Estrogen-sensitive morphological plasticity in the third ventricle of seasonally anovulatory mares

Abstract

A method was developed for fixation of equine brain tissue for examination by electron microscopy. Scanning electron microscopy (SEM) was used to examine the surface featured of the third ventricle in seasonally anovulatory mares treated with estradiol-17β. The cellular population of the third ventricle of untreated mares was similar to that reported in other species: heavily ciliated cells covered the superior section of the third ventricle, ciliated cells became less dense inferiorly, and cells in the infundibular recess were well defined, covered with microvilli or miniblebs, and generally void of cilia. Supraependymal (SE) cells, which appeared to be type 1 as described in other species, were observed infrequently in the median eminence area of untreated mares. Treatment of sesonally anovulatory mares for 16 days with estradiol resulted in a decrease in the amount of ciliated cells and an increase in the number of SE cells in localized areas of the third ventricle. The apparent increase in supraependymal cell numbers in areas of the third ventricle other than the infundibular recess was observed in association with deciliation and therefore may be due to increased visibility of the cell surface in estradiol-treated mares. In the infundibular recess, increases in supraependymal cell numbers did not appear to be due to increased visibility of the cell surface since the amount of cilia in this area was not affected by estradiol treatment. These results suggest that estradiol has variable localized effects on the morphology of ependyma in the third ventricle of the horse not limited to the area of the median eminence but also affecting hypothalamic ependymal morphology.