Figure 3.
Self-administration of oxycodone. Number of 0.15 mg/kg/injection oxycodone reinforcers earned by F344/N (blue), BN/NHsd (green), ACI/N (pink), and WKY/N (orange) rats across all 14 sessions (panel A), the mean of the last three sessions (panel B) and the cumulative number of reinforcers in the last session (panel C). Number of reinforcers earned across the four acquisition sessions (by session) (panel D), and the total number of reinforcers earned during acquisition (panel E). Ratio of Cmax of oxycodone to Cmax oxymorphone (panel F) and percentage of reinforcers earned during burst episodes in session 4 of the acquisition phase (panel G). Percentage of reinforcers earned during burst episodes (panel H) and average interval between rewards in the last session (panel I). Escalation Z score, beginning with session 5, for each strain of rats (panel J) as well as the average escalation Z score for the last three sessions (panel K). Number of reinforcers earned, and the corresponding final ratio completed during the progressive ratio session, as a measure of motivation (panel L). Number of responses made during the reinstatement test after 4 weeks of protracted withdrawal as a measure of seeking behavior (panel M). Data are shows as mean ± S.E.M. and include individual subjects for the bar graphs. Post hoc analyses indicated significant differences between strains: * p < 0.05; ** p < 0.01; **** p < 0.001