Ultrastructure of the Epithelium of the Vaginal Complex During the Proestrus and Luteal Phases of the Estrous Cycle in the White-Eared Opossum (Didelphis albiventris).

The white-eared opossum (Didelphis albiventris) is a Neotropical opportunistic marsupial widely distributed in the Brazilian territory, occupying both open and forest formations. The anatomy of the marsupial female genital tract consists of two ovaries, oviducts, double uterus, two lateral vaginae, vaginal sinus and a urogenital sinus. The two lateral vaginae, vaginal sinus and urogenital sinus constitute the called vaginal complex that is the most variable part of the anatomy of the marsupial female tract. Thus, this study aimed to investigate the ultrastructure of the vaginal complex in the proestrus and luteal phases in the five females of D. albiventris. The vaginal surface is thrown into numerous longitudinal folds separated by furrows. The same morphological architecture was observed in the lining epithelium of the cranial, middle and caudal portions of the lateral vaginae. The lining epithelium of the lateral vaginae presented morphological changes according to the period of the estrous cycle studied: proestrus and luteal phases. The lining epithelium was formed by four cellular strata in the proestrus phase: basale, spinosum, granulosum and corneum. Keratin was present in the lumen of the lateral vaginae in the proestrus phase. The stratum corneum and keratin were not observed in the luteal phase. These findings agree with the previous studies in the Grey short-tailed opossum which is another Neotropical marsupial that inhabits Brazil and belongs to the Family Didelphidae. Moreover, this description makes available data that is fundamental to the studies of Neotropical marsupials reproductive biology.