Depression is a recurring and life-threatening illness that affects up to 120 million people worldwide. In the present study, we show that chronic social defeat stress, an ethologically validated model of depression in mice, increases SIRT1 levels in the nucleus accumbens (NAc), a key brain reward region. Increases in SIRT1, a well characterized class III histone deacetylase, after chronic social defeat suggest a role for this enzyme in mediating depression-like behaviors. When resveratrol, a pharmacological activator of SIRT1, was directly infused bilaterally into the NAc, we observed an increase in depression-and anxiety-like behaviors. Conversely, intra-NAc infusions of EX-527, a SIRT1 antagonist, reduced these behaviors; EX-527 also reduced acute stress responses in stress-naive mice. Next, we increased SIRT1 levels directly in NAc by use of viral-mediated gene transfer and observed an increase in depressive-and anxiety-like behaviors when mice were assessed in the open-field, elevated-plus-maze, and forced swim tests. Using a Cre-inducible viral vector system to overexpress SIRT1 selectively in dopamine D1 or D2 subpopulations of medium spiny neurons (MSNs) in the NAc, we found that SIRT1 promotes depressive-like behaviors only when overexpressed in D1 MSNs, with no effect seen in D2 MSNs. Conversely, selective ablation of SIRT1 in the NAc using viral-Cre in floxed Sirt1 mice resulted in decreased depression-and anxiety-like behaviors. Together, these results demonstrate that SIRT1 plays an essential role in the NAc in regulating mood-related behavioral abnormalities and identifies a novel signaling pathway for the development of innovative antidepressants to treat major depressive disorders.

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