Posttraining intrahippocampal estradiol injections enhance spatial memory in male rats: interaction with cholinergic systems.

Male Long-Evans rats received an 8-trial training session in a spatial water maze task, followed by a unilateral posttraining intrahippocampal injection of either estradiol (1.0 microgram/0.5 microliter) or saline. Retention was tested 24 hr later, and latency to escape was used as a measure of memory. Retention test escape latencies of rats given intrahippocampal injections of estradiol were lower than those of saline-treated rats, indicating an enhancement of memory. Intrahippocampal injections of estradiol delayed 2 hr posttraining did not affect retention. In Experiment 2, the memory enhancing effect of intrahippocampal injection of estradiol was blocked by peripheral administration of a subeffective dose (0.1 mg/kg) of the cholinergic antagonist scopolamine. Intrahippocampal injections of estradiol enhance memory in male rats, and estradiol may influence memory through an interaction with muscarinic cholinergic systems.