Effects of acute stress and corticosterone on fear memory extinction in mice

Memory extinction is the process that being after recalled and actively previously consolidated memories. Although recent studies suggest that acute stress and glucocorticoids have modulatory effects on fear memory extinction, but their effects are not known clearly. The aim of this study was to determine the effects of acute stress and corticosterone on fear memory extinction in passive avoidance task in mice. In this exprimental study, 48 male albino mice (25-30 gr) were used, which were trained in one trial inhibitory avoidance task (1mA, 3 s footshock). Corticosterone (0.5, 1 and 3 mg/kg) was systemically administrated 30 min prior to memory reactivation. In addtion, acute stress was induced in some groups using restrainer (plexiglass tube) for 10 min at the same time of cortisterone adminstration. The process of memory extinction was assessed by retention tests given 2, 5, 7 and 9 days after memory reativation. The latency to re-enter dark compartment of the apparatus was recorded. The results showed that systemic injection of corticosterone (1 or 3 mg/kg) or acute stress facilitates fear-related memory extiction significantly. Our findings indicate that glucocorticoid system and acute stress play an important role in fear memory extiction. Our findings might be helpful to develop therapeutic methods to treat pathological emotional memories such as those seen in post-traumatic disorders and phobia.