Comparison of novel object recognition performance in wild-type and CB1 receptor knockout mice on the 1st and 7th day of MDMA withdrawal (10 mg/kg, i.p., daily for 7 days). Each graph shows the discrimination ratio in the test trial. Data represent the mean±SEM (n=8–15). *p<0.05, ***p<0.001 vs vehicle-treated mice. Open and closed bars indicate wild-type and CB1 receptor knockout mice, respectively. Vehicle means results for mice administered saline.