A. During the preconditioning phase, female and male CIS rats displayed a pre-test preference for the white side of the chamber. Thus, a biased CPP design was used in which rats were placed in the least-preferred side following the oxycodone injection. On the testing day, saline-injected (Sal) rats showed no preference for either chamber. However, the percent change in preference score for the oxycodone-injected (Oxy) chamber is higher in CIS female rats compared to their Sal counterparts. Oxy-CIS males did not show a significantly greater preference for the oxycodone chamber than their saline-injected counterparts. SF, Sal-female; SM, Sal-male; OF, Oxy-female; OM, Oxy-male. *p ≤ 0.05; N = 6 rats per group.