FIGURE 5.

Effects of previous morphine experience and withdrawal on oxycodone dose–response in male and female rats. A, In preparation for the dose response test, rats went through a small extinction procedure in which saline was substituted for oxycodone for 4 days until the number of infusions (saline d3, 4) was significantly less than those on saline d1 (^{^^}p < 0.01). Subsequently, rats self-administered either oxycodone (0.01 mg/kg/infusion) or saline on alternate days for a total of 6 days to demonstrate that rats could behaviorally differentiate between saline and oxycodone (^#p < 0.05 comparing infusions on oxycodone days to saline d3, 4). B, In the dose response test, rats self-administered one dose/day of oxycodone (0.003–0.3 mg/kg/infusions; one dose/trial/day), presented in random order. Data are presented as the total number of oxycodone infusions during each days’ 2-h dose–response test. ^{^^}p < 0.01 main effect of dose. N = 7–14 rats/group