Changes in the Epithelium of the Vaginal Complex during the Estrous Cycle of the Marsupial <i>Monodelphis domestica</i>

Abstract

The vaginal complex of marsupials differs from that of eutherians. Cervices open separately in a sinus vaginalis or cul-de-sac. Two lateral vaginae adjoin the sinus vaginalis and fuse at the level of the urethra opening and form the sinus urogenitalis. During the estrous cycle the vaginal epithelium undergoes a number of specified morphological changes. This paper is the first to describe these changes on an ultrastructural level in a marsupial. Investigations in Monodelphis vagina reveal that a cyclic switch exists between a keratinized and a stratified nonkeratinized epithelium. Keratinization starts during proestrus and reaches its maximum during estrus. In the postestrus, desquamation of the stratum corneum takes place, mostly in two steps. In metestrus one to two additional layers of the now nonkeratinized surface cells are shed into the vaginal lumen. Typical cell structures, such as keratin filaments, keratohyalin and membrane-coating granules, are involved in the keratinization process. Keratohyalin is found in the cytoplasm as well as in the nucleus of stratum granulosum cells, a phenomenon which is known from other parakeratinized epithelia of rapid turnover. Membrane-coating granules, responsible for the permeability barrier between the epithelial cells, are of the nonlamellated type in the nonkeratinized epithelium and produce an amorphous material in the intercellular spaces after extrusion. At periods, however, when the epithelium is keratinized, membrane-coating granules are of the lamellated type and form a lamellated barrier structure after extrusion in the intercellular space. The loss of the protective keratinized layers asks for an additional defense mechanism for the epithelium. The migration of leukocytes through the epithelium predominantly during post- and metestrus and their presence in the vaginal lumen may play a protective role together with the bacterial content.

Changes in the Epithelium of the Vaginal Complex during the Estrous Cycle of the Marsupial <i>Monodelphis domestica</i>

“…In M. domestica, vaginal epithelium changes during the estrous cycle have been analyzed by light and transmission electron microscopy [Regli and Kress, 2002]. In this scanning electron-microscopic study the same four stages of the estrous cycle will be characterized as in our previous transmission electron-microscopic paper, namely proestrus, estrus, postestrus and a transitional metestrus and the results will be correlated with the previous findings and possible functional implications.…”

“…3a). The superficial layers are sometimes ortho-but mostly parakeratinized [Regli and Kress, 2002]. The transition from the highly keratinized epithelium of the sinus vaginalis to the columnar cervical epithelium is abrupt ( fig.…”

“…Since the female genital tract epithelium changes in a hormone-dependent manner a complete baseline is critical for comparison with later experimental findings. For this reason, the evaluation of the cyclic changes in the surface epithelium of the genital tract of the female marsupial Monodelphis domestica has been undertaken [Regli and Kress, 2002;Wick and Kress, 2002a, b].…”

“…The stage of epithelial differentiation may vary considerably within the same animal and even adjacent areas of the same anatomical region [Regli and Kress, 2002].…”

Comparison of the production, quality, and in vitro maturation capacity of oocytes from untreated cycling and intermediate phase equine serum gonadotropin-treated fat-tailed dunnarts (Sminthopsis crassicaudata)

“…The period of increased CEC, dictated by elevated E 2 concentrations, which results in proliferation and desquamation of vaginal epithelial cells, was used in the present study to designate cytological estrus (de Brux 1958, Regli & Kress 2002. The use of monitoring CEC in S. crassicaudata has been broadly described by Godfrey (1969), Godfrey & Crowcroft (1971) and Bennett et al (1979) who reported estrus and mating at times of increased CEC.…”