Effects of acute injection of corticosterone and progesterone on memory retrieval in the proestrus and diestrous stages in adult female rats

Acute injection of corticosterone impairs memory retrieval in experimental animals.  On the other hand, sex hormones can modulate memory retrieval. The aim of this study was to examine the effects of concurrent injections of corticosterone and progesterone on memory retrieval in the proestrus (when the levels of endogenous estrogen and progesterone are high) and diestrous (when the levels of endogenous estrogen and progesterone are low) stages in adult female rats.

Adult female Wistar rats were trained in an inhibitory avoidance task (1mA, 3s). The latency to reenter the dark compartment and also time spent in the dark chamber were recorded in the retention test performed 48 h after training. In experiments 1 and 2, corticosterone (3 mg/kg, i.p) or vehicle was injected to intact female rats in the proestrus or diestrus phases 30 min before retention test. In experiments 3 and 4, rats in the proestrus or diestrus phase were received vehicle or progesterone (5 mg/kg, i.p) 60 min, and vehicle or corticosterone (3 mg/kg) 30 min before the test.

Acute injection of corticosterone to female rats in the diestrous stage, but not in the proestrus stage impaired memory retrieval. Pretreatment with progesterone did not influence the corticosterone effects on memory retrieval in the proestrus or diestrus phases.

Corticosterone impairs memory retrieval only in the proestrus phase and this effect did not change with pharmacological levels of progesterone.