These genes differentially expressed in the human chronic cocaine brains we studied are involved in diverse cellular functions, but there were patterns that strongly implicated certain cellular functions. Cocaine depressed the transcript levels for all five members of the BEX gene family (BEX 1–5), which encodes brain expressed, X-linked proteins that are thought to mediate neurotrophin signaling and neuronal differentiation (Vilar et al., 2006). There were also significant expression changes for some histone protein genes. Genes involved in regulation of transcription, gene silencing, and chromatin modification were also affected. Several of these genes had been previously implicated in cocaine addiction, including DNMT3a, a DNA methyltransferase which was reported to play an important role in regulating cocaine response and spine plasticity in the NAc in the rat (LaPlant et al., 2010) and HDAC2, a histone deacetylase found to be involved in cocaine-induced transcription changes in rat NAc and cocaine seeking behavior (Chandrasekar & Dreyer, 2010). In addition, there was also convergent evidence that chronic cocaine exposure alters expression of genes involved in RNA processing, including significant alteration in the expression of
