Evolution of the Oxytocin and Vasopressin Systems in Humans and Great Apes Open Access

Rogers, Christina (Summer 2019)

Permanent URL: https://etd.library.emory.edu/concern/etds/d791sh09h?locale=en


Humans share a close phylogenetic relationship with chimpanzees and bonobos. We share approximately 98% of our genes with both species. Yet despite this similarity, there is a remarkable diversity of social behavior among the three species in mating systems, aggression, territoriality, and anxiety. A growing literature suggests a role for the neuropeptides oxytocin and vasopressin in the regulation of these behaviors. Most of this research has been done in rodents, and little is known about the basic neurobiology of the oxytocin and vasopressin systems in primates. This project explores variation in these systems in humans, chimpanzees, bonobos, and rhesus macaques, positing potential proximate mechanisms that may underlie variation in social behavior. First, this study examines the distribution of neurons producing oxytocin and vasopressin across the four species and the targets of their axonal fiber projections. We find a greater density of vasopressin fibers in chimpanzees than in bonobos or humans, which may be related to higher levels of aggression and territoriality in chimpanzees. We also find fiber projections into the cortex in great apes to a greater extent than rhesus macaques, suggesting a mechanism for spatially and temporally specific modulation by oxytocin and vasopressin of regions implicated in social cognitive processes such as empathy. Finally, we characterize the distribution of receptors in chimpanzees, comparing the results to published data from human studies. We find a lower density of oxytocin and vasopressin in reward areas as compared with humans, which may relate to differences in pair-bonding. We also find vasopressin receptors in the amygdala of chimpanzees, consistent with the presence of axonal fibers. These findings can add to anthropological theories of social behavior changes over the course of human evolution, such as the human self-domestication hypothesis and the cooperative breeding hypothesis.

Table of Contents

Chapter 1: Introduction - 1

Social Animals - 2

Oxytocin and Vasopressin: Social Behavior Across Taxa - 3

Oxytocin and Vasopressin: Systems within Systems - 13

Socio-behavioral and Neurobiological Differences among Humans, Chimpanzees, and Bonobos - 17

The Oxytocin and Vasopressin Systems in Non-Human Primate Brains - 27

The Oxytocin and Vasopressin Systems in Human Brains - 31

The Present Study - 41

References - 44

Chapter 2: Oxytocin (OT) and arginine-vasopressin (AVP) cell bodies and fibers in rhesus macaques, bonobos, chimpanzees, and humans - 80

Abstract - 81

Introduction - 82

Methods - 85

Results - 88

Discussion - 103

References - 108

Chapter 3: Oxytocin and arginine vasopressin-containing fibers in the cortex of humans, chimpanzees, and rhesus macaques - 114

Abstract - 115

Introduction - 116

Methods - 120

Results - 123

Discussion - 131

References - 136

Chapter 4: Neuroanatomical distribution of oxytocin and vasopressin v1a receptors in chimpanzees - 146

Abstract - 147

Introduction - 148

Methods - 154

Results - 155

Discussion - 160

References - 164

Chapter 5: Discussion - 171

Introduction - 171

Neuroanatomy of the OT and AVP Systems across Primate Species - 162

Evolutionary Perspectives - 185

Future Directions - 192

Conclusions - 194

References - 196

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