Nitric oxide and histone deacetylases modulate cocaine-induced mu-opioid receptor levels in PC12 cells

To assess the effects of cocaine on MOR levels, two treatment regimens were tested in PC12 cells: single continuous or multiple intermittent. MOR protein levels were assessed by western blot analysis and quantitative PCR was used to determine relative MOR mRNA expression levels. To evaluate the role of nitric oxide (NO) and histone acetylation in cocaine-induced MOR expression, cells were pre-treated with the NO synthase inhibitor Nω-nitro-L-arginine methylester (L-NAME) or the non-selective histone acetyltransferase inhibitor curcumin.Both cocaine treatment regimens significantly increased MOR protein levels and protein stability, but only multiple intermittent treatments increased MOR mRNA levels as well as c-fos mRNA levels and activator protein 1 binding activity. Both regimens increased NO production, and pre-treatment with L-NAME prevented cocaine-induced increases in MOR protein and mRNA levels. Single and multiple cocaine treatment regimens inhibited histone deacetylase activity, and pre-treatment with curcumin prevented cocaine-induced up-regulation of MOR protein expression.In the PC12 cell model, both NO and histone deacetylase activity regulate cocaine-induced MOR expression at both the transcriptional and post-transcriptional levels. Based on these novel findings, it is hypothesized that epigenetic mechanisms are implicated in cocaine’s action on MOR expression in neurons.Endogenous opioid systems are involved in several aspects of cocaine addiction [1-5], and several studies have indicated that cocaine increases μ-opioid receptor (MOR) mRNA and peptide expression [6-11] in regions of the brain known to regulate incentive motivation and stress reactivity [12-14]. In rats, cocaine-induced increases in MOR mRNA expression have been consistently observed in the ventral striatum [15,16], a region of the brain critical to drug motivated behaviors [17,18]. Furthermore, PET studies in abstinent cocaine users have established correlations between elevations in