Fig. 2.

D1 receptor mutant mice do not acquire CPP at multiple cocaine doses. Five groups each of D1 receptor mutant (D1−/−) and wild-type (WT) mice received either cocaine (2.5, 5, 10, 20 mg/kg, n=12–16 per group) or saline (n=10 per group) injections alternatively and were confined to CPP chambers. Mice were then tested for place preference without injections at the indicated time points. Results represent mean ± SEM time spent on the drug-paired side minus the saline-paired side. Wild-type mice showed significant place preference at all 4 cocaine doses. In contrast, D1 receptor mutant mice did not. Saline-treated D1 receptor mutant and wild-type mice did not show significant preference. *p<0.05 compared with the same mouse group before drug administration (pre-test). #p<0.05 compared between two genotype at the same dose and test.