As described in the previous sections, functional annotation of transcriptional changes suggest that different abused substances affect a number of similar functional classes, including myelination, synaptic plasticity and cytoskeleton-related functions, while other changes appear to be specific to the type of drug which is abused. While it is important to identify transcripts that are regulated by a specific drug, it is also instructive to look at transcripts regulated across different abused drugs. Additionally, examination of the similarities and differences in the response of different brain regions across these drugs may further provide information pertaining to the regional transcriptional neurobiology. Expression changes were identified for a large number of individual transcripts in nine studies reporting gene lists of significantly changed gene expression in postmortem brain from nicotine, alcohol, cocaine, heroin, cannabis or phencyclidine users.17–23,25,27 Thirty-eight specific gene transcripts were reported in 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
