REORGANIZATION OF SPINAL INHIBITORY SYNAPTIC CIRCUITS AFTER NERVE INJURY

项目概述（见说明书）：外周神经损伤后，轴突可以再生并重建外周的连通性；然而，恢复的运动功能是不正常的。以前我们已经证明了一些缺陷，如缺乏单突触反射，可以用本体感觉突触从运动神经元的永久收缩来解释。我们现在提出，电路重组是相对全局的，也影响脊髓间回路，不仅控制受伤的运动神经元，还控制控制同一肢体的其他运动池。因此，一种新的肢体控制模式出现了，它允许一些功能，但显然也是病态的。在提议的工作中，我们将寻求确认脊髓神经元间回路的结构变化。这项工作将与项目1中提出的功能研究并行。我们将详细分析反复抑制和相互抑制的突触组织，这两个关键的抑制回路调节和模式运动神经元放电，因此肌肉收缩。反复抑制通过一个被称为Renshaw细胞的中间神经元对运动输出进行反馈控制，Renshaw细胞接受来自运动轴突棘内侧枝的直接兴奋。相互抑制是由la抑制性中间神经元介导的，它们接受某些运动池的共同输入，包括来自la传入事件的输入，并通过拮抗剂作用抑制运动神经元，例如在运动过程中实现平滑的屈伸交替。我们假设两个中间神经元在神经损伤后分别从运动轴突和la传入事件失神经。我们认为这些改变导致了脊髓回路的重大变化。在目的1中，我们将检验Renshaw细胞的失神经支配与受损的运动轴突耦合导致整个脊髓节段复发性抑制的突触重组的假设。在目标2中，我们将检验这样一种假设，即相互通路中抑制性和兴奋性中间神经元的差异去传入神经导致平衡偏向兴奋的转变。这可以解释神经损伤后观察到的拮抗剂过度共收缩。连接的详细分析将结合技术进行，包括允许揭示微电路连接的新型逆行跨突触病毒追踪。

PROJECT SUMMARY (See Instructions): After peripheral nerve injuries axons can regenerate and reestablish connectivity in the periphery; however restored motor function is not normal. Previously we have shown that some deficits, like lack of monosynaptic reflexes, can be explained by the permanent retraction of la proprioceptive synapses from motoneurons. We now propose that circuit reorganizations are relatively global and affect also spinal intermeuronal circuits that exert control over not only injured motoneurons, but also other motor pools controlling the same limb. As a result, a novel limb control pattern emerges that allows some function, but is also clearly pathological. In the proposed work we will seek confirmation for structural changes in spinal interneuronal circuits. The work will parallel functional studies proposed in project 1. We will analyze in detail the synaptic organization of recurrent and reciprocal inhibition, two key inhibitory circuits that modulate and pattern motoneuron firing and therefore muscle contractions. Recurrent inhibition exerts feedback control of motor output through an interposed interneuron named the Renshaw cell that receives direct excitation from intraspinal collaterals of motor axons. Reciprocal inhibition is mediated by la inhibitory interneurons which receive common inputs with certain motor pools, including those from la afferents, and inhibit motoneurons with antagonist action allowing for example smooth flexion-extension alternation during movement. We hypothesize that both interneurons become denervated from respectively, motor axons and la afferents after nerve injury. We propose that these alterations cause major changes in spinal circuitry. In aim 1 we will test the hypothesis that denervation of Renshaw cells coupled to injured motor axons causes synaptic reorganizations of recurrent inhibition in the whole spinal segment. In aim 2 we will test the hypothesis that differential la de-afferentation of inhibitory and excitatory interneurons in reciprocal pathways causes a shift in balance favoring excitation. These could explain the excessive co-contraction of antagonists observed after nerve injuries. Detail analyses of connectivity will be performed with a combination of techniques, including novel retrograde transynaptic viral tracing that allows revealing microcircuit connectivity.