Jansen J K, Fladby T
Institute of Physiology, Oslo University, Norway.
Prog Neurobiol. 1990;34(1):39-90. doi: 10.1016/0301-0082(90)90025-c.
(1) The perinatal reorganization of muscle innervation is executed in a setting established by the earlier embryonic developmental processes. Prominent among these is the generation of a stereotyped set of skeletal muscles, each innervated in an orderly fashion from an appropriate pool of spinal motoneurons. The muscles contain functionally specialized types of fibers which differentiate in patterns characteristic for each muscle even without innervation. (2) Cholinergic motoneurons are required for functional innervation of skeletal muscles. In addition the muscle fibers must be in a receptive state. Denervation or paralysis recreates the receptive state. Chemically the receptive state is not well defined. It is associated with an immature distribution of AChRs and NCAM. (3) Nmjs are located in an orderly fashion on muscle fibers. Their normal distribution can be disrupted by paralysis during development. When junctions are first formed the nerve terminal induces local aggregation, stabilization and mature ionophore kinetics of the AChRs, as well as appearance of junctional specific AChE. Some of the effects require muscle activity. Terminal-derived substances like agrin and CGRP may normally contribute to these processes, as may other not yet identified agents. (4) Numerically, motoneuronal pools are regulated according to the available target. At the same time, the generation of secondary myotubes requires innervation by active motoneurons, and may also be quantitatively regulated by the number of innervating motoneurons. The generation of the primary generation of myotubes is independent of innervation. (5) Soon after the muscle fiber is first innervated additional terminals from other axons form junctions at the same site. The extent of polyneuronal innervation differs between muscles and between fiber types in the same muscle. Following a delay of several days after birth the individual terminals increase their contact area by arborization. The postsynaptic differentiation with redistribution of AChR, AChE and formation of subsynaptic folds is initiated. The complete maturation of the endplate requires several weeks. (6) Around birth or a few days later processes which eliminate redundant terminals are initiated. The rate of elimination appears to be aimed at nearly synchronous completion of the process in muscles with related functions. (7) There are two types of processes involved in the elimination of supernumerary terminals. The one gives rise to a competitive interaction between terminals innervating the same muscle fiber. The second is related to the reduction in the number of terminals which a motoneuron can maintain in the muscle. The two normally act in concert to determine the mature pattern of innervation of a muscle.(ABSTRACT TRUNCATED AT 400 WORDS)
（1）肌肉神经支配的围产期重组是在早期胚胎发育过程所建立的背景下进行的。其中突出的是一组定型骨骼肌的生成，每块骨骼肌都由适当的脊髓运动神经元池以有序方式支配。这些肌肉包含功能上特化的纤维类型，即使在没有神经支配的情况下，它们也会以每种肌肉特有的模式分化。（2）胆碱能运动神经元是骨骼肌功能神经支配所必需的。此外，肌纤维必须处于接受状态。去神经支配或麻痹会重新产生接受状态。从化学角度来看，接受状态尚未明确界定。它与乙酰胆碱受体（AChR）和神经细胞黏附分子（NCAM）的不成熟分布有关。（3）神经肌肉接头（Nmjs）以有序方式位于肌纤维上。它们的正常分布在发育过程中可能会因麻痹而受到干扰。当接头最初形成时，神经末梢会诱导AChR的局部聚集、稳定以及成熟的离子载体动力学，以及接头特异性乙酰胆碱酯酶（AChE）的出现。其中一些效应需要肌肉活动。像聚集蛋白和降钙素基因相关肽（CGRP）等由末梢衍生的物质通常可能有助于这些过程，其他尚未确定的因子也可能如此。（4）在数量上，运动神经元池根据可用靶点进行调节。同时，次级肌管的生成需要活跃运动神经元的神经支配，并且也可能由支配运动神经元的数量进行定量调节。初级肌管的生成与神经支配无关。（5）在肌纤维首次接受神经支配后不久，来自其他轴突的额外末梢会在同一部位形成接头。多神经元支配的程度在不同肌肉之间以及同一肌肉的不同纤维类型之间存在差异。出生几天后经过一段时间延迟，单个末梢通过分支增加其接触面积。随后启动AChR重新分布、AChE以及突触下褶皱形成的突触后分化。终板的完全成熟需要数周时间。（6）在出生前后或几天后，开始启动消除多余末梢的过程。消除速率似乎旨在使具有相关功能的肌肉中该过程几乎同步完成。（7）消除多余末梢涉及两种类型的过程。一种会导致支配同一肌纤维末梢之间的竞争性相互作用。另一种与运动神经元在肌肉中能够维持的末梢数量减少有关。这两种过程通常协同作用以确定肌肉神经支配的成熟模式。（摘要截断于400字）
