Ultrastructural Changes of Follicular Germinal Disc Region in PMSG-Primed and Hypophysectomized Chickens with Reference to the Mechanism of Ovulation

Abstract

The aim of this study was to examine the mechanism by which the follicles become ovulable. Pregnant mare serum gonadotropin (PMSG)-priming and hypophysectomy make follicles ovulable. We observed ultrastructural changes of follicular germinal disc region after PMSG-priming and hypophysectomy and determined a common feature of ovulable follicle. In the second largest (F2) and smaller follicles of control birds, those are not ovulable, many smooth endoplasmic reticulum-like vesicles were localized in germinal disc and cytoplasmic process of granulosa cells formed gap junctions with oolemma. On the other hand, in the germinal disc region of large follicles of PMSGprimed and F2 follicle of hypophysectomized birds which are ovulable, gap junctions between cytoplasmic process of granulosa cells and oolemma were disintegrated, and vesicles in germinal disc were shrunken. We assume that these histological changes in the granulosa cell-to-oocyte communications and smooth endoplasmic reticulum may be involved in the process by which a follicle becomes ovulable.