SEASONAL-CHANGES IN THE OVARY OF THE BLIND MOLE-RAT (SPALAX-EHRENBERGI)

The present study is the first to examine closely the ovary of the bli nd mole rat (Spalax ehrenbergi), a solitary, highly aggressive subterr anean rodent. It provides basic data on the female reproductive biolog y which should assist in the notoriously difficult attempts to breed t his unique species. Although the mole rat is considered a seasonal bre eder, large antral follicles were found to be present in the ovary thr oughout the year. Constant darkness and high temperatures simulating t he natural burrow environment in the summer did not cause the ovary to regress. This was evident from the surprising abundance of large antr al follicles, some even in the preovulatory state. Because injection o f human chorionic gonadotropin (hCG) during the summer induces ovulati on of these follicles, it would appear that mole rats are potentially able to reproduce outside of the known winter breeding season. The pre sent work further strengthens previous assumptions (based on vaginal s mears) that the mole rat is a reflex ovulator: first, preovulatory fol licles are always present in the ovary during the winter breeding seas on; and second, injection of 50 i.u. hCG to randomly selected females resulted in ovulation in 67% of the females. Although at the time of c opulation ovaries contained large preovulatory follicles, following co pulation ovulation did not occur and pregnancy did not ensue. This sug gests that copulatory stimulation by the male did not reach the ovulat ory threshold. An injection of hCG immediately after sperm transfer mi ght overcome this obstacle in future breeding attempts.