Inhibitory synapses and axon regeneration in adults after injury-induced axotomy

运动神经和感觉神经在神经损伤后被切断后在外周再生。这 容量允许一些功能恢复，但这往往是次优的，因为效率相对较低 轴突再生是一个主要问题，尤其是距离肌肉一定距离的损伤。轴突切断术诱导 促进轴突生长的运动神经元的遗传变化，但这一过程相当缓慢，需要数月或数年的时间 在肢体受伤后，轴突到达它们的目标。这与这样一个事实相结合，即 运动神经元仅限于一个很短的时间窗口，慢性失神经会导致肌肉萎缩，如 以及中央环路的变化，所有这些都损害了恢复。因此，人们对机制重新产生了兴趣 以促进轴突再生。其中一位私家侦探最近强调并深入研究了一种机制 (A.W.英格利希博士)是活动和锻炼在促进轴突再生方面的效果。然而，这种方法 是有限的，因为患者经常要么患肢被固定要么卧床休息以防止 实施适当的锻炼计划。我们现在正在为一种机械的解释寻找证据，这种解释可能 也可以通过被动康复和/或药理学来招募。轴突切断后运动神经元增加 兴奋性和脱落兴奋性突触，同时保持抑制性突触。此外，钾 氯共转运体异构体2(KCC2)下调，改变抑制性突触的性质 从超极化到去极化。该提案中的另一位私人侦探(F.J.阿尔瓦雷斯博士)是脊椎抑制方面的专家 中间神经元和突触。两位P.I.共同假设，在轴突切断后，抑制性突触是 运动神经元活动的主要驱动力，并可刺激轴突再生。有一个很强的科学前提 对于这一假设：GABA的作用在早期发育和操纵中促进轴突延长 加强对轴突切断运动神经元抑制性突触的保护与更快的功能相关 恢复。直接测试轴突切断后运动神经元的抑制性突触活动是否促进轴突 我们在目标1中提出用破伤风阻断轴突切断运动神经元上的抑制性突触的再生 神经毒素A，并研究其对运动轴突再生和肌肉再神经支配的影响。在《目标2》中，我们将使用 以再生运动神经元的细胞体为靶标的中间神经元的小鼠模型 这可能会提供一种去极化的突触驱动。然后我们将使用遗传编码的活动修饰物来 检查它们的活动是否影响运动轴突再生。这些目标的解决将揭示 首次发现抑制突触活动是否是成人和脊髓轴突再生的驱动力 可能对此负责的神经元。从翻译的角度来看，这是非常重要的，因为它将 指出通过药物手段或通过招募关键字来增强“抑制”驱动力的新方法 中间神经元通过各种操作，如伸展或刺激拮抗肌肉和神经。

Motor and sensory nerves regenerate in the periphery after being axotomized following nerve injuries. This capacity allows some functional recovery, however this is frequently suboptimal being the relative inefficiency of axon regeneration a major problem, particularly for injuries at some distance from muscle. Axotomy induces genetic changes in motoneurons that promote axon growth, yet this is rather slow taking months or years for axons to reach their targets after limb injuries. This compounds with the fact that the regenerative capacity of motoneurons is limited to a short temporal window and that chronic denervation results in muscle atrophy, as well as changes in central circuits, all impairing recovery. Therefore there is renewed interest on mechanisms to promote axon regeneration. One mechanism recently highlighted and intensely studied by one of the P.I.s (Dr. A.W. English) is the effect of activity and exercise in promoting axon regeneration. However, this approach is limited since patients are frequently either with the affected limbs immobilized or in bed rest preventing implementation of adequate exercise programs. We now seek proof for a mechanistic explanation that could be recruited also with passive rehabilitation and/or pharmacology. After axotomy motoneurons increase their excitability and shed excitatory synapses while maintaining inhibitory synapses. In addition, the potassium chloride co-transporter isoform 2 (KCC2) is downregulated changing the nature of inhibitory synapses from hyperpolarizing to depolarizing. The other P.I. in this proposal (Dr. F.J. Alvarez) is an expert in spinal inhibitory interneurons and synapses. Together, both P.I.s hypothesized that after axotomy inhibitory synapses are the main drivers of motoneuron activity and could stimulate axon regeneration. There is a strong scientific premise for this hypothesis: GABA actions promote axon elongation during early development and manipulations that enhanced preservation of inhibitory synapses on axotomized motoneurons correlated with faster functional recovery. To directly test whether inhibitory synaptic activity on axotomized motoneurons promotes axon regeneration we propose in Aim 1 to block inhibitory synapses on axotomized motoneurons using tetanus neurotoxin A and study the effects on motor axon regeneration and muscle reinnervation. In Aim 2 we will use mouse models to genetically define the interneurons targeting the cell body of regenerating motoneurons and that could provide a depolarizing synaptic drive. We will then use genetically-encoded activity modifiers to examine whether their activity influences motor axon regeneration. Resolution of these aims will reveal for the first time whether inhibitory synapse activity is a driving force for axon regeneration in the adult and the spinal neurons that might be responsible. This is of high significance from a translational point of view since it will point to new approaches to enhance “inhibitory” drive by either pharmacological means or by recruiting key interneurons through various manipulations, like stretching or stimulating the antagonist muscles and nerves.