Gestational Exposure to Ethane Dimethanesulfonate: MATERIALS AND METHODS(8)
Each morning (between 0700 and 0900 h; lights on at 0600 h) of the 10-day study, the vagina of each of the two females was examined for the presence of a postcoital plug. In the event a plug was observed, the female was designated as GD 0, promptly removed from the box with the male, and group housed with other females (up to 10 per box) that had cohabited with a specific male. In the event that a plug was not observed, the female remained in the box with the male until she presented with a postcoital vaginal plug but not to exceed 4 days. If a female did not present with a vaginal postcoital plug after 4 days, she was removed from the box with the male on the morning of the fifth day of cohabitation and placed in the box with the other females that had cohabited with that specific male.
This 4-day maximum was chosen to ensure that the female had completed one full estrous cycle while in the presence of a male. Each evening of the 10-day study (at 1700 h; lights out at 1800 h), the female mice that had been removed that morning were replaced with new virgin female mice, assuring that two females cohabited with each male every evening. At the completion of the 10-day study, the males were necropsied at PND 82 and the females that had cohabited with a male were group housed according to the male they cohabited with until GD 14. On GD 14, females were euthanized with CO2 followed by cervical dislocation and cesarean section. The following parameters were evaluated in pregnant dams: litter size, number of fetal resorptions, and observations of gross terata.