two or more studies (Table 1). These likely represent a conservative estimate of the similarities in genes that are regulated by drugs of abuse, in that different microarray platforms and criteria for significance were employed, and since similar, but not identical, transcripts from the same gene family and functional group were identified in more studies. Among those that were consistently detected, oligodendrocytic function and myelination appeared to be targeted by different classes of drugs of abuse and across brain regions, such that a number of transcripts encoding oligodendrocyte and myelination-related genes were altered in the nucleus accumbens19 and dorsolateral prefrontal cortex21 from cocaine users, and in the nucleus accumbens25 and frontal cortical areas17–18,24–25 from alcoholic cases. Among substance use cases (Table 1), changes in the expression of myelin-associated glycoprotein (MAG) and peripheral myelin protein 22 (PMP22) were exclusively identified in alcoholic cases.17–18,24–25 In contrast, changes in gene expression for proteolipid protein 1 (PLP1), the primary constituent of myelin, was identified to be significantly regulated in the nucleus accumbens19 and dorsolateral prefrontal cortex21 of human cocaine users and in diverse cortical regions in alcoholic cases.17–18,24–25 Changes in PLP1 expression was also identified in schizophrenic cases.29–31 Such changes in oligodendroglial metabolism and
