As mentioned above, the “heroin/stress control” received saline during self-administration, no foot-shock prior to the first reinstatement test, and saline prior to the second test. Also this group did not receive the stress “challenge” prior to tissue collection. Although other controls (heroin self-administration only, stress reinstatement only, heroin reinstatement only) could have been included, this was the only group necessary for the interpretations of inter-group individual differences in gene expression.
