Effect of cocaine on HDAC activity, and inhibition of HAT on cocaine-induced MOR protein levels. (A) Nuclear extracts were obtained from lysates of PC12 cells treated with cocaine (500 μM SCT or 100 μM RIT) for 24 or 36 hours. HDAC enzyme activity was determined using a fluorescent microplate reader and expressed as specific activity, in pM/min/mg. Statistical analysis revealed a significant decrease in HDAC activity following both cocaine treatment regimens at both 24 and 36 h. (B) Densitometric analysis of MOR protein levels relative to α-tubulin in control and 72 h cocaine (100 μM SCT and 500 μM RIT) treated cells grown in the presence and absence of 1, 3 or 5 μM curcumin. Compared to control, both SCT and RIT with cocaine increased MOR protein levels. For SCT, there was a significant decrease in MOR expression after pre-treatment with 3 μM curcumin compared to cells treated with cocaine alone. Pre-treatment with 1, 3 and 5 μM curcumin also prevented the increase in relative MOR protein levels resulting from 100 μM RIT. Results are representative of at least 5 independent experiments and data are presented as mean ± SEM (*p<0.05, ****p<0.0001 compared to control, #p<0.05, ####p<0.0001 compared to cocaine alone).