Lowrie M B, Vrbová G
Division of Biomedical Sciences, Imperial College School of Medicine, London, SW7 2AZ, United Kingdom.
Exp Neurol. 2001 Sep;171(1):170-5. doi: 10.1006/exnr.2001.7739.
Injury to the sciatic nerve of newborn rats causes motoneuron death, while the same insult inflicted 5 days later does not. In this study the effects of prolonging the period of target deprivation and axonal regeneration were investigated by inflicting a second nerve crush 6 days after the first, just before reinnervation of the muscle occurred. Two to 4 months later the number of motoneurons supplying soleus, tibialis anterior, and extensor digitorum longus muscles was established by retrograde labeling with horseradish peroxidase injected into the muscle. After nerve injury at 5 days there was no significant loss of motoneurons to any muscle. However, when the injury was repeated, the number of labeled motoneurons was reduced, suggesting that a significant proportion had died. Motoneurons to soleus were affected more than those to the fast muscles, reflecting their lesser maturity. Moreover, motoneurons to soleus that survived both injuries to their axon failed to grow to their full size. The relative impairment of recovery of the muscles, indicated by weight and maximal tetanic tension, mirrored the loss of motoneurons in each case. Previous studies have suggested that repeated nerve injuries in adult animals can enhance reinnervation. However, the present results along with those of other recent studies suggest that immature motoneurons that are repeatedly induced to support growth of their axons are at greater risk of death and can result in poorer reinnervation of the muscles.
新生大鼠坐骨神经损伤会导致运动神经元死亡，而在5天后施加同样的损伤则不会。在本研究中，通过在首次神经挤压6天后（恰好在肌肉重新获得神经支配之前）施加第二次神经挤压，来研究延长靶剥夺和轴突再生时间的影响。两到四个月后，通过向肌肉注射辣根过氧化物酶进行逆行标记，确定支配比目鱼肌、胫骨前肌和趾长伸肌的运动神经元数量。在出生5天时神经损伤后，任何肌肉的运动神经元均无明显损失。然而，当重复损伤时，标记的运动神经元数量减少，表明相当一部分已经死亡。支配比目鱼肌的运动神经元比支配快肌的运动神经元受影响更大，这反映出它们成熟度较低。此外，在轴突遭受两次损伤后存活下来的支配比目鱼肌的运动神经元未能发育到其正常大小。由重量和最大强直张力表明的肌肉恢复的相对受损情况，在每种情况下都反映了运动神经元的损失。先前的研究表明，成年动物反复的神经损伤可增强神经再支配。然而，目前的结果以及其他近期研究的结果表明，反复被诱导支持其轴突生长的未成熟运动神经元死亡风险更大，并且可能导致肌肉的神经再支配情况更差。
