Posttraining estradiol injections enhance memory in ovariectomized rats: cholinergic blockade and synergism

Neurobiol Learn Mem. 1997 Sep;68(2):172-88. doi: 10.1006/nlme.1997.3785.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / drug effects
  • Brain / physiology
  • Cholinergic Fibers / drug effects
  • Cholinergic Fibers / physiology*
  • Dose-Response Relationship, Drug
  • Escape Reaction / drug effects
  • Escape Reaction / physiology
  • Estradiol / pharmacology
  • Estradiol / physiology*
  • Female
  • Maze Learning / drug effects
  • Maze Learning / physiology
  • Mental Recall / drug effects
  • Mental Recall / physiology*
  • Muscarinic Agonists / pharmacology
  • Ovariectomy
  • Ovary / physiology*
  • Oxotremorine / pharmacology
  • Rats
  • Receptors, Muscarinic / drug effects
  • Receptors, Muscarinic / physiology*
  • Retention, Psychology / drug effects
  • Retention, Psychology / physiology


  • Muscarinic Agonists
  • Receptors, Muscarinic
  • Estradiol
  • Oxotremorine