Responding on a PR schedule is inflated in Bdnf+/− mice. a, Bdnf+/− mice achieved higher breakpoint ratios on a PR schedule of reinforcement, particularly during test sessions 4–7. b, Despite this, responding was equally selective for the active, relative to inactive, apertures between groups. c, d, Comparisons of the average first, median, and last PRPs from sessions 1–3, when breakpoint ratios did not significantly differ, and sessions 4–7, when breakpoints differed, revealed main effects of time as expected, but no genotype effects. These patterns suggest that motivational differences between wild-type and Bdnf+/− mice cannot obviously account for differences in breakpoints. e, vmPFC expression of p-trk, GluR1, and pERK1/2 were decreased in Bdnf+/− mice. The latter could be attributed reduced phosphorylation of the ERK2 isoform. Representative bands are adjacent. Bars and symbols represent means ± SEMs per group. *p < 0.05; **p < 0.001. wt, Wild-type. n = 13–14 per group.