Table 1.

Operant self-administration measures in Alk^WT vs. Alk^KO mice during fixed ratio sessions.

Measure	AlkWT	AlkKO	F	p
	Mean ± SEM	Mean ± SEM
Active lever presses	64 ± 10	71 ± 9	F(1,28) = 0.25	0.62
Inactive lever presses	44 ± 9	29 ± 6	F(1,28) = 1.86	0.18
Total lever presses	108 ± 14	100 ± 14	F(1,28) = 0.17	0.68
Active lever preference	0.62 ± 0.04	0.73 ± 0.04	F(1,26) = 3.391	0.08
Reinforcers earned	17.2 ± 2.7	19.0 ± 2.7	F(1,28) = 0.23	0.64

Data are per session values, averaged over all 16 1-h fixed ratio operant self-administration sessions. ¹WS df = 26 due to two subjects being excluded from this analysis for having no lever presses during one session.