mairesse
flammatory cytokines TNF-a and IL-1b as well as the et al., 2019). Similarly, an additional ancient function of
number of prefrontal cortex cells labeled with ionized oxytocin is the protection against painful stimuli, in-
calcium-binding adapter molecule 1, a microglial cluding a behavior response that alleviates stress.
marker (Yuan et al., 2016). In microglia cultures Within zebrafish, hypothalamic oxytocin neurons drive
846 Carter et al.

nocifensive behavior after the exposure to a noxious oxidative stress and reactive oxygen species (Tyzio
stimulus, suggesting a conserved stress-coping mecha- et al., 2006; Khazipov et al., 2008). In rodent models of
nism of oxytocin (Wee et al., 2019). Moreover, in autism wherein this oxytocin-mediated switch is absent
mammals, oxytocin cells in the PVN control acute at birth, offspring are characterized by altered social
inflammatory pain perception, whereas oxytocin in the behaviors and neuronal hyperexcitability, demonstrat-
spinal cord controls nociception, and oxytocin in the ing that oxytocin’s neuroprotective effects during a ma-
amygdala regulates the processing of emotional pain jor inflammatory event give rise to appropriate social
(Poisbeau et al., 2018). behaviors in adolescence (Tyzio et al., 2014).
Whereas oxytocin dampens inflammatory processes However, oxytocin appears to have dose-dependent
mediated by microglia, the tissue-resident macrophages effects at birth, particularly when administered exoge-
of the CNS, similar effects are observed for oxytocin nously, with higher doses conferring less neuroprotec-
acting on macrophages outside of the CNS (Fig. 4). For tion in vitro (Ceanga et al., 2010) as well as an increased
instance, THP-1 and human primary macrophages risk for autism for male offspring (Soltys et al., 2020).
stimulated with LPS upregulate OXTR expression Possible explanations to explain the loss of oxytocin’s
and protein production relative to nonstimulated cells protection when administered exogenously at high
(Szeto et al., 2017). LPS treatment also upregulates IL- concentrations are oxytocin-induced receptor desensiti-
6 mRNA and protein in THP-1 macrophages and zation (Plested and Bernal, 2001; Robinson et al., 2003)
murine macrophages (including tissue-resident murine and/or oxygen desaturation of the fetal blood supply
peritoneal macrophages), and this effect is attenuated (i.e., greater hypoxia) that can occur after synthetic
when THP-1 cells are pretreated with oxytocin (Szeto oxytocin-induced uterine hyperstimulation (Simpson
et al., 2017). Furthermore, blocking NF-kB activation and James, 2008). A third explanation may be the
prevents this upregulation of Oxtr and IL-6 expres- promiscuous binding of oxytocin to the vasopressin
sion, suggesting that the OXTR acts as an acute receptor AVPR1A when administered exogenously at
phase protein that reduces macrophage-mediated high doses, as AVPR1A can mediate proinflammatory
inflammatory responses both within and outside of signaling (Bordt et al., 2019) and exacerbate neural
the CNS. Interestingly, LPS challenge downregu- toxicity during hypoxia/hypoglycemia (Tanaka et al.,
lates AVPR2 in primary human macrophages, and 1994; Spoljaric et al., 2017). Thus, the protective nature
pretreatment of THP-1 cells with vasopressin has no of endogenous versus exogenous oxytocin as well as its
effect on LPS-induced IL-6 secretion, highlighting dose-dependent effects at birth require further study
the anti-inflammatory function of oxytocin as op- given the widespread use of synthetic oxytocin to
posed to vasopressin (Szeto et al., 2017). manage labor.

D. Oxytocin Protects against Inflammation Associated E. Oxytocin, Oxidative Stress, and Mitochondria
with Birth Oxytocin also protects neural cells against hypoxic-
Oxytocin also plays a significant anti-inflammatory ischemic conditions by preserving mitochondrial
role at birth protecting the fetal brain against the function, reducing oxidative stress, and decreasing
hypoxic-like conditions that accompany labor (reviewed a chromatin protein that is released during inflamma-
in Kingsbury and Bilbo (2019); Fig. 4). It also likely tion (Kaneko et al., 2016), which can activate microglia
preserves mitochondrial function (Kaneko et al., 2016), through the receptor for advanced glycation end prod-
potentially by acting on the mitochondrial unfolded ucts (RAGE) (Massey et al., 2019; Yamamoto and
protein response (Bordt et al., 2019). The process of Higashida, 2020). All of these effects are abolished in
parturition is considered an inflammatory/immune the presence of OXTR antagonism (Tyzio et al., 2006;
event in which offspring are exposed to reduced oxygen Ceanga et al., 2010; Kaneko et al., 2016) and are
and blood flow (Lagercrantz and Slotkin, 1986; Tyzio consistent with the anti-inflammatory and neuropro-
et al., 2006; Maron et al., 2010), a surge in stress tective functions of oxytocin signaling during hypoxic-
hormones (Lagercrantz and Slotkin, 1986), elevated ischemic events, including birth. Moreover, the serum of
fetal cytokines (Castillo-Ruiz et al., 2018), and antigen pregnant women administered the OXTR antagonist
colonization (Costello et al., 2012; Castillo-Ruiz et al., atosiban for preterm labor displays an increase in
2018). Under hypoxic-ischemic conditions, oxytocin has oxidative stress and a decrease in antioxidant capac-
been shown to confer neuroprotection to fetal tissue on ity compared with women in preterm labor who did
the day of birth by reducing the metabolic demand of not receive atosiban (Grzesiak et al., 2018). Similarly,
neurons through a dramatic and precise switch in the plasma of offspring born to pregnant rats treated
GABAergic signaling that attenuates the elevation of with atosiban is characterized by increased oxidative
intracellular chloride (Tyzio et al., 2006; Khazipov et al., stress compared with the plasma of offspring born to
2008). This oxytocin-mediated switch delays the time to saline-injected mothers (Simsek et al., 2012). Finally,
anoxic depolarization, a process of accelerated cell term babies born to mothers who underwent elective
death that is characterized by significant increases in cesarean sections at term are characterized by
 Oxytocin As Medicine 847

significantly lower levels of serum oxytocin at birth as polyneuropathy (Erbas et al., 2017), and attenuates
compared with vaginally delivered infants (Marchini stress-induced GI motility disorders (Yang et al., 2019).
et al., 1988), suggesting a reduction in the protective,
anti-inflammatory actions of oxytocin with cesarean G. Oxytocin Is Protective to the Developing Gut
deliveries. The increased expression of OXTR in enteric neurons
and enterocytes in intestinal tissue coincides with the
periods of birth and lactation, a time when the fetal gut
F. Oxytocin and Gastrointestinal Inflammation is simultaneously exposed to both endogenous maternal
A rich literature demonstrates that oxytocin also acts oxytocin (via maternal release at birth and during
as an anti-inflammatory protective molecule for the breastfeeding) and inflammatory processes, such as
adult and developing gastrointestinal system, including amino acid–insufficiency stress, bacterial antigen stim-
the period of gut microbial colonization at birth and ulation, and microbial colonization (Welch et al., 2009;
lactation during which the fetal gut is exposed to Klein et al., 2017; Kingsbury and Bilbo, 2019). The
significant antigen stimulation from thousands of bac- absence of Oxtr during development in Oxtr knockout
terial species (reviewed in Kingsbury and Bilbo (2019)) mice results in increased intestinal inflammation in
(Fig. 5). Within adult rodents, stress- and/or chemical- addition to increased macromolecular gut permeability,
induced colitis increases intestinal damage, oxidative increased gut motility, and disruption of mucosal
stress, neutrophil infiltration, the expression of inflam- maintenance (Welch et al., 2014), indicating that the
matory pathway genes, and anxiety-related behavior oxytocin-signaling system has important functions for
(Iseri et al., 2008; Cetinel et al., 2010; Welch et al., the establishment of the gastrointestinal system. Spe-
2014). Oxytocin treatment dampens the severity of cifically, oxytocin signaling has been shown to reduce
intestinal damage and alleviates anxiety, whereas co- cellular stress within Caco2BB cells, a human gut cell
administration of an OXTR antagonist or the use of Oxtr line used as an enterocyte model, by modulating the
knockout mice prevents oxytocin’s protective effects unfolded protein response (UPR) in the endoplasmic
(Iseri et al., 2008; Cetinel et al., 2010; Welch et al., reticulum (UPRER)) (Klein et al., 2013, 2014, 2016). The
2014). Similar to offering neuroprotection to the brain UPRER can be activated during inflammation or im-
during hypoxic-ischemic events, oxytocin appears to mune challenges or in response to other stressors (Bordt
protect the gut during reduced intestinal blood flow et al., 2019) and is a cellular stress response that
within a model of burn-induced gastric injury (Iseri occurs when there is a buildup of unfolded and/or
et al., 2008). Thermal burns produce transient splanch- misfolded proteins within the endoplasmic reticulum
nic vasoconstriction followed by oxidative and nitro- of cells. This accumulation of proteins activates the
sative intestinal injury and increased reperfusion UPRER, which serves to trigger signaling cascades
injury and, if severe enough, increased intestinal per- that halt protein synthesis, reduce protein load, and
meability, sepsis, and organ failure (Iseri et al., 2008). restore cellular homeostasis (Schroder and Kaufman,
Whereas rats exposed to a thermal burn followed by 2005; Hetz et al., 2011; Hetz, 2012). In addition to the
a subcutaneous saline injection are characterized by UPRER, oxytocin also modulates autophagy, a process
greater levels of malondialdehyde and myeloperoxidase in which cellular components are degraded and
activity, greater gastric neutrophil infiltration, and recycled to restore homeostasis (Klein et al., 2014).
greater microscopic damage scores of the gastric mucosa
and skin, experimental rats that received two sub- H. Oxytocin and Breast Milk
cutaneous injections of oxytocin had a significant atten- In an effort to simulate the exposure of developing
uation of skin damage and burn-induced oxidative enterocytes to bacterial endotoxin via breast milk, Klein
damage of the intestinal mucosa (Iseri et al., 2008). et al. (2016) treated Caco2BB cells with LPS. Whereas
Furthermore, Erdman and colleagues have shown that LPS increased NF-kB proinflammatory signaling and
the gut bacterium, Lactobacillus reuteri, acting through suppressed the UPRER within Caco2BB cells, oxytocin
vagal nerve stimulation promotes the endogenous re- treatment prevented these LPS-mediated effects (Klein
lease of oxytocin, which functions to accelerate wound et al., 2016). This led Klein and associates (Klein et al.,
healing of the skin by activating CD4+Foxp3+CD25+– 2017) to propose that, during the lactation period,
immune regulatory T cells (Poutahidis et al., 2013; oxytocin in colostrum and breast milk both protects
Varian et al., 2017). Moreover, in a rodent model of enterocytes from apoptotic cell death amid low level
necrotizing enterocolitis induced by formula feeding, antigen microbial stimulation and modulates cellular
maternal separation, and intermittent hypoxia, oxyto- metabolism via phasic UPR runs to promote enterocyte
cin administration decreases the severity of intestinal cell differentiation. Klein et al. (2017) further showed
inflammation, whereas the OXTR antagonist exacer- that both colostrum oxytocin and exogenous oxytocin
bates it (Gross Margolis et al., 2017). Oxytocin also protect primary intestinal rat villi at birth from cellular
reduces visceral hypersensitivity, a feature of intesti- stress induced by amino acid starvation, a period of
nal bowel syndrome (Xu et al., 2018) and diabetic nutrient insufficiency between birth and first feeding.
848 Carter et al.

Fig. 5. Oxytocin acts as an anti-inflammatory molecule for the gastrointestinal system in the presence of stressors. For the developing gut, oxytocin
confers protection in the presence of a stressor by inhibiting the activation of proinflammatory cascades by activating the UPRER and by enhancing
autophagy. For the adult gut, oxytocin confers protection in the presence of a stressor by inhibiting proinflammatory cascades by inhibiting enteric glia
and NF-kB signaling by activating the UPRER by enhancing autophagy and by decreasing oxidative stress. Although oxytocin mediates many aspects
of social behavior and cognition after stress-aggravated colitis, oxytocin has been shown to decrease anxiety-like behavior (Cetinel et al., 2010).
Inflammatory cascades are shown in purple, and oxytocin signaling is shown in red. All of oxytocin’s protective effects shown here are believed to be
mediated by oxytocin binding to the OXTR. CCR5, C-C chemokine receptor-5; GSH, reduced glutathione; LDH, lactate dehydrogenase; MDA,
malondialdehyde; MPO, myeloperoxidase.

Specifically, oxytocin dampens inflammatory process, system (Karelina and DeVries, 2011; Bordt et al.,
halts protein translation, and promotes autophagy in 2019; Kingsbury and Bilbo, 2019). Interestingly, some
newborn intestinal villi. of oxytocin’s wound-healing properties are mediated via
vagal nerve stimulation by the intestinal bacteria L.
I. Oxytocin and the Healing of Damaged Tissues reuteri, which causes an elevation in PVN oxytocin
In addition to its protective role for developing and followed by an increase in systemic oxytocin (Varian
adult gastrointestinal tissue, endogenous oxytocin, at et al., 2017).
high levels, has been implicated in human wound
healing (Gouin et al., 2010) and is protective against J. Oxytocin and Developmentally
cardiovascular dysfunction via a suppression of inflam- Induced Inflammation
matory processes mediated by neutrophils, macro- Benefits of oxytocin are often seen in developmental
phages, T lymphocytes, TNF-a, and IL-6 (Jankowski rodent models, such as maternal separation or phar-
et al., 2016; Reiss et al., 2019). Among other commonly macological or genetic models capable of creating
studied models in which oxytocin has been shown to be animals with atypical patterns of social behavior and
anti-inflammatory are those involving the healing of associated elevations in inflammation. Neonatal
tissue flaps (Xu et al., 2017) and ovarian cancer (Cuneo rodents respond with increases in inflammation after
et al., 2019). Within human patients, higher levels of nutrient insufficiency, maternal separation, or injec-
ascites oxytocin were associated with lower levels of the tions that induce inflammation (Klein et al., 2018). In
proinflammatory cytokine IL-6 and a significant sur- all of these cases, there is evidence that oxytocin is
vival advantage. Moreover, oxytocin inhibited IL-6 pro- protective. Atypical behaviors, tissue damage, and
duction in cancer cell lines (Cuneo et al., 2019). Oxytocin microglial activation can be reduced by oxytocin treat-
also may restore tissue after procedures that damage ments (Wang et al., 2018; Zinni et al., 2018; Mairesse
the nervous system, intestines, and cardiovascular et al., 2019).
 Oxytocin As Medicine 849

K. Oxytocin, CD38, Immune Function, and reported to improve social behavioral deficits within
Social Behavior autistic patients and animal models (Higashida et al.,
Previous as well as recent findings suggest that some 2018). Intriguingly, this model helps explain our earlier
of oxytocin’s protective effects on immune function and findings of greater hypothalamic oxytocin-Fos colocali-
social behaviors are mediated by CD38. CD38 is a well- zation in subordinate and nonsocial stressed finches
known immune marker that is expressed by a range of (Goodson et al., 2015) as well as the facilitation of
immune cells (T cells, B cells, macrophages, natural partner preference formation in LPS-injected female
killer cells), is involved in the proliferation and immune prairie voles (Bilbo et al., 1999).
responses of lymphocytes, and serves as a diagnostic
marker for lymphoma, leukemia, myeloma, and human L. Oxytocin Regulates Probiotic Bacteria
immunodeficiency virus infection (Malavasi et al., Other treatments that may act through oxytocin
2008). Within the brain, CD38 is a transmembrane include the benefits of probiotic bacteria, such as L.
receptor on hypothalamic neurons that catalyzes the reuteri (Erdman and Poutahidis, 2016; Sgritta et al.,
formation of cyclic ADP-ribose (cADPR) and nicotinic 2019), found in colostrum and breast milk (Klein et al.,
acid adenine dinucleotide phosphate from NAD+ and 2018). For instance, adequate levels of intestinal L.
NAD phosphate (Deaglio and Malavasi, 2006). These reuteri stimulate adequate oxytocin PVN production
molecules play an integral role in the regulation of that is necessary for typical social affiliation (Sgritta
intracellular Ca2+ and control highly conserved pro- et al., 2019), particularly after prenatal exposure to an
cesses, such as egg fertilization, muscle contraction, inflammatory maternal high-fat diet (Buffington et al.,
hormone secretion, and immune function (Malavasi 2016). Some of these in vivo anti-inflammatory benefits
et al., 2008). In the hypothalamus, both cADPR and of oxytocin are autonomically mediated by the vagal
nicotinic acid adenine dinucleotide phosphate serve to pathways (Garrott et al., 2017; Reyes-Lagos et al.,
increase intracellular Ca2+, thereby triggering the 2019). Importantly, anti-inflammatory and beneficial
central and peripheral release of oxytocin that is behavioral effects of oxytocin have been detected both
important for a variety of social behaviors (Higashida in vivo and in vitro (Szeto et al., 2008; Gutkowska and
et al., 2012) Within CD38 knockout mice, neuroana- Jankowski, 2012; Szeto et al., 2017), indicating that the
tomical findings are consistent with deficits in hypotha- benefits of oxytocin are not limited to indirect neural or
lamic oxytocin secretion, and females show defects in endocrine actions.
maternal care, whereas males display social memory
impairments (Jin et al., 2007). These social behaviors M. Vasopressin and Inflammation
were rescued by subcutaneous OT injections or CD38 re- Vasopressin and AVPR1A have also been implicated
expression (Jin et al., 2007). Within humans, single- in immune function with effects that, in general, are
nucleotide polymorphisms of the CD38 gene have been proinflammatory and often opposite in direction from
associated with oxytocin inhibition and an increased those of oxytocin (Li et al., 2017b; Bordt et al., 2019). For
risk for autism (Lerer et al., 2010; Higashida et al., instance, vasopressin signaling exacerbates inflamma-
2012), a disorder characterized by immune dysfunction tory processes in the brain after ischemic stroke and
(McDougle et al., 2015). Moreover, human lymphoblas- traumatic brain injury (Szmydynger-Chodobska et al.,
toid cell lines derived from autistic patients show 2010, 2011). Furthermore, like oxytocin, vasopressin
reduced CD38 expression compared with those derived has roles for immune-system development, yet vaso-
from nonautistic controls (Lerer et al., 2010). Recent pressin may play a more limited role in immune-system
research also suggests that autism risk associated with regulation and in some cases can function to augment
vitamin A deficiency may be mediated through the oxytocin’s related immune effects (Li et al., 2017b).
CD38-oxytocin pathway (Gamliel et al., 2016; Lai
et al., 2018). In an intriguing review by Higashida N. Sex Differences in the Immune System
et al. (2018), evidence is put forth that hypothalamic As detailed below, recent research also links sex
oxytocin secretion is increased after social stress in differences and sexual differentiation to the immune
subordinate animals via a CD38-cADPR–dependent system (McCarthy et al., 2017; Dantzer, 2018, 2019).
mobilization of Ca2+ from intracellular stores and after These effects differ according to the social history of the
hyperthermia (triggered by LPS endotoxin exposure, individual, contributing to what has been termed
social stress, or stress coping) via a transient receptor “context” (Bartz et al., 2010; Carter, 2017). These effects
potential melastatin-2–dependent influx of Ca2+. also differ in physiology, with females more protected
Higashida et al. (2018) elaborate on how stress- than males in the context of stressors, such as birth,
induced oxytocin release caused by fever may explain because of their perinatal hormonal status and an
the transient recovery of social functions within autistic inherently greater antioxidant capacity within their
individuals during hyperthermia (Zhong et al., 2016), brains (Kingsbury and Bilbo, 2019). Thus, these effects
similar to how exogenous OT administration has been likely give rise to differences in how males and females
850 Carter et al.

respond to the protective functions of endogenous and can modify both of these peptides and their receptors.
exogenous oxytocin. During development, the vasopressin receptors appear
to be particularly sensitive to tuning by exogenous
peptides, with effects that also differ between males
XVI. Sex Differences
and females. For example, research in voles indicates
Oxytocin and vasopressin are produced by both males that vasopressin and its receptors can be developmen-
and females; however, the functions of these peptides tally regulated by exposure to exogenous oxytocin, thus
vary between sexes and among species (Carter and contributing to altered capacity to form pair bonds (Bales
Perkeybile, 2018). Because of the adaptive nature of et al., 2007). In both sexes, exposure to a relatively low
these hormonal systems and the fact that sexual differ- dose of exogenous oxytocin shortly after birth reduces the
entiation is influenced by genetics, epigenetics, and expression of AVPR1A in several other brain areas
physiologic processes (including inflammation) across (Bales et al., 2007). However, in male prairie voles, the
the lifespan (McCarthy et al., 2017), the relationship same treatment increases the expression of vasopressin
between sex and peptides is not very well-understood. receptors in the ventral pallidum, a brain region associ-
Steroids, including estrogen and testosterone of either ated with reward and pair bonding. In another experi-
endogenous or exogenous origins, can influence both ment in prairie voles using a wide range of doses of
oxytocin and vasopressin as well as the expression of vasopressin, dose-dependent increases in vasopressin in
their receptors (Jirikowski et al., 2018). The study of sex the 1st week of life were followed by increases in
differences in oxytocin and vasopressin is further compli- aggression in adulthood. These effects on aggression,
cated by dynamic changes in steroids that are experi- necessary for mate guarding, also were most pronounced
enced in both sexes across the lifecycle. in males (Stribley and Carter, 1999).
A thorough description of factors regulating sex differ-
ences is beyond the scope of this review, although this topic C. Sex Differences in Response to Stress and Trauma
is discussed in some depth in earlier reviews from our group
Sex differences in the oxytocin-vasopressin system
(Carter, 2003, 2014, 2017; Carter et al., 2009; Carter and
often are most apparent in the face of stressful experi-
Perkeybile, 2018; Kenkel et al., 2019). However, knowledge
ences, including social and hormonal experiences in
of sex differences with regard to the functions of oxytocin
early life (Carter et al., 2009; Kenkel et al., 2019).
and vasopressin is greatly needed in the development of
Glucocorticoids and other hormones released during
peptide-based treatments for mental and physical disor-
stressful experiences also can have major effects on
ders, including substance abuse, schizophrenia, and trauma
oxytocin, and oxytocin can act to moderate the release of
(Macdonald, 2013). This is particularly important since,
and effects of glucocorticoids. For example, glucocorti-
for several of these disorders, one sex often has greater
coids and exposure to stressors have been shown to
vulnerability for social and cognitive dysfunction.
upregulate the oxytocin receptor (Liberzon and Young,
A. Sex Differences in Vasopressin 1997).
Effects of vasopressin are often more apparent in males
versus females. Of particular relevance to understanding D. Sex Differences in Strategies Used to
interactions between oxytocin and vasopressin is the Manage Challenges
consistent finding that vasopressin in the nervous system We can speculate that activation of central vasopres-
is affected by androgens. In rodent brains, endogenous sin or its receptors and associated increases in the
vasopressin synthesis is androgen-dependent and sexually sympathetic nervous system would allow more active or
dimorphic within an axis that modulates self-defensive mobilized responses to emotional and physiologic chal-
behavior (de Vries and Forger, 2015; Dumais and Veenema, lenge including the capacity for aggression and physical
2016). Vasopressin receptors also vary regionally between violence. For example, it is possible that a male-biased
males and females (DiBenedictis et al., 2017). dependence on vasopressin might help explain the
Responses to exogenous vasopressin also can differ in capacity of male prairie voles to form social bonds in
males and females (Dantzer, 1998; Thompson et al., the face of extreme challenges, whereas stress inhibits
2006; Carter et al., 2009). However, vasopressin also heterosexual pair-bond formation in females (DeVries
functions in conjunction with oxytocin to facilitate et al., 1996). Dependence on vasopressin would leave
selective social behaviors, including social bonds and males more capable of responding to challenges associated
selective aggression (Cho et al., 1999; Carter, 2017). with defending the family using mobilized responses.
However, if generalized to other species, this sex difference
B. Developmental Effects of Oxytocin and Vasopressin may also leave males more vulnerable to disorders or
Are Often Sexually Dimorphic injury associated with increased aggression and risk
Adding to the complexity of the sex differences in taking (Carter, 1998, 2007; Dantzer, 2019). Concurrently,
these peptides are findings that indicate that the males appear to be protected against shut-down responses,
presence of oxytocin or vasopressin during development especially in life-threatening situations, via vasopressin
 Oxytocin As Medicine 851

and associated increases in alertness or arousal in the face bleeding, and an early “sensitive” period for mother-
of threats. infant bonding (Nissen et al., 1995).

E. Females and Vasopressin H. Gonadal Steroids

Females also produce and rely on the physiologic Species variation also reflects differential sensitivity
effects of vasopressin. However, females are signifi- to gonadal steroids among mammals. For example,
cantly more vulnerable to disorders associated with behavioral patterns in socially monogamous species
shut-down responses or immobilization, such as de- may be particularly reliant on peptides, including
pression and post-traumatic stress disorder. In general, oxytocin and vasopressin, whereas fewer social species,
in adulthood females also may be more dependent on especially males of nonmonogamous species, seem more
estrogen and estrogen-oxytocin interactions. Thus, in behaviorally dependent on gonadal steroids, including
the presence of deficiencies in either oxytocin or its androgens (Carter and Perkeybile, 2018). Adaptive
receptor, females may be more vulnerable to disorders, variations in the relative importance of steroids and
including symptoms of depression, characterized by peptides are critical to understanding the origins of
either generalized anxiety or passive responses. For species and sex differences but also may help in un-
example, female humans also are at least twice as likely derstanding individual differences in the consequences
to be victims of trauma or other adversities, which in of treatments with exogenous molecules.
turn can increase later vulnerability to emotional
disorders (Altemus et al., 2014). XVII. Implications for Oxytocin in Mental and
F. Sex Differences in Response to Exogenous Peptides Physical Health

The consequences of treatment with exogenous pep- A. Social Support and Perceived Safety
tides can vary by sex in humans (Thompson et al., 2006; The effects of endogenous oxytocin and vasopressin
Domes et al., 2010; Taylor et al., 2010), nonhuman on brain-body connections, including the immune and
primates (Jiang and Platt, 2018), and other mammals autonomic nervous system may help to explain the
(De Vries and Panzica, 2006; Carter, 2007; Albers, 2015; profound health-related effects of social relationships or
Okhovat et al., 2018). In postmenopausal women, their absence. Despite the complexity associated with
increases in endogenous oxytocin have been associated using exogenous peptides as medicines, there has been
with “gaps in social relationships” (Taylor et al., 2006). considerable optimism generated by short-term behav-
Releasing oxytocin may be a component of a self- ioral effects of oxytocin. Oxytocin appears to be of
regulatory process that helps mammals deal with iso- special relevance to physical and mental protective
lation, stress coping, and recovery from trauma. For adaptations that involve high levels of sociality or social
example, female prairie voles subjected to a 1-hour support and a sense of psychologic safety as well as
immobilization stress recovered faster in the presence emotional regulation and autonomic stability that are
of their male partner as opposed to recovering alone, necessary for mental health and higher levels of
displaying less anxiety-like behavior, lower levels of the cognitive functions (Carter, 2014).
stress hormone corticosterone, and increased PVN
oxytocin release (Smith and Wang, 2014). Furthermore, B. Oxytocin in Psychologic Functioning
the benefits of this oxytocin-mediated social buffering A recurring issue in attempts to use oxytocin as
were recapitulated in stressed females that were sub- a medicine is the need to understand its role in
sequently isolated after they received injections of behavioral and physiologic adaptations and resilience
oxytocin in the PVN (rather than access to their in the face of stressors and trauma. Nervous system
partner) (Smith and Wang, 2014). These hormonal activity, neural connectivity, and responses to social
responses could also facilitate subsequent social en- stimuli have been related to peripheral peptide concen-
gagement and relationships as well as boost the im- trations in both neurotypical individuals (Lancaster
mune system (see below), functions that would be et al., 2018a) and those diagnosed with various mental
especially adaptive in females who may be less able illnesses, such as schizophrenia or bipolar disorder
than males to survive alone (Taylor et al., 2010). (Rubin et al., 2018). Peripheral levels of oxytocin and
vasopressin or variations in their receptors have been
G. The Stress of Birth associated with function in Williams syndrome (Dai
Oxytocin may be of special relevance in helping et al., 2012), autism spectrum disorders (Oztan et al.,
infants (Tyzio et al., 2006, 2008) and mothers recover 2018b), schizophrenia (Rubin et al., 2014, 2018), de-
from the trauma of birth while simultaneously engaging pression (Cyranowski et al., 2008; Goekoop et al., 2011),
in mother-infant bonding (Nissen et al., 1995). For postpartum depression (Zelkowitz et al., 2014; Bell
instance, there are peaks in serum oxytocin immedi- et al., 2015), borderline personality disorders (Brune,
ately postpartum in women that correspond with the 2016), eating disorders (Aulinas et al., 2019), and sub-
expulsion of the placenta, contractions to reduce uterine stance abuse (Buisman-Pijlman et al., 2014).
852 Carter et al.

XVIII. Examples of the Complexity Encountered childhood abuse, with generally lower levels in individuals
in Treating Disease with Oxytocin-Like Drugs who have experienced greater emotional adversity in early
life (Heim et al., 2009; Toepfer et al., 2017). Moreover, the
A large scientific literature, beyond the scope of this
release of oxytocin differs according to the adult attach-
review, has implicated oxytocin in both health and
ment style of the individual. In one study, oxytocin levels
illness. However, the relationships between endoge-
were elevated in trauma survivors, supporting the hypoth-
nous and responses to exogenous oxytocin have not
esis that oxytocin serves a “stress-coping” function. How-
been easily identified. In some individuals and for
ever, a lower level of increase in oxytocin in response to
a subset of disorders, the effects of exogenous oxytocin
a stressor was seen in individuals with a “dismissive”
have been negative. Below, we offer examples of the
attachment style compared with more securely attached
complexity associated with the use of oxytocin as
individuals (Pierrehumbert et al., 2012). However, “se-
a therapeutic in postpartum depression and cancer.
cure” attachment or a “sense of safety,” as used in
Among the sources of variation in outcomes are genet-
psychologic research, is a theoretical construct, which
ics, epigenetics, and especially adversity in early life. In
must be translated into physiologic states. The relation-
addition, as described below in the case of cancer, effects
ship between oxytocin and trauma in adulthood has not
of oxytocin on different subcellular signaling pathways
yielded consistent results (Engel et al., 2019), and
will need to be considered in creating safe medicines
perhaps a fuller consideration of early life experience
based on oxytocin-like molecules.
could resolve this. Thus, psychologic context can manifest
as physiology, with consequences for the actions of
A. Postpartum Depression oxytocin and vasopressin; this of course complicates the
Because of its central role in birth and lactation, attempts to study these peptides in clinical populations.
oxytocin was a logical target as an explanation for and The effects of the relationship between oxytocin and
treatment of postpartum depression. We hypothesized the symptoms of postpartum depression are particu-
that endogenous oxytocin, including that released as larly obvious in women experiencing stress (Zelkowitz
a consequence of lactation, would be protective against the et al., 2014; Massey et al., 2016) or with a history of
development of postpartum mood shifts, possibly in part by adversity (Walsh et al., 2018). Furthermore, early life
reducing susceptibility to social or environmental stressors stress and the emotional history of an individual can
(Carter and Altemus, 1997). There is increasing experimen- influence the reaction to exogenous oxytocin. For exam-
tal evidence for this hypothesis (Gust et al., 2020). ple, in a placebo-controlled experiment, intranasal
Comparatively lower concentrations of plasma oxyto- oxytocin was administered to women diagnosed with
cin, both prenatally and postpartum, have been associ- postpartum depression (Walsh et al., 2018). In that
ated with increased symptomology (Skrundz et al., study, oxytocin decreased symptoms in women who did
2011; Stuebe et al., 2013; Cox et al., 2015; Garfield not have a history of early life stress but increased
et al., 2015). Specific polymorphisms within both OXT symptoms in women with a history of stress.
(Jonas et al., 2013) and OXTR (Apter-Levy et al., 2013; Depression, used in a more general sense, also has
Mileva-Seitz et al., 2013) also appear to confer vulner- proven difficult to reliably relate to endogenous oxytocin.
ability to developing postpartum depression. Women Several studies show a decrease in peripheral oxytocin
with higher reported levels of psychosocial stress in with increased depressive symptoms (Frasch et al., 1995;
early pregnancy and postpartum had lower depressive Scantamburlo et al., 2007; Ozsoy et al., 2009; Seay et al.,
symptoms if they had higher levels of circulating oxytocin 2014). However, individuals with increased depressive
(Zelkowitz et al., 2014). In addition, epigenetic modifica- symptoms sometimes exhibit increased levels of oxytocin
tion of OXTR via DNA methylation at specific CpG sites in (Parker et al., 2010; Holt-Lunstad et al., 2011; Seay et al.,
the promoter region also increased the risk of postpartum 2014). Furthermore, high levels of oxytocin-staining cells
depression, with effects that were expressed in a geno- have been detected in postmortem tissue; people with
type-specific manner (Bell et al., 2015). major depressive disorder had a greater number of
However, there is considerable individual variation in oxytocin and vasopressin-immunoreactive cells in the
oxytocin concentrations and in the oxytocin receptor in PVN compared with controls (Purba et al., 1996). There
pregnancy and postpartum. It is possible that knowl- are also reports of increased variability in oxytocin levels
edge of these differences, especially in the context of in people with depressive symptoms compared with
individual variations in life history, as well as the controls (van Londen et al., 1997; Cyranowski et al.,
specific levels of peptides and receptors for both oxyto- 2008). Studies such as these suggest dysregulation in the
cin and vasopressin, can be used to predict or treat oxytocin-vasopressin system possibly associated with
disorders, such as postpartum depression. Further- stressful experiences across the lifespan and the emo-
more, in humans it appears that the adult response to tional experiences described as major depression (Bao
exogenous oxytocin is moderated by early life experi- and Swaab, 2018). These studies also illustrate the
ences including trauma (Walsh et al., 2018). The release challenges associated with using oxytocin as therapy for
of endogenous oxytocin also has been related to early behavioral disorders.
 Oxytocin As Medicine 853

B. Oxytocin and Cancer: a Complex Relationship historical applications of oxytocin as an intranasal

The use of oxytocin as a pharmaceutical also requires “lactational aid” or as an intravenous treatment in
attention to possible physical side effects of prolonged labor induction. Both of these applications were origi-
exposure to this molecule. In many physical disorders, nally used in women who were pregnant or who had just
including cancer, social support is associated with given birth. Whether these doses and treatment regi-
reduced risk of disease progression (Hinzey et al., mens extrapolate to men and nonpregnant subjects,
2016). Lactation has long been associated with reduc- including children, is not well-studied.
tions in breast cancer (Lerman et al., 2018). In these Studies using different amounts of oxytocin are
cases, oxytocin is a plausible protective mechanism. For needed to examine possible threshold differences
example, a variety of experiments, including animal among individuals as a function of sex, experience,
research and in vitro studies supports the hypothesis and emotional lability (Goldman et al., 2011). Different
that oxytocin can inhibit tumor growth in breast cancer. doses of a given peptide can produce different effects
In addition, breast tumor growth is inhibited (or (Ceanga et al., 2010; Klein et al., 2014; Borland et al.,
perhaps prevented) by exercise, another effect that 2019), and dose-response curves are only just appearing
has been attributed to the capacity of exercise to release in the in vivo literature (Price et al., 2017).
oxytocin (Alizadeh et al., 2018). B. Individual and Sex Differences Are to Be Expected
In another example, the finding of exceptionally high in Both the Production of and Response to Oxytocin
levels of oxytocin in samples taken from ovarian cancers
is particularly intriguing. Levels of oxytocin measured As discussed above, the production of oxytocin varies
within tumors were associated with inflammatory among individuals, between males and females
markers, including IL-6, as well as patient survival. (Borland et al., 2019), and across the lifespan as well
Thus, tissues challenged by cancer may produce healing as in the capacity to respond to either endogenous or
levels of oxytocin (Cuneo et al., 2019). exogenous hormones (Plasencia et al., 2019). For exam-
However, the effect of oxytocin may not be universally ple, studies of the effects of oxytocin on neural responses
beneficial. For example, there is conflicting evidence measured by functional magnetic resonance imaging
from several studies that prostate cancer, breast cancer, have revealed marked sex differences in the effects of
uterine cancer, and osteosarcomas can be either in- even a single intranasal treatment (Domes et al., 2010).
creased or decreased by oxytocin (Lerman et al., 2018). Connectivity in the orbital frontal cortex, which is
Among the types of cancer for which there are indica- important in emotion processing, was correlated with
tions that exogenous oxytocin can increase proliferation oxytocin in women and vasopressin in men (Rubin et al.,
and thus could be dangerous are prostate, uterine, and 2018). The developmental effects of these peptides are of
small cell lung cancer. special concern and are different in males and females
The complex relationships between oxytocin and (Carter, 2003; Bales et al., 2007) and in the face of
cancer provide insight into the specificity of oxytocin’s adversity and stressful experiences.
effects. The local availability of oxytocin or its receptor, C. The Basic Biochemistry of Oxytocin, Including Its
the tumor cell type, and the differential activation of Capacity to Bond to Other Molecules, Creates
subcellular signaling pathways downstream of OXTR Special Challenges
can give rise to a unique oxytocin effect. For instance,
there are three different subtypes of the guanine The crosstalk between oxytocin, vasopressin, and
nucleotide–binding protein-a (Ga) (Gai, Gas, and Gaq) their receptors (Figs. 2 and 3) has complicated attempts
that couple to OXTR and that have separable functions. to create a medicine based on one or the other of these
Gaq has been implicated in muscle contractions and peptides (Caldwell, 2017; Carter, 2017; Song and
cellular proliferation, whereas Gai and Gas may be Albers, 2018; Wang et al., 2019). The evolutionary basis
antiproliferative (Lerman et al., 2018). Thus, effects on of the oxytocin-vasopressin system permits a large
different subcellular signaling pathways could have number of functional permutations and creates signif-
opposite effects on cancer. Observations like these icant obstacles to the creation of “medicines” based on
illustrate the challenges for creating drugs that opti- these molecules. These interactions need to be consid-
mize the benefits of oxytocin while reducing risks. ered if oxytocin-based molecules are to be used as the
basis of a medicine (Feng et al., 2015; Li et al., 2017a).
Moreover, as discussed here, developing effective phar-
XIX. Pharmacology and Oxytocin: Issues in maceuticals based on oxytocin requires awareness of
Therapeutic Applications functional issues associated with oxytocin-vasopressin
interactions and the biologic factors through which
A. The Effects of Oxytocin Are Dose-Dependent experience alters the functions of these molecules. As
Doses of oxytocin currently used in human research just one example, as described above, our research in
have been restricted by availability and reliable access. prairie voles has revealed that small changes in expe-
Moreover, doses that were available were based on rience or hormonal exposure, especially in early life,
854 Carter et al.

have epigenetic consequences for the expression of Oxtr with a role in regulating inflammation—once more
(Kenkel et al., 2019; Perkeybile et al., 2019). implicating oxytocin in the body’s adaptive response to
immune challenges (Figs. 4 and 5).
Imaging studies in rats comparing the effects of
XX. Methods for Administering Oxytocin or
oxytocin given intravenously versus intracerebral in-
Stimulating the Oxytocin System
fusion revealed that these two methods had very differ-
Studies of the effects of peripherally administered ent consequences for blood oxygen level–dependent
oxytocin offered a new perspective on the role of activity within the nervous system (Ferris et al., 2015).
oxytocin in human behavior and aroused great interest Imaging studies in humans also reveal that different
in therapeutic applications of oxytocin (Kosfeld et al., methods of administration of oxytocin can produce
2005; Macdonald and Feifel, 2013). Dozens of clinical different outcomes. For example, intranasal spray versus
trials are now examining the functional effects of OXTR a nebulizer elicited responses, albeit in different brain
agonists, including oxytocin and related drugs, such as areas and possibly in different regions of the olfactory
the selective oxytocin receptor agonist carbetocin. Clin- tract (Martins et al., 2020). These findings support the
ical studies typically report positive outcomes in at least potential usefulness of intranasal administration but
a subset of patients. leave the mechanisms of action open to further investi-
In behavioral studies oxytocin has been most typi- gation. It also remains to be determined which methods
cally administered by intranasal spray. However, the of administration of exogenous oxytocin might be most
behavioral effects of oxytocin have been questioned by functionally comparable to the effects of endogenously
complex findings from those studies, as detailed in released peptides.
many reviews (De Dreu, 2012; Macdonald and Feifel,
2013; Bethlehem et al., 2014; Bernaerts et al., 2017; B. Placental Transport of Oxytocin
Hurlemann and Grinevich, 2018). Moreover, even trials The weak penetrance of oxytocin through both the
based on the classic nine–amino acid oxytocin molecule placenta and blood-brain barrier has been used as
are often limited by the use of acute treatment protocols; a justification for the wide use of Pitocin in labor
in most cases a single treatment is used. Analysis of induction. However, the evidence for transplacental
repeated and long-term effects of oxytocin or oxytocin- passage of oxytocin has been mixed, with both positive
like molecules are rare, although even in adults, the and negative results reported [reviewed Kenkel et al.
effects of oxytocin-like drugs differ by the duration and (2014)]. Interestingly, levels of oxytocin in cord blood
dose used, and the effects may last for weeks beyond the measured within 1 minute of birth were significantly
time of treatment (Moy et al., 2019). Interpretation of elevated in infants born via a vaginal birth (without
these findings needs to be considered in the context of maternal exogeneous oxytocin administration) as com-
early life experience and the capacity of oxytocin to pared with infants born via elective cesarean section
interact with vasopressin receptors (Carter, 2017) as before labor started (Marchini et al., 1988). Further
well as other features of oxytocin’s functions detailed in complicating understanding of their mechanisms of
the current review. action, peptide receptors exist throughout the viscera,
such as in the digestive tract (Welch et al., 2014). These
A. Does Peripherally Administered Oxytocin Reach receptors may allow oxytocin-like molecules to stimu-
the Brain? late vagal afferents, thereby circumventing the blood-
In its classic nine–amino acid form, it was tradition- brain barrier in the transmission of information back to
ally argued that oxytocin did not readily cross the blood- the brain.
brain barrier (Leng and Ludwig, 2016). However, in
studies done in monkeys, intranasally administered C. Oral Oxytocin
oxytocin labeled with deuterium was detected in cere- Oxytocin is present in milk, and oral treatments with
brospinal fluid (Lee et al., 2018) and in brain regions oxytocin, especially in young animals, may be an
where oxytocin activity influences motivated behaviors important route for influencing this system. Recent
(Lee et al., 2020). This argument also is diminished by research in mice demonstrates that oxytocin is resistant
recent awareness of the capacity of RAGE to act as an to digestion (Yamamoto and Higashida, 2020) and is
oxytocin-binding protein facilitating the transport of active in milk and colostrum, with effects on brain and
oxytocin across the blood-brain barrier and through behavior, especially in preweaning animals (Welch
other tissues (Yamamoto and Higashida, 2020). RAGE et al., 2014; Higashida et al., 2017; Klein et al., 2018;
exists in a soluble form in blood and is also bound to cell Tabbaa and Hammock, 2020). For example, Tabbaa and
membranes. Of particular interest to the functions of Hammock (2020) report that orally administered oxy-
oxytocin, the directionality of this transport is 5– tocin affects the nervous system in young mice. Fur-
10 times higher from the blood to the brain, in thermore, RAGE transports oxytocin readily across the
comparison with brain to blood transport. Furthermore, intestinal epithelium during the first postnatal week in
RAGE is a member of the immunoglobulin superfamily mice when the intestinal barrier is still fairly permeable
 Oxytocin As Medicine 855

(Higashida et al., 2017). Although oxytocin absorption Furman, 2011; Hinzey et al., 2016). As describe above,
from the gut lumen to the blood can occur in adults, a 10- oxytocin also has powerful immune consequences (Figs.
fold higher concentration of oxytocin is required 4 and 5), may promote longevity, and could have played
(Higashida et al., 2017). As described above, comparable a central role in human evolution (Carter, 2014).
processes that are dependent on RAGE appear to occur However, attempts to create safe drugs based on this
in the nervous system, permitting crossing of the blood- molecule must take into account oxytocin’s unique
brain barrier (Yamamoto et al., 2019). Knowledge of evolutionary history and complex integrative adaptive
RAGE suggests yet another method for regulating the properties that span the physiologic and social realms.
availability of and transport of oxytocin (Yamamoto and
Higashida, 2020). For example, individual differences Acknowledgments
in RAGE could help to predict cellular access to oxytocin We are very grateful to Katie Krol, Josh Danoff, and Pat Kratoch-
and might also facilitate access to oxytocin under well for editorial assistance.
conditions of stress or illness (Higashida et al., 2018;
Yamamoto et al., 2019). Authorship Contributions
Wrote or contributed to the writing of the manuscript: Carter,
D. Increasing the Bioavailability of Oxytocin
Kenkel, MacLean, Wilson, Perkeybile, Yee, Ferris, Nazarloo, Porges,
Recent studies using methods to increase oxytocin’s Davis, Connelly, Kingsbury.
access to the nervous system have employed nano-
particle encapsulation (Oppong-Damoah et al., 2019). References
This method of drug-delivery increases bioavailability Acher R, Chauvet J, and Chauvet MT (1995) Man and the chimaera. Selective versus
of the oxytocin molecule both in cell-culture models of neutral oxytocin evolution. Adv Exp Med Biol 395:615–627.
Aguilera G, Subburaju S, Young S, and Chen J (2008) The parvocellular vaso-
the blood-brain barrier and in a mouse model of social pressinergic system and responsiveness of the hypothalamic pituitary adrenal axis
during chronic stress. Prog Brain Res 170:29–39.
behavior. Intranasal application of nanoparticle- Albers HE (2015) Species, sex and individual differences in the vasotocin/vasopressin
encapsulated of oxytocin had larger prosocial effects system: relationship to neurochemical signaling in the social behavior neural
network. Front Neuroendocrinol 36:49–71.
and behavioral changes that were sustained for at least Alizadeh AM, Heydari Z, Rahimi M, Bazgir B, Shirvani H, Alipour S, Heidarian Y,
3 days after treatment. It is likely that new methods for Khalighfard S, and Isanejad A (2018) Oxytocin mediates the beneficial effects of
the exercise training on breast cancer. Exp Physiol 103:222–235.
delivering oxytocin will have dramatic effects on this Altemus M, Sarvaiya N, and Neill Epperson C (2014) Sex differences in anxiety and
depression clinical perspectives. Front Neuroendocrinol 35:320–330.
field in the near future (Gulliver et al., 2019). Amini-Khoei H, Mohammadi-Asl A, Amiri S, Hosseini MJ, Momeny M, Hassanipour
M, Rastegar M, Haj-Mirzaian A, Mirzaian AH, Sanjarimoghaddam H, et al. (2017)
Oxytocin mitigated the depressive-like behaviors of maternal separation stress
through modulating mitochondrial function and neuroinflammation. Prog Neuro-
XXI. Summary psychopharmacol Biol Psychiatry 76:169–178.
Andari E, Nishitani S, Kaundinya G, Caceres GA, Morrier MJ, Ousley O, Smith AK,
Oxytocin has effects on the regulation of physiologic Cubells JF, and Young LJ (2020) Epigenetic modification of the oxytocin receptor
gene: implications for autism symptom severity and brain functional connectivity.
processes and emotional states associated with coping Neuropsychopharmacology 45:1150–1158.
and healing, with increasing evidence for beneficial Apter-Levy Y, Feldman M, Vakart A, Ebstein RP, and Feldman R (2013) Impact of
maternal depression across the first 6 years of life on the child’s mental health,
actions mediated by the autonomic and immune sys- social engagement, and empathy: the moderating role of oxytocin. Am J Psychiatry
tems. Oxytocin has special relevance for mammals, 170:1161–1168.
Arrowsmith S and Wray S (2014) Oxytocin: its mechanism of action and receptor
linking individuals to each other, with beneficial effects signalling in the myometrium. J Neuroendocrinol 26:356–369.
Aulinas A, Plessow F, Pulumo RL, Asanza E, Mancuso CJ, Slattery M, Tolley C,
on reproduction, social behavior, and stress coping. Thomas JJ, Eddy KT, Miller KK, et al. (2019) Disrupted oxytocin-appetite sig-
Endogenous oxytocin and vasopressin are integral naling in females with anorexia nervosa. J Clin Endocrinol Metab 104:4931–4940.
Avanti C, Hinrichs WLJ, Casini A, Eissens AC, Van Dam A, Kedrov A, Driessen
components of the body’s capacity to cope with stress. AJM, Frijlink HW, and Permentier HP (2013) The formation of oxytocin dimers is
However, the effects of exogenous oxytocin are context- suppressed by the zinc-aspartate-oxytocin complex. J Pharm Sci 102:1734–1741.
Baker M, Lindell SG, Driscoll CA, Zhou Z, Yuan Q, Schwandt ML, Miller-Crews I,
and dose-dependent (Huang et al., 2014). In individuals Simpson EA, Paukner A, Ferrari PF, et al. (2017) Early rearing history influences
oxytocin receptor epigenetic regulation in rhesus macaques. Proc Natl Acad Sci
with a history of extreme stress or trauma, the effects of USA 114:11769–11774.
oxytocin have been especially unpredictable (Walsh Bales KL, Plotsky PM, Young LJ, Lim MM, Grotte N, Ferrer E, and Carter CS (2007)
Neonatal oxytocin manipulations have long-lasting, sexually dimorphic effects on
et al., 2018). The reasons for this are unclear, but it is vasopressin receptors. Neuroscience 144:38–45.
possible that stimulation of the vasopressin receptor(s) Bao AM and Swaab DF (2018) The human hypothalamus in mood disorders: the HPA
axis in the center. IBRO Rep 6:45–53.
occurs, producing more primitive forms of response, Barnabi F and Cechetto DF (2001) Neurotransmitters in the thalamus relaying
visceral input to the insular cortex in the rat. Am J Physiol Regul Integr Comp
such as defensive behaviors or even behavioral or Physiol 281:R1665–R1674.
metabolic shutdown (Porges and Furman, 2011). Bartz JA, Zaki J, Ochsner KN, Bolger N, Kolevzon A, Ludwig N, and Lydon JE (2010)
Effects of oxytocin on recollections of maternal care and closeness. Proc Natl Acad
Oxytocin and its receptors are comparatively modern Sci USA 107:21371–21375.
molecules with particular relevance in mammalian Batra S (1986) Effect of oxytocin on calcium influx and efflux in the rat myometrium.
Eur J Pharmacol 120:57–61.
evolution, physiology, and social behaviors (Carter, Bell AF, Carter CS, Steer CD, Golding J, Davis JM, Steffen AD, Rubin LH, Lillard
TS, Gregory SP, Harris JC, et al. (2015) Interaction between oxytocin receptor
2014). Oxytocin, possibly acting via the autonomic DNA methylation and genotype is associated with risk of postpartum depression in
nervous system, seems to play a central role in support- women without depression in pregnancy. Front Genet 6:243.
Ben-Ari Y (2018) Oxytocin and vasopressin, and the GABA developmental shift
ive relationships and psychologic safety, helping to during labor and birth: friends or foes? Front Cell Neurosci 12:254.
protect and heal in the face of stress and adversity Bernaerts S, Prinsen J, Berra E, Bosmans G, Steyaert J, and Alaerts K (2017) Long-
term oxytocin administration enhances the experience of attachment. Psycho-
(Carter, 1998; Karelina and DeVries, 2011; Porges and neuroendocrinology 78:1–9.
856 Carter et al.

Bernhard A, van der Merwe C, Ackermann K, Martinelli A, Neumann ID, Chini B, Verhage M, and Grinevich V (2017) The action radius of oxytocin release in
and Freitag CM (2018) Adolescent oxytocin response to stress and its behavioral the mammalian CNS: from single vesicles to behavior. Trends Pharmacol Sci 38:
and endocrine correlates. Horm Behav 105:157–165. 982–991.
Bethlehem RA, Baron-Cohen S, van Honk J, Auyeung B, and Bos PA (2014) The Cho MM, DeVries AC, Williams JR, and Carter CS (1999) The effects of oxytocin and
oxytocin paradox. Front Behav Neurosci 8:48. vasopressin on partner preferences in male and female prairie voles (Microtus
Bilbo SD, Klein SL, DeVries AC, and Nelson RJ (1999) Lipopolysaccharide facilitates ochrogaster). Behav Neurosci 113:1071–1079.
partner preference behaviors in female prairie voles. Physiol Behav 68:151–156. Clodi M, Vila G, Geyeregger R, Riedl M, Stulnig TM, Struck J, Luger TA,
Bocheva A and Dzambazova-Maximova E (2004) Antiopioid properties of the TYR- and Luger A (2008) Oxytocin alleviates the neuroendocrine and cytokine re-
MIF-1 family. Methods Find Exp Clin Pharmacol 26:673–677. sponse to bacterial endotoxin in healthy men. Am J Physiol Endocrinol Metab
Bordt EA, Smith CJ, Demarest TG, Bilbo SD, and Kingsbury MA (2019) Mitochon- 295:E686–E691.
dria, oxytocin, and vasopressin: unfolding the inflammatory protein response. Costello EK, Stagaman K, Dethlefsen L, Bohannan BJ, and Relman DA (2012) The
Neurotox Res 36:239–256. application of ecological theory toward an understanding of the human micro-
Borland JM, Rilling JK, Frantz KJ, and Albers HE (2019) Sex-dependent regulation biome. Science 336:1255–1262.
of social reward by oxytocin: an inverted U hypothesis. Neuropsychopharmacology Cox EQ, Stuebe A, Pearson B, Grewen K, Rubinow D, and Meltzer-Brody S (2015)
44:97–110. Oxytocin and HPA stress axis reactivity in postpartum women. Psychoneur-
Bosch OJ and Young LJ (2018) Oxytocin and social relationships: from attachment to oendocrinology 55:164–172.
bond disruption. Curr Top Behav Neurosci 35:97–117. Cuneo MG, Szeto A, Schrepf A, Kinner EM, Schachner BI, Ahmed R, Thaker
Bowen MT, Carson DS, Spiro A, Arnold JC, and McGregor IS (2011) Adolescent PH, Goodheart M, Bender D, Cole SW, et al. (2019) Oxytocin in the tumor
oxytocin exposure causes persistent reductions in anxiety and alcohol consumption microenvironment is associated with lower inflammation and longer survival
and enhances sociability in rats. PLoS One 6:e27237. in advanced epithelial ovarian cancer patients. Psychoneuroendocrinology
Brandtzaeg OK, Johnsen E, Roberg-Larsen H, Seip KF, MacLean EL, Gesquiere LR, 106:244–251.
Leknes S, Lundanes E, and Wilson SR (2016) Proteomics tools reveal startlingly Cyranowski JM, Hofkens TL, Frank E, Seltman H, Cai HM, and Amico JA (2008)
high amounts of oxytocin in plasma and serum. Sci Rep 6:31693. Evidence of dysregulated peripheral oxytocin release among depressed women.
Brüne M (2016) On the role of oxytocin in borderline personality disorder. Br J Clin Psychosom Med 70:967–975.
Psychol 55:287–304. Dai L, Carter CS, Ying J, Bellugi U, Pournajafi-Nazarloo H, and Korenberg JR (2012)
Buemann B and Uvnäs-Moberg K (2020) Oxytocin may have a therapeutical poten- Oxytocin and vasopressin are dysregulated in Williams Syndrome, a genetic dis-
tial against cardiovascular disease. Possible pharmaceutical and behavioral order affecting social behavior. PLoS One 7:e38513.
approaches. Med Hypotheses 138:109597. Dale HH (1906) On some physiological actions of ergot. J Physiol 34:163–206.
Buffington SA, Di Prisco GV, Auchtung TA, Ajami NJ, Petrosino JF, and Costa- Dantzer R (1998) Vasopressin, gonadal steroids and social recognition. Prog Brain
Mattioli M (2016) Microbial reconstitution reverses maternal diet-induced social Res 119:409–414.
and synaptic deficits in offspring. Cell 165:1762–1775. Dantzer R (2018) Neuroimmune interactions: from the brain to the immune system
Buisman-Pijlman FT, Sumracki NM, Gordon JJ, Hull PR, Carter CS, and Tops M and vice versa. Physiol Rev 98:477–504.
(2014) Individual differences underlying susceptibility to addiction: role for the Dantzer R (2019) Can immunopsychiatry help in understanding the basis of sex
endogenous oxytocin system. Pharmacol Biochem Behav 119:22–38. differences in major depressive disorder? Biol Psychiatry Cogn Neurosci Neuro-
Bunck M, Czibere L, Horvath C, Graf C, Frank E, Kessler MS, Murgatroyd C, Müller- imaging 4:606–607.
Myhsok B, Gonik M, Weber P, et al. (2009) A hypomorphic vasopressin allele Deaglio S and Malavasi F (2006) The CD38/CD157 mammalian gene family: an
prevents anxiety-related behavior. PLoS One 4:e5129. evolutionary paradigm for other leukocyte surface enzymes. Purinergic Signal 2:
Burbach JP, Bohus B, Kovács GL, Van Nispen JW, Greven HM, and De Wied D 431–441.
(1983) Oxytocin is a precursor of potent behaviourally active neuropeptides. Eur De Dreu CK (2012) Oxytocin modulates cooperation within and competition between
J Pharmacol 94:125–131. groups: an integrative review and research agenda. Horm Behav 61:419–428.
Burbach JP, De Kloet ER, and De Wied D (1980) Oxytocin biotransformation in the DeVries AC, DeVries MB, Taymans SE, and Carter CS (1996) The effects of stress on
rat limbic brain: characterization of peptidase activities and significance in the social preferences are sexually dimorphic in prairie voles. Proc Natl Acad Sci USA
formation of oxytocin fragments. Brain Res 202:401–414. 93:11980–11984.
Burns P, Bowditch J, McFadyen J, Loiacono R, Albiston AL, Pham V, and Chai SY de Vries GJ and Forger NG (2015) Sex differences in the brain: a whole body per-
(2019) Social behaviour is altered in the insulin-regulated aminopeptidase spective. Biol Sex Differ 6:15.
knockout mouse. Behav Brain Res 376:112150. De Vries GJ and Panzica GC (2006) Sexual differentiation of central vasopressin and
Busnelli M and Chini B (2018) Molecular basis of oxytocin receptor signalling in the vasotocin systems in vertebrates: different mechanisms, similar endpoints. Neu-
brain: what we know and what we need to know. Curr Top Behav Neurosci 35:3–29. roscience 138:947–955.
Caldwell HK (2017) Oxytocin and vasopressin: powerful regulators of social behavior. de Wied D, Elands J, and Kovács G (1991) Interactive effects of neurohypophyseal
Neuroscientist 23:517–528. neuropeptides with receptor antagonists on passive avoidance behavior: mediation
Caldwell HK and Albers HE (2016) Oxytocin, vasopressin, and the motivational by a cerebral neurohypophyseal hormone receptor? Proc Natl Acad Sci USA 88:
forces that drive social behaviors. Curr Top Behav Neurosci 27:51–103. 1494–1498.
Carson DS, Garner JP, Hyde SA, Libove RA, Berquist SW, Hornbeak KB, Jackson DiBenedictis BT, Nussbaum ER, Cheung HK, and Veenema AH (2017) Quantitative
LP, Sumiyoshi RD, Howerton CL, Hannah SL, et al. (2015) Arginine vasopressin is mapping reveals age and sex differences in vasopressin, but not oxytocin, immu-
a blood-based biomarker of social functioning in children with autism. PLoS One noreactivity in the rat social behavior neural network. J Comp Neurol 525:
10:e0132224. 2549–2570.
Carter CS (1998) Neuroendocrine perspectives on social attachment and love. Psy- Dölen G (2015) Autism: oxytocin, serotonin, and social reward. Soc Neurosci 10:
choneuroendocrinology 23:779–818. 450–465.
Carter CS (2003) Developmental consequences of oxytocin. Physiol Behav 79: Domes G, Lischke A, Berger C, Grossmann A, Hauenstein K, Heinrichs M,
383–397. and Herpertz SC (2010) Effects of intranasal oxytocin on emotional face processing
Carter CS (2007) Sex differences in oxytocin and vasopressin: implications for autism in women. Psychoneuroendocrinology 35:83–93.
spectrum disorders? Behav Brain Res 176:170–186. du Vigneaud V, Gish DT, Katsoyannis PG, and Hess GP (1958) Synthesis of the
Carter CS (2014) Oxytocin pathways and the evolution of human behavior. Annu Rev pressor-antidiuretic hormone, arginine vasopressin. J Am Chem Soc 80:
Psychol 65:17–39. 3355–3358.
Carter CS (2017) The oxytocin-vasopressin pathway in the context of love and fear. du Vigneaud V, Ressler C, Swan JM, Roberts CW, and Katsoyannis PG (1954) The
Front Endocrinol (Lausanne) 8:356. synthesis of oxytocin. J Am Chem Soc 76:3115–3121.
Carter CS and Altemus M (1997) Integrative functions of lactational hormones in Duchemin A, Seelke AM, Simmons TC, Freeman SM, and Bales KL (2017) Locali-
social behavior and stress management. Ann N Y Acad Sci 807:164–174. zation of oxytocin receptors in the prairie vole (Microtus ochrogaster) neocortex.
Carter CS, Boone EM, Pournajafi-Nazarloo H, and Bales KL (2009) Consequences of Neuroscience 348:201–211.
early experiences and exposure to oxytocin and vasopressin are sexually di- Dumais KM and Veenema AH (2016) Vasopressin and oxytocin receptor systems in
morphic. Dev Neurosci 31:332–341. the brain: sex differences and sex-specific regulation of social behavior. Front
Carter CS and Perkeybile AM (2018) The monogamy paradox: what do love and sex Neuroendocrinol 40:1–23.
have to do with it? Front Ecol Evol 6:202. Ebner NC, Lin T, Muradoglu M, Weir DH, Plasencia GM, Lillard TS, Pournajafi-
Carter CS, Pournajafi-Nazarloo H, Kramer KM, Ziegler TE, White-Traut R, Bello D, Nazarloo H, Cohen RA, Sue Carter C, and Connelly JJ (2019) Associations between
and Schwertz D (2007) Oxytocin: behavioral associations and potential as a sali- oxytocin receptor gene (OXTR) methylation, plasma oxytocin, and attachment
vary biomarker. Ann N Y Acad Sci 1098:312–322. across adulthood. Int J Psychophysiol 136:22–32.
Castillo-Ruiz A, Mosley M, George AJ, Mussaji LF, Fullerton EF, Ruszkowski EM, Ehrensing RH (2015) An extraordinary relationship involving MIF-1 and other
Jacobs AJ, Gewirtz AT, Chassaing B, and Forger NG (2018) The microbiota peptides. Peptides 72:73–74.
influences cell death and microglial colonization in the perinatal mouse brain. Elkabir DR, Wyatt ME, Vellucci SV, and Herbert J (1990) The effects of separate or
Brain Behav Immun 67:218–229. combined infusions of corticotrophin-releasing factor and vasopressin either in-
Ceanga M, Spataru A, and Zagrean AM (2010) Oxytocin is neuroprotective against traventricularly or into the amygdala on aggressive and investigative behaviour in
oxygen-glucose deprivation and reoxygenation in immature hippocampal cultures. the rat. Regul Pept 28:199–214.
Neurosci Lett 477:15–18. Engel S, Klusmann H, Laufer S, Pfeifer AC, Ditzen B, van Zuiden M, Knaevelsrud C,
Cetinel S, Hancioglu S, Sener E, Uner C, Kiliç M, Sener G, and Ye gen BC (2010) and Schumacher S (2019) Trauma exposure, posttraumatic stress disorder and
Oxytocin treatment alleviates stress-aggravated colitis by a receptor-dependent oxytocin: a meta-analytic investigation of endogenous concentrations and receptor
mechanism. Regul Pept 160:146–152. genotype. Neurosci Biobehav Rev 107:560–601.
Chagnon YC, Potvin O, Hudon C, and Préville M (2015) DNA methylation and single Engert V, Koester AM, Riepenhausen A, and Singer T (2016) Boosting recovery
nucleotide variants in the brain-derived neurotrophic factor (BDNF) and oxytocin rather than buffering reactivity: higher stress-induced oxytocin secretion is asso-
receptor (OXTR) genes are associated with anxiety/depression in older women. ciated with increased cortisol reactivity and faster vagal recovery after acute
Front Genet 6:230. psychosocial stress. Psychoneuroendocrinology 74:111–120.
 Oxytocin As Medicine 857
Erbas O, Taşkıran D, Oltulu F, Yavaşoglu A, Bora S, Bilge O, Çınar BP, and Peker G Grippo AJ, Pournajafi-Nazarloo H, Sanzenbacher L, Trahanas DM, McNeal N,
(2017) Oxytocin provides protection against diabetic polyneuropathy in rats. Clarke DA, Porges SW, and Sue Carter C (2012) Peripheral oxytocin administra-
Neurol Res 39:45–53. tion buffers autonomic but not behavioral responses to environmental stressors in
Erdman SE and Poutahidis T (2016) Microbes and oxytocin: benefits for host phys- isolated prairie voles. Stress 15:149–161.
iology and behavior. Int Rev Neurobiol 131:91–126. Grippo AJ, Trahanas DM, Zimmerman RR II, Porges SW, and Carter CS (2009)
Feldman R, Monakhov M, Pratt M, and Ebstein RP (2016) Oxytocin pathway genes: Oxytocin protects against negative behavioral and autonomic consequences of long-
evolutionary ancient system impacting on human affiliation, sociality, and psy- term social isolation. Psychoneuroendocrinology 34:1542–1553.
chopathology. Biol Psychiatry 79:174–184. Gross Margolis K, Vittorio J, Talavera M, Gluck K, Li Z, Iuga A, Stevanovic K,
Feng C, Hackett PD, DeMarco AC, Chen X, Stair S, Haroon E, Ditzen B, Pagnoni G, Saurman V, Israelyan N, Welch MG, et al. (2017) Enteric serotonin and oxytocin:
and Rilling JK (2015) Oxytocin and vasopressin effects on the neural response to endogenous regulation of severity in a murine model of necrotizing enterocolitis.
social cooperation are modulated by sex in humans. Brain Imaging Behav 9:754–764. Am J Physiol Gastrointest Liver Physiol 313:G386–G398.
Ferris CF, Yee JR, Kenkel WM, Dumais KM, Moore K, Veenema AH, Kulkarni P, Grunewald R, Seelke AM, Perkeybile AM, Cooke DF, Bales KL, and Krubitzer L
Perkybile AM, and Carter CS (2015) Distinct BOLD activation profiles following (2012) Effects of Early Parenting Experience on Cortical Connections in Prairie
central and peripheral oxytocin administration in awake rats. Front Behav Neu- Voles (Microtus Ochrogaster), Society for Neuroscience, New Orleans, LA.
rosci 9:245. Grzesiak M, Gaj Z, Kocyłowski R, Suliburska J, Oszukowski P, Horzelski W, von
Filippi S, Vignozzi L, Vannelli GB, Ledda F, Forti G, and Maggi M (2003) Role of Kaisenberg C, and Banach M (2018) Oxidative stress in women treated with ato-
oxytocin in the ejaculatory process. J Endocrinol Invest 26 (Suppl):82–86. siban for impending preterm birth. Oxid Med Cell Longev 2018:3919106.
Franke AA, Li X, Menden A, Lee MR, and Lai JF (2019) Oxytocin analysis from Gulliver D, Werry E, Reekie TA, Katte TA, Jorgensen W, and Kassiou M (2019)
human serum, urine, and saliva by orbitrap liquid chromatography-mass spec- Targeting the oxytocin system: new pharmacotherapeutic approaches. Trends
trometry. Drug Test Anal 11:119–128. Pharmacol Sci 40:22–37.
Frasch A, Zetzsche T, Steiger A, and Jirikowski GF (1995) Reduction of plasma Gust K, Caccese C, Larosa A, and Nguyen TV (2020) Neuroendocrine effects of lac-
oxytocin levels in patients suffering from major depression. Adv Experim Med Biol tation and hormone-gene-environment interactions. Mol Neurobiol 57:2074–2084.
395:257–258. Gutkowska J and Jankowski M (2012) Oxytocin revisited: its role in cardiovascular
Freeman SM, Palumbo MC, Lawrence RH, Smith AL, Goodman MM, and Bales KL regulation. J Neuroendocrinol 24:599–608.
(2018) Effect of age and autism spectrum disorder on oxytocin receptor density in Gutkowska J, Jankowski M, and Antunes-Rodrigues J (2014) The role of oxytocin in
the human basal forebrain and midbrain. Transl Psychiatry 8:257. cardiovascular regulation. Braz J Med Biol Res 47:206–214.
Freeman SM and Young LJ (2016) Comparative perspectives on oxytocin and vaso- Hammock EA (2015) Developmental perspectives on oxytocin and vasopressin.
pressin receptor research in rodents and primates: translational implications. Neuropsychopharmacology 40:24–42.
J Neuroendocrinol 28:1–22. Hammock EA and Young LJ (2005) Microsatellite instability generates diversity in
Gainer H (2012) Cell-type specific expression of oxytocin and vasopressin genes: an brain and sociobehavioral traits. Science 308:1630–1634.
experimental odyssey. J Neuroendocrinol 24:528–538. Han W, Tellez LA, Perkins MH, Perez IO, Qu T, Ferreira J, Ferreira TL, Quinn D,
Galina ZH and Kastin AJ (1986) Existence of antiopiate systems as illustrated by Liu ZW, Gao XB, et al. (2018) A neural circuit for gut-induced reward. Cell 175:
MIF-1/Tyr-MIF-1. Life Sci 39:2153–2159. 665–678.e23.
Gamliel M, Anderson KL, Ebstein RP, Yirmiya N, and Mankuta D (2016) The oxy- Hatton GI, Perlmutter LS, Salm AK, and Tweedle CD (1984) Dynamic neuronal-glial
tocin-CD38-vitamin A axis in pregnant women involves both hypothalamic and interactions in hypothalamus and pituitary: implications for control of hormone
placental regulation. J Matern Fetal Neonatal Med 29:2685–2690. synthesis and release. Peptides 5 (Suppl 1):121–138.
Garfield L, Giurgescu C, Carter CS, Holditch-Davis D, McFarlin BL, Schwertz D, Hatton GI and Wang YF (2008) Neural mechanisms underlying the milk ejection
Seng JS, and White-Traut R (2015) Depressive symptoms in the second trimester burst and reflex. Prog Brain Res 170:155–166.
relate to low oxytocin levels in African-American women: a pilot study. Arch Hayes EJ and Weinstein L (2008) Improving patient safety and uniformity of care by
Womens Ment Health 18:123–129. a standardized regimen for the use of oxytocin. Am J Obstet Gynecol 198:
Garrison JL, Macosko EZ, Bernstein S, Pokala N, Albrecht DR, and Bargmann CI 622.e1-622.e7.
(2012) Oxytocin/vasopressin-related peptides have an ancient role in reproductive Heim C, Young LJ, Newport DJ, Mletzko T, Miller AH, and Nemeroff CB (2009)
behavior. Science 338:540–543. Lower CSF oxytocin concentrations in women with a history of childhood abuse.
Garrott K, Dyavanapalli J, Cauley E, Dwyer MK, Kuzmiak-Glancy S, Wang X, Mol Psychiatry 14:954–958.
Mendelowitz D, and Kay MW (2017) Chronic activation of hypothalamic oxytocin Herman JP, McKlveen JM, Solomon MB, Carvalho-Netto E, and Myers B (2012)
neurons improves cardiac function during left ventricular hypertrophy-induced Neural regulation of the stress response: glucocorticoid feedback mechanisms. Braz
heart failure. Cardiovasc Res 113:1318–1328. J Med Biol Res 45:292–298.
Geenen V (2006) Thymus-dependent T cell tolerance of neuroendocrine functions: Hernández VS, Hernández OR, Perez de la Mora M, Gómora MJ, Fuxe K, Eiden LE,
principles, reflections, and implications for tolerogenic/negative self-vaccination. and Zhang L (2016) Hypothalamic vasopressinergic projections innervate central
Ann N Y Acad Sci 1088:284–296. amygdala gabaergic neurons: implications for anxiety and stress coping. Front
Gibbs DM (1986) Vasopressin and oxytocin: hypothalamic modulators of the stress Neural Circuits 10:92.
response: a review. Psychoneuroendocrinology 11:131–139. Hetz C (2012) The unfolded protein response: controlling cell fate decisions under ER
Gimpl G and Fahrenholz F (2001) The oxytocin receptor system: structure, function, stress and beyond. Nat Rev Mol Cell Biol 13:89–102.
and regulation. Physiol Rev 81:629–683. Hetz C, Martinon F, Rodriguez D, and Glimcher LH (2011) The unfolded protein
Gobrogge K and Wang Z (2016) The ties that bond: neurochemistry of attachment in response: integrating stress signals through the stress sensor IRE1a. Physiol Rev
voles. Curr Opin Neurobiol 38:80–88. 91:1219–1243.
Gobrogge KL, Jia X, Liu Y, and Wang Z (2017) Neurochemical mediation of affiliation Hicks C, Ramos L, Reekie TA, Narlawar R, Kassiou M, and McGregor IS (2015) WAY
and aggression associated with pair-bonding. Biol Psychiatry 81:231–242. 267,464, a non-peptide oxytocin receptor agonist, impairs social recognition
Goekoop JG, de Winter RF, Wolterbeek R, van Kempen GM, and Wiegant VM (2011) memory in rats through a vasopressin 1A receptor antagonist action. Psycho-
Evidence of vasopressinergic-noradrenergic mechanisms in depression with above- pharmacology (Berl) 232:2659–2667.
normal plasma vasopressin concentration with and without psychotic features. Higashida H, Furuhara K, Yamauchi AM, Deguchi K, Harashima A, Munesue S,
J Psychopharmacol 25:345–352. Lopatina O, Gerasimenko M, Salmina AB, Zhang JS, et al. (2017) Intestinal
Goldman MB, Gomes AM, Carter CS, and Lee R (2011) Divergent effects of two transepithelial permeability of oxytocin into the blood is dependent on the receptor
different doses of intranasal oxytocin on facial affect discrimination in schizo- for advanced glycation end products in mice. Sci Rep 7:7883.
phrenic patients with and without polydipsia. Psychopharmacology (Berl) 216: Higashida H, Yokoyama S, Kikuchi M, and Munesue T (2012) CD38 and its role in
101–110. oxytocin secretion and social behavior. Horm Behav 61:351–358.
Goodson JL (2013) Deconstructing sociality, social evolution and relevant non- Higashida H, Yuhi T, Akther S, Amina S, Zhong J, Liang M, Nishimura T, Liu HX,
apeptide functions. Psychoneuroendocrinology 38:465–478. and Lopatina O (2018) Oxytocin release via activation of TRPM2 and CD38 in the
Goodson JL, Evans AK, and Wang Y (2006) Neuropeptide binding reflects convergent hypothalamus during hyperthermia in mice: implication for autism spectrum
and divergent evolution in species-typical group sizes. Horm Behav 50:223–236. disorder. Neurochem Int 119:42–48.
Goodson JL, Kelly AM, and Kingsbury MA (2012) Evolving nonapeptide mechanisms Hinzey A, Gaudier-Diaz MM, Lustberg MB, and DeVries AC (2016) Breast cancer
of gregariousness and social diversity in birds. Horm Behav 61:239–250. and social environment: getting by with a little help from our friends. Breast
Goodson JL, Schrock SE, and Kingsbury MA (2015) Oxytocin mechanisms of stress Cancer Res 18:54.
response and aggression in a territorial finch. Physiol Behav 141:154–163. Holt-Lunstad J, Birmingham W, and Light KC (2011) The influence of depressive
Gottlieb MM (2016) Pitocin and autism: an analysis of oxytocin receptor de- symptomatology and perceived stress on plasma and salivary oxytocin before,
sensitization in the fetus. Behav Brain Res 298 (Pt B):246–247. during and after a support enhancement intervention. Psychoneuroendocrinology
Gouin JP, Carter CS, Pournajafi-Nazarloo H, Glaser R, Malarkey WB, Loving TJ, 36:1249–1256.
Stowell J, and Kiecolt-Glaser JK (2010) Marital behavior, oxytocin, vasopressin, Huang H, Michetti C, Busnelli M, Managò F, Sannino S, Scheggia D, Giancardo L,
and wound healing. Psychoneuroendocrinology 35:1082–1090. Sona D, Murino V, Chini B, et al. (2014) Chronic and acute intranasal oxytocin
Green L, Fein D, Modahl C, Feinstein C, Waterhouse L, and Morris M (2001) Oxy- produce divergent social effects in mice. Neuropsychopharmacology 39:1102–1114.
tocin and autistic disorder: alterations in peptide forms. Biol Psychiatry 50: Hurlemann R and Grinevich V (2018) Behavioral Pharmacology of Neuropeptides:
609–613. Oxytocin, Springer, Cham, Switzerland.
Gregory SG, Connelly JJ, Towers AJ, Johnson J, Biscocho D, Markunas CA, Lintas C, Işeri SO, Gedik IE, Erzik C, Uslu B, Arbak S, Gedik N, and Ye gen BC (2008) Oxy-
Abramson RK, Wright HH, Ellis P, et al. (2009) Genomic and epigenetic evidence tocin ameliorates skin damage and oxidant gastric injury in rats with thermal
for oxytocin receptor deficiency in autism. BMC Med 7:62. trauma. Burns 34:361–369.
Grewen KM and Light KC (2011) Plasma oxytocin is related to lower cardiovascular Jack A, Connelly JJ, and Morris JP (2012) DNA methylation of the oxytocin receptor
and sympathetic reactivity to stress. Biol Psychol 87:340–349. gene predicts neural response to ambiguous social stimuli. Front Hum Neurosci 6:280.
Grinevich V, Knobloch-Bollmann HS, Eliava M, Busnelli M, and Chini B (2016) Jacob S, Brune CW, Carter CS, Leventhal BL, Lord C, and Cook EH Jr. (2007)
Assembling the puzzle: pathways of oxytocin signaling in the brain. Biol Psychiatry Association of the oxytocin receptor gene (OXTR) in Caucasian children and ado-
79:155–164. lescents with autism. Neurosci Lett 417:6–9.
858 Carter et al.

Jankowski M, Broderick TL, and Gutkowska J (2016) Oxytocin and cardioprotection Kramer KM, Cushing BS, Carter CS, Wu J, and Ottinger MA (2004) Sex and species
in diabetes and obesity. BMC Endocr Disord 16:34. differences in plasma oxytocin using an enzyme immunoassay. Can J Zool 82:
Jiang Y and Platt ML (2018) Oxytocin and vasopressin increase male-directed 1194–1200.
threats and vocalizations in female macaques. Sci Rep 8:18011. Krol KM, Moulder RG, Lillard TS, Grossmann T, and Connelly JJ (2019a) Epigenetic
Jin D, Liu HX, Hirai H, Torashima T, Nagai T, Lopatina O, Shnayder NA, Yamada K, dynamics in infancy and the impact of maternal engagement. Sci Adv 5:eaay0680.
Noda M, Seike T, et al. (2007) CD38 is critical for social behaviour by regulating Krol KM, Puglia MH, Morris JP, Connelly JJ, and Grossmann T (2019b) Epigenetic
oxytocin secretion. Nature 446:41–45. modification of the oxytocin receptor gene is associated with emotion processing in
Jirikowski GF, Ochs SD, and Caldwell JD (2018) Oxytocin and steroid actions. Curr the infant brain. Dev Cogn Neurosci 37:100648.
Top Behav Neurosci 35:77–95. Kroll-Desrosiers AR, Nephew BC, Babb JA, Guilarte-Walker Y, Moore Simas TA,
Jonas W, Mileva-Seitz V, Girard AW, Bisceglia R, Kennedy JL, Sokolowski M, and Deligiannidis KM (2017) Association of peripartum synthetic oxytocin ad-
Meaney MJ, Fleming AS, and Steiner M; MAVAN Research Team (2013) ministration and depressive and anxiety disorders within the first postpartum
Genetic variation in oxytocin rs2740210 and early adversity associated with year. Depress Anxiety 34:137–146.
postpartum depression and breastfeeding duration. Genes Brain Behav 12: Kusui C, Kimura T, Ogita K, Nakamura H, Matsumura Y, Koyama M, Azuma C,
681–694. and Murata Y (2001) DNA methylation of the human oxytocin receptor gene pro-
Jong TR, Menon R, Bludau A, Grund T, Biermeier V, Klampfl SM, Jurek B, Bosch moter regulates tissue-specific gene suppression. Biochem Biophys Res Commun
OJ, Hellhammer J, and Neumann ID (2015) Salivary oxytocin concentrations in 289:681–686.
response to running, sexual self-stimulation, breastfeeding and the TSST: the Lagercrantz H and Slotkin TA (1986) The “stress” of being born. Sci Am 254:100–107.
Regensburg Oxytocin Challenge (ROC) study. Psychoneuroendocrinology 62: Lai X, Wu X, Hou N, Liu S, Li Q, Yang T, Miao J, Dong Z, Chen J, and Li T (2018)
381–388. Vitamin A deficiency induces autistic-like behaviors in rats by regulating the
Jurek B and Neumann ID (2018) The oxytocin receptor: from intracellular signaling RARb-CD38-oxytocin axis in the hypothalamus. Mol Nutr Food Res 62:1–10.
to behavior. Physiol Rev 98:1805–1908. Lancaster K, Carter CS, Pournajafi-Nazarloo H, Karaoli T, Lillard TS, Jack A, Davis
Kagerbauer SM, Martin J, Schuster T, Blobner M, Kochs EF, and Landgraf R (2013) JM, Morris JP, and Connelly JJ (2015) Plasma oxytocin explains individual dif-
Plasma oxytocin and vasopressin do not predict neuropeptide concentrations in ferences in neural substrates of social perception. Front Hum Neurosci 9:132.
human cerebrospinal fluid. J Neuroendocrinol 25:668–673. Lancaster K, Goldbeck L, Pournajafi-Nazarloo H, Connelly JJ, Carter CS, and Morris
Kaneko Y, Pappas C, Tajiri N, and Borlongan CV (2016) Oxytocin modulates JP (2018a) The role of endogenous oxytocin in anxiolysis: structural and functional
GABAAR subunits to confer neuroprotection in stroke in vitro. Sci Rep 6:35659. correlates. Biol Psychiatry Cogn Neurosci Neuroimaging 3:618–625.
Karelina K and DeVries AC (2011) Modeling social influences on human health. Lancaster K, Goldbeck L, Puglia MH, Morris JP, and Connelly JJ (2018b) DNA
Psychosom Med 73:67–74. methylation of OXTR is associated with parasympathetic nervous system activity
Karelina K, Stuller KA, Jarrett B, Zhang N, Wells J, Norman GJ, and DeVries AC and amygdala morphology. Soc Cogn Affect Neurosci 13:1155–1162.
(2011) Oxytocin mediates social neuroprotection after cerebral ischemia. Stroke 42: Landgraf R and Neumann ID (2004) Vasopressin and oxytocin release within the
3606–3611. brain: a dynamic concept of multiple and variable modes of neuropeptide com-
Kelly AM and Goodson JL (2014) Social functions of individual vasopressin-oxytocin munication. Front Neuroendocrinol 25:150–176.
cell groups in vertebrates: what do we really know? Front Neuroendocrinol 35: Lang RE, Heil JWE, Ganten D, Hermann K, Unger T, and Rascher W (1983) Oxy-
512–529. tocin unlike vasopressin is a stress hormone in the rat. Neuroendocrinology 37:
Kemp AH, Quintana DS, Kuhnert RL, Griffiths K, Hickie IB, and Guastella AJ (2012) 314–316.
Oxytocin increases heart rate variability in humans at rest: implications for social Lee MR, Scheidweiler KB, Diao XX, Akhlaghi F, Cummins A, Huestis MA, Leggio L,
approach-related motivation and capacity for social engagement. PLoS One 7: and Averbeck BB (2018) Oxytocin by intranasal and intravenous routes reaches
e44014. the cerebrospinal fluid in rhesus macaques: determination using a novel oxytocin
Kendrick KM, Keverne EB, and Baldwin BA (1987) Intracerebroventricular oxytocin assay. Mol Psychiatry 23:115–122.
stimulates maternal behaviour in the sheep. Neuroendocrinology 46:56–61. Lee MR, Shnitko TA, Blue SW, Kaucher AV, Winchell AJ, Erikson DW, Grant KA,
Kenkel WM, Paredes J, Lewis GF, Yee JR, Pournajafi-Nazarloo H, Grippo AJ, Porges and Leggio L (2020) Labeled oxytocin administered via the intranasal route rea-
SW, and Carter CS (2013) Autonomic substrates of the response to pups in male ches the brain in rhesus macaques. Nat Commun 11:2783.
prairie voles. PLoS One 8:e69965. Leng G and Ludwig M (2016) Intranasal oxytocin: myths and delusions. Biol Psy-
Kenkel WM, Perkeybile AM, Yee JR, Pournajafi-Nazarloo H, Lillard TS, Fer- chiatry 79:243–250.
guson EF, Wroblewski KL, Ferris CF, Carter CS, and Connelly JJ (2019) Leng G and Russell JA (2019) The osmoresponsiveness of oxytocin and vasopressin
Behavioral and epigenetic consequences of oxytocin treatment at birth. Sci neurones: mechanisms, allostasis and evolution. J Neuroendocrinol 31:e12662.
Adv 5:eaav2244. Lerer E, Levi S, Israel S, Yaari M, Nemanov L, Mankuta D, Nurit Y, and Ebstein RP
Kenkel WM, Yee JR, and Carter CS (2014) Is oxytocin a maternal-foetal signalling (2010) Low CD38 expression in lymphoblastoid cells and haplotypes are both as-
molecule at birth? Implications for development. J Neuroendocrinol 26:739–749. sociated with autism in a family-based study. Autism Res 3:293–302.
Khan RS, Yu C, Kastin AJ, He Y, Ehrensing RH, Hsuchou H, Stone KP, and Pan W Lerman B, Harricharran T, and Ogunwobi OO (2018) Oxytocin and cancer: an
(2010) Brain activation by peptide Pro-Leu-Gly-NH(2) (MIF-1). Int J Pept 2010: emerging link. World J Clin Oncol 9:74–82.
537639. Li Q, Zhang B, Cao H, Liu W, Guo F, Shen F, Ye B, Liu H, Li Y, and Liu Z (2020)
Khazipov R, Tyzio R, and Ben-Ari Y (2008) Effects of oxytocin on GABA signalling in Oxytocin Exerts Antidepressant-like effect by potentiating dopaminergic synaptic
the foetal brain during delivery. Prog Brain Res 170:243–257. transmission in the mPFC. Neuropharmacology 162:107836.
Kheterpal I, Kastin AJ, Mollah S, Yu C, Hsuchou H, and Pan W (2009) Mass spec- Li T, Chen X, Mascaro J, Haroon E, and Rilling JK (2017a) Intranasal oxytocin, but
trometric quantification of MIF-1 in mouse brain by multiple reaction monitoring. not vasopressin, augments neural responses to toddlers in human fathers. Horm
Peptides 30:1276–1281. Behav 93:193–202.
King LB, Walum H, Inoue K, Eyrich NW, and Young LJ (2016) Variation in the Li T, Wang P, Wang SC, and Wang YF (2017b) Approaches mediating oxytocin
oxytocin receptor gene predicts brain region-specific expression and social attach- regulation of the immune system. Front Immunol 7:693.
ment. Biol Psychiatry 80:160–169. Liberzon I and Young EA (1997) Effects of stress and glucocorticoids on CNS oxytocin
Kingsbury MA and Bilbo SD (2019) The inflammatory event of birth: how oxytocin receptor binding. Psychoneuroendocrinology 22:411–422.
signaling may guide the development of the brain and gastrointestinal system. Lockard MA, Ebert MS, and Bargmann CI (2017) Oxytocin mediated behavior in
Front Neuroendocrinol 55:100794. invertebrates: an evolutionary perspective. Dev Neurobiol 77:128–142.
Klein BY, Tamir H, Anwar M, Ludwig RJ, Kaidbey JH, Glickstein SB, and Welch MG Macdonald K and Feifel D (2013) Helping oxytocin deliver: considerations in the
(2018) Assessing cellular stress and inflammation in discrete oxytocin-secreting development of oxytocin-based therapeutics for brain disorders. Front Neurosci 7:
brain nuclei in the neonatal rat before and after first colostrum feeding. J Vis Exp 35.
141:e58341. Macdonald KS (2013) Sex, receptors, and attachment: a review of individual factors
Klein BY, Tamir H, Hirschberg DL, Glickstein SB, Ludwig RJ, and Welch MG (2014) influencing response to oxytocin. Front Neurosci 6:194.
Oxytocin modulates markers of the unfolded protein response in Caco2BB gut cells. Mackenzie K (1911) An experimental investigation of the mechanism of milk secre-
Cell Stress Chaperones 19:465–477. tion, with special reference to the action of animal extracts. Q J Exp Physiol 4:
Klein BY, Tamir H, Hirschberg DL, Glickstein SB, and Welch MG (2013) Oxytocin 305–330.
modulates mTORC1 pathway in the gut. Biochem Biophys Res Commun 432: MacLean EL, Gesquiere LR, Gee NR, Levy K, Martin WL, and Carter CS (2017a)
466–471. Effects of affiliative human-animal interaction on dog salivary and plasma oxytocin
Klein BY, Tamir H, Hirschberg DL, Ludwig RJ, Glickstein SB, Myers MM, and Welch and vasopressin. Front Psychol 8:1606.
MG (2016) Oxytocin opposes effects of bacterial endotoxin on ER-stress signaling in MacLean EL, Gesquiere LR, Gee N, Levy K, Martin WL, and Carter CS (2018)
Caco2BB gut cells. Biochim Biophys Acta 1860:402–411. Validation of salivary oxytocin and vasopressin as biomarkers in domestic dogs.
Klein BY, Tamir H, Ludwig RJ, Glickstein SB, Welch MG, and Anwar M (2017) J Neurosci Methods 293:67–76.
Colostrum oxytocin modulates cellular stress response, inflammation, and MacLean EL, Gesquiere LR, Gruen ME, Sherman BL, Martin WL, and Carter CS
autophagy markers in newborn rat gut villi. Biochem Biophys Res Commun 487: (2017b) Endogenous oxytocin, vasopressin, and aggression in domestic dogs. Front
47–53. Psychol 8:1613.
Klein BY, Tamir H, and Welch MG (2011) PI3K/Akt responses to oxytocin stimula- MacLean EL, Wilson SR, Martin WL, Davis JM, Nazarloo HP, and Carter CS (2019)
tion in Caco2BB gut cells. J Cell Biochem 112:3216–3226. Challenges for measuring oxytocin: the blind men and the elephant? Psychoneur-
Knobloch HS and Grinevich V (2014) Evolution of oxytocin pathways in the brain of oendocrinology 107:225–231.
vertebrates. Front Behav Neurosci 8:31. Mairesse J, Zinni M, Pansiot J, Hassan-Abdi R, Demene C, Colella M, Charriaut-
Kosfeld M, Heinrichs M, Zak PJ, Fischbacher U, and Fehr E (2005) Oxytocin Marlangue C, Rideau Batista Novais A, Tanter M, Maccari S, et al. (2019) Oxytocin
increases trust in humans. Nature 435:673–676. receptor agonist reduces perinatal brain damage by targeting microglia. Glia 67:
Kovács GL, Bohus B, Versteeg DH, de Kloet ER, and de Wied D (1979) Effect of 345–359.
oxytocin and vasopressin on memory consolidation: sites of action and catechol- Malavasi F, Deaglio S, Funaro A, Ferrero E, Horenstein AL, Ortolan E, Vaisitti T,
aminergic correlates after local microinjection into limbic-midbrain structures. and Aydin S (2008) Evolution and function of the ADP ribosyl cyclase/CD38 gene
Brain Res 175:303–314. family in physiology and pathology. Physiol Rev 88:841–886.
 Oxytocin As Medicine 859
Mann A, Verma V, Basu D, Skoblenick KJ, Beyaert MGR, Fisher A, Thomas N, Parker KJ, Oztan O, Libove RA, Sumiyoshi RD, Jackson LP, Karhson DS, Summers
Johnson RL, and Mishra RK (2010) Specific binding of photoaffinity-labeling JE, Hinman KE, Motonaga KS, Phillips JM, et al. (2017) Intranasal oxytocin
peptidomimetics of Pro-Leu-Gly-NH2 to the dopamine D2L receptor: evidence for treatment for social deficits and biomarkers of response in children with autism.
the allosteric modulation of the dopamine receptor. Eur J Pharmacol 641:96–101. Proc Natl Acad Sci USA 114:8119–8124.
Manning M, Stoev S, Chini B, Durroux T, Mouillac B, and Guillon G (2008) Peptide Pedersen CA and Prange AJ Jr. (1979) Induction of maternal behavior in virgin rats
and non-peptide agonists and antagonists for the vasopressin and oxytocin V1a, after intracerebroventricular administration of oxytocin. Proc Natl Acad Sci USA
V1b, V2 and OT receptors: research tools and potential therapeutic agents. Prog 76:6661–6665.
Brain Res 170:473–512. Perkeybile AM, Carter CS, Wroblewski KL, Puglia MH, Kenkel WM, Lillard TS,
Marchini G, Lagercrantz H, Winberg J, and Uvnäs-Moberg K (1988) Fetal and ma- Karaoli T, Gregory SG, Mohammadi N, Epstein L, et al. (2019) Early nurture
ternal plasma levels of gastrin, somatostatin and oxytocin after vaginal delivery epigenetically tunes the oxytocin receptor. Psychoneuroendocrinology 99:128–136.
and elective cesarean section. Early Hum Dev 18:73–79. Peter J, Burbach H, Adan RA, Lolait SJ, van Leeuwen FW, Mezey E, Palkovits M,
Maron JL, Johnson KL, Parkin C, Iyer L, Davis JM, and Bianchi DW (2010) Cord and Barberis C (1995) Molecular neurobiology and pharmacology of the vaso-
blood genomic analysis highlights the role of redox balance. Free Radic Biol Med pressin/oxytocin receptor family. Cell Mol Neurobiol 15:573–595.
49:992–996. Pierrehumbert B, Torrisi R, Ansermet F, Borghini A, and Halfon O (2012) Adult
Martins DA, Mazibuko N, Zelaya F, Vasilakopoulou S, Loveridge J, Oates A, Mal- attachment representations predict cortisol and oxytocin responses to stress. At-
tezos S, Mehta M, Wastling S, Howard M, et al. (2020) Effects of route of admin- tach Hum Dev 14:453–476.
istration on oxytocin-induced changes in regional cerebral blood flow in humans. Plasencia G, Luedicke JM, Nazarloo HP, Carter CS, and Ebner NC (2019) Plasma
Nat Commun 11:1160. oxytocin and vasopressin levels in young and older men and women: functional
Massey N, Puttachary S, Mahadev-Bhat S, Kanthasamy AG, and Charavaryamath C relationships with attachment and cognition. Psychoneuroendocrinology 110:
(2019) HMGB1-RAGE signaling plays a role in organic dust-induced microglial 104419.
activation and neuroinflammation. Toxicol Sci 169:579–592. Plested CP and Bernal AL (2001) Desensitisation of the oxytocin receptor and other
Massey SH, Schuette SA, Pournajafi-Nazarloo H, Wisner KL, and Carter CS (2016) G-protein coupled receptors in the human myometrium. Exp Physiol 86:303–312.
Interaction of oxytocin level and past depression may predict postpartum de- Poisbeau P, Grinevich V, and Charlet A (2018) Oxytocin signaling in pain: cellular,
pressive symptom severity. Arch Women Ment Health 19:799–808. circuit, system, and behavioral levels. Curr Top Behav Neurosci 35:193–211.
McCarthy MM, Nugent BM, and Lenz KM (2017) Neuroimmunology and neuro- Porges SW (1998) Love: an emergent property of the mammalian autonomic nervous
epigenetics in the establishment of sex differences in the brain. Nat Rev Neurosci system. Psychoneuroendocrinology 23:837–861.
18:471–484. Porges SW (2009) The polyvagal theory: new insights into adaptive reactions of the
McCullough ME, Churchland PS, and Mendez AJ (2013) Problems with measuring autonomic nervous system. Cleve Clin J Med 76 (Suppl 2):S86–S90.
peripheral oxytocin: can the data on oxytocin and human behavior be trusted? Porges SW (2012) The polyvagal theory: neurophysiological foundations of emotions,
Neurosci Biobehav Rev 37:1485–1492. attachment, communication, self-regulation, J Can Acad Child Adolesc Psychiatry
McDougle CJ, Landino SM, Vahabzadeh A, O’Rourke J, Zurcher NR, Finger BC, 21, pp 313–314.
Palumbo ML, Helt J, Mullett JE, Hooker JM, et al. (2015) Toward an immune- Porges SW and Furman SA (2011) The early development of the autonomic nervous
mediated subtype of autism spectrum disorder. Brain Res 1617:72–92. system provides a neural platform for social behavior: a polyvagal perspective.
Meguro Y, Miyano K, Hirayama S, Yoshida Y, Ishibashi N, Ogino T, Fujii Y, Infant Child Dev 20:106–118.
Manabe S, Eto M, Nonaka M, et al. (2018) Neuropeptide oxytocin enhances m Pournajafi-Nazarloo H, Partoo L, Yee J, Stevenson J, Sanzenbacher L, Kenkel W,
opioid receptor signaling as a positive allosteric modulator. J Pharmacol Sci Mohsenpour SR, Hashimoto K, and Carter CS (2011) Effects of social isolation on
137:67–75. mRNA expression for corticotrophin-releasing hormone receptors in prairie voles.
Mileva-Seitz V, Steiner M, Atkinson L, Meaney MJ, Levitan R, Kennedy JL, Soko- Psychoneuroendocrinology 36:780–789.
lowski MB, and Fleming AS (2013) Interaction between oxytocin genotypes and Poutahidis T, Kearney SM, Levkovich T, Qi P, Varian BJ, Lakritz JR, Ibrahim YM,
early experience predicts quality of mothering and postpartum mood. PLoS One 8: Chatzigiagkos A, Alm EJ, and Erdman SE (2013) Microbial symbionts accelerate
e61443. wound healing via the neuropeptide hormone oxytocin. PLoS One 8:e78898.
Moy SS, Teng BL, Nikolova VD, Riddick NV, Simpson CD, Van Deusen A, Janzen Price D, Burris D, Cloutier A, Thompson CB, Rilling JK, and Thompson RR (2017)
WP, Sassano MF, Pedersen CA, and Jarstfer MB (2019) Prosocial effects of an Dose-dependent and lasting influences of intranasal vasopressin on face processing
oxytocin metabolite, but not synthetic oxytocin receptor agonists, in a mouse model in men. Front Endocrinol (Lausanne) 8:220.
of autism. Neuropharmacology 144:301–311. Puglia MH, Connelly JJ, and Morris JP (2018) Epigenetic regulation of the oxytocin
Murgatroyd CA, Hicks-Nelson A, Fink A, Beamer G, Gurel K, Elnady F, Pittet F, receptor is associated with neural response during selective social attention.
and Nephew BC (2016) Effects of chronic social stress and maternal intranasal Transl Psychiatry 8:116.
oxytocin and vasopressin on offspring interferon-g and behavior. Front Endocrinol Puglia MH, Lillard TS, Morris JP, and Connelly JJ (2015) Epigenetic modification of
(Lausanne) 7:155. the oxytocin receptor gene influences the perception of anger and fear in the hu-
Murgatroyd CA and Nephew BC (2013) Effects of early life social stress on maternal man brain. Proc Natl Acad Sci USA 112:3308–3313.
behavior and neuroendocrinology. Psychoneuroendocrinology 38:219–228. Purba JS, Hoogendijk WJG, Hofman MA, and Swaab DF (1996) Increased number of
Nersesyan Y, Demirkhanyan L, Cabezas-Bratesco D, Oakes V, Kusuda R, Dawson T, vasopressin- and oxytocin-expressing neurons in the paraventricular nucleus of the
Sun X, Cao C, Cohen AM, Chelluboina B, et al. (2017) Oxytocin modulates noci- hypothalamus in depression. Arch Gen Psychiatry 53:137–143.
ception as an agonist of pain-sensing TRPV1. Cell Rep 21:1681–1691. Quintana DS, Dieset I, Elvsåshagen T, Westlye LT, and Andreassen OA (2017)
Neumann ID and Slattery DA (2016) Oxytocin in general anxiety and social fear: Oxytocin system dysfunction as a common mechanism underlying metabolic syn-
a translational approach. Biol Psychiatry 79:213–221. drome and psychiatric symptoms in schizophrenia and bipolar disorders. Front
Nissen E, Lilja G, Widström AM, and Uvnäs-Moberg K (1995) Elevation of oxytocin Neuroendocrinol 45:1–10.
levels early post partum in women. Acta Obstet Gynecol Scand 74:530–533. Quintana DS and Guastella AJ (2020) An allostatic theory of oxytocin. Trends Cogn
Ocampo Daza D, Lewicka M, and Larhammar D (2012) The oxytocin/vasopressin Sci 24:515–528.
receptor family has at least five members in the gnathostome lineage, inclucing two Quintana DS, Kemp AH, Alvares GA, and Guastella AJ (2013) A role for autonomic
distinct V2 subtypes. Gen Comp Endocrinol 175:135–143. cardiac control in the effects of oxytocin on social behavior and psychiatric illness.
Okhovat M, Berrio A, Wallace G, Ophir AG, and Phelps SM (2015) Sexual fidelity Front Neurosci 7:48.
trade-offs promote regulatory variation in the prairie vole brain. Science 350: Quintana DS, Rokicki J, van der Meer D, Alnæs D, Kaufmann T, Córdova-Palomera
1371–1374. A, Dieset I, Andreassen OA, and Westlye LT (2019) Oxytocin pathway gene net-
Okhovat M, Chen IC, Dehghani Z, Zheng DJ, Ikpatt JE, Momoh H, and Phelps SM works in the human brain. Nat Commun 10:668.
(2018) Genetic variation in the developmental regulation of cortical avpr1a among Quintana DS, Westlye LT, Smerud KT, Mahmoud RA, Andreassen OA,
prairie voles. Genes Brain Behav 17:36–48. and Djupesland PG (2018) Saliva oxytocin measures do not reflect peripheral
Okhovat M, Maguire SM, and Phelps SM (2017) Methylation of avpr1a in the cortex plasma concentrations after intranasal oxytocin administration in men. Horm
of wild prairie voles: effects of CpG position and polymorphism. R Soc Open Sci 4: Behav 102:85–92.
160646. Ragnauth AK, Goodwillie A, Brewer C, Muglia LJ, Pfaff DW, and Kow LM (2004)
Ophir AG (2017) Navigating monogamy: nonapeptide sensitivity in a memory neural Vasopressin stimulates ventromedial hypothalamic neurons via oxytocin receptors
circuit may shape social behavior and mating decisions. Front Neurosci 11:397. in oxytocin gene knockout male and female mice. Neuroendocrinology 80:92–99.
Oppong-Damoah A, Zaman RU, D’Souza MJ, and Murnane KS (2019) Nanoparticle Reiss AB, Glass DS, Lam E, Glass AD, De Leon J, and Kasselman LJ (2019) Oxy-
encapsulation increases the brain penetrance and duration of action of intranasal tocin: potential to mitigate cardiovascular risk. Peptides 117:170089.
oxytocin. Horm Behav 108:20–29. Reyes-Lagos JJ, Ledesma-Ramírez CI, Pliego-Carrillo AC, Peña-Castillo MA, Echeverría
Ozsoy S, Esel E, and Kula M (2009) Serum oxytocin levels in patients with depression JC, Becerril-Villanueva E, Pavón L, and Pacheco-López G (2019) Neuroautonomic
and the effects of gender and antidepressant treatment. Psychiatry Res 169: activity evidences parturition as a complex and integrated neuro-immune-endocrine
249–252. process. Ann N Y Acad Sci 1437:22–30.
Oztan O, Garner JP, Constantino JN, and Parker KJ (2020) Neonatal CSF vaso- Robinson C, Schumann R, Zhang P, and Young RC (2003) Oxytocin-induced de-
pressin concentration predicts later medical record diagnoses of autism spectrum sensitization of the oxytocin receptor. Am J Obstet Gynecol 188:497–502.
disorder. Proc Natl Acad Sci USA 117:10609–10613. Rodrigues SM, Saslow LR, Garcia N, John OP, and Keltner D (2009) Oxytocin re-
Oztan O, Garner JP, Partap S, Sherr EH, Hardan AY, Farmer C, Thurm A, Swedo ceptor genetic variation relates to empathy and stress reactivity in humans. Proc
SE, and Parker KJ (2018a) Cerebrospinal fluid vasopressin and symptom severity Natl Acad Sci USA 106:21437–21441.
in children with autism. Ann Neurol 84:611–615. Rogers-Carter MM and Christianson JP (2019) An insular view of the social decision-
Oztan O, Jackson LP, Libove RA, Sumiyoshi RD, Phillips JM, Garner JP, Hardan making network. Neurosci Biobehav Rev 103:119–132.
AY, and Parker KJ (2018b) Biomarker discovery for disease status and symptom Rogers-Carter MM, Varela JA, Gribbons KB, Pierce AF, McGoey MT, Ritchey M,
severity in children with autism. Psychoneuroendocrinology 89:39–45. and Christianson JP (2018) Insular cortex mediates approach and avoidance
Parker KJ, Kenna HA, Zeitzer JM, Keller J, Blasey CM, Amico JA, and Schatzberg responses to social affective stimuli. Nat Neurosci 21:404–414.
AF (2010) Preliminary evidence that plasma oxytocin levels are elevated in major Rotondo F, Butz H, Syro LV, Yousef GM, Di Ieva A, Restrepo LM, Quintanar-Ste-
depression. Psychiatry Res 178:359–362. phano A, Berczi I, and Kovacs K (2016) Arginine vasopressin (AVP): a review of its
860 Carter et al.

historical perspectives, current research and multifunctional role in the increases social behavior and plasma oxytocin in adulthood. Horm Behav 65:
hypothalamo-hypophysial system. Pituitary 19:345–355. 488–496.
Rubin LH, Carter CS, Bishop JR, Pournajafi-Nazarloo H, Drogos LL, Hill SK, Ruocco Szeto A, McCabe PM, Nation DA, Tabak BA, Rossetti MA, McCullough ME,
AC, Keedy SK, Reilly JL, Keshavan MS, et al. (2014) Reduced levels of vasopressin Schneiderman N, and Mendez AJ (2011) Evaluation of enzyme immunoassay and
and reduced behavioral modulation of oxytocin in psychotic disorders. Schizophr radioimmunoassay methods for the measurement of plasma oxytocin. Psychosom
Bull 40:1374–1384. Med 73:393–400.
Rubin LH, Li S, Yao L, Keedy SK, Reilly JL, Hill SK, Bishop JR, Sue Carter C, Szeto A, Nation DA, Mendez AJ, Dominguez-Bendala J, Brooks LG, Schneiderman
Pournajafi-Nazarloo H, Drogos LL, et al. (2018) Peripheral oxytocin and vaso- N, and McCabe PM (2008) Oxytocin attenuates NADPH-dependent superoxide
pressin modulates regional brain activity differently in men and women with activity and IL-6 secretion in macrophages and vascular cells. Am J Physiol
schizophrenia. Schizophr Res 202:173–179. Endocrinol Metab 295:E1495–E1501.
Saameli K (1963) An indirect method for the estimation of oxytocin blood concen- Szeto A, Sun-Suslow N, Mendez AJ, Hernandez RI, Wagner KV, and McCabe PM
tration and half-life in pregnant women near term. Am J Obstet Gynecol 85: (2017) Regulation of the macrophage oxytocin receptor in response to in-
186–192. flammation. Am J Physiol Endocrinol Metab 312:E183–E189.
Saníger MA, Ramírez-Expósito MJ, de la Chica S, Carrera-González MP, Mayas MD, Szmydynger-Chodobska J, Fox LM, Lynch KM, Zink BJ, and Chodobski A (2010)
and Manuel Martínez-Martos J (2011) Alpha-1-adrenergic receptor blockade Vasopressin amplifies the production of proinflammatory mediators in traumatic
modifies insulin-regulated aminopeptidase (IRAP) activity in rat prostate and brain injury. J Neurotrauma 27:1449–1461.
modulates oxytocin functions. Drug Metab Lett 5:192–196. Szmydynger-Chodobska J, Zink BJ, and Chodobski A (2011) Multiple sites of vaso-
Sannino S, Chini B, and Grinevich V (2017) Lifespan oxytocin signaling: maturation, pressin synthesis in the injured brain. J Cereb Blood Flow Metab 31:47–51.
flexibility, and stability in newborn, adolescent, and aged brain. Dev Neurobiol 77: Tabbaa M and Hammock EAD (2020) Orally administered oxytocin alters brain ac-
158–168. tivation and behaviors of pre-weaning mice. Horm Behav 118:104613.
Sawchenko PE and Swanson LW (1985) Localization, colocalization, and plasticity of Talati C, Carvalho JCA, Luca A, and Balki M (2019) The effect of intermittent oxy-
corticotropin-releasing factor immunoreactivity in rat brain. Fed Proc 44:221–227. tocin pretreatment on oxytocin-induced contractility of human myometrium
Scantamburlo G, Hansenne M, Fuchs S, Pitchot W, Maréchal P, Pequeux C, Ansseau in vitro. Anesth Analg 128:671–678.
M, and Legros JJ (2007) Plasma oxytocin levels and anxiety in patients with major Tanaka T, Shishido Y, Shibata S, and Watanabe S (1994) Facilitatory effect of va-
depression. Psychoneuroendocrinology 32:407–410. sopressin on the ischemic decrease of the CA1 presynaptic fiber spikes in rat
Scharrer E and Scharrer B (1939) Secretory cells within the hypothalamus. Research hippocampal slices. Brain Res 644:343–346.
Publications - Association for Research in Nervous and Mental Disease 20:170–194. Taylor SE, Gonzaga GC, Klein LC, Hu P, Greendale GA, and Seeman TE (2006)
Schröder M and Kaufman RJ (2005) ER stress and the unfolded protein response. Relation of oxytocin to psychological stress responses and hypothalamic-pituitary-
Mutat Res 569:29–63. adrenocortical axis activity in older women. Psychosom Med 68:238–245.
Seay JS, Lattie E, Schneiderman N, Antoni MH, Fekete EM, Mendez AJ, Szeto A, Taylor SE, Saphire-Bernstein S, and Seeman TE (2010) Are plasma oxytocin in
and Fletcher MA (2014) Linear and quadratic associations of plasma oxytocin with women and plasma vasopressin in men biomarkers of distressed pair-bond rela-
depressive symptoms in ethnic minority women living with HIV. J Appl Biobehav tionships? Psychol Sci 21:3–7.
Res 19:70–78. Theodosis DT (2002) Oxytocin-secreting neurons: a physiological model of morpho-
Seelke AM, Perkeybile AM, Grunewald R, Bales KL, and Krubitzer LA (2016a) In- logical neuronal and glial plasticity in the adult hypothalamus. Front Neuro-
dividual differences in cortical connections of somatosensory cortex are associated endocrinol 23:101–135.
with parental rearing style in prairie voles (Microtus ochrogaster). J Comp Neurol Thompson RR, George K, Walton JC, Orr SP, and Benson J (2006) Sex-specific
524:564–577. influences of vasopressin on human social communication. Proc Natl Acad Sci USA
Seelke AM, Yuan SM, Perkeybile AM, Krubitzer LA, and Bales KL (2016b) Early 103:7889–7894.
experiences can alter the size of cortical fields in prairie voles (Microtus Thompson RR, Walton JC, Bhalla R, George KC, and Beth EH (2008) A primitive
ochrogaster). Environ Epigenet 2:dvw019. social circuit: vasotocin-substance P interactions modulate social behavior through
Seng J, Miller J, Sperlich M, van de Ven CJ, Brown S, Carter CS, and Liberzon I a peripheral feedback mechanism in goldfish. Eur J Neurosci 27:2285–2293.
(2013) Exploring dissociation and oxytocin as pathways between trauma exposure Toepfer P, Heim C, Entringer S, Binder E, Wadhwa P, and Buss C (2017) Oxytocin
and trauma-related hyperemesis gravidarum: a test-of-concept pilot. J Trauma pathways in the intergenerational transmission of maternal early life stress.
Dissociation 14:40–55. Neurosci Biobehav Rev 73:293–308.
Sgritta M, Dooling SW, Buffington SA, Momin EN, Francis MB, Britton RA, Tost H, Kolachana B, Hakimi S, Lemaitre H, Verchinski BA, Mattay VS, Weinberger
and Costa-Mattioli M (2019) Mechanisms underlying microbial-mediated changes DR, and Meyer-Lindenberg A (2010) A common allele in the oxytocin receptor gene
in social behavior in mouse models of autism spectrum disorder. Neuron 101: (OXTR) impacts prosocial temperament and human hypothalamic-limbic structure
246–259.e6. and function. Proc Natl Acad Sci USA 107:13936–13941.
Simpson KR and James DC (2008) Effects of oxytocin-induced uterine hyperstimu- Towers AJ, Tremblay MW, Chung L, Li XL, Bey AL, Zhang W, Cao X, Wang X, Wang
lation during labor on fetal oxygen status and fetal heart rate patterns. Am P, Duffney LJ, et al. (2018) Epigenetic dysregulation of Oxtr in Tet1-deficient mice
J Obstet Gynecol 199:34.e1-5. has implications for neuropsychiatric disorders. JCI Insight 3:120592.
Simsek Y, Celik O, Karaer A, Yılmaz E, Gul M, Ozerol E, Bilgic S, and Celik N (2012) Tyzio R, Cossart R, Khalilov I, Minlebaev M, Hübner CA, Represa A, Ben-Ari Y,
Elevated cardiac oxidative stress in newborn rats from mothers treated with ato- and Khazipov R (2006) Maternal oxytocin triggers a transient inhibitory
siban. Arch Gynecol Obstet 285:655–661. switch in GABA signaling in the fetal brain during delivery. Science 314:
Skrundz M, Bolten M, Nast I, Hellhammer DH, and Meinlschmidt G (2011) Plasma 1788–1792.
oxytocin concentration during pregnancy is associated with development of post- Tyzio R, Minlebaev M, Rheims S, Ivanov A, Jorquera I, Holmes GL, Zilberter Y, Ben-
partum depression. Neuropsychopharmacology 36:1886–1893. Ari Y, and Khazipov R (2008) Postnatal changes in somatic gamma-aminobutyric
Smith AS and Wang Z (2014) Hypothalamic oxytocin mediates social buffering of the acid signalling in the rat hippocampus. Eur J Neurosci 27:2515–2528.
stress response. Biol Psychiatry 76:281–288. Tyzio R, Nardou R, Ferrari DC, Tsintsadze T, Shahrokhi A, Eftekhari S, Khalilov I,
Soltys SM, Scherbel JR, Kurian JR, Diebold T, Wilson T, Hedden L, Groesch K, Tsintsadze V, Brouchoud C, Chazal G, et al. (2014) Oxytocin-mediated GABA in-
Diaz-Sylvester PL, Botchway A, Campbell P, et al. (2020) An association of hibition during delivery attenuates autism pathogenesis in rodent offspring. Sci-
intrapartum synthetic oxytocin dosing and the odds of developing autism. Au- ence 343:675–679.
tism 24:1400–1410. Ulrich-Lai YM and Herman JP (2009) Neural regulation of endocrine and autonomic
Song Z and Albers HE (2018) Cross-talk among oxytocin and arginine-vasopressin stress responses. Nat Rev Neurosci 10:397–409.
receptors: relevance for basic and clinical studies of the brain and periphery. Front Uvnäs Moberg K, Handlin L, Kendall-Tackett K, and Petersson M (2019) Oxytocin is
Neuroendocrinol 51:14–24. a principal hormone that exerts part of its effects by active fragments. Med Hy-
Song Z, Larkin TE, Malley MO, and Albers HE (2016) Oxytocin (OT) and arginine- potheses 133:109394.
vasopressin (AVP) act on OT receptors and not AVP V1a receptors to enhance Vaccari C, Lolait SJ, and Ostrowski NL (1998) Comparative distribution of vaso-
social recognition in adult Syrian hamsters (Mesocricetus auratus). Horm Behav pressin V1b and oxytocin receptor messenger ribonucleic acids in brain. Endocri-
81:20–27. nology 139:5015–5033.
Song Z, McCann KE, McNeill JK IV, Larkin TE II, Huhman KL, and Albers HE Vaidyanathan R and Hammock EAD (2020) Oxytocin receptor gene loss influences
(2014) Oxytocin induces social communication by activating arginine-vasopressin expression of the oxytocin gene in C57BL/6j mice in a sex- and age-dependent
V1a receptors and not oxytocin receptors. Psychoneuroendocrinology 50:14–19. manner. J Neuroendocrinol 32:e12821.
Spoljaric A, Seja P, Spoljaric I, Virtanen MA, Lindfors J, Uvarov P, Summanen M, van Londen L, Goekoop JG, van Kempen GMJ, Frankhuijzen-Sierevogel AC, Wie-
Crow AK, Hsueh B, Puskarjov M, et al. (2017) Vasopressin excites interneurons to gant VM, van der Velde EA, and De Wied D (1997) Plasma levels of arginine
suppress hippocampal network activity across a broad span of brain maturity at vasopressin elevated in patients with major depression. Neuropsychopharmacology
birth. Proc Natl Acad Sci USA 114:E10819–E10828. 17:284–292.
Stevenson EL and Caldwell HK (2012) The vasopressin 1b receptor and the neural Varian BJ, Poutahidis T, DiBenedictis BT, Levkovich T, Ibrahim Y, Didyk E,
regulation of social behavior. Horm Behav 61:277–282. Shikhman L, Cheung HK, Hardas A, Ricciardi CE, et al. (2017) Microbial lysate
Stoop R (2012) Neuromodulation by oxytocin and vasopressin. Neuron 76:142–159. upregulates host oxytocin. Brain Behav Immun 61:36–49.
Stoop R, Hegoburu C, and van den Burg E (2015) New opportunities in vasopressin Vartak AP, Skoblenick K, Thomas N, Mishra RK, and Johnson RL (2007) Allosteric
and oxytocin research: a perspective from the amygdala. Annu Rev Neurosci 38: modulation of the dopamine receptor by conformationally constrained type VI beta-
369–388. turn peptidomimetics of Pro-Leu-Gly-NH2. J Med Chem 50:6725–6729.
Stribley JM and Carter CS (1999) Developmental exposure to vasopressin increases Viveiros ATM, Jatzkowski A, and Komen J (2003) Effects of oxytocin on semen re-
aggression in adult prairie voles. Proc Natl Acad Sci USA 96:12601–12604. lease response in African catfish (Clarias gariepinus). Theriogenology 59:
Stuebe AM, Grewen K, and Meltzer-Brody S (2013) Association between maternal 1905–1917.
mood and oxytocin response to breastfeeding. J Womens Health (Larchmt) 22: Walsh EC, Eisenlohr-Moul TA, Pedersen CA, Rubinow DR, Girdler SS, and Dichter
352–361. GS (2018) Early life abuse moderates the effects of intranasal oxytocin on symp-
Suraev AS, Bowen MT, Ali SO, Hicks C, Ramos L, and McGregor IS (2014) Adoles- toms of premenstrual dysphoric disorder: preliminary evidence from a placebo-
cent exposure to oxytocin, but not the selective oxytocin receptor agonist TGOT, controlled trial. Front Psychiatry 9:547.
 Oxytocin As Medicine 861
Wang P, Wang SC, Yang H, Lv C, Jia S, Liu X, Wang X, Meng D, Qin D, Zhu H, et al. the b2-adrenergic receptor in the modulation of ERK1/2 activation are mediated by
(2019) Therapeutic potential of oxytocin in atherosclerotic cardiovascular disease: heterodimerization. Cell Signal 24:342–350.
mechanisms and signaling pathways. Front Neurosci 13:454. Wrzal PK, Goupil E, Laporte SA, Hébert TE, and Zingg HH (2012b) Functional
Wang Y, Zhao S, Liu X, Zheng Y, Li L, and Meng S (2018) Oxytocin improves animal interactions between the oxytocin receptor and the b2-adrenergic receptor: impli-
behaviors and ameliorates oxidative stress and inflammation in autistic mice. cations for ERK1/2 activation in human myometrial cells. Cell Signal 24:333–341.
Biomed Pharmacother 107:262–269. Xu PF, Fang MJ, Jin YZ, Wang LS, and Lin DS (2017) Effect of oxytocin on the
Wang Z and Aragona BJ (2004) Neurochemical regulation of pair bonding in male survival of random skin flaps. Oncotarget 8:92955–92965.
prairie voles. Physiol Behav 83:319–328. Xu S, Qin B, Shi A, Zhao J, Guo X, and Dong L (2018) Oxytocin inhibited stress
Wee CL, Nikitchenko M, Wang WC, Luks-Morgan SJ, Song E, Gagnon JA, Randlett induced visceral hypersensitivity, enteric glial cells activation, and release of
O, Bianco IH, Lacoste AMB, Glushenkova E, et al. (2019) Zebrafish oxytocin proinflammatory cytokines in maternal separated rats. Eur J Pharmacol 818:
neurons drive nocifensive behavior via brainstem premotor targets. Nat Neurosci 578–584.
22:1477–1492. Yamamoto Y and Higashida H (2020) RAGE regulates oxytocin transport into the
Welch MG, Margolis KG, Li Z, and Gershon MD (2014) Oxytocin regulates gastro- brain. Commun Biol 3:70.
intestinal motility, inflammation, macromolecular permeability, and mucosal Yamamoto Y, Liang M, Munesue S, Deguchi K, Harashima A, Furuhara K, Yuhi T,
maintenance in mice. Am J Physiol Gastrointest Liver Physiol 307:G848–G862. Zhong J, Akther S, Goto H, et al. (2019) Vascular RAGE transports oxytocin into
Welch MG, Tamir H, Gross KJ, Chen J, Anwar M, and Gershon MD (2009) Ex- the brain to elicit its maternal bonding behaviour in mice. Commun Biol 2:76.
pression and developmental regulation of oxytocin (OT) and oxytocin receptors Yamashita K and Kitano T (2013) Molecular evolution of the oxytocin-oxytocin re-
(OTR) in the enteric nervous system (ENS) and intestinal epithelium. J Comp ceptor system in eutherians. Mol Phylogenet Evol 67:520–528.
Neurol 512:256–270. Yang Y, Yu H, Babygirija R, Shi B, Sun W, Zheng X, and Zheng J (2019) Intranasal
Welch MG, Welch-Horan TB, Anwar M, Anwar N, Ludwig RJ, and Ruggiero DA administration of oxytocin attenuates stress responses following chronic compli-
(2005) Brain effects of chronic IBD in areas abnormal in autism and treatment by cated stress in rats. J Neurogastroenterol Motil 25:611–622.
single neuropeptides secretin and oxytocin. J Mol Neurosci 25:259–274. Yee JR, Kenkel WM, Frijling JL, Dodhia S, Onishi KG, Tovar S, Saber MJ, Lewis GF,
White-Traut R, Watanabe K, Pournajafi-Nazarloo H, Schwertz D, Bell A, and Carter Liu W, Porges SW, et al. (2016) Oxytocin promotes functional coupling between
CS (2009) Detection of salivary oxytocin levels in lactating women. Dev Psychobiol paraventricular nucleus and both sympathetic and parasympathetic cardior-
51:367–373. egulatory nuclei. Horm Behav 80:82–91.
Williams JR, Insel TR, Harbaugh CR, and Carter CS (1994) Oxytocin administered Yuan L, Liu S, Bai X, Gao Y, Liu G, Wang X, Liu D, Li T, Hao A, and Wang Z (2016)
centrally facilitates formation of a partner preference in female prairie voles Oxytocin inhibits lipopolysaccharide-induced inflammation in microglial cells and
(Microtus ochrogaster). J Neuroendocrinol 6:247–250. attenuates microglial activation in lipopolysaccharide-treated mice.
Wilson LC, Goodson JL, and Kingsbury MA (2016) Seasonal variation in group size is J Neuroinflammation 13:77.
related to seasonal variation in neuropeptide receptor density. Brain Behav Evol Zelkowitz P, Gold I, Feeley N, Hayton B, Carter CS, Tulandi T, Abenhaim HA,
88:111–126. and Levin P (2014) Psychosocial stress moderates the relationships between oxy-
Witt DM, Carter CS, and Lnsel TR (1991) Oxytocin receptor binding in female prairie tocin, perinatal depression, and maternal behavior. Horm Behav 66:351–360.
voles: endogenous and exogenous oestradiol stimulation. J Neuroendocrinol 3: Zhong J, Amina S, Liang M, Akther S, Yuhi T, Nishimura T, Tsuji C, Tsuji T, Liu HX,
155–161. Hashii M, et al. (2016) Cyclic ADP-ribose and heat regulate oxytocin release via
Witt DM, Carter CS, and Walton DM (1990) Central and peripheral effects of oxy- CD38 and TRPM2 in the hypothalamus during social or psychological stress in
tocin administration in prairie voles (Microtus ochrogaster). Pharmacol Biochem mice. Front Neurosci 10:304.
Behav 37:63–69. Zinni M, Colella M, Batista Novais AR, Baud O, and Mairesse J (2018) Modulating
Wrzal PK, Devost D, Pétrin D, Goupil E, Iorio-Morin C, Laporte SA, Zingg HH, the oxytocin system during the perinatal period: a new strategy for neuroprotection
and Hébert TE (2012a) Allosteric interactions between the oxytocin receptor and of the immature brain? Front Neurol 9:229.