Sanes J R, Marshall L M, McMahan U J
J Cell Biol. 1978 Jul;78(1):176-98. doi: 10.1083/jcb.78.1.176.
Axons regenerate to reinnervate denervated skeletal muscle fibers precisely at original synaptic sites, and they differentiate into nerve terminals where they contact muscle fibers. The aim of this study was to determine the location of factors that influence the growth and differentiation of the regenerating axons. We damaged and denervated frog muscles, causing myofibers and nerve terminals to degenerate, and then irradiated the animals to prevent regeneration of myofibers. The sheath of basal lamina (BL) that surrounds each myofiber survives these treatments, and original synaptic sites on BL can be recognized by several histological criteria after nerve terminals and muscle cells have been completely removed. Axons regenerate into the region of damage within 2 wk. They contact surviving BL almost exclusively at original synaptic sites; thus, factors that guide the axon's growth are present at synaptic sites and stably maintained outside of the myofiber. Portions of axons that contact the BL acquire active zones and accumulations of synaptic vesicles; thus by morphological criteria they differentiate into nerve terminals even though their postsynaptic targets, the myofibers, are absent. Within the terminals, the synaptic organelles line up opposite periodic specializations in the myofiber's BL, demonstrating that components associated with the BL play a role in organizing the differentiation of the nerve terminal.
轴突再生，精确地在原来的突触部位重新支配失神经支配的骨骼肌纤维，并分化为与肌纤维接触的神经末梢。本研究的目的是确定影响再生轴突生长和分化的因素的位置。我们损伤并使青蛙肌肉失神经支配，导致肌纤维和神经末梢退化，然后对动物进行照射以防止肌纤维再生。围绕每个肌纤维的基底层（BL）鞘在这些处理后存活下来，并且在神经末梢和肌肉细胞完全去除后，可以通过几种组织学标准识别BL上原来的突触部位。轴突在2周内再生到损伤区域。它们几乎只在原来的突触部位与存活的BL接触；因此，引导轴突生长的因素存在于突触部位，并在肌纤维外稳定维持。与BL接触的轴突部分获得活性区和突触小泡聚集；因此，根据形态学标准，即使它们的突触后靶标（肌纤维）不存在，它们也分化为神经末梢。在末梢内，突触细胞器与肌纤维BL中的周期性特化相对排列，表明与BL相关的成分在组织神经末梢的分化中起作用。
