A and B, time courses of the effect of SKF81297 (3 and 4 mg/kg, intraperitoneal) on locomotion, measured as the distance traveled. C, time courses of the effect of amphetamine (3 mg/kg, intraperitoneal) on locomotion. D, quantification of total distance traveled by the mice for 60 min after SKF81297 (45–105 min) and amphetamine (120–180 min) administration. PSD-95 KO and WT littermates (n = 6) were habituated in a locomotor activity monitor for 60 min or until the mice were fully habituated. The mice were then injected (arrows) with dopamine receptor agonists at the doses indicated. Horizontal activity, measured as the distance traveled, was continuously recorded in blocks of 4 or 5 min. All data are mean ± S.E. *, p < 0.05 versus WT mice, Student’s t test.