Effects of CB1 and opioid receptor antagonists on WIN 55,212-2-induced increases in 5-HT in the nucleus accumbens. Data are expressed as percent of average baseline values (% mean ± s.e.m.). Mean baseline level of extracellular 5-HT was  pg/sample in the NAcc (). The arrows indicate the time of injection of antagonists 30 min before WIN 55,212-2. The effect of WIN 55,212-2 on 5-HT efflux in the NAcc was blocked by SR 147778 (5 mg/kg i.p.; (a)) and AM251 (5 mg/kg, i.p; (b)), but not by naloxone (10 mg/kg, s.c.; (c)). * and *** versus vehicle examined by the repeated measures ANOVA followed by post hoc Scheffe test.