A zebrafish model to study functional regeneration of motor circuits

项目摘要 损伤后的功能恢复是运动控制中一个重要而又难以实现的目标。脊髓运动神经元 由于支配周围肌肉的长轴突，特别容易受到损伤。运动神经元 也有影响运动输出的中央轴突侧支，但我们对它们对损伤的反应知之甚少。这 这很重要，因为运动神经元兴奋性的变化伴随着脊髓损伤，有助于短期内 痉挛和长期康复。这个探索性的R21提案的目标是开发一个新的模型系统 从被忽视的运动神经元开始，了解损伤后中央脊髓回路是如何重组的 对伤害的反应。像所有脊椎动物一样，斑马鱼有慢、中、快三种类型的脊髓运动单位 由它们的目标肌肉系统定义，每种类型都显示中央轴突侧支。然而，与所有其他的不同 脊椎动物可以追踪相同的脊髓运动神经元及其中枢和外周连接 在生活、养殖斑马鱼受伤前后。在使用双光子轴突切割术的试点实验中，我们发现 一些运动神经元再生并成功地重新支配目标肌肉系统，而另一些则无法退出 而是长出精致的中央轴突，形成突触。这也反映了一个现象 观察到成年猫脊髓运动神经元的轴突切断。这些观察表明，一些轴突切除 运动神经元正在创造可能影响运动控制的异位电路。但条件是什么呢？ 外周再生与中枢再生以及异位中枢运动神经轴突是否整合到功能回路中？在……里面 目的1，我们将评估发育时间和运动单位特性对轴突切断的相对贡献。 回应。在目标2中，我们将确定轴突切断的运动神经元是否被招募并与其他 脊髓神经元。这些目的将描述运动神经元形成异位循环回路的能力。 并将为探索损伤后脊髓回路结构的适应不良和适应性变化的研究提供信息。

Project Summary The recovery of function after damage is an important, yet elusive goal in motor control. Spinal motor neurons are particularly vulnerable to damage thanks to long axons that innervate peripheral muscles. Motor neurons also have central axon collaterals that impact motor output, but we know little of their response to injury. This is important because changes in motor neuron excitability accompany spinal injury, contributing to short-term spasticity and long-term recovery. The goal of this exploratory R21 proposal is to develop a new model system to understand how central spinal circuits reorganize after injury, beginning with an overlooked motor neuron response to injury. Like all vertebrates, zebrafish have slow, intermediate and fast types of spinal motor units defined by their target musculature and each type exhibits central axon collaterals. However, unlike all other vertebrates it is possible to track the same spinal motor neurons and their central and peripheral connections before and after injury in living, growing zebrafish. In pilot experiments using two-photon axotomies, we found that some motor neurons regrow and successfully re-innervate target musculature, while others fail to exit spinal cord and instead grow elaborate central axons and form synapses. This mirrors a phenomenon also observed in axotomized spinal motor neurons of adult cats. These observations suggest that some axotomized motor neurons are creating ectopic circuits that could impact motor control. But what conditions predict peripheral versus central regeneration and do ectopic central motor axons integrate into functional circuits? In Aim 1, we will assess the relative contribution of time of development and motor unit identity to axotomy responses. In Aim 2, we will determine if axotomized motor neurons are recruited and connected to other spinal neurons. These aims will characterize the capacity for motor neurons to form ectopic recurrent circuits and will inform studies exploring maladaptive and adaptive changes in spinal circuit structure following injury.