alcohol dehydrogenase gene. Furthermore histone H3K9 acetylation was increased in the promoter and coding regions of the gene (Pal-Bhadra et al., 2007; Park et al., 2012). Histone methylation is a dynamic reversible process and is under the control of two opposing groups of enzymes-the lysine methyltransferases and the lysine demethylases (Kouzarides, 2007). Genome-wide association studies have found KDM4C (a lysine demethlyase of the jumonji domain 2 (JMJD2) family) loci associated with alcohol withdrawal (Wang, Liu, Zhang, Wu, & Zeng, 2012). Other drugs of abuse, such as cocaine, resulted in a reduction of G9a and G9a-like protein (GLP) (lysine dimethyltransferases), which corresponded to a decrease in H3K9me2, and an increase in spine density in the NAc and cocaine place preference, whereas overexpression was able to reverse these effects (Maze et al., 2010). In the case of the repressive mark, H3K9me3, repeated cocaine caused a decrease in H3K9me3 binding to non-coding retro-transposon associated inter-genic regions (Maze et al., 2011).
