| Summary: | Introduction: Memory extinction is the process that being after recalled and actively previouslyconsolidated memories. Although recent studies suggest that acute stress and glucocorticoids havemodulatory effects on fear memory extinction, but their effects are not known clearly. The aim of this studywas to determine the effects of acute stress and corticosterone on fear memory extinction in passiveavoidance task in mice.Material and Methods: In this exprimental study, 48 male albino mice (25-30 gr) were used, which weretrained in one trial inhibitory avoidance task (1mA, 3 s footshock). Corticosterone (0.5, 1 and 3 mg/kg) wassystemically administrated 30 min prior to memory reactivation. In addtion, acute stress was induced insome 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 memoryreativation. The latency to re-enter dark compartment of the apparatus was recorded.Results: The results showed that systemic injection of corticosterone (1 or 3 mg/kg) or acute stressfacilitates fear-related memory extiction significantly.Conclusion: Our findings indicate that glucocorticoid system and acute stress play an important role infear memory extiction. Our findings might be helpful to develop therapeutic methods to treat pathologicalemotional memories such as those seen in post-traumatic disorders and phobia
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