Fig. 4.

Effect of naltrexone on mean (± SEM) dialysate dopamine concentrations from the nucleus accumbens before, during, and after self-administration of ethanol. Basal (BASAL) represents dialysate dopamine levels while rats were resting in their home cage. The arrows indicate the administration of naltrexone (n = 16) or vehicle (saline;n = 13). A, The effects of the injection and the response during the waiting (WAITING) period during which rats were placed in the operant chambers but did not have access to ethanol. B, The same basal shown inA for comparison with the response during the 30 min self-administration session (SELF-ADMIN) and the 10 min period after the session ended (POST). Data for the waiting period were not shown in this panel to facilitate comparison of basal with the response during self-administration; * indicates a significant difference from the respective pooled basal concentration (p < 0.05, determined by planned contrasts, Bonferroni-corrected, after significant interaction between groups and time in the overall ANOVA).