Effect of oxotremorine on the acquisition of a conditioned avoidance response is modified by the estrous cycle, ovariectomy, and estradiol replacement in rats.

This study was designed to evaluate the influence of the hormonal status of the rat on the effects of a potent reversible muscarinic agonist, oxotremorine, on the acquisition of conditioning avoidance responses (CARs) and the performance of some spontaneous motor behaviors. Oxotremorine (OXO 50 and 100 micrograms/kg, intraperitoneally) given 5 min before testing improved active conditioned avoidance in intact female rats at estrus and in ovariectomized rats after estradiol replacement, and impaired performance in female rats at diestrus and after ovariectomy without estradiol replacement. No significant differences due to hormonal status of the rat in some spontaneous motor behaviors were observed. In fact, OXO in this dose range failed to induce significant changes in spontaneous motor activity, the number of rears diminished, and the time spent in grooming behavior increased in all groups studied. These results provided behavioral evidence for the hypothesis that central cholinergic activity is function of the hormonal status of the animal. Relationships between ovarian hormones and cholinergic system are discussed.