Depicts preconditioning response of mice (left panel, open bar) or conditioned place preference among mice conditioned with cocaine (10 mg/kg, s.c.; n = 24, gray bar), U50,488 (0.3 mg/kg, i.p.) 15 min prior to cocaine (10 mg/kg, s.c.; n = 15; right panel, gray hatched bar), or U50,488 (0.3 mg/kg, i.p.) 15 min prior to saline (s.c.; n = 24; right panel, closed bar). * indicates significant difference from pre-conditioned group (p < 0.05). † indicates significant difference from cocaine (10 mg/kg, s.c.)-conditioned group (p < 0.05).