Tanycytes in long‐term ovariectomized ewes treated with estrogen exhibit ultrastructural features associated with increased cellular activity

Ependymal tanycytes on the floor of the third ventricle of longterm ovariectomized (OVX) female sheep (ewes) and OVX ewes treated with 17β‐estradiol (E2β) were investigated with scanning and transmission electron microscopy (SEM and TEM) for evidence of differences in ultrastructure. Plasma concentrations of luteinizing hormone (LH) in the same ewes that were analyzed ultrastructurally were 45.1 ± 28.7 ng/ml in the nontreated OVX group, and 2.2 ± 1.3 ng/ml in the OVX + E2β group, confirming the widely reported negative feedback effect of estrogen on LH. With SEM, the most prominent difference between groups was that tanycytes on the floor of the third ventricle in OVX ewes had very few surface membrane modifications, particularly microvilli, and appeared relatively bare‐surfaced compared to those from the estrogen‐treated group. Tissues from estrogen‐treated OVX ewes were, for the most part, covered with a fuzzy nap of delicate microvilli. Transmission electron microscopy confirmed and extended this impression. With TEM, tanycytes in E2β‐treated ewes exhibited not only a more luxurious display of microvilli but also a much richer complement of welldeveloped organelles including rough endoplasmic reticulum, ribosomes, Golgi complexes, microtubules, and filaments than tanycytes in OVX alone ewes. Collectively, the fine structural data indicates a positive correlation between tanycytes displaying well‐developed features associated with heightened cellular activity – synthesis, secretion and/or absorption – and the presence of estrogen.