Abstract
There is a lack of understanding of the neural mechanisms regulating the rewarding effects of social interactions. A significant contributor to this lack of clarity is the diversity of social behaviors and animal models utilized to investigate mechanisms. Other sources of the lack of clarity are the diversity of brain regions that can regulate social reward and the diversity of signaling pathways that regulate reward. To provide some clarity into the mechanisms of social reward, this review focused on the brain region most implicated in reward for multiple stimuli, the nucleus accumbens, and surveyed (systematically reviewed) studies that investigated the relationship between social interaction and five signaling systems implicated in the regulation of reward and social behavior: oxytocin, vasopressin, serotonin, opioids and endocannabinoids. Moreover, all of these studies were organized by the type of social behavior studied: affiliative interactions, play behavior, aggression, social defeat, sex behavior, pair-bonding, parental behavior and social isolation. From this survey and organization, this review concludes that oxytocin, endocannabinoids and mu-opioid receptors in the nucleus accumbens positively regulate the rewarding social behaviors, and kappa-opioid receptors negatively regulate the rewarding social behaviors. The opposite profile is observed for these signaling systems for the aversive social behaviors. More studies are needed to investigate the directional role of the serotonin system in the nucleus accumbens in the regulation of many types of social behaviors, and vasopressin likely does not act in the nucleus accumbens in the regulation of the valence of social behaviors. Many of these different signaling systems are also interdependent of one another in the regulation of different types of social behaviors. Finally, the interaction of these signaling systems with dopamine in the nucleus accumbens is briefly discussed.