Einsiedel L J, Luff A R
Department of Physiology, Monash University, Clayton, Victoria, Australia.
J Neurol Sci. 1992 Oct;112(1-2):178-84. doi: 10.1016/0022-510x(92)90148-e.
The ageing neuromuscular system is thought to undergo a continual process of reorganization as motoneurones are lost and surviving motor nerves reinnervate neighbouring denervated muscle fibres. However, the extent to which collateral reinnervation is able to compensate for neural deficits in the ageing individual is unknown. The ability of the senescent motoneurone to increase the size of its peripheral field was therefore investigated following transection of the right L5 ventral root in male Sprague Dawley rats aged 775 +/- 50 days. This procedure resulted in an extensive partial denervation of the right medial gastrocnemius muscle. After a recovery period of between 28 and 31 days the isometric contractile properties of surviving motor units were compared to control motor units from both the contralateral muscle and a group of unoperated control animals aged 791 +/- 39 days. Motor unit force was found to be unchanged after partial denervation and the absence of any alteration in motor unit size was confirmed by histological analysis. However, the time course of the isometric twitch was significantly longer for both fast and slow motor unit types and the conduction velocity of motoneurones innervating fast units was decreased following partial denervation. These results demonstrate that senescent motor nerves are unable to substantially increase the size of their peripheral fields by extensive collateral reinnervation.
随着运动神经元的丧失以及存活的运动神经对邻近失神经支配的肌纤维进行重新支配，衰老的神经肌肉系统被认为会经历一个持续的重组过程。然而，在衰老个体中，侧支神经再支配能够补偿神经缺陷的程度尚不清楚。因此，在775±50日龄的雄性Sprague Dawley大鼠中，切断右侧L5腹根后，研究了衰老运动神经元扩大其外周野大小的能力。该操作导致右侧腓肠肌内侧广泛部分失神经支配。在28至31天的恢复期后，将存活运动单位的等长收缩特性与对侧肌肉以及一组791±39日龄未手术对照动物的对照运动单位进行比较。发现部分失神经支配后运动单位力量未改变，并且组织学分析证实运动单位大小没有任何改变。然而，快速和慢速运动单位类型的等长收缩时程均显著延长，并且部分失神经支配后支配快速单位的运动神经元的传导速度降低。这些结果表明，衰老的运动神经无法通过广泛的侧支神经再支配大幅增加其外周野的大小。
