A, DA concentration transients (top) and color plots (bottom) before and after cocaine (bold) for Drd2loxP/loxP (left) and iMSN-Drd2KO mice (right). B-C, Effect of cocaine on the decay time constant Tau (B), and the peak and area (C) of DA signals in Drd2loxP/loxP (n = 8-3) and iMSN-Drd2KO (n = 7-3) mice. D, Timecourse of the locomotor response to the D1-like agonist SKF81297 (7.5 mg/kg, red). E, Locomotor activity during first hour after saline or SKF81297 administration expressed as percent of the activity over 1 hour before injection. **p< 0.01, ****p < 0.0001. All data expressed as mean ± s.e.m.