Figure 6.

Pharmacological activation of D2 receptors accentuates the inhibitory effects of glucose on operant responding for sucrose pellets. (a) Experimental design: mice were injected IP with either vehicle (Veh) or bromocriptine (BC; 10 mg/kg) and 15 min later injected again IP with Veh or glucose (Glu; 2 g/kg, IP) and assessed on an operant fixed ratio 1 (FR1) sucrose pellet self-administration schedule for 150 min. Mice were tested for a total of four consecutive sessions. (b) Total active lever presses during the task. Veh-treated mice show discrete temporal FR1 responses. Glu significantly blunted FR responses at 30 and 90 min into the task. BC accentuated the inhibitory effect of glucose on FR responding. ***P⩽0.001, **p⩽0.01, and *p⩽0.05, two-way repeated measures ANOVA with Holm–Šídák post hoc tests. (c) Inactive lever presses during the task. (d) Glu significantly decreased the total number of pellets earned during each session compared with both Veh/Veh sessions. Pretreatment with BC accentuated the Glu-mediated decrease in pellets earned. **P⩽0.01 and *p⩽0.05, t=0.052, two-way repeated measures ANOVA with Holm–Šídák post hoc tests. (e) Glu significantly decreased the total number of pellets consumed during each session compared with both Veh/Veh sessions. Pretreatment with BC completely abolished sucrose pellet consumption. ***P⩽0.001 and *p⩽0.05, two-way repeated measures ANOVA with Holm–Šídák post hoc tests. Data are shown as mean±SEM.