Fig. 5.

Reversal of metyrapone’s effect on fear memory extinction with corticosterone. Metyrapone-treated animals given corticosterone following reactivation of a fear memory show significantly less fear memory compared to metryapone-treated mice given vehicle [mixed ANOVA, main effect of group F(1, 22) = 26.30, p = 0.00004; main effect of day F(3, 66) = 9.47, p = 0.000028; group × day interaction F(3, 66) = 3.83, p = 0.014), post hoc comparisons for days 1–3 [Fisher LSD, p = 0.63, p = 0.0044, p < 0.000001, respectively]. When the underlying memory trace was examined 1 day later in the absence of corticosterone or metyrapone, inhibition of fear expression remained enhanced in the corticosterone-treated group (post hoc comparisons, Fisher LSD, day 4: Met.–Veh. vs. Met.–Cort., p = 0.0025). Furthermore, extinction was exhibited in the corticosterone-treated group (main effect of day F(3, 33) = 21.96, p < 0.000001) but not seen in vehicle-treated animals (no main effect of day F(3, 33) = 1.096, p = 0.365). No significant differences were observed during training across groups (p > 0.05). N = 12 for all groups.