Control of Skilled Forelimb Movements by Cerebellar Feedback Circuits

描述（由申请人提供）： 阐明神经回路如何塑造前肢行为可以深入了解疾病或损伤引起的运动功能障碍，并可能改善诊断和治疗。熟练的前肢运动的精确性被认为取决于运动命令的内部副本到小脑回路的传递，小脑回路改善了运动行为。然而，由于无法选择性地进入内部复制途径，因此很难评估它们的功能。这个建议的目标是评估前肢行为是如何控制的一组颈椎propriospinal神经元（PNs），有一个简单的解剖手段，通过它来传达运动前信号的副本内部; PNs接收下行运动命令输入，并发送分叉轴突输出前肢运动神经元以及外侧网状核（LRN），前小脑中继。这些双重预测提出的问题，是否由PN内部复制分支调节前肢运动的信息中继。我们利用小鼠的遗传易处理性：i）消融PN，揭示了到达行为的选择性破坏; ii）选择性地操纵PN轴突输入到LRN，揭示了快速的小脑运动反馈回路。基于这些观察结果，我们假设PN内部反馈电路有助于达到过程中的电机输出的在线校正。 在本建议中，我的目的是解决三个核心问题的组织和功能的PN电路。在奖励的K99阶段，我将通过表征行为期间PN-LRN回路活动的动态来确定前肢运动的哪些方面招募了这种反馈通路（目标1）。为了评估PN反馈的作用，我将开发病毒工具来抑制PN-LRN回路，并采用行为方法来引入精确定时的肢体扰动（目标2; K99）。利用这些方法，在R 00阶段期间，I将在施加的分支扰动期间使PN输出静默，以研究PN反馈对在线到达校正的贡献（目标2; R 00）。最后，我将描述由PN反馈招募的脊髓上回路在达到校正（目标3）。总之，这些研究将有助于阐明小脑反馈通路如何建立运动精度。该培训计划由哥伦比亚大学的托马斯·斯佩尔博士担任主要导师，为在示范性和协作性神经科学环境中获得必要的实验和专业技能提供了全面的策略。一个经验丰富的导师和合作者团队将提供对我的短期和长期成功至关重要的技能培训，包括：神经元活动的体内成像，突触输出的急性沉默，神经回路的电生理映射，以及前肢行为测定的严格设计。有针对性的导师指导，以及频繁的数据演示和正式和非正式的指导，将为我向独立过渡提供至关重要的沟通和领导技能。从长远来看，这种支持将使我能够领导一个实验室，将分子和系统方法结合起来，探索熟练运动的神经基础。

DESCRIPTION (provided by applicant): Clarifying how neural circuits shape forelimb behaviors can provide insight into motor dysfunction caused by disease or injury, and can potentially improve diagnosis and treatment. The precision of skilled forelimb movements is thought to depend on the conveyance of internal copies of motor commands to cerebellar circuits that refine motor behavior. The inability to access internal copy pathways selectively, however, has made it difficult to assess their function. The goal of this proposal is to evaluate how forelimb behavior is controlled by a set of cervical propriospinal neurons (PNs) that have a simple anatomical means by which to convey copies of pre-motor signals internally; PNs receive descending motor command input, and send bifurcating axonal output to forelimb motor neurons as well as to the lateral reticular nucleus (LRN), a pre-cerebellar relay. These dual projections raise the issue of whether information relayed by the PN internal copy branch regulates forelimb movement. We took advantage of the genetic tractability of mice to: i) ablate PNs, uncovering a selective disruption of reaching behavior; and ii) manipulate PN axonal input to the LRN selectively, revealing a rapid cerebellar-motor feedback loop. Based on these observations, we hypothesize that PN internal feedback circuits contribute to the on-line correction of motor output during reaching. In this proposal, I aim to address three central questions about the organization and function of the PN circuit. During the K99 phase of the award, I will identify which aspects of forelimb movement recruit this feedback pathway by characterizing the dynamics of PN-LRN circuit activity during behavior (Aim 1). To enable assessment of the role of PN feedback, I will develop viral tools to inhibit the PN-LRN circuit, and behavioral approaches to introduce precisely timed perturbations of the limb (Aim 2; K99). With these methods in hand, during the R00 phase I will silence PN output during imposed limb perturbation to investigate the contribution of PN feedback to on-line reaching correction (Aim 2; R00). Finally, I will characterize the supraspinal circuits that are recruited by PN feedback durin reaching correction (Aim 3). Together, these studies will help clarify how cerebellar feedback pathways establish motor precision. The training plan, under the primary mentorship of Dr. Thomas Jessell at Columbia University, provides a comprehensive strategy for acquiring the necessary experimental and professional skills within an exemplary and collaborative neuroscience environment. An experienced team of mentors and collaborators will provide training in skills critical for my short- and long-term success, including: in vivo imaging of neurl activity, acute silencing of synaptic output, electrophysiological mapping of neural circuits, and rigorous design of forelimb behavioral assays. Focused mentor guidance, alongside frequent data presentation and formal and informal instruction, will provide the communication and leadership skills vital for my transition to independence. In the long-term, this support will equi me to lead a laboratory that merges molecular and systems approaches to explore the neural basis of skilled movement.