Morphometric analysis of primary sensory neuron in aged rats

通过对青年大鼠和老年大鼠初级感觉神经元的形态计量学比较研究，得出以下结论。老年大鼠与青年大鼠相比，1）有髓纤维数量减少，2）髓鞘呈节段性脱髓鞘，然后再髓鞘化，3）前根髓鞘改变严重，4）有髓纤维轴突变性较多，5）脊髓背根神经节内神经细胞体密度增高，胞浆皱缩，（6）延髓薄核内多见轴索样突起和球状体，而腰髓背侧核和第一腰髓Clarke背侧核内少见。（7）延髓薄核内神经终末体密度降低，（8）第一骶髓背根节神经细胞体总数减少，以直径较大者减少明显，9）无髓纤维有数量减少的趋势，但未发现无髓纤维持续变性的现象，因此，初级感觉神经元的髓鞘、轴突、神经末梢和神经细胞体的各个组成部分均发生了组织病理学改变。大直径感觉神经元在衰老过程中似乎是最脆弱的。

In the comparative morphometric studies of the primary sensory neuron between young and old rats, the following conclusions were obtained. In older rats compared with younger rats, 1)the number of myelinated fibers was decreased, 2)the myelin sheath showed segmental demyelination followed by remyelination, 3)the myelin change was severe in the ventral root, 4)axonal degeneration of the myelinated fiber was more frequently found, 5)the nerve cell body in the spinal dorsal root ganglion showed higher density and shrinkage of the cytoplasm, 6)axonal swellings and spheroids were frequently found in the gracile nucleus of the medulla, but they were rare in the dorsal born of the lumbar spinal cord and in the dorsal nucleus of clarke of the first lumbar spinal cord, 7)the volume density of the nerve terminal was decreased in the gracile nucleus of the medulla, dorsal born of the lumbar spinal cord and dorsal nucleus of clarke of the first lumbar spinal cord, and the decrease was prominent in the gracile nucleus, 8)the total number of nerve cell bodies in the first sacral dorsal root ganglion was decreased, and the decrease of those with larger diameters was prominent, and 9)the unmyelinated fibers showed the tendency of the decrease in number, but the ongoing degenerative findings of unmyelinated fibers were not found. Therefore, it was concluded that the primary sensory neuron shows histopathological alterations in each component of the myelin sheath, axon, nerve terminal and nerve cell body. The large diameter sensory neuron seems to be most vulnerable in the aging process.