<原著>マウスの神経管形成機構 III. : 神経管の形成様式とその妊娠令に関する実体顕微鏡的観察
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The manner and timing of neural fold fusion in primary neurulation in Jcl : ICR mouse embryos were studied. Any virgin female exhibiting external signs of estrus was placed with a male of the same stock for 2 hours, from 8 : 30 to lO : 30 A.M., under poor lighting conditlons. Copulation was confirmed by the presence of vaginal plug. The fourth hour after the midpoint of this time period, 1 : 30 P. M., was regarded as hour O on day O of gestation (GT). A total of 34 pregnant females were killed by swift cervical dislocation at 3-hour intervals between hour 18 on day 7 and hour 6 on day 9,and at hour 12 on day 9 and hour 0 on day 10 of GT. Their uterine horns were immediately removed and fixed in Bouin's solution for 3 days at room temperature. A total of 418 normal neurulating mouse embryos were obtained from these uterine horns and studied by using binocular dissection and light microscopy. The initial fusion of apposing neural folds occurred at the level of the intermediate point between the third and fourth somites. i. e, . the caudal part of future myelencephalon and proceeded both rostrally and caudally. The embryos, the neural fold fusion of which were proceeding on the future myelencephalon and the cervical spinal cord, were found between hour 21 on day 7 and hour 12 on day 8 of GT. A second fusion occurred at what was originally the rostral end of the neural plate and proceeded anterodorsally. A third fusion occurred in the diencephalon and proceeded both rostrally and caudally. At this time, the future neural tubes of these embryos had three large openings, i. e., the telencephalic neuropore, the metencephalic neuropore and the posterior/caudal neuropore. The embryos with these three openings were found between hour 6 and hour 15 on day 8 of GT. This was followed by complete closure of the telencephalic neuropore. The embryos at this phase were found between hour 9 on day 8 and hour 0 on day 9 of GT. Then this was followed by complete closure of the metencephalic neuropore. The neural tube of these embryos had only one opening, i. e., the posterior/caudal neuropore. The embryos at this phase were found on and after hour 15 on day 8 of GT. A fourth fusion occurred at what was originally the caudal end of the neural plate and proceeded rostrally. Finally, the posterior neuropore completely closed. The embryos with the completely closed neural tubes were found on and after hour 12 on day 9 of GT. In conclusion, the first fusion of the apposing neural fold started within a short period of time, i. e., a 9-hour period between hour 21 on day 7 and hour 6 on day 8 of GT, and the third fusion of the apposing neural fold also started within a short period of time, i. e., a 9-hour period between hour 6 and hour 15 on day 8 of GT.
- 1997-03-30