In a previous study, administration of high doses of estradiol benzoate (100 microgram/kg for 3 days im) to ovariectomized Long-Evans rats counteracted impairments of reinforced T-maze alternation induced by systemic administration of scopolamine, a muscarinic receptor blocker. In the current study, daily administration of lower doses of estradiol benzoate (5 microgram/kg for 3 weeks sc) increased the number of correct reinforced alternations during T-maze acquisition in ovariectomized rats compared to oil-treated controls and prevented impairments of reinforced alternation induced by injection of scopolamine hydrobromide (0.2 mg/kg ip). Furthermore, scopolamine (20 microgram) delivered bilaterally to the dorsal hippocampus reduced reinforced T-maze alternation in ovariectomized rats previously trained to complete this task while daily treatment with estradiol benzoate (5 microgram/kg sc) for 1 week prior to scopolamine infusion counteracted this impairment. In summary, physiological levels of estrogen improved performance during acquisition of reinforced T-maze alternation and prevented impairments induced by scopolamine administered systemically or intrahippocampally.
Copyright 1998 Academic Press.