Progressive ratio test performance.

Performance in the PR test is shown for when animals of both genotypes were deprived to 85% of their free-feeding body weight (graphs to the left in each figure panel) and when the deprivation level of WT rats had been adjusted to achieve equal food consumption rates between genotypes (graphs on the right of each figure panel). (A) Baseline performance during six consecutive PR sessions preceding the prefeeding tests. The ratio, where a given break point was reached, is indicated. (B) Performance during prefeeding with reward pellets (top panel) and regular food (bottom panel). The drop in motivation is displayed as percentage of baseline performance for break point 600. The graphs show group mean plus standard error of the mean. Two-way ANOVA results are displayed above each graph, and results from post-hoc analysis are shown for individual data points. Significant genotype differences are indicated by (p<0.05) *, (p<0.01) **, (p<0.001) *** and (p<0.0001) ****.