Posttraining estradiol injections enhance memory in ovariectomized rats: cholinergic blockade and synergism.
The present experiments examined acute posttraining estrogenic influences on memory in ovariectomized rats. In experiment 1 rats received a single 8-trial (30-s ITI) training session with a submerged escape platform located in the same quadrant of a circular water maze on all trials. Following trial 8, rats received a posttraining intraperitoneal injection 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, the 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 posttraining did not affect retention, demonstrating a time-dependent effect of estradiol on memory storage processes. In experiment 2a, posttraining injections of the cholinergic muscarinic receptor antagonist scopolamine (0.4 mg/kg) impaired memory in ovariectomized rats. In experiment 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 and muscarinic cholinergic systems in memory modulation. In experiment 3a, posttraining injections of the cholinergic muscarinic receptor agonist oxotremorine (0.2 mg/kg) enhanced memory in ovariectomized rats. In experiment 3b, concurrent posttraining injection a subeffective dose of estradiol (0.1 mg/kg) and a subeffective dose of oxotremorine (0.1 mg/kg) enhanced memory, indicating a synergistic effect of estradiol and muscarinic receptor activation on memory.
Packard
M G
MG
Department of Psychology, University of New Orleans, Louisiana 70148, USA. mgpps@uno.edu
Teather
L A
LA
D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology; D002799:Cholinergic Fibers / Q000187:drug effects / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004924:Escape Reaction / Q000187:drug effects / Q000502:physiology; D004958:Estradiol / Q000494:pharmacology / Q000502:physiology*; D005260:Female; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D011939:Mental Recall / Q000187:drug effects / Q000502:physiology*; D018721:Muscarinic Agonists / Q000494:pharmacology; D010052:Ovariectomy; D010053:Ovary / Q000502:physiology*; D010095:Oxotremorine / Q000494:pharmacology; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D012153:Retention, Psychology / Q000187:drug effects / Q000502:physiology
D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D004958:Estradiol; D010095:Oxotremorine