Development of Synaptic Inputs on Spinal Interneurons

项目概要（30行） 运动依赖于协调肌肉动作所必需的脊髓运动输出模式。这 反过来，取决于脊髓中间神经元微电路，调节运动神经元的募集和放电。的 最近，基因定义的中间神经元的大量出现彻底改变了脊髓运动回路的研究 希望能对这些重要的网络进行更全面、更完整的剖析。开始的工作 通过设计遗传策略来识别、标记、研究和修改大群中间神经元的活性， 由它们源自特定的祖域来定义。这是以前大多数情况下采用的方法。 年获得了许多新的信息，但最大的惊喜是内部的巨大异质性。 脊髓中间神经元的每个域谱系。因此，现在有必要研究不同的子类， 每个区域内的中间神经元。这只能通过新的动物模型来实现， 使用交叉遗传学的限制性亚组，其中多于一个的组合表达 基因是条件表达荧光蛋白或活性调节剂所必需的，以研究它们。 该项目主要针对V1组。这些是抑制性中间神经元，与同侧连接， 脊髓和具有重要作用的运动神经元活动。多年来，我们和其他人 报道了V1中间神经元的多种功能，包括通过反复和 相互抑制，即所有Renshaw细胞和一些但不是全部Ia抑制性中间神经元（IaIN） 源自V1。它们还有助于调节运动过程中的屈伸交替， 运动速度，在节律运动期间分别提供异相和同相抑制。 这种功能多样性与许多不同的遗传定义的亚群的存在是平行的 (by有些人估计超过50）组织成四个主要的V1分支。现在重要的是分析 每个子集是否集成在不同的微电路中并负责专门的功能。我们 在接下来的五年里，他们选择专注于由转录因子Foxp 2定义的最大的V1进化枝。数据 在上一次拨款期间收集的数据表明，这一群体至少由三个主要亚型组成， 包括一些具有典型IaIN突触学的细胞。我们已经测试了各种交叉策略， 从解剖学上（使用各种病毒方法）研究Foxp 2-V1与不同运动神经元的连接性， 池和初级传入，以及这些连接的出生后发育（Aim 1）。那就 分析Foxp 2-V1是否是V1-IaIN的唯一来源，以及相互抑制如何受到 基因沉默（目标2）。最后，我们将可逆地沉默这些细胞在新生儿和成人 并使用慢性EMG记录和运动学来分析它们在肌肉中的作用 在节律性运动行为期间的激活选择（目标3）。主要目标是揭示 这一主要V1组的组织及其在出生后运动功能成熟过程中的影响。

PROJECT SUMMARY (30-lines) Movement depends on patterned spinal cord motor output necessary for coordinated muscle actions. This in turn, depends on spinal interneuron microcircuits that modulate motoneuron recruitment and firing. The recent explosion of genetically-defined interneurons has revolutionized the study of spinal motor circuits promising a more comprehensive and complete dissection of these important networks. The work started by devising genetic strategies to identify, label, study and modify activity of large groups of interneurons defined by their derivation from specific progenitor domains. This is the approach mostly taken in previous years. Much new information was obtained, but the biggest surprise was the large heterogeneity within each domain-lineage of spinal interneurons. It is thus now necessary to study the different subclasses of interneurons within each domain. This can only be accomplished with new animal models to target more restricted subgroups using intersectional genetics in which combinatorial expression of more than one gene is necessary for conditionally expressing fluorescent proteins or activity modulators to study them. This grant focuses on the V1 group. These are inhibitory interneurons with ipsilateral connections in the spinal cord and that have important roles shaping motoneuron activity. Over the years we and others have reported a variety of functions for V1 interneurons, including control of motoneuron firing by recurrent and reciprocal inhibition, being all Renshaw cells and some, but not all, Ia inhibitory interneurons (IaINs) derived from V1s. They also contribute to regulate flexion-extension alternation during movement and locomotion speed, providing respectively out-of-phase and in-phase inhibition during rhythmic locomotion. This functional diversity is parallel by the existence of many different genetically-defined subpopulations (by some estimates more than 50) organized into four major V1 clades. It is now important to analyze whether each subset is integrated in distinct microcircuits and responsible for specialized functions. We chose to focus in the next five years on the largest V1clade defined by the transcription factor Foxp2. Data gathered during the previous grant suggest this group is composed of at least three major subtypes and includes some cells with synaptology typical of IaINs. We have tested various intersectional strategies to study anatomically (using various viral approaches) the connectivity of Foxp2-V1s with different motor pools and primary afferents, and the postnatal development of these connections (Aim1). Then, we will analyze whether Foxp2-V1s are the only sources of V1-IaINs and how reciprocal inhibition is affected by genetically silencing them (Aim 2). Finally, we will reversibly silence these cells in the neonate and adult during locomotor stepping and use chronic EMG recordings and kinematics to analyze their role in muscle activation selection during rhythmic motor behaviors (Aim 3). The major goal is to uncover the functional organization of this major V1 group and their impact during postnatal maturation of motor function.