D32fl/fl/D2cre+ mice exhibit increased impulsive choice behavior for sucrose. (a) Performance during the intolerance to delay (ITD) pretraining stage. Total lever pressing was significantly greater in D32fl/fl/D2cre+ mice than in controls. ***P⩽0.001, one-way ANOVA. (b) During training, D32fl/fl/D2cre+ mice showed significantly greater locomotor activity compared with controls, ***p⩽0.001, one-way ANOVA. (c) Design of ITD experiment. (d) D32fl/fl/D2cre+ mice showed significantly lower % choice for the large reinforcer as a function of increasing delay compared with controls, ***p⩽0.001, two-way repeated measures ANOVA, group main effect. (e) Control mice showed significantly greater pressing for L5 over L1 levers. *P⩽0.05, **p⩽0.01, and ***p⩽0.001, two-way repeated measures ANOVA with Holm–Šídák post hoc tests. (f) D32fl/fl/D2cre+ mice showed significantly greater pressing for L5 over L1 levers at short delay intervals and significantly higher L1 vs L5 lever pressing at longer delay intervals. *P⩽0.05, two-way repeated measures ANOVA with Holm–Šídák post hoc tests. Data are shown as mean±SEM.