Running Head: THE ROLE OF DOPAMINE AFFERENTS IN NAC AND CEA 1 Optogenetic Stimulation of Dopamine Afferents in Nucleus Accumbens and Central Amygdala Reveals Differential Roles in Food and Social Motivation

Dopamine cells are densely located in the ventral tegmental area (VTA) and project to several forebrain structures such as the Nucleus Accumbens (NAc) and the Central Amygdala (CeA) to influence various forms of motivated actions. Previous studies have suggested that dopaminergic projections from the VTA to NAc are involved in instantaneous forms of motivation, while VTA to CeA projections may be involved in amplifying and narrowing incentive motivation to a single reward target. (Fields, Hjelmstad, Margolis, & Nicola, 2007; M. J. Robinson, Warlow, & Berridge, 2014). Here we examined both projections in the same task using optogenetic excitation of dopamine projections from VTA to either NAc or CeA to understand the differential roles that dopamine (DA) serves in influencing motivation for food and social interaction. Stimulation of DA afferents from VTA to NAc shell via optogenetic virus in Th-Cre rats caused rats to instantly bias their choice for one sucrose pellet paired with VTA to NAc stimulation over another identical sucrose pellet not paired with stimulation. Stimulation of DA afferents from VTA to CeA caused an equally intense bias as VTA to NAc, but which did not appear until the third day. Overall, rats receiving VTA to NAc DA stimulation pressed more at their laser-paired lever than those receiving VTA to CeA stimulation, earning them more sucrose pellets. Neither pathway supported self-stimulation when rats were given the opportunity to earn laser stimulation alone. In a social paradigm, rats displayed more social interactions with an unfamiliar rat when the VTA to NAc was stimulated. Our findings propose that DA afferents from VTA mediate different aspects of motivated behavior, depending on whether they project to CeA or NAc.