The changing architecture of the neonatal rat ovary during histogenesis

Abstract

The purpose of this study was to describe the changing histological organization of the rat ovary during postpartum days one through three (pl-p3). A PC-based image-combining microscope system was used to reconstruct the ovary in three dimensions. On pl, cylindrical pocket-like structures radiated from the core of the ovary that were open toward the surface epithelium. The walls of the pockets contained connective tissue cells and capillaries (stroma). By p2, these pockets had completely closed; each pocket enclosed a small nest of oocytes and a few presumptive granulosa cells. By p3, the pocket-like organization had disappeared. On pl, only one or two primordial follicle-like structures were observed in the core and toward the periphery of the ovary; most oocytes were not enclosed in follicles. By p3, very few naked oocytes remained; primordial follicles predominated in all the regions of the ovary and some of the follicles had multiple layers of granulosa cells. There were changes in location, area, and volume of the rete tubules during these postnatal days. The extraovarian rete was visible on all 3 days but changed its orientation relative to the ovary. The connecting rete was found beneath the epithelial layer of the ovary on all 3 days and showed dramatic increase in area on p2. The wide lumen of the intraovarian rete was in direct contact with some of the oocytes near by on all 3 days, but these "communication points" were most abundant on p2. Based on our observations of different cell-cell associations during this time period, we hypothesize (1) that the mesenchymalpresumptive granulosa cell association is essential for the completion of folliculogenesis, and (2) the rete ovarii may have an inductive role in follicle assembly. These observations suggest that the first 3 days postpartum are critically important for studying the heterogeneous cell interactions that lead to the assembly of primordial follicles. The regional differences in tissue organization during this formative period may have significant implications on later aspects of follicular development. o 1992 Wiley-Liss, Inc.

Quantification of healthy follicles in the neonatal and adult mouse ovary: evidence for maintenance of primordial follicle supply

“…We noted that the superficial cortex particularly in day 1 ovaries shows smaller oocytes, many still in cell nests, together with primordial follicles. A similar sequence of primordial follicle formation suggesting a medullary-cortical gradient of maturation has been reported in the mouse ovary by Peters (1969) and McClellan et al (2003), the rat-(Hirshfield 1992, Rajah et al 1992, Hirshfield & DeSanti 1995 and the sheep ovary (Sawyer et al 2002) and appears to be a developmental pattern intrinsic to the neonatal mammalian ovary . As oocytes in the ovarian medulla mature earlier than those in the superficial cortex, i.e.…”

Follicular assembly: mechanisms of action

“…This is similar to other studies on the mouse and also on humans where oocyte loss has been observed during fetal development (De Pol et al 1997, De Felici et al 1999, McClellan et al 2003, Ghafari et al 2007). In the rat, follicles are first observed in the core of the ovary and formation gradually shifts toward the surface (Rajah et al 1992). The follicles closer to the medullary region are also the follicles that begin to develop first (Hirshfield & DeSanti 1995).…”

Interactions between progesterone and tumor necrosis factor-α in the regulation of primordial follicle assembly

“…Each primordial follicle is composed of a single oocyte arrested in the diplotene stage of the first meiotic division and surrounded by a single layer of squamous pre-granulosa cells. In rodents follicle assembly occurs in the first few days after birth (Peters & Byskov 1975, Cran & Moor 1980, Hirshfield 1991, Rajah & Glaser 1992. In humans, follicle assembly begins during midgestation near week 18 and continues into the third trimester (Baker 1963, Fulton & Martins da Silva 2005.…”