POSTTRAINING ESTRADIOL INJECTIONS ENHANCE MEMORY IN OVARIECTOMIZED RATS - CHOLINERGIC BLOCKADE AND SYNERGISM

The present experiments examined acute posttraining estrogenic influen ces on memory in ovariectomized rats. In experiment 1 rats received a single 8-trial (30-s ITI) training session with a submerged escape pla tform located in the same quadrant of a circular water maze on all tri als. Following trial 8, rats received a posttraining intraperitoneal i njection of either an estradiol-cyclodextrin inclusion complex (0.1, 0 .2, or 0.4 mg/kg) or saline. On a retention test session 24 h later, t he escape latencies of rats given injections of estradiol (0.2 mg/kg) were significantly lower than those of saline-treated rats, indicating an enhancement of memory. Injections of estradiol delayed 2 h posttra ining did not affect retention, demonstrating a time-dependent effect of estradiol on memory storage processes. In experiment 2a, posttraini ng injections of the cholinergic muscarinic receptor antagonist scopol amine (0.4 mg/kg) impaired memory in ovariectomized rats. In experimen t 2b, the memory-enhancing effect of estradiol (0.2 mg/kg) was blocked by concurrent posttraining administration of a subeffective dose (0.1 mg/kg) of scopolamine, suggesting an interaction between estradiol an d muscarinic cholinergic systems in memory modulation. In experiment 3 a, posttraining injections of the cholinergic muscarinic receptor agon ist oxotremorine (0.2 mg/kg) enhanced memory in ovariectomized rats. I n experiment 3b, concurrent posttraining injection of a subeffective d ose of estradiol (0.1 mg/kg) and a subeffective dose of oxotremorine ( 0.1 mg/kg) enhanced memory, indicating a synergistic effect of estradi ol and muscarinic receptor activation on memory. (C) 1997 Academic Pre ss.