Effects of CP55,940 on overall duration, frequency and latency of social approaches in C57BL/6 mice pre-exposed to chronic treatment of vehicle (polyethylene glycol: saline = 9:1) (VEH1) or AM251 (1 mg/kg/day, IP, for 21 days). For all groups, n= 10–12. Doses are given in mg/kg (IP). Values represent mean ± SEM for each treatment. VEH2, vehicle of CP55,940 (Tween 80:polyethylene glycol: saline = 18:1:1); #P<0.05, ###P<0.001 compared with AM251+VEH2.