【Animal Modeling】-Comparison of Two Staining Methods for Rat Vaginal Smears

  OBJECTIVE: To find a simple staining method for determining the four stages of the rat estrous cycle by staining the vaginal smears of SD female rats to observe the cell morphology.

  Methods: Twenty SD female mice aged 10-13 weeks and weighing 216-234g (225±6g) were randomly divided into two groups (10 mice in each group), and vaginal smears were taken every day for 6 consecutive days. The vagina of female mice was 0.5-1.0 cm in diameter and turned gently for 1-2 circles, and then spread on a clean glass slide dripped with normal saline. After natural air-drying, rapid Gram staining and crystal violet staining were performed to distinguish the estrus cycle of female mice under a light microscope.

  Results: Crystal violet staining stained the nucleus into dark purple, cytoplasm into lavender, and leukocytes into dark purple. Rapid Gram staining stained the nucleus into purple, cytoplasm into rose red, and leukocytes into dark red. The average estrous cycle of SD female mice was It lasts for 4 to 5 days and is divided into four stages: pre-estrus, estrus, post-estrus and inter-estrus. In pre-estrus, mainly nucleated epithelial cells; in estrus, almost all non-nucleated keratinocytes can form clusters ; In the late estrus, a large number of leukocytes and a small amount of anucleated keratinocytes can be seen; in the interestrus phase, leukocytes, nucleated cells and anucleated keratinocytes coexist, mainly leukocytes. The two staining methods are relatively simple and can be distinguished. During the four stages of the estrous cycle of SD rats, the morphology of crystal violet-stained cells is sometimes slightly deformed, and the rapid Gram-stained cells have complete morphology and clear images, and the time is short without the need for fixation with absolute ethanol.

  Conclusion: The rapid Gram staining method can easily and quickly distinguish the various stages of the estrous cycle of SD female mice without changing the reproductive cycle of SD female mice, and it can be extended in large sample experiments.