Regulation of post-transcriptional and post-translational modulators of SIRT1. A, B, Chronic (7 d) cocaine increases both HuR transcript levels (A; n = 6–8) and protein levels (B; n = 7) in NAc. A similar increase in HuR protein is induced in NAc by chronic morphine (n = 8–10; B). C, D, Cocaine also increases SUMO-1 transcript levels (C; n = 6–8) and protein levels (D; n = 7–8). Chronic morphine likewise induces SUMO-1 protein in NAc (n = 8–10; D). *p < 0.05, **p < 0.01.