Desmond M E, Field M C
Department of Biology, Villanova University, Pennsylvania 19085.
J Comp Neurol. 1992 May 8;319(2):246-60. doi: 10.1002/cne.903190205.
Although it is known that rapid expansion of the vertebrate brain begins near the time that the spinal neurocoel is occluded, it still remains unknown when occlusion occurs in relation to neurulation. Since both morphogenetic events are critical for normal brain growth, it is important to decipher the temporal relationship between the two processes. This study assessed the temporal relationship of the two events with the rationale that if it could be demonstrated that occlusion occurs coincident with the completion of neurulation, then it could be argued that factors shown to direct neurulation could also initiate occlusion. Nearly 600 chick embryos (stages 9- through 12+) were cultured atop egg-agar, the caudal extent of neurulation determined, the cranial five pairs of somites removed and the neurocoels assessed for occlusion. In stage 9- through 10- chicks, neurulation of the spinal cord is incomplete. Stages 10 through 12+ exhibit neurulation and occlusion from the 8th to 19th somites. When lateral tissues were removed in embryos 8 through 10-, the neural folds became dysraphic whereas in embryos stage 10 and older, the folds remained fused dorsomedially and occluded. The only surgical manipulation that was found to prevent occlusion was elimination of the lateral tissues responsible for elevation and closure of the neural folds. Analysis of particular components of the lateral tissues essential for convergence, by treating embryos (n = 75) with chemicals known to degrade tissue-tissue bonds or specific components of the perineural matrix, indicated that more than 75% of the embryos treated with EDTA, EDTA plus Ca2+, trypsin, collagenase, or hyaluronidase exhibited little or no effect on convergence, dorsomedial fusion, and concomitant occlusion.
虽然已知脊椎动物大脑的快速扩张在脊髓神经腔闭塞时开始，但关于神经腔闭塞相对于神经胚形成的发生时间仍不清楚。由于这两个形态发生事件对正常大脑发育都至关重要，所以解读这两个过程之间的时间关系很重要。本研究评估了这两个事件的时间关系，其基本原理是，如果能够证明神经腔闭塞与神经胚形成的完成同时发生，那么就可以认为那些被证明可指导神经胚形成的因素也能启动神经腔闭塞。将近600只鸡胚（9期至12 +期）培养在卵琼脂上，确定神经胚形成的尾端范围，去除头部的五对体节，并评估神经腔是否闭塞。在9期至10 -期的鸡胚中，脊髓的神经胚形成不完全。10期至12 +期的鸡胚从第8对到第19对体节表现出神经胚形成和神经腔闭塞。当在8期至10 -期的胚胎中去除外侧组织时，神经褶会出现不连续，而在10期及更大的胚胎中，神经褶在背内侧仍保持融合并闭塞。唯一被发现可防止神经腔闭塞的手术操作是去除负责神经褶抬高和闭合的外侧组织。通过用已知可降解组织 - 组织连接或神经周基质特定成分的化学物质处理胚胎（n = 75），对外侧组织中对融合至关重要的特定成分进行分析，结果表明，用乙二胺四乙酸（EDTA）、EDTA加Ca2 +、胰蛋白酶、胶原酶或透明质酸酶处理的胚胎中，超过75%的胚胎在融合、背内侧融合及伴随的神经腔闭塞方面几乎没有或没有受到影响。
