Figure 1.

KO mice made fewer lever presses early in lever press training (FR1, alternating, no-choice). A, KO mice (n = 31) presented a slight decrease in body weight compared with WT (n = 29) mice. B, KO mice made fewer responses early in lever press training. C, Percent responses allocated to the preferred lever did not differ between KO and WT mice during BP session (all choice trials). D, Percent food pellets consumed did not differ between KO and WT mice (cumulative, Sessions 1–5, and BP). *p < 0.05, ***p < 0.001 vs WT.