Table 2.

Cocaine discrimination accuracy at criteria and dose-effect curve

Genotype	%DAR saline	%DAR cocaine	A50 DAR	A50 rate reduction
Wild-type	1.9 ± 0.6	98.6 ± 0.5	1.49 [1.04 – 2.14]	9.77 [8.22 – 11.6]
M1−/−	1.0 ± 0.6	97.4 ± 0.8	2.05 [1.23 – 3.43]	11.8 [7.42 – 16.6]
M4−/−	1.2 ± 0.4	98.6 ± 0.7	1.49 [0.69 – 3.19]	10.3 [6.42 – 16.5]

%DAR saline and %DAR cocaine represent average performance over the block of sessions that satisfied discrimination criteria (group means ± s.e.m.). Group sizes: wild-type, N = 13, M₁^−/−, N = 9, M₄^−/− mice, N = 8. Reductions in response rates by at least 50% were not observed in all of the subjects, and A₅₀ for rate reduction was calculated from 12 wild-type mice, 5 M₁^−/− mice, and 6 M₄^−/− mice.