Although Marston & Chang (1965) have noted that the Mongolian gerbil breeds best by monogamous pairing, mating is always unpredictable even when a pro-oestrous female is caged with a male. This causes great difficulty in obtaining a reasonable number of pregnant animals for experimental purposes. The present study was intended to investigate the feasibility of artificial insemination and induction of pseudopregnancy in the Mongolian gerbil in order to obtain a desired number of pregnant

more »

... The female Mongolian gerbils of the Worcester Foundation stock and the Tumblebrook Farm stock (West Brookfield, Massachusetts), 2\ m=1/ 2\ to 7 months old, were maintained in animal quarters at 20 to 24\s=deg\C, under artificial light from 07.00 to 19.00 hours. They were provided with oatmeal, Charles River rat chow and water, supplemented twice weekly with vegetables or apples. The females usually came into pro-oestrus 2 to 3 days after an intraperitoneal (i.p.) injection of 5 to 10 i.u. PMSG (Sigma Chemical Co., St Louis) given during metoestrus or dioestrus. To ensure ovulation, the gerbils received an i.p. injection of 1\ m=. \ 5 to 5 i.u. HCG at 13.00 to 14.00 hours on the day of prooestrus. At 15.30 to 17.30 hours, the animals were anaesthetized with sodium pentobarbital (60 mg/kg) ; the uteri were exposed through a mid-line abdominal incision and 0-03 to 0-05 ml of sperm suspension containing 5 to 11 106 spermatozoa was injected into the lumen of each uterine horn. The sperm suspension was prepared just before use by flushing one cauda epididymidis with 0-4 ml Medium 199 containing 1000 units of penicillin G/ml, by means of a 30-gauge needle attached to a 1-ml syringe. The males, 4 to 9 months old, were derived from the Worcester Foundation stock. For the induction of pseudopregnancy, the uterine cervix was stimulated with a small plastic rod attached to the tip of an electric engraver which had been adjusted to provide suitable vibrations, as in the method described by De Feo (1966) . A similar technique had been routinely used for the induction of pseudopregnancy in rats, with a success rate of over 95 % (J. T. Wu, un¬ published results). Each gerbil received three 1-min periods of cervical stimu¬ lation: once in the afternoon of pro-oestrus about 15 to 30 min before anaes¬ thesia for artificial insemination, and twice the next day (= Day 1) at 09.00 to 10.00 and at 16.00 to 17.00 hours.