Departments of Orthopaedics and Neurology, Johns Hopkins Hospital, and The Raymond M. Curtis Hand Center, Union Memorial Hospital, Baltimore, MD (U.S.A.).
Restor Neurol Neurosci. 1990 Jan 1;1(3):281-7. doi: 10.3233/RNN-1990-13416.
Previous experiments have shown that motor axons regenerating in mixed nerve will preferentially reinnervate a distal motor branch. The present experiments examine the mechanism through which this sensory-motor specificity is generated. An enclosed 0.5 mm gap was created in the proximal femoral nerves of juvenile rats. Two, three or eight weeks later the specificity of motor axon regeneration was evaluated by simultaneous application of horseradish peroxidase (HRP) to one distal femoral branch (sensory or motor) and Fluoro-Gold to the other. Motoneurons were then counted as projecting (i) correctly to the motor branch, (ii) incorrectly to the sensory branch, and (iii) simultaneously to both branches (double-labeled). Motor axon regeneration was random at 2 weeks, with equal numbers of motoneurons projecting to sensory and motor branches. However, the number of correct projections increased dramatically between 2 and 3 weeks. Twenty-six percent of neurons labeled at 2 weeks contained both tracers, indicating axon collateral projections to both sensory and motor branches. This number decreased significantly at each time period. Axon collaterals were thus 'pruned' from the sensory branch, increasing the number of correct projections at the expense of double-labeled neurons. These findings suggest random reinnervation of the distal stump, with specificity generated through trophic interaction between axons and the pathway and/or end organ.
先前的实验已经表明，在混合神经中再生的运动轴突将优先重新支配远端运动分支。本实验通过检查产生这种感觉运动特异性的机制来研究这个问题。在幼年大鼠的股骨近端神经中创建了一个封闭的 0.5 毫米间隙。两、三或八周后，通过同时将辣根过氧化物酶 (HRP) 应用于一个远端股骨分支（感觉或运动）和荧光金应用于另一个分支，评估运动轴突再生的特异性。然后，将投射到（i）正确的运动分支、（ii）错误的感觉分支和（iii）同时到两个分支（双标记）的运动神经元进行计数。在 2 周时，运动轴突再生是随机的，有相同数量的运动神经元投射到感觉和运动分支。然而，在 2 至 3 周之间，正确投射的数量显著增加。在 2 周时标记的神经元中有 26%同时含有两种示踪剂，表明轴突侧支投射到感觉和运动分支。这个数量在每个时间段都显著减少。因此，轴突侧支被“修剪”掉了感觉分支，增加了正确投射的数量，牺牲了双标记神经元。这些发现表明，远端残端存在随机的再支配，通过轴突与途径和/或终末器官之间的营养相互作用产生特异性。
