Figure 2.

Yohimbine facilitates long-term context fear extinction. Separate experiments examined the effects of vehicle, yohimbine, and propranolol on extinction with 0 (A), 20 (B), 40 (C), or 60 (D) min of context exposure (eight to 12 mice/group). The data shown represent freezing during a single 5-min context exposure given 1 d after the extinction sessions (drug free). The final summary panel (E) shows the results of the four experiments with fear normalized to freezing in groups of mice that were injected with vehicle and not exposed to the feared context on Day 2 (retention control mice, RC). (^*) p < 0.05 versus RC mice; (+) p < 0.05 versus vehicle-extinction mice.