Microscopic Structure of Ovary and Ovarian Activity of Different Seasons in Tree Shrew (Tupaia belangeri chinensis)

Microscopic structure of ovary and follicular development in wild adult tree shrews from Kunming,Yunnan were observed at different seasons.Interstitial gland tissues are rare,but medullar cords of "testis cord" type are commonly present in ovaries of this species.Follicle development appears to be similar to typical pattern of mammals.Nearly ripe follicles have rather larger follicular antra and thinner theca interna interrupting zone of thecal gland cells.The mature corpus luteum in pregnancy cycle is considerably big and there is an extremely small connective tissue center.Large polyhedral luteal cells with round nuclei accumulate abundant lipid droplets in cytoplasm.Accessory corpus luteum (ACL) structure with degenerative zona pellucida is seen in some animals,and some of ACL are present with gravid corpus luteum.Development of secondary follicles and medium-sized vesicular follicles seem to be no seasonal differences,but development of larger vesicular follicles and nearly ripe follicles occurs obviously in Jan and Apr.It is possible that there are more ovarian cycles of follicular prophase and follicular phase in these groups.Corpus luteum of pregnancy cycle and ACL are seen in Jul.No structure of pregnancy cyclic ovary is discovered in Oct,and there are more inactive ovaries which have almost no development of actively growing larger vesicular follicles in this group.These results suggest that seasonal changes in ovarian activity appear in this species.The earliest onset of estrus may begin in Jan.It is fully non-breeding season in Oct.The seasonal disruption of ovarian cycle may be controlled by some of the environmental and endocrine factors.