Histological Studies on Onset of Meiosis and on the Time of Appearance of Follicles in Different Stages in Immature Rabbit Ovaries

幼若(生後0、7、10、14、21、25、28、35、57、70、107、161日齢)および成熟家兎卵巣を用いて、減数分裂の進行と各発育段階にある卵胞の出現時期を組織学的に観察した。生後0日齢の卵巣内で減数分裂は既に開始されており(leptotene, 5.6%; zygotene, 1.4%)、10日齢ではzygotene(42.6%)、14日齢ではpachytene(51.0%)が多く、21日齢では多くの卵母細胞がdiplotene(88.0%)に達していたが、殆ど全て町紳慢細胞がdiploteneに達したのは28日齢であった。卵胞形成が初めて認められたのは7日齢であり、28日齢では多くの卵胞が一層の卵胞細胞層を持つ卵胞(Type 3a)に発育していた。Type 5bの卵胞(未熟な胞状卵胞)は57日齢以降の卵巣で観察された。107日齢ではType 7の卵胞(単一な卵胞腔を持つ卵胞)が出現した。161日齢では間質が卵巣表層部から髄質にかけて広く分布し、Type 8の卵胞(成熟卵胞)が出現した。57日齢以降の全ての胞状卵胞内の生殖細胞の直径をtype別に測定したところ、70日齢のType 6及び107日齢のType 5bの卵胞内の生殖細胞の直径と成熟家兎卵巣のType 8のものとの間に有意差は認められなかった。以上の結果より家兎における第一減数分裂は0日齢では既に開始しており、28日頃に完全に休止するものと考えられた。また、各発育段階の卵胞を組織学的観点から見た場合、70日齢頃より成熟卵子回収の可能性を示唆する卵胞が発育していることが明らかとなった。

Progress of the prophase in meiosis I and time of the first appearance of follicles in each developmental stage in ovaries of young rabbits were investigated histologically. Oocytes in leptotene and zygotene were located in 5.6% and 1.4% of all ovaries of newborn rabbits, respectively, indicating that some transition of oogonia to oocytes had occurred at day 0. The percentage of oocytes in diplotene was very high (86%) on day 21, and this stage had been completed by day 28. Follicles of Type 2 (in the classification by PEDERSEN and PETERS, 1968) appeared first in ovaries of 7-day-old rabbits. Follicular formation was initiated on day 7 when oocytes within the follicles reached the stage of diplotene or the transitional phase between pachytene and diplotene. The first small antral follicles were recognized in ovaries on clay 70, meaning that formation of such follicles started between day 57 and day 70, though atretic follicles were frequently found and secondary interstitial tissue appeared at this age. Fully developed follicles (Type 8) appeared in one of two does on day 107. Through all stages of follicular growth, more developed follicles were located generally in the deep ovarian cortex adjoining the medulla and containing well developed blood vessels.