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，可以深入了解由疾病或损伤引起的运动功能障碍，并有可能改善诊断和治疗。熟练的前肢运动的精确度被认为依赖于将运动指令的内部拷贝传递到小脑回路，从而改进运动行为。然而，无法选择性地访问内部复制途径使得难以评估其功能。这一建议的目的是评估如何前肢行为是由一组颈椎本体神经元（PNs）控制的，这些神经元具有简单的解剖手段，可以在内部传递运动前信号的拷贝；PNs接收下行的运动指令输入，并将分叉的轴突输出发送到前肢运动神经元和外侧网状核（LRN），这是一个小脑前中继。这些双重预测提出了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易感性：i)消融PNs，发现对到达行为的选择性破坏；ii)选择性地操纵PN轴突输入到LRN，揭示一个快速的小脑-运动反馈回路。基于这些观察，我们假设PN内部反馈电路有助于在到达过程中对电机输出进行在线校正。在本提案中，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，我将通过描述行为过程中PN-LRN回路活动的动态来确定前肢运动的哪些方面需要这种反馈通路（目的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，以及行为方法来引入肢体的精确定时扰动（Aim 2; K99）。有了这些方法，在R00阶段，我将在施加的肢体扰动期间沉默PN输出，以研究PN反馈对在线达到校正的贡献（Aim 2; R00）。最后，我将描述在达到纠正期间由PN反馈招募的棘上回路（目的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。在哥伦比亚大学Thomas Jessell博士的主要指导下，该培训计划提供了一个全面的策略，在一个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。一个由经验丰富的导师和合作者组成的团队将为我提供短期和长期成功的关键技能培训，包括：神经活动的体内成像，突触输出的急性沉默，神经回路的电生理映射，以及前肢行为分析的严格设计。有针对性的导师指导，加上频繁的数据展示和正式和非正式的指导，将提供沟通和领导技能，这对我向独立过渡至关重要。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.