Matings to Obtain Pseudopregnaney in Females

It has been found that experienced mothers make better surrogate mothers compared to virgins. A colony of such rats are maintained and are smeared vaginally (see Section 3.3.) every morning to determine their estrous stage. Female rats maintained on a 12-h day and 12-h night cycle will ovulate roughly every 4 d (see Note 5). The cell characteristics of each of the stages of the estrous cycle are listed in Table 1.

1. On the morning of microinjection, separate female rats that are, by vaginal smearing, determined to be in the proestrous stage and place individually in the cage of vasectomized rats at 1800 h.

2. Alternatively, insertion of a smooth glass rod with a diameter of 7 mm into the vagina of the rat for 1 min will induce pseudopregnaney.

3. There will be no copulatory plug, neither will there be sperm in the vagina to indicate a successfiil mating since vasectomized rats are used. Hence, rats in the proestrous stage are usually prodded with the glass rod as a back-up procedure before placing them with vasectomized rats

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