A generalized motor deficit in the L-RI rats following foot shock stress is unlikely as they displayed similar levels of lever-pressing responses during self-administration sessions and during the heroin-induced reinstatement session. Also, the difference between the H-RI and L-RI groups cannot be caused by differences in amount of heroin consumption: H-RI and L-RI rats had very similar total heroin intake over 7 days of self-administration. To our knowledge, this is the first demonstration that there is a relationship between individual differences in AVP gene expression and a propensity for the heroin-seeking behavior in response to acute stress. A formal test of this hypothesis would require studying the effect of the over-expression of the AVP gene or administration of AVP V1b antagonists into the Me/BLA prior to acute stress-induced reinstatement tests.
