Figure 2.

D32^fl/fl/D2cre⁺ mice exhibit increased responding for sucrose. (a) D32^fl/fl/D2cre⁺ and D32^fl/fl/D2cre^- mice did not differ in body weight. (b) D32^fl/fl/D2cre⁺ mice showed significantly greater locomotor activity than controls. **P⩽0.01, two-way repeated measures ANOVA, group main effect. (c) D32^fl/fl/D2cre⁺ mice showed significantly greater (c) active but not (d) inactive lever pressing compared with controls. *P⩽0.05, **p⩽0.01, and ***p⩽0.001, two-way repeated measures ANOVA with Holm–Šídák post hoc tests. (e) Across sessions 8 and 9 (when lever pressing was most stable), D32^fl/fl/D2cre⁺ mice showed twice as many active lever presses and (f) significantly lower active lever response latency than controls **P⩽0.05, two-sample t-test. Data are shown as mean±SEM.