RESUMEN
The mesolimbic dopamine (DA) system (MDS) is the canonical "reward" pathway that has been studied extensively in the context of the rewarding properties of sex, food, and drugs of abuse. In contrast, very little is known about the role of the MDS in the processing of the rewarding and aversive properties of social stimuli. Social interactions can be characterized by their salience (i.e., importance) and their rewarding or aversive properties (i.e., valence). Here, we test the novel hypothesis that projections from the medial ventral tegmental area (VTA) to the nucleus accumbens (NAc) core codes for the salience of social stimuli through the phasic release of DA in response to both rewarding and aversive social stimuli. In contrast, we hypothesize that projections from the lateral VTA to the NAc shell codes for the rewarding properties of social stimuli by increasing the tonic release of DA and the aversive properties of social stimuli by reducing the tonic release of DA. Using DA amperometry, which monitors DA signaling with a high degree of temporal and anatomical resolution, we measured DA signaling in the NAc core or shell while rewarding and aversive social interactions were taking place. These findings, as well as additional anatomical and functional studies, provide strong support for the proposed neural circuitry underlying the response of the MDS to social stimuli. Together, these data provide a novel conceptualization of how the functional and anatomical heterogeneity within the MDS detect and distinguish between social salience, social reward, and social aversion. Significance Statement: Social interactions of both positive and negative valence are highly salient stimuli that profoundly impact social behavior and social relationships. Although DA projections from the VTA to the NAc are involved in reward and aversion little is known about their role in the saliency and valence of social stimuli. Here, we report that DA projections from the mVTA to the NAc core signal the salience of social stimuli, whereas projections from the lVTA to the NAc shell signal valence of social stimuli. This work extends our current understanding of the role of DA in the MDS by characterizing its subcircuit connectivity and associated function in the processing of rewarding and aversive social stimuli.