Fig. 2.

Effects of buprenorphine + naltrexone on cocaine self-administration in rats under FR and PR schedules. After the determination of baseline cocaine self-administration under a PR schedule, the rats received an injection of buprenorphine (3 mg/kg) plus naltrexone (0, 0.3, 1, 3, and 10 mg/kg) for 2 consecutive days. Cocaine self-administration was assessed under an FR schedule on the first treatment day and under a PR schedule on the second treatment day. The testing sequence of the drug mixtures was counterbalanced across rats. (A and B) Cocaine self-administration in response to buprenorphine + naltrexone, assessed on an FR schedule for the ShA group (1-hour session) (A) and LgA group (first hour) (B). (C and D) Cocaine self-administration in response to buprenorphine + naltrexone on PR responding in both ShA and LgA groups. The data are expressed as a percentage of baseline responding in the baseline FR and PR sessions that immediately preceded the FR and PR test sessions to account for the differences in baseline responding observed in Fig. 1. A two-way ANOVA revealed the following for the FR data (A and B): access × naltrexone interaction (F_5,75 = 2.5, P < 0.05), main effect of access (F_1,75 = 0.01, P > 0.05), and main effect of naltrexone (F_5,75 = 11.4, P < 0.001). A two-way ANOVA revealed the following for the PR data (C and D): access × naltrexone interaction (F_5,75 = 3.1, P < 0.05), main effect of access (F_1,75 = 1.5, P > 0.05), and main effect of naltrexone (F_5,75 = 6.7, P < 0.001). For the effects of buprenorphine-naltrexone on cocaine self-administration compared with vehicle with a given access group, the Bonferroni post hoc test yielded *P < 0.05, **P < 0.01, and ***P < 0.001 compared with vehicle treatment. For the effects of buprenorphine on cocaine self-administration between the ShA and the LgA groups, the Bonferroni post hoc test yielded P < 0.05.