What techniques can I use to obtain mouse fetuses of a known gestational age?
Timed pregnancies in mice can be set up in two ways: 1) use vaginal cytology to determine the stage of a mouse’s estrous cycle and the appropriate time for mating; and/or 2) check females for vaginal plugs to determine if mating has occurred. Evaluating vaginal cytology To obtain a vaginal specimen for determining the stage of the estrous cycle, insert a moistened cotton-tipped swab into the vaginal opening of a manually-restrained mouse. Most commercially available swabs are too large to fit easily into the vaginal opening of an average-sized mouse, but a swab of the appropriate size can be made by wrapping a small amount of sterile cotton wool around the blunt end of a toothpick. Rotate the swab gently but firmly within the mouse’s vagina, taking care to maintain contact with the vaginal wall. After removing the swab, wipe it on a clean glass microscope slide to transfer the vaginal specimen to the slide. Allow the slide to air dry, then apply a 0.1% aqueous solution of methylene blu
