<原著>マウスの神経管形成機構 IV. : 神経管の形成様式とその体節齢に関する実体顕微鏡的観察
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The somite stages of neural fold fusion in primary neurulation in jcl : ICR mouse embryos were studied. Any virgin female exhibiting signs of estrus was placed with a male of the same stock for 2 hours, from 8 : 30 to 10 : 30 A. M., under poor lighting conditions. 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 0 on day 0 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 also 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. After the fixation, they were stoked in 70% alcohol until after observation. A total of 4l8 normal neurulating mouse embryos were obtained from these uterine horns and studied by using binocular dissection microscopy. The initial fusion of apposing neural folds occurred at the caudal part of future myelencephalon was found between 6 and 8 somite stages and then the fusion proceeded both rostrally and caudally. The embryos, of which the neural fold fusion were were proceeding on the future myelencephalon and on the future cervical spinal cord, were found between 6 and 16 somite stages. A second fusion occurred at what was originally the rostral end of the neural groove and then a third fusion occurred in the future diencephalic roof. 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 11 and 16 somite stages. This was followed by complete closure of the telencephalic neuropore. The embryos with two large neuropores at this phase were found between 14 and 20 somite stages. Then this was followed by complete closure of the metencephalic neuropore. The embryos with only one neuropore at this phase were found between 15 and 31 somite stages. A fourth fusion occurred at what was originally the caudal end of the neural groove and proceeded rostrally. Finally, the posterior/caudal neuropore completely closed at the caudal part of spinal cord. The embryos with the completely closed neural tubes were found on and after 25 somite stage. In conclusion, the first fusion of the apposing neural fold at the future myelencephalic roof started within a very short period of somite stages, i.e. between 6 and 8 somite stages.
- 1998-03-30