Sex-dependent regulation of social reward by oxytocin in the mesolimbic reward circuitry

PROJECT SUMMARY The rewarding properties of social interactions are critical to the expression of adaptive social behavior and to the development and maintenance of social relationships. Little is known, however, about the factors that determine the reward value of social interactions or about the basic neural mechanisms that underlie social reward, particularly in females. We do know that the mesolimbic dopamine system (MDS) is central to the neural circuitry controlling the rewarding properties of many other stimuli such as drugs of abuse. A primary component of the MDS is dopamine (DA)-containing neurons in the ventral tegmental area (VTA) that project to the nucleus accumbens (NAc) as well as to other sites such as the medial prefrontal cortex. Critical inputs to the MDS include oxytocin (OT)-containing projections from the hypothalamus. We and others have demonstrated that, in male rodents, activation of OT receptors in the caudal VTA and in the NAc is essential for the rewarding properties of social interaction. Remarkably, despite the considerable evidence for sex differences in OT regulation of social behaviors, the role of OT in regulating social reward in females has not been investigated. This project will provide substantial new information on the factors that determine the reward value of social interactions and on the neural mechanisms that mediate social reward by testing this series of integrated hypotheses in male and female Syrian hamsters. Based on published and preliminary data from our lab and others, we have hypothesized that: 1) there is an inverted U relationship between the “dose” of social interactions and social reward, 2) this dose-response relationship is initiated at lower doses in females than in males, and 3) this sex difference is mediated by differential OT-induced DA release in the MDS. This project has substantial potential for translation to clinically-related problems by providing: 1) new information on how social stimuli can transition from being rewarding to being less rewarding or even aversive, 2) potential mechanisms for understanding well-known sex differences in the incidence of neuropsychiatric and neurodevelopmental disorders for which dysfunctional social relationships are an important symptom, and 3) the potential for development of gender- specific treatments for these disorders.