Gatzinsky K P
Department of Anatomy and Cell Biology, University of Göteborg, Sweden.
Microsc Res Tech. 1996 Aug 15;34(6):492-506. doi: 10.1002/(SICI)1097-0029(19960815)34:6<492::AID-JEMT2>3.0.CO;2-M.
Lysosomes play an important role for the maintenance of a normal internal milieu in the cell. In neurons lysosomes are abundant in the perikaryon and dendrites, but have been observed to a much lesser degree in the axon. A general opinion has therefore formed among biologists interested in the nervous system that axonal material destined for degradation has to be transported to the neuronal perikaryon. The lysosomal occurrence and distribution at the level of the axon have, however, not been investigated systematically. This review summarizes recent morphological data based on light, fluorescence, and electron microscopic observations in peripheral nerve fibres of cats and rats providing evidence that node-paranode regions mainly along the peripheral parts of alpha motor axons, where the axon cross-section area decreases to 10-25% of internodal values, can control the passage and participate in a lysosome-mediated degradation of axonally transported materials directed towards the neuronal perikaryon. An important role is played by the paranodal axon-Schwann cell networks, which are lysosome-rich entities whereby the Schwann cells can sequester material from the axoplasm of large myelinated peripheral nerve fibres. The networks also seem to serve as depots for axonal waste products. The degradative ability of node-paranode regions in alpha-motor axons could be of some significance for the protection of the motor neuron perikarya from being flooded with and perhaps injured by indigestible materials as well as potentially deleterious, exogenous substances imbibed by the axon terminals in the muscle. A similar degradative capacity may not be needed in nerve fibres with synaptic terminals in the CNS where the local environment is regulated by the blood-brain barrier.
溶酶体在维持细胞内正常环境方面发挥着重要作用。在神经元中，溶酶体在胞体和树突中大量存在，但在轴突中观察到的数量要少得多。因此，对神经系统感兴趣的生物学家普遍形成了一种观点，即注定要降解的轴突物质必须被运输到神经元胞体。然而，轴突水平上溶酶体的存在和分布尚未得到系统研究。这篇综述总结了基于对猫和大鼠外周神经纤维的光学、荧光和电子显微镜观察的最新形态学数据，这些数据表明，主要沿着α运动轴突外周部分的结旁区域，轴突横截面积减小到节间值的10 - 25%，可以控制物质的通过，并参与溶酶体介导的、将轴突运输物质导向神经元胞体的降解过程。结旁轴突 - 施万细胞网络发挥着重要作用，这些网络富含溶酶体，施万细胞可以从大的有髓外周神经纤维的轴浆中隔离物质。这些网络似乎还充当轴突废物的储存库。α运动轴突中结旁区域的降解能力对于保护运动神经元胞体免受无法消化的物质以及可能由肌肉中轴突终末吸收的潜在有害外源性物质的充斥和可能的损伤可能具有一定意义。在中枢神经系统中具有突触终末的神经纤维中，可能不需要类似的降解能力，因为那里的局部环境由血脑屏障调节。
