ESTROGEN IMPROVES PERFORMANCE OF REINFORCED T-MAZE ALTERNATION AND PREVENTS THE AMNESTIC EFFECTS OF SCOPOLAMINE ADMINISTERED SYSTEMICALLY OR INTRAHIPPOCAMPALLY

In a previous study, administration of high doses of estradiol benzoat e (100 mu g/kg for 3 days im) to ovariectomized Long-Evans rats counte racted impairments of reinforced T-maze alternation induced by systemi c administration of scopolamine, a muscarinic receptor blocker. In the current study, daily administration of lower doses of estradiol benzo ate (5 mu g/kg for 3 weeks sc) increased the number of correct reinfor ced alternations during T-maze acquisition in ovariectomized rats comp ared to oil-treated controls and prevented impairments of reinforced a lternation induced by injection of scopolamine hydrobromide (0.2 mg/kg ip). Furthermore, scopolamine (20 mu g) delivered bilaterally to the dorsal hippocampus reduced reinforced T-maze alternation in ovariectom ized rats previously trained to complete this task while daily treatme nt with estradiol benzoate (5 mu g/kg sc) for 1 week prior to scopolam ine infusion counteracted this impairment. In summary, physiological l evels of estrogen improved performance during acquisition of reinforce d T-maze alternation and prevented impairments induced by scopolamine administered systemically or intrahippocampally. (C) 1998 Academic Pre ss.