DNA methylation/demethylation mechanisms have been implicated in a variety of alcohol phenotypes in both central and peripheral tissues. For example, chronic ethanol treatment of mouse embryonic cortical neurons revealed DNA demethylation at the NMDA receptor (NR2B) gene promoter, which correlated with an upregulation of NR2B expression. However, acute ethanol treatment did not alter the methylation of NR2B gene promoter or NR2B expression in adult mouse cortex or in mouse fetal cortical neurons (Ravindran & Ticku, 2004, 2005). The DNMT inhibitor 5-aza mimicked these chronic ethanol effects independently and also in combination with ethanol (Ravindran & Ticku, 2004, 2009). Using a chronic intermittent ethanol (CIE) exposure model, a decrease in site-specific (proximal to transcription factor binding AP-1 and CRE sites) DNA methylation was observed, which persisted following ethanol withdrawal. Moreover, these changes were associated with CIE-induced NR2B expression (Qiang et al., 2010; Qiang, Denny, & Ticku, 2007). Human post-mortem studies have revealed three single-nucleotide polymorphisms in the prodynorphin gene that are associated with alcohol dependence which overlap with CpG sites and are differentially methylated (Taqi et al., 2011). Prefrontal cortical tissue
