Northcutt R G, Brändle K
Neurobiology Unit, Scripps Institution of Oceanography, School of Medicine, University of California, San Diego, La Jolla 92093-0201, USA.
J Comp Neurol. 1995 May 8;355(3):427-54. doi: 10.1002/cne.903550309.
The differentiation of neural crest and ectodermal placodes was examined in the axolotl in order to clarify the contribution of these tissues to the formation of the sensory ganglia of the branchiomeric and lateral line cranial nerves in salamanders. The most rostral branchiomeric nerves, the profundal and trigeminal nerves, appear to arise solely from an ectodermal placode and from neural crest, respectively. The sensory ganglia of the more caudal branchiomeric nerves--the facial, glossopharyngeal, and vagal nerves--are formed by a medial component that differentiates from the dorsomedial surface of migrating bands of neural crest associated with each of the developing branchial arches and with one or more lateral components that arise from epibranchial placodes located immediately dorsal and caudal to each pharyngeal pouch. Neuroblasts destined to form these sensory ganglia begin to differentiate from the epibranchial placodes as early as stage 26, whereas neural crest-derived neuroblasts can be recognized by stage 30. Centrally directed neurites of both groups of neuroblasts enter the medulla by stage 34, and their peripherally directed neurites form recognizable rami by stage 35. Five cranial lateral line nerves, in addition to the octaval nerve, can be recognized in axolotls. Each of these nerves arises from a separate dorsolateral placode that initially gives rise to the neuroblasts of a sensory ganglion whose peripheral neurites innervate sensory receptors subsequently formed from each placode. The time course of the differentiation of these nerves and receptors is comparable to that of the branchiomeric nerves. The possible roles of rhombomeres and their associated regulatory genes and pharyngeal pouches in the induction and specification of neural crest and ectodermal placodes are explored.
为了阐明这些组织对蝾螈鳃弓和侧线颅神经感觉神经节形成的贡献，对蝾螈中神经嵴和外胚层基板的分化进行了研究。最靠前的鳃弓神经，即 profundal 神经和三叉神经，似乎分别仅起源于外胚层基板和神经嵴。更靠后的鳃弓神经——面神经、舌咽神经和迷走神经——的感觉神经节由内侧成分和外侧成分形成，内侧成分从与每个发育中的鳃弓相关的神经嵴迁移带的背内侧表面分化而来，外侧成分则起源于位于每个咽囊背侧和尾侧紧邻处的鳃上基板。注定要形成这些感觉神经节的神经母细胞早在第26阶段就开始从鳃上基板分化，而神经嵴衍生的神经母细胞在第30阶段才能被识别。两组神经母细胞向中枢延伸的神经突在第34阶段进入延髓，它们向周围延伸的神经突在第35阶段形成可识别的分支。除了听神经外，在蝾螈中还可识别出五条颅侧线神经。这些神经中的每一条都起源于一个单独的背外侧基板，该基板最初产生一个感觉神经节的神经母细胞，其周围神经突支配随后由每个基板形成的感觉感受器。这些神经和感受器分化的时间进程与鳃弓神经的相似。探讨了菱脑节及其相关调控基因和咽囊在神经嵴和外胚层基板诱导和特化中的可能作用。
