Figure 2.

(a) Schematic of the timeline of experimental design and age of rats in postnatal days (PND) from the start to the completion of the study. (b) Active and inactive lever responses during extended access sessions of methamphetamine self-administration (MethSA). * p < 0.05 vs. session 1–4 by repeated measures ANOVA. (c) Active lever responses during sessions 11 to 14 of methamphetamine self-administration. * p < 0.05 vs. session 12 by paired t test. (d) Percent change in active lever responses on vehicle day and CNO days. ^$ p < 0.05, significant interaction, # p < 0.05 vs. hM₄D and * p < 0.05 vs. vehicle day by repeated measures ANOVA. (e,f) Percent change in inactive lever responses (e) on CNO days vs. vehicle day and percent change in time out responses (f) on CNO days vs. vehicle day. n = 5–10 in each group. Data is represented as mean ± SEM.