Comparative Studies on Oogenesis and Prespermatogenesis in the Wistar Rat Under Normal and Pathological Conditions

Comparative studies of oogenesis and prespermatogenesis show that oogonia are the population parellel to the dividing gonocytes (I-gonocytes), and that oocytes correspond to the resting gonocytes (II-gonocytes).Contrary to oocytes, which pass through the characteristic stages of meiotic prophase, the II-gonocytes do not show any conspicuous morphological changes.After the oocytes have passed a relatively short G-i phase, they enter the S-phase prenatally in preleptotene stage between days 17 and i8 of gestation.On the other hand, II-gonocytes spend a very long G-r phase of about 7 -9 days before entering the S-phase from postnatal day 3 onwards.The duration of the S-phase of II-gonocytes, determined by double labeling with 14 C and 3 H-thymidine, is found to be about 11 .5 hours.The duration value of the S-phase of the oocytes, deter- mined by the same method, is comparable to that of the 11-gonocytes.Myleran (Busulfan), administered i.p. at day 14 , 15 , or 1 6 of gestation, destroys oogonia and I-gonocytes ; when given between days y and 2 r of gestation, it reduces the number of supporting cells.II-gonocytes are also very sensitive to Myleran, and a large number of them degenerate from postnatal day 5 on- wards.°