Oxytocin: co-evolution of human and domesticated animals

Abstract

The neuropeptide oxytocin (OT) and its homologs are produced in specialized neurons located in vertebrates exclusively in a deep and evolutionarily old part of the forebrain, the hypothalamus. The axons of OT neurons form the classical hypothalamic-neurohypophyseal tract terminating in the blood vessels of the neurohypothysis to release OT into the system’s blood circulation. However, as was recently demonstrated in mammals, collaterals of OT axons concomitantly project to various forebrain regions to modulate the activity of the local networks. At the behavioral level, OT facilitates intraspecific social contacts in mammals via various mechanisms ranging from the suppression of neuroendocrine stress responses to direct OT action on the neurons of the socially relevant brain regions. Recent reports have indicated the possible contribution of OT to the formation of a social bond between domesticated mammals (dog, sheep, cattle) and humans. Indeed, the social interaction between humans and domesticated animals resulted in the elevation of peripheral OT levels (in blood, saliva, or urine) and, in congruence, exogenous (intranasal) OT application led to more frequent contacts between the owner and the domesticated animal. It has been known for decades that domesticated animals exhibit profound socio-communicative abilities accompanied by suppressed aggression and stress responsiveness. These peculiarities of their behavior and physiology may be influenced by the activity of the central OT system. Therefore, in the present mini review, we focus on the role of OT in the orchestration of distinct forms of social behavior, including the monogamous bond, maternal care, social memory and recognition, aggression, and anxiety. As a conclusion, we propose possible directions for exploring the OT contribution to the empathy between humans and domesticated animals, which was likely established in the course of their coevolution during last 10000–15000 years.