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一直是一个基本的 进化的力量塑造神经系统的形式和功能。控制要与之交互的前肢 世界上最重要的成就之一是哺乳动物的运动系统，但不幸的是，这些 行为特别容易受到疾病和伤害的影响。熟练的肢体动作的执行需要 数十块肌肉的运动输出持续精细化，表明存在反馈 实现快速调整的路径。然而，外周通路的时间延迟表明 仅凭感觉反馈不能解释在线运动控制的复杂性。原则上，一个更快的 反馈的来源将是将运动命令的副本内部传送到小脑以产生 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 很难从实验上分离出来，这使得它们对运动的贡献尚不清楚。小鼠遗传 工具提供了一种方法来探索不同类别的脊髓中间神经元作为内部复制的神经底物。 颈固有脊髓神经元(PNS)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，另一个分支投射到外侧网状核(LRN)， 主要的小脑输入，提供了一种在解剖上直接在内部传送运动副本的方法。还没有 不同类别的PN-LRN电路是如何组织的，以及它们各自如何对肢体的不同元素做出贡献 其行为仍不清楚。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 动作分为构成要素(如伸手、抓握、姿势控制)和客观手段 在小鼠身上量化这些行为。假设：不连续类别的PN回路传递不同类型的脊髓 电机将信息复制到LRN，每个信息都是前肢控制的不同方面所必需的；此功能逻辑 可以通过更定量、高分辨率和标准化的行为分析来解决。为了测试这一点 最重要的假设，目标1使用分子-遗传回路作图方法和单细胞RNA- 测序以确定四类PN-LRN回路的解剖和分子组织。识别 这些不同途径的细粒度结构对于确定内部拷贝的程度至关重要 传递到小脑以控制前肢行为。目标2满足了对更敏感和 通过开发前肢行为和机器的离散元素的新分析来实现无偏见的行为工具 前肢运动学自动量化的学习方法。最后，《目标3》将这些小说融合在一起 使用交叉遗传工具、电生理记录和特定电路的行为方法 摄动功能解剖PN-LRN电路并确定其对灵巧臂的模数贡献 控制力。最终，这些研究将深入了解整个神经系统内部复制电路的功能。 系统，并有助于为更好地诊断和治疗运动障碍奠定基础。

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.