Wood Ryan L, Calvo Paula M, McCallum William M, English Arthur W, Alvarez Francisco J
Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia, USA.
Eur J Neurosci. 2025 Mar;61(5):e70045. doi: 10.1111/ejn.70045.
Motor axon regeneration after traumatic nerve injuries is a slow process that adversely influences patient outcomes because muscle reinnervation delays result in irreversible muscle atrophy and suboptimal axon regeneration. This advocates for investigating methods to accelerate motor axon growth. Electrical nerve stimulation and exercise both enhance motor axon regeneration in rodents and patients, but these interventions cannot always be easily implemented. A roadblock to uncover novel therapeutic approaches based on the effects of activity is the lack of understanding of the synaptic drives responsible for activity-mediated facilitation of axon regeneration. We hypothesized that the relevant excitatory inputs facilitating axon regrowth originate in GABA/glycine synapses, which become depolarizing after downregulation of the potassium chloride cotransporter 2 in motoneurons following axotomy. To test this, we injected tetanus toxin (TeTx) into the tibialis anterior (TA) muscle of mice to block the release of GABA/glycine specifically onto TA motoneurons. Thereafter, we axotomized all sciatic motoneurons by nerve crush and analyzed the time courses of muscle reinnervation in TeTx-treated (TA) and untreated (lateral gastrocnemius [LG]) motoneurons. Muscle reinnervation was slower in TA motoneurons with blocked GABA/glycine synapses, as measured by recovery of M responses and anatomical reinnervation of neuromuscular junctions. Post hoc immunohistochemistry confirmed the removal of the vesicle-associated membrane proteins 1 and 2 by TeTx activity, specifically from inhibitory synapses. These proteins are necessary for the exocytotic release of neurotransmitters. Therefore, we conclude that GABA/glycine neurotransmission on regenerating motoneurons facilitates axon growth and muscle reinnervation, and we discuss possible interventions to modulate these inputs on regenerating motoneurons.
创伤性神经损伤后运动轴突的再生是一个缓慢的过程，会对患者的预后产生不利影响，因为肌肉再支配延迟会导致不可逆的肌肉萎缩和轴突再生不理想。这就提倡研究加速运动轴突生长的方法。电神经刺激和运动都能增强啮齿动物和患者的运动轴突再生，但这些干预措施并非总能轻易实施。基于活动效应发现新的治疗方法的一个障碍是缺乏对负责活动介导的轴突再生促进作用的突触驱动的理解。我们假设促进轴突再生的相关兴奋性输入起源于GABA/甘氨酸突触，在轴突切断后运动神经元中的氯化钾共转运体2下调后，这些突触会发生去极化。为了验证这一点，我们将破伤风毒素（TeTx）注射到小鼠的胫前肌（TA）中，以特异性阻断GABA/甘氨酸释放到TA运动神经元上。此后，我们通过神经挤压切断所有坐骨运动神经元，并分析了TeTx处理组（TA）和未处理组（外侧腓肠肌[LG]）运动神经元的肌肉再支配时间进程。通过M反应的恢复和神经肌肉接头的解剖学再支配来测量，TA运动神经元中GABA/甘氨酸突触被阻断后，肌肉再支配较慢。事后免疫组织化学证实了TeTx活性导致囊泡相关膜蛋白1和2的去除，特别是从抑制性突触中去除。这些蛋白质是神经递质胞吐释放所必需的。因此，我们得出结论，再生运动神经元上的GABA/甘氨酸神经传递促进轴突生长和肌肉再支配，并且我们讨论了调节这些再生运动神经元输入的可能干预措施。
