EFFECT OF ESTROGEN ON RESPONSIVITY OF HYPOTHALAMIC AND MESENCEPHALIC NEURONS IN FEMALE CAT

The responsivity of hypothalamic and mesencephalic neurons to somatic, visual, acoustic and vaginal stimulation was studied in ovariectomized (anestrous) and estrogen-treated ovariectomized conscious cats (estrous) immobilized with Flaxedil. Comparison between the results obtained in the two groups revealed that in the anterior and medial hypothalamus estrogen facilitated the appearance of excitatory responses to all the types of stimulus used, whereas it reduced the number of inhibitory responses to vaginal stimulation. Excitatory responses to all sensory modalities clearly predominated over inhibitory ones in the mesencephalic reticular formation of anestrous cats. By contrast, a marked increased in the proportion of inhibitory responses, particularly to vaginal stimulation, was observed in estrous subjects. Our results suggest that estrogen affects differentially the responsivity of hypothalamic and mesencephalic neurons to peripheral stimulation. © 1969.