The Sheep Third Ventricle: Scanning Electron Microscopy of Estrous, Anestrous and Estrogen-Progesterone-Treated Anestrous Ewes

Surface features of the third ventricle in estrous, anestrous and anestrous estrogen-progesterone (E2+P)-treated ewes were examined with scanning electron microscopy (SEM). To ensure uniformly good preparations, a procedure for rapid perfusion of sheep brains was developed as well as the use of critical point drying. Ependymal surfaces on the dorsal aspects of the lateral walls as viewed by SEM were heavily ciliated while the ventral aspect of the lateral walls and ventral floor were not. In all groups, the appearance of the lateral walls was similar while that of the ventral floor-median eminence appeared to vary with the absence or presence of gonadal steroids. In estrous ewes there were numerous stubby microvilli and miniblebs on ependyma of the ventrolateral wall-floor, many of which are presumed to be tanycytes. This contrasted with the appearance of similar regions in anestrous ewes where there were patchy smooth bare areas on ependymal surfaces with fewer microvilli and small surface protrusions. Anestrous E2+P-treated ewes showed an appearance intermediate between the other two groups. The SEM data support a correlation between reproductive status and the relative presence or absence of surface modifications on the ventral floor of the sheep third ventricle.