Glucocorticoid-induced impairment of long-term memory retrieval in female rats: Influences of estrous cycle and estrogen

Using an inhibitory avoidance (IA) task, the effects of glucocorticoids on memory retrieval in intact and ovariectomized (OVX) female rats were investigated. Young adult female rats were trained in a one trial IA task (1-mA, 3-s footshock). The latency to reenter the dark compartment of the apparatus was recorded in the retention test performed 48 h after training. Pre-retrieval injection of corticosterone (CORT, 1, 3, and 10 mg/kg) to OVX rats impaired memory retrieval at all doses tested. Similar administration of CORT (3 mg/kg) in intact female rats impaired memory retrieval in the estrus phase (when endogenous plasma levels of estrogen are low) but not in the proestrus phase (when endogenous levels of estrogen are high). Concurrent administration of CORT (3 mg/kg) and 17-β-estradiol (15 μg/kg) in both proestrus and estrous phases impaired memory retrieval. Our findings indicate that the effects of corticosterone on memory retrieval are modulated by the estrous cycle and 17-β-estradiol.