Ralston H J, Ralston D D
J Comp Neurol. 1982 Dec 20;212(4):435-48. doi: 10.1002/cne.902120410.
The projections of dorsal root axons to the deeper laminae (IV, V, and VI) of the Macaque spinal cord were examined by the use of experimentally induced degeneration following dorsal rhizotomy or by injection of dorsal root ganglia with tritiated amino acids followed by light and electron microscopic autoradiography. Following dorsal rhizotomy, neurofilamentous degeneration of synaptic profiles occurs in each of the three deep laminae, more commonly in laminae IV and V than in lamina VI. The neurofilamentous degeneration is seen both in central glomerular (C) profiles and in many of the round vesicle (R) profiles. Neurofilamentous degeneration occurs as early as 18 hours following rhizotomy and the degenerating terminals are most numerous at 3-4 days postrhizotomy. None are seen after 7 days survival. The neurofilamentous profiles form axodendritic and, occasionally, axosomatic synapses with neurons of the dorsal horn. They are also seen to be postsynaptic to flat vesicle (F) profiles in axoaxonal synapses. A second type of degeneration, electron-lucent degeneration, is seen in laminae V and VI, and only occasionally in lamina IV. The lucent degeneration occurs somewhat later after rhizotomy than does the neurofilamentous degeneration and reaches its peak at 5 days postrhizotomy. No lucent terminals are seen after 7 days survival. Electron-dense degeneration, so common in lamina II, is not seen in the deeper dorsal horn. Autoradiographic techniques show that both C and R terminals are labelled in the deeper dorsal horn. Both of these terminals form axodendritic synapses and a significant number are found to be postsynaptic in axoaxonal synapses. Most of the C terminals degenerate following rhizotomy or are labelled following injection of the parent dorsal root ganglia with tritiated amino acids. Approximately one-fifth of the R profiles are derived from dorsal roots. F profiles do not appear to be of dorsal root origin in any case. It is concluded that neurofilamentous alterations represent the degeneration of larger-diameter (A beta) axons which distribute to the deeper dorsal horn and that electron-lucent degeneration represents the termination of A delta fibers. Electron-dense degeneration thought to represent the termination of nonmyelinated axons (C fibers) in the superficial dorsal horn is not seen in the deeper dorsal and it is concluded that C fibers do not project to the deeper laminae.
通过背根切断术后实验性诱导退变，或向背根神经节注射氚标记氨基酸后进行光镜和电镜放射自显影，研究了猕猴脊髓背根轴突向深层板层（IV、V和VI）的投射。背根切断术后，在三个深层板层中均出现突触轮廓的神经丝退变，IV层和V层比VI层更常见。神经丝退变在中央小球状（C）轮廓和许多圆形囊泡（R）轮廓中均可见。神经丝退变在切断后18小时就开始出现，退变的终末在切断后3 - 4天数量最多。存活7天后未见退变。神经丝轮廓与背角神经元形成轴-树突突触，偶尔也形成轴-体突触。在轴-轴突触中，它们也被观察到是扁平囊泡（F）轮廓的突触后成分。第二种退变类型，即电子透明退变，见于V层和VI层，IV层偶尔可见。透明退变在切断后比神经丝退变出现得稍晚，在切断后5天达到高峰。存活7天后未见透明终末。电子致密退变在II层很常见，在深层背角未见，由此得出结论，C纤维不投射到深层板层。放射自显影技术显示，C和R终末在深层背角均有标记。这两种终末均形成轴-树突突触，并且发现相当数量的终末在轴-轴突触中是突触后成分。大多数C终末在切断后退变，或在向其母背根神经节注射氚标记氨基酸后被标记。大约五分之一的R轮廓来自背根。无论如何，F轮廓似乎不是背根起源。结论是，神经丝改变代表分布到深层背角的较大直径（Aβ）轴突的退变，而电子透明退变代表Aδ纤维的终末。被认为代表非髓鞘轴突（C纤维）在浅表背角终末的电子致密退变在深层背角未见，由此得出结论，C纤维不投射到深层板层。
