SIRT1 regulates dendritic spine density and expression of plasticity-related genes in NAc. A, qPCR analysis of NAc of mice treated for 7 d (20 mg/kg) with cocaine or saline for plasticity-related genes (n = 7–8). B, C, Cocaine increases dendritic spines on NAc medium spiny neurons (n = 11 dendrites in 4–5 animals; B), an effect mimicked by HSV-SIRT1 (n = 25–28 dendrites in 4–5 animals; C). *p < 0.05, **p < 0.01.