Reproductive Tract Changes During the Mouse Estrous Cycle

Chapter Summary The laboratory mouse is an essential model for investigation of normal mammalian physiology, dysfunction, and disease. Under conditions of long photoperiod, mice breed continuously throughout the year. In unbred mice, the estrous cycle is a continuum of approximately 4 days in length, characterized by hormonal variation and consequent morphological and physiological changes to the reproductive tract. Four stages of varying duration are recognized. Proestrus is the period during which pre- and peri-ovulatory development take place in the ovary, with consequent synthesis and secretion of estrogens. Estrus, the brief interval during which the female accepts the male and during which ovulation occurs, follows. Next is metestrus, the early luteal phase, followed by diestrus, during which progesterone is the dominant hormonal influence. Two cell types, polymorphonuclear leukocytes and squamous epithelial cells, predominate in the exfoliative cytology of mouse vagina. Stages of the estrous cycle can be identified from the assemblage of these cells. In this chapter, the continuum of morphological changes in the reproductive tract and in vaginal cytology is documented to provide tools for reproductive management of a mouse colony.