Dose-finding experiments for sulpiride and quinpirole. (A) Protocol for dose-finding experiment for sulpiride. Dark box indicates phase of experiment shown in graphs. Mice were injected with vehicle or the indicated doses of sulpiride 45 min before fear conditioning with three pairings of CS and US. One day later, they were tested for fear of the CS in a different context. Dark box indicates the part of the protocol illustrated in the graph below. (B) Average freezing during three CS presentations at test. (*) P < 0.05 vs. vehicle-treated animals. n's = 8/group. (C) Protocol for the dose-finding experiment for quinpirole. Mice were fear conditioned with three CS–US pairings on Day 1. On Day 2, they were injected with vehicle or the indicated doses of quinpirole 30 min before 30 CS presentations, or no CS presentations for retention control (RC) groups, in a different context from conditioning. On Day 3, all groups were tested for fear of the CS in the extinction context. (D) Average freezing during three CS presentations at test. (+) P < 0.01 vs. both RC groups. (*) P < 0.05 vs. vehicle-treated. n's = 7 or 8/group.