The behavioral sensitization produced by repeated cocaine treatment represents the neural adaptations underlying some of the features of addiction in humans. Cocaine administrations induce neural adaptations through regulation of gene expression. Several studies suggest that epigenetic modifications, including DNA methylation, are the critical regulators of gene expression in the adult central nervous system. DNA methylation is catalyzed by DNA methyltransferases (DNMTs) and consequent promoter region hypermethylation is associated with transcriptional silencing. In this study a potential role for DNA methylation in a cocaine-induced behavioral sensitization model in mice was explored. We report that acute cocaine treatment caused an upregulation of DNMT3A and DNMT3B gene expression in the nucleus accumbens (NAc). Using methylated DNA immunoprecipitation, DNA bisulfite modification, and chromatin immunoprecipitation assays, we observed that cocaine treatment resulted in DNA hypermethylation and increased binding of methyl CpG binding protein 2 (MeCP2) at the protein phosphatase-1 catalytic subunit (PP1c) promoter. These changes are associated with transcriptional downregulation of PP1c in NAc. In contrast, acute and repeated cocaine administrations induced hypomethylation and decreased binding of MeCP2 at the fosB promoter, and these are associated with transcriptional upregulation of fosB in NAc. We also found that pharmacological inhibition of DNMT by zebularine treatment decreased cocaine-induced DNA hypermethylation at the PP1c promoter and attenuated PP1c mRNA downregulation in NAc. Finally, zebularine and cocaine co-treatment delayed the development of cocaine-induced behavioral sensitization. Together, these results suggest that dynamic changes of DNA methylation may be an important gene regulation mechanism underlying cocaine-induced behavioral sensitization.

No abstract

The behavioral sensitization produced by repeated amphetamine treatment may represent the neural adaptations underlying some of the features of psychosis and addiction in humans. Chromatin modification (specifically histone hyperacetylation) was recently recognized as an important regulator of psychostimulant-induced plasticity. We have investigated the effects of treatment with the histone deacetylase (HDAC) inhibitors butyric acid (BA, 630 mg/kg, i.p) and valproic acid (VPA, 175 mg/kg, i.p.) on the psyhcostimulant locomotor sensitization induced by amphetamine (AMPH, 2.0 mg/kg, i.p.). Neither BA nor VPA had locomotor effects alone, but both significantly potentiated the amphetamine-induced behavioral sensitization in mice. At the molecular level, VPA and amphetamine produced an increase of histone H4 acetylation in the striatum as detected by Western blot analysis, while co-treatment with VPA and AMPH produced an additive effect on histone H4 acetylation. We then administered the HDAC inhibitors after treatment with amphetamine for 8 days to establish locomotor sensitization. We found that repeated administration of VPA or BA for 6 days inhibited the expression of sensitized response following amphetamine challenge. Finally, in a context-specific model we studied the effect of HDAC inhibitors on amphetamine-induced association of the treatment environment (associative learning). We found that VPA and BA enhance the context-specificity of expression of amphetamine sensitization. Thus, HDAC inhibitors differentially modulate the induction and expression of amphetamine-induced effects. Together, these results suggest that dynamic changes in chromatin modification may be an important mechanism underlying amphetamine-induced neuronal plasticity and associative learning.