Two studies compared transcriptional changes within a brain region for cocaine use and heroin20, cannabis22 and phencyclidine.22 One study by Albertson examined postmortem nucleus accumbens and found significant differences between opioid and cocaine users.20 An increased expression of transcripts associated with synaptic machinery was identified in heroin users, but not for cocaine users. Conversely, a decrease in myelin-related transcripts previously observed for cocaine use cases19 was absent in heroin users20. Interestingly, a few transcripts were significantly and similarly regulated in both groups. Examining differences and similarities across different types of substance use was the premise of another microarray study by our group.22 This study employed postmortem anterior prefrontal cortex from cases who had predominantly used cocaine, cannabis or phencyclidine as determined by case history, hair testing and other toxicology, and found more differences than similarities between drugs in significantly regulated transcripts (Figure 1). A small subset of transcripts did, however, share a significant and similar regulation for cocaine, cannabis and phencyclidine use cases. Functional annotation of the shared transcripts demonstrated a consistent regulation for three functional groups, including a decrease
