Ovarian surface epithelium in newborn rats: germ cells warehouse

Abstract

Ovarian surface epithelium (OSE) is a very dynamic part of the ovary with an important role in ovulation during reproductive period. It represents a source of germ cells in fetal period but data concerning that role of OSE in postnatal period are contradictory. Though OSE is a subject of research in past few years, it’s ultrastructure in newborn rats has not been studied yet. The aim of the study was to define ultrastructure features of OSE in rats in the first 24h hours after birth. Six newborn rats within first 24 hours after birth were euthanized. Ovaries were fixed in 4% glutaraldehyde, post-fixed in 1% osmium tetroxide, routinely dehydrated and embedded in araldite. Semi-thin sections were stained with toluidine blue and used to select areas of interest. Ultra-thin sections of selected areas were mounted on copper grids and examined on a Philips CM12 transmission electron microscope. Descriptive ultrastrustructure analysis was performed. OSE in newborn rats was mostly single layered and sporadically pseudostratified, consisted from mostly cuboidal and columnar cells. These cells were with centrally positioned nucleus, mostly with irregularly dispersed chromatin. Microvili and cytoplasmic projections extended to peritoneal cavity from the surface of the cells. No continuous tunica albuginea was found, but in places, groups of fibroblast-like cells were present, indicating the onset of its formation. Numerous oogonia and oocytes were identified between OSE cells or up to the basal part of them. This may indicate that extrusion (the release of germ cells into a peritoneal cavity) may be an important way of germ cells elimination. Early postnatal period in rat ovaries characterize with massive cell death of oogonia and oocytes, mostly by apoptosis and autophagy, but further investigation might reveal the participation of this way of germ cells elimination realizing the importance of appropriate course of cell death process in terms of reproductive health.