The Role of Reward and Dopamine Signaling in Prairie Vole (Microtus ochrogaster) Peer Relationships

Same-sex peer relationships are an important component in the social structures of group living species, yet they have been understudied compared to reproductive relationships (e.g. pair bonds between mates and parent-offspring bonds). Voles provide an ideal opportunity to assess the neural mechanisms underlying social behavior across species and social systems (socially monogamous prairie voles vs. socially non-monogamous meadow voles), and relationship type (reproductive mate vs. non-reproductive peer). Whereas prairie voles (Microtus ochrogaster) have largely been studied for their selective, enduring pair bonds with mates and biparental care, meadow voles (Microtus pennsylvanicus) have largely been studied as a contrast to prairie voles and for their similarly selective, long-lasting female-female peer relationships. Prairie voles also display peer relationships, and assessing the mechanisms mediating the formation and maintenance of these relationships allows for understanding of the specificity and generality of mechanisms underlying social behavior in voles. First, a comparative project was conducted to lay the behavioral foundations for mechanistic work. Prairie voles displayed highly selective peer relationships (i.e. strong preference for a familiar peer over a same-sex stranger). Prairie voles also exhibited more aggression and social exploration, and less anxiety, than meadow voles. The role of dopamine signaling was then investigated via pharmacological manipulations and assessment of structural changes in dopamine D1 receptor density. Dopamine plays an essential role in the formation of prairie vole pair bonds. In contrast, there is evidence that dopamine is not necessary to meadow vole peer affiliation. Dopamine was also not necessary for prairie vole peer affiliation, consistent with findings in meadow voles. Peer relationships may not depend on dopamine neurotransmission, likely because they are non-reproductive and are therefore less highly motivating than reproductive relationships such as pair bonding. However, prairie voles exhibited reinforcement and motivation for peers, although less so than for mates. Finally, dopamine D1 receptor upregulation is associated with the maintenance of prairie vole pair bonds. Although this was not the case with prairie vole peer relationships, housing and behavioral differences and correlations in D1 binding suggest that higher D1 binding in the nucleus accumbens was associated with less sociality