Defining the anatomical, molecular and functional logic of internal copy circuits involved in dexterous forelimb behaviors

项目摘要 行为就是运动，而运动的有效和高效执行是行为的根本。 形成神经系统的形式和功能的进化力量。控制前肢与 世界是哺乳动物运动系统最重要的成就之一，但不幸的是， 行为特别容易受到疾病和伤害。熟练的肢体动作的执行需要 数十块肌肉的运动输出不断完善，表明反馈的存在 使快速调整成为可能的途径。然而，外周通路的时间延迟表明， 感觉反馈本身不能解释在线运动控制的复杂性。原则上，更快 反馈的来源是将运动指令的副本内部传送到小脑， 预测运动结果，减少对延迟感觉信息的依赖。然而假定的复制电路 很难通过实验分离出来，因此它们对运动的贡献还不清楚。小鼠遗传 工具提供了一种手段来探索不同类别的脊髓中间神经元作为内部复制的神经基质。 颈脊髓本体神经元（PN）接受下行运动指令输入并延伸分叉轴突; 一个分支投射到前肢运动神经元，另一个投射到外侧网状核（LRN）， 小脑的主要输入，提供了一个解剖学上直接的手段来传达内部的运动副本。然而 PN-LRN回路的不同类别是如何组织的，以及它们各自如何对肢体的不同元素做出贡献 行为仍不清楚。使问题复杂化的是，该领域缺乏强大的方法来解构复杂的肢体 运动到组成元素（例如，达到，抓住，姿势控制），以及客观的手段， 量化小鼠的这些行为。假设：PN回路的离散类传达不同类型的脊髓 运动复制信息到LRN，每一个都是前肢控制的单独方面所必需的;这种功能逻辑 可以通过更定量、高分辨率和标准化的行为分析来解决。为了验证这一 总体假设，目标1使用分子遗传电路映射方法和单细胞RNA- 测序以定义四类PN-LRN回路的解剖学和分子组织。识别 这些不同途径的精细结构对于确定内部拷贝是如何 传递到小脑来控制前肢的行为。目标2涉及需要更敏感和 通过开发前肢行为和机器的离散元素的新测定， 自动量化前肢运动学的学习方法。最后，Aim 3融合了这些新颖的 行为方法与交叉遗传工具，电生理记录和电路特定 扰动功能解剖PN-LRN电路，并定义其模块化的贡献灵巧肢体 控制最终，这些研究将深入了解整个神经系统内部复制回路的功能。 系统，并有助于为更好地诊断和治疗运动缺陷奠定基础。

Project Summary Behavior is movement, and the effective and efficient execution of movement has served as a fundamental evolutionary force shaping the form and function of the nervous system. Control of the forelimbs to interact with the world is one of the most essential achievements of the mammalian motor system, yet unfortunately these behaviors are particularly vulnerable to disease and injury. The execution of skilled limb movements requires the continuous refinement of motor output across dozens of muscles, suggesting the existence of feedback pathways that enable rapid adjustments. The temporal delays of peripheral pathways, however, suggest that sensory feedback alone cannot explain the sophistication of online motor control. In principle, a more rapid source of feedback would be to convey copies of motor commands internally to the cerebellum to generate predictions of motor outcome, reducing dependence on delayed sensory information. Yet putative copy circuits have been difficult to isolate experimentally, leaving their contributions to movement unclear. Mouse genetic tools offer a means to explore a diverse class of spinal interneurons as a neural substrate for internal copies. Cervical propriospinal neurons (PNs) receive descending motor command input and extend bifurcating axons; one branch projects to forelimb motor neurons and the other projects to the lateral reticular nucleus (LRN), a major cerebellar input, providing an anatomically straightforward means to convey motor copies internally. Yet how diverse classes of PN-LRN circuits are organized and how they each contribute to distinct elements of limb behavior remain unclear. Complicating the problem, the field lacks robust ways for deconstructing complex limb movements into component elements (e.g. reaching, grasping, postural control), and objective means for quantifying these behaviors in mice. Hypothesis: Discrete classes of PN circuits convey distinct types of spinal motor copy information to the LRN, each necessary for separate aspects of forelimb control; this functional logic can be resolved with more quantitative, high-resolution and standardized behavioral assays. To test this overarching hypothesis, Aim 1 uses molecular-genetic circuit mapping approaches and single-cell RNA- sequencing to define the anatomical and molecular organization of four classes of PN-LRN circuits. Identifying the fine-grained structure of these diverse pathways will be essential for establishing how internal copies are conveyed to the cerebellum to control forelimb behavior. Aim 2 addresses the need for more sensitive and unbiased behavioral tools by developing novel assays of discrete elements of forelimb behavior and machine learning approaches for automated quantification of forelimb kinematics. Finally, Aim 3 merges these novel behavioral approaches with intersectional genetic tools, electrophysiological recording and circuit-specific perturbation to functionally dissect PN-LRN circuits and define their modular contributions to dexterous limb control. Ultimately, these studies will yield insight into the function of internal copy circuits throughout the nervous system, and help to lay the foundation for better diagnosis and treatment of motor deficits.