Fig. 5.

Nifedipine blocks extinction, but not expression, of cued fear. A, Experimental design. Extinction sessions began 24 hr after cue fear acquisition (5 cue–shock pairings). B, Freezing during the first 15 CS presentations, after injections of nifedipine (40 mg/kg dose shown, 20 min pretreatment) or vehicle. C, Freezing 24 hr later during a 2 min, drug-free CS test (n values = 8 for extinction groups). Retention control mice (RC;n = 16) were injected with vehicle and placed in the extinction chamber on day 2 but were not exposed to any CS.D, E, Identical experiment with a longer pretreatment (50 min) of a single nifedipine dose (40 mg/kg) or vehicle (n values = 8). Freezing was also scored during a 2 min acclimation period (Pre-CS). *p < 0.05 versus retention control; +p < 0.05 versus vehicle–extinction.