Effects of an Agonist and an Antagonist of Nα7-Cholinoreceptors on Active Learning and Sex Hormone Levels in Ovariectomized Female Rats

Abstract

The effects of combined administration of an agonist and an antagonist of Nα7-cholinoreceptors with a low dose of 17β-estradiol on the dynamics of the acquisition and extinction of an active avoidance reflex and behavior in the open field test, as well as on the levels of trophic and peripheral sex hormones, in ovariectomized (OE) female rats. The Nα7-cholinoreceptor agonist RJR-2403 (1.0 mg, i.p.) and the antagonist of these receptors mecamylamine (1.0 mg/kg, i.p.) were given chronically (14 days) alone or combined with a low dose of 17β-estradiol (0.5 μg per animal, s.c.) in female rats after ovariectomy. RJR-2403 in combination with low-dose 17β-estradiol completely restored the dynamics of active learning and increased investigative activity and grooming reactions in the open field test in OE females. This group of rats showed decreases in serum follitropin (FSH) and lutropin (LH) levels, along with increases in the estradiol level. Conversely, mecamylamine given alone or in combination with a low dose of 17β-estradiol had no significant effect on the nature of active learning or behavior in the open field test in OE females. The results obtained here provide evidence of the positive effects of stimulating Nα7-cholinoreceptors on the background of low-dose 17β-estradiol on active learning and on the concentrations of gonadotropins and estradiol in conditions of estrogen deficiency.