Figure 2.

Cocaine dose-effect functions in wild-type, M₁^−/− and M₄^−/− mice trained to discriminate 10 mg/kg cocaine from saline. Abscissae: cocaine dose in mg/kg, “Sal” indicates saline; ordinates: percentage cocaine-appropriate responses (top panels), response rates in responses per second (bottom panels). Wild-type data are shown in both left (M₁^−/−) and right (M₄^−/−) panels to facilitate comparison. Data are groups means ± one S.E.M. Group sizes: wild-type, N=13; M₁^−/−, N=9; M₄^−/−, N=8.