Plasticity of spinal neural networks directly impacts motor control following peripheral nerve injury

项目总结/摘要 周围神经损伤（PNI）后，感觉和运动神经元（MN）轴突在损伤部位远端变性 但两者都保持了再生和再神经支配其肌肉目标的能力。运动神经元恢复了 并且大多数肌肉传入神经（“本体感受器”）重新支配肌肉 纺锤体和火对肌肉拉伸的反应。然而，不管外周再生是否成功， 经历PNI的患者继续遭受终身运动并发症， 失调和肌肉共同收缩。这一建议的核心假设是， 神经损伤后运动前脊髓回路的连通性导致永久性运动缺陷。 特定目的1（K99），假设：神经刺激后脊髓运动前中间神经元的超兴奋驱动 横切促进肌肉共同收缩。在脊髓MN上突触的本体感受器Ia传入轴突是 在神经切断后在椎板IX中永久降解，导致牵张反射的丧失。但这些 相同的传入神经使它们在深背角中的突触加倍，在那里， interneurons驻留。这些神经元的一个特定子集是表达Isl 1的神经元。该特定人群 的神经元是突触能的，投射到不同的运动池，并接收本体传感器输入。不平衡 在突触驱动这些细胞可以促进肌肉共同收缩。这将使用 使用多电极阵列（MEA）和转基因模型的组合方法来鉴定和操纵 使用化学遗传学检测Isl 1+神经元的活性，试图恢复损伤后的正常肌肉活性。 特定目标2（R 00），假设：神经挤压消除了Ia传入神经的突触前抑制，并导致 过度的牵张反射力与神经切断不同，挤压伤后的牵张反射不仅 恢复后会产生超常的肌肉力量这两者在解剖学上的一个显著差异是 损伤类型是，在压碎再生后，MN上的Ia传入突触恢复，但它们失去了 显著数量的突触前抑制性终扣（p-终扣），其门控Ia突触传递。的 这一目的的一个假设是，p-终扣的缺失是导致过度牵张反射反应的原因 在Crush之后。在这个目标中，将利用化学遗传学来激活和/或抑制Gad 2+中间神经元， 牵张反射过程中的突触前抑制，以研究调节这些细胞的活性如何影响神经元的功能。 反射的强度。然后，提供剩余p-结的Gad 2中间神经元将被刺激， 化学遗传学，以减少反射亢进后挤压。最后，将向神经提供电刺激， 研究传入神经的持续活动是否阻止了p-终扣的丢失并恢复正常 肌肉力量的产生对拉伸的反应。

Project Summary/Abstract Following peripheral nerve injury (PNI), sensory and motoneuron (MN) axons degenerate distal to the injury site but both maintain the ability to regenerate and reinnervate their muscle targets. Motoneurons regain the ability to produce muscle force and the majority of the muscle afferents (“propriosensors”) reinnervate the muscle spindles and fire in response to muscle stretch. However, regardless of successful peripheral regeneration, patients who experience PNI continue to suffer from life-long motor complications such as limb inter-joint discoordination and muscle co-contraction. The central hypothesis of this proposal is that plasticity in the connectivity of pre-motor spinal circuits following nerve injury results in permanent motor deficits. Specific Aim 1 (K99), hypothesis: hyper-excitatory drive to the spinal pre-motor interneurons following nerve transection promotes muscle co-contraction. Proprioceptor Ia afferent axons that synapse on spinal MNs are permanently degraded in lamina IX following nerve cut resulting in the loss of the stretch reflex. However, these same afferents double their synapses in the deep dorsal horn, where a heterogenous population of pre-motor interneurons reside. One specific subset of these neurons are those that express Isl1. This specific population of neurons are glutamatergic, project to divergent motor pools, and receive propriosensor input. An imbalance in synaptic drive to these cells could facilitate muscle co-contraction. This will be investigated using a combinatory approach with multi-electrode arrays (MEAs) and transgenic models to identify and manipulate the activity of the Isl1+ neurons using chemogenetics in an attempt to restore normal muscle activity following injury. Specific Aim 2 (R00), hypothesis: nerve crush abolishes presynaptic inhibition of Ia afferents and results in an exaggerated stretch reflex force. In difference to a nerve cut, following a crush injury the stretch reflex is not only restored it results in supra-normal levels of muscle force. One striking anatomical difference between these two injury types is that Ia afferent synapses are restored on MNs following crush regeneration but they lose a significant number of presynaptic inhibitory boutons (p-boutons) that gate Ia synaptic transmission. The hypothesize of this aim is that the loss in p-boutons is responsible for the exaggerated stretch reflex response after crush. In this aim will utilize chemogenetics to activate and/or suppress Gad2+ interneurons that provide presynaptic inhibition during the stretch reflex to investigate how modulating the activity of these cells impact the strength of the reflex. Then, Gad2 interneurons that provide the remaining p-boutons will be stimulated using chemogenetics to reduces hyperreflexia after crush. Finally, electrical stimulation will be provided to the nerve after crush to investigate if sustained activity of the afferents prevents the loss of p-boutons and restores normal muscle force generation in response to stretch.