Goodman L A, Covell D 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 Aug;8(8):3025-34. doi: 10.1523/JNEUROSCI.08-08-03025.1988.
In the medulla of the axolotl (Ambystoma mexicanum), Mauthner cells (M-cells) occur as a pair of large identifiable neurons at the level of entry of the vestibular nerve (nVIII). Each receives synapses from the ipsilateral nVIII; the terminals can be identified as club endings and are restricted to a specific set of M-cell dendritic branches. We have examined these branches for morphologic changes following long-term deafferentation in the presence and absence of nerve regeneration. Deafferentation was brought about in a group of young larvae by unilaterally severing nVIII. The nerve was allowed to regenerate in half of the larvae. In those remaining, the nVIII ganglion was damaged to preclude or limit nerve regeneration. The contralateral side served as control. After 3 months survival, the larvae were killed and the medullae prepared for microscopy. To estimate the extent of nerve regeneration, axons in the experimental nVIII tract were counted and compared with the number in the control. The mean number of axons in the nVIII tract ipsilateral to intact ganglia indicated that 69% of the fibers had regenerated. In contrast, only 31% regenerated in larvae with damaged ganglia. Electron microscopic analysis of selected sections revealed that the mean number of nVIII terminals per section through M-cells ipsilateral to destroyed ganglia was significantly less than the mean number in analogous sections through either control cells or cells ipsilateral to intact ganglia. Control and experimental M-cells were reconstructed from serial sections. Deprived M-cells had significantly reduced dendritic branching patterns in the region that normally receives nVIII input. On the other hand, the extent of branching on cells receiving regenerated afferents from intact ganglia was like that of their contralateral controls. The distribution of dendritic branches on many reinnervated M-cells, however, was broader than that on control cells. Electron microscopic examination of the displaced dendritic branches (those extending into adjacent tracts) revealed that they received vestibular synapses. Thus, in some animals, regenerated vestibular fibers were not restricted to the nVIII tract. Deafferentation of the M-cells results in a reduction of dendritic branches in the region deprived of vestibular contacts.(ABSTRACT TRUNCATED AT 400 WORDS)
在美西螈（钝口螈属墨西哥钝口螈）的延髓中，Mauthner细胞（M细胞）作为一对大型可识别神经元出现在前庭神经（第八对脑神经）进入的水平位置。每个M细胞都接收来自同侧第八对脑神经的突触；这些终末可被识别为杵状终末，且局限于一组特定的M细胞树突分支。我们研究了在存在和不存在神经再生的情况下，长期去传入神经支配后这些分支的形态变化。通过单侧切断第八对脑神经，在一组幼体中造成去传入神经支配。让一半幼体的神经再生。在其余幼体中，第八对脑神经节受损以阻止或限制神经再生。对侧作为对照。存活3个月后，处死幼体并制备延髓用于显微镜检查。为了估计神经再生的程度，对实验侧第八对脑神经束中的轴突进行计数，并与对照侧的数量进行比较。完整神经节同侧第八对脑神经束中的轴突平均数量表明，69%的纤维已经再生。相比之下，神经节受损的幼体中只有31%的纤维再生。对选定切片的电子显微镜分析显示，通过受损神经节同侧M细胞的每切片第八对脑神经终末平均数量显著少于通过对照细胞或完整神经节同侧细胞的类似切片中的平均数量。从连续切片重建对照和实验M细胞。去传入神经支配的M细胞在正常接收第八对脑神经输入的区域树突分支显著减少。另一方面，从完整神经节接收再生传入神经的细胞的分支程度与其对侧对照相似。然而，许多重新受支配的M细胞上树突分支的分布比对照细胞上的更广泛。对移位的树突分支（那些延伸到相邻束中的分支）的电子显微镜检查显示它们接收前庭突触。因此，在一些动物中，再生的前庭纤维并不局限于第八对脑神经束。M细胞的去传入神经支配导致在缺乏前庭接触的区域树突分支减少。（摘要截短至400字）
