Cocaine conditioned place preference is similar in D1-GFP, and D2-GFP hemizygotes and littermate controls. CPP score in wild-type (D1-GFP^−/−) littermates (n = 4 saline, n = 7 cocaine); D1-GFP^+/− (n = 7 saline, n = 10 cocaine), wild-type (D2-GFP^−/−) littermates (n = 4 saline, n = 6 cocaine); and D2-GFP^+/− (n = 5 saline, n = 6 cocaine).