Control of Skilled Forelimb Movements by Cerebellar Feedback Circuits

描述(由申请人提供)：澄清神经回路如何塑造前肢行为可以提供对疾病或损伤导致的运动功能障碍的洞察，并有可能改进诊断和治疗。熟练的前肢动作的精确度被认为依赖于运动指令的内部副本传递到小脑回路，小脑回路精炼运动行为。然而，无法选择性地访问内部复制通路，使得评估它们的功能变得困难。这项提议的目的是评估一组颈部固有脊髓神经元(PNS)是如何控制前肢行为的，这些神经元具有简单的解剖学手段，可以在内部传递运动前信号的副本；PNS接受下行运动命令输入，并将分叉轴突输出发送到前肢运动神经元和小脑前继电器外侧网状核(LRN)。这些双重投射提出了PN内部复制分支传递的信息是否调节前肢运动的问题。我们利用小鼠的遗传可控性：i)消融PNS，揭示了到达行为的选择性中断；ii)选择性地操纵LRN的PN轴突输入，揭示了快速的小脑-运动反馈环路。基于这些观察结果，我们假设PN内部反馈电路在REACH过程中对电机输出的在线校正有贡献。在这项提案中，我的目标是解决关于PN电路的组织和功能的三个核心问题。在K99阶段的奖项中，我将通过描述行为过程中PN-LRN回路活动的动力学特征来确定前肢运动的哪些方面招募了这种反馈通路(目标1)。为了能够评估PN反馈的作用，我将开发病毒工具来抑制PN-LRN电路，并开发行为方法来引入肢体的精确定时扰动(目标2；K99)。有了这些方法，在R00阶段I将在施加肢体扰动期间静默PN输出，以调查PN反馈对在线到达校正的贡献(目标2；R00)。最后，我将描述在达到校正(目标3)时由PN反馈招募的脊髓上回路的特征。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确度。该培训计划在哥伦比亚大学Thomas Jessell博士的主要指导下，为在模范和协作的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战略。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方面的培训，包括：神经元活动的活体成像、突触输出的急性沉默、神经回路的电生理标测以及前肢行为分析的严格设计。有重点的导师指导，加上频繁的数据展示和正式和非正式的指导，将提供对我向独立过渡至关重要的沟通和领导技能。从长远来看，这种支持将让我领导一个实验室，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.