Goodman L A, Model P G
Department of Neuroscience, Rose F. Kennedy Center for Research in Mental Retardation and Human Development, Albert Einstein College of Medicine, Bronx, New York 10461.
J Neurosci. 1988 Mar;8(3):776-91. doi: 10.1523/JNEUROSCI.08-03-00776.1988.
Mauthner cells (M-cells) occur as a pair of large, uniquely identifiable neurons at ear level in the hindbrain of premetamorphic amphibians. Each receives synapses from the ipsilateral vestibular nerve (nVIII); these morphologically distinctive terminals, or club endings, are confined to the proximoventral surface and branches of the M-cell lateral dendrite. We have superinnervated this portion of the M-cell to examine the extent to which forming afferent contacts regulate the growth and branching of the lateral dendrite. Superinnervation was brought about in the developing axolotl (Ambystoma mexicanum) by unilaterally implanting an extra vestibular primordium rostral to the in situ one. The contralateral side served as control. When the larvae reached 21 mm in length, the ectopic nerve was labeled with HRP. Subsequent microscopic examination revealed that the grafts developed into anatomically normal ears. The HRP-labeled ectopic axons entered the medulla at the level of nV and confined to the nVIII tract, coursed caudad toward the ipsilateral M-cell. Electron microscopic analysis demonstrated labeled club endings on the appropriate region of the M-cell lateral dendrite. The number of club endings on experimental M-cells was significantly greater than that on the contralateral controls, and the extra terminals appeared to be distributed randomly among unlabeled ones. Comparison of reconstructed experimental and control M-cells revealed that superinnervation produced a localized enhancement of dendritic branching in the region receiving the extra nVIII synapses. In the donor embryos (those from which the vestibular primordium was removed), M-cells were unilaterally deprived of nVIII afferents. Comparison of reconstructed experimental and control M-cells in 21 mm donor larvae demonstrated that deprivation produced a localized decrease of dendritic surface in the region that normally receives nVIII synapses. Together, these data show that ingrowing axons stimulate dendritic growth and thus regulate the development of a normal dendritic branching pattern on target neurons.
毛特纳细胞（M细胞）是一对大型、具有独特辨识度的神经元，位于变态前两栖动物后脑的耳部水平位置。每个M细胞都接收来自同侧前庭神经（第八对脑神经）的突触；这些形态独特的终末，即杵状终末，局限于M细胞外侧树突的近腹侧表面和分支上。我们对M细胞的这一部分进行了过度支配，以研究形成传入性接触在多大程度上调节外侧树突的生长和分支。通过在发育中的美西螈（墨西哥钝口螈）原位前庭原基的吻侧单侧植入一个额外的前庭原基，实现了过度支配。对侧作为对照。当幼虫长到21毫米时，用辣根过氧化物酶（HRP）标记异位神经。随后的显微镜检查显示，移植的组织发育成解剖结构正常的耳朵。HRP标记的异位轴突在第五对脑神经水平进入延髓，并局限于第八对脑神经束，向尾侧延伸至同侧M细胞。电子显微镜分析表明，在M细胞外侧树突的适当区域有标记的杵状终末。实验性M细胞上的杵状终末数量明显多于对侧对照，并且额外的终末似乎随机分布在未标记的终末之间。对重建的实验性和对照性M细胞进行比较发现，过度支配在接受额外第八对脑神经突触的区域产生了树突分支的局部增强。在供体胚胎（即前庭原基被移除的胚胎）中，M细胞被单侧剥夺了第八对脑神经传入纤维。对21毫米供体幼虫中重建的实验性和对照性M细胞进行比较表明，剥夺在正常接收第八对脑神经突触的区域产生了树突表面的局部减少。这些数据共同表明，向内生长的轴突刺激树突生长，从而调节靶神经元上正常树突分支模式的发育。
