Project Summary The neurotransmitter dopamine (DA) and the neuropeptide oxytocin (OT) are characterized by their ability to modulate reward and social behavior, respectively. The DA system influences behavior in a variety of contexts, including drugs of abuse and associative learning, and has more recently been implicated in social behavior. DA may alter social behavior through complex interactions with the OT system. DA may be the link that associates social interactions as rewarding and therefore may be a target system for understanding dysfunction of social ability. The first aim of this proposal will characterize the effect of dopaminergic manipulation on male-female social relationships in pair-living marmosets. Experimental treatments will involve administration of pharmacological agents (both agonists and antagonists) that target D1- and D2-like dopamine receptors. The second aim of the proposal examines the interaction between the OT and DA systems in the production of both pair- related social behavior and partner preference. OT agonists and antagonists will be co-administered with DA treatments to assess independent or dependent mediation of sociality by these two signaling pathways. The third aim of the proposal will examine a VNTR polymorphism in the regulatory region of the DA transporter gene (DAT1/SLC6A3). This polymorphism is associated with differential sensitivity to food reward in marmosets, and Aim 3 will evaluate whether individual differences in social relationships and reactivity to novel stimuli are explained by genetic variation. Together, these experiments will identify the independent and co-modulatory role of DA in complex social relationships, and test whether gene-based variation in one component of DA signaling (reuptake of synaptic DA) can predict the qualitative and quantitative differences of partner-directed social behavior.