Abstract The nucleus accumbens (NAc) is a crucial brain region for emotionally-relevant behaviors. The NAc is mainly composed of medium spiny neurons (MSN) expressing either dopamine receptor D1 (D1-MSNs) or D2 (D2-MSNs). D1-MSNs project to the ventral tegmental area (VTA) and ventral pallidum (VP), while D2-MSNs project only to the VP. In this work, we selectively manipulated D1-MSN projections to the VP and VTA, and D2-MSN projections to the VP during classical anxiety behavioral paradigms in naïve mice. We found that optogenetic activation of D1-MSN to VP or VTA did not trigger significant anxious-like behaviors. Interestingly, optical activation of D2-MSN-VP projections significantly increased anxious-like behavior in all of the tests performed. This phenotype was associated with a decrease in the activity of VP putative GABAergic neurons. Importantly, pre-treating D2-MSN-VP animals with the GABA modulator diazepam prevented the optically-triggered anxious-like behavior. Overall, our results suggest that D2-MSN-VP projections contribute for the development of anxious-like behavior, through modulation of GABAergic activity in the VP.

Involvement of nucleus accumbens D2-MSN projections to the ventral pallidum in anxious-like behavior