Mouse estrous cycle identification tool and images

Abstract

The efficiency of producing timed pregnant or pseudopregnant mice can be increased by identifying those in proestrus or estrus. Visual observation of the vagina is the quickest method, requires no special equipment, and is best used when only proestrus or estrus stages need to be identified. Strain to strain differences, especially in coat color can make it difficult to determine the stage of the estrous cycle accurately by visual observation. Presented here are a series of images of the vaginal opening at each stage of the estrous cycle for 3 mouse strains of different coat colors: black (C57BL/6J), agouti (CByB6F1/J) and albino (BALB/cByJ). When all 4 stages (proestrus, estrus, metestrus, and diestrus) need to be identified, vaginal cytology is regarded as the most accurate method. An identification tool is presented to aid the user in determining the stage of estrous when using vaginal cytology. These images and descriptions are an excellent resource for learning how to determine the stage of the estrous cycle by visual observation or vaginal cytology.

Figure 1. Estrous cycle stage identification tool.

This tool is a visual representation of cell types and relative proportion of each type present during the four stages of the estrous cycle. The lines in the circle mark where the stage of estrous changes. The size of each quadrant (between 2 lines) is a rough estimate of the length of each stage. The total cycle takes about 4–5 days. To use this chart, vaginal cells are examined and the relative number of each cell type is determined. Then, an imaginary arrow is placed on the chart with the end on the center of the chart like a hand on a clock. The arrow is moved clockwise until the cell types and proportion appear under the arrow. Once the arrow is placed, it points to the corresponding stage of estrous. For example, an arrow in the position of 9 o'clock represents a vaginal smear with all leukocytes and a mouse in diestrus. An arrow at 3 o'clock represents a smear with approximately half cornified epithelial and half nucleated epithelial cells and a mouse in proestrus.

Figure 2. Four stages of estrous in BALB/cByJ mice.

The four stages of estrous are shown for an albino strain (proestrus (A), estrus (B), metestrus (C), diestrus (D)).

Figure 3. Four stages of estrous in CByB6F1/J mice.

The four stages of estrous are shown for an agouti strain (proestrus (A), estrus (B), metestrus (C), diestrus (D)).

Figure 4. Four stages of estrous in C57BL/6J mice.

The four stages of estrous are shown for a non-agouti black strain (proestrus (A), estrus (B), metestrus (C), diestrus (D)).

Figure 5. Vaginal cytology representing each stage of estrous.

Three cell types are identified: leukocytes (circle), cornified epithelial (black arrow), and nucleated epithelial (white arrow). Stages of estrous include proestrus (A), estrus (B), metestrus (C), diestrus (D).