Mechanisms of locomotor rhythm generation in rodent spinal cord

摘要 运动是一种基本的行为，它允许人类和动物在他们的环境中移动和 与生活的方方面面息息相关。这种行为在许多疾病、障碍和 损伤，包括脊髓损伤、中风和各种共济失调。产生运动的所有必要的电路 节律和模式位于胸腰段脊髓，最常位于神经损伤水平以下。 这些电路可以通过各种中枢和外周刺激方法直接进入，包括但不是 仅限于硬膜外刺激。节律产生电路是启动和控制节律的切入点 运动，影响与运动相关的所有下游神经元，因此，是建立 脊椎运动的控制。节律发生器的成功激活在临床上受到了阻碍，因为 脊髓神经回路产生协调节律输出的机制仍然很差。 理解并代表了我们对运动的神经控制的理解上的一个重大差距。新一代人 有节奏性的运动行为是建立在三位一体的基础上的：(1)允许个体产生节律性的特定属性 神经元产生节律性振荡，(2)相互兴奋相互作用使神经元活动同步 节律性群体爆发，以及(3)网络抑制以协调不同神经元之间的活动 种群，这既可以塑造运动模式，也可以控制频率。三合会组件高度 相互关联，每个组成部分的参与是取决于条件的。拟议的研究将使用 高度集成的电生理、药理学、遗传学和计算方法，以系统地 探索这些机制的具体贡献以及它们之间的相互作用，在 运动节奏的模式。利用转录鉴定的转基因小鼠脊髓神经元 因素Shox2作为一个具有代表性的节奏生成群体，我们将检验节奏的总体假设 脊髓的发生机制涉及细胞、群体和网络三者之间的相互作用。 属性，其对节律发生的贡献是相互依赖的，导致灵活性和适应性 因为在不同的条件下，三和弦的相对平衡发生了变化。我们将首先确定电压门控 成年Shox2神经元自发细胞振荡的潜在电流。然后我们将评估兴奋性 节律产生神经元之间的相互作用。最后，我们将确定同侧和对侧的作用 调节运动频率的网络相互作用，并决定这些通路在 传入诱发的运动。总之，我们的多学科研究将揭示节奏产生的机制， 建立首个基于真节律产生细胞和细胞的哺乳动物运动神经网络模型 网络特性，并确定传入刺激可能影响运动节律的方式 和在脊髓中产生的模式。这些研究的结果将确定特定的神经靶点 未来的设备和策略旨在恢复受伤或运动障碍后的运动能力。

ABSTRACT Locomotion is a fundamental behavior that allows humans and animals to move through their environments and is critically involved in all aspects of life. This behavior is impeded in a number of diseases, disorders, and injuries, including spinal cord injury, stroke, and various ataxias. All of the essential circuity to generate locomotor rhythm and pattern is located in the thoracolumbar spinal cord, most often below the level of neural damage. These circuits can be accessed directly via various central and peripheral stimulation methods, including but not limited to epidural stimulation. Rhythm generating circuits are the entry point for initiation and control of locomotion, affect all downstream neurons related to locomotion, and, therefore, are the first step in establishing spinal control of locomotion. Successful activation of the rhythm generator clinically has been hampered because the mechanisms by which spinal neuronal circuits generate coordinated rhythmic output remain poorly understood and represents a major gap in our understanding of neural control of movement. The generation of rhythmic motor behaviors is based on a triad involving: (1) specific “rhythmogenic” properties allowing individual neurons to generate rhythmic oscillations, (2) mutual excitatory interactions to synchronize neuronal activity into rhythmic populational bursting, and (3) network inhibition to coordinate activity between different neuronal populations, which can both shape locomotor pattern and control frequency. Triad components are highly interconnected and the involvement of each component is condition-dependent. The proposed study will use highly integrated electrophysiological, pharmacological, genetic, and computational approaches to systematically explore the specific contributions of these mechanisms and the interactions between them, in the generation and patterning of the locomotor rhythm. Utilizing spinal neurons identified in transgenic mice by the transcription factor Shox2 as a representative rhythm generating population, we will test the overarching hypothesis that rhythm generating mechanisms in the spinal cord involve interplay between the triad of cellular, population, and network properties, whose contribution to rhythmogenesis is interdependent, leading to flexibility and adaptability seen as alterations in the relative balance of the triad in different conditions. We will first determine the voltage-gated currents underlying spontaneous cellular oscillations in adult Shox2 neurons. We will then assess excitatory interactions between rhythm generating neurons. Lastly, we will establish the role of ipsilateral and contralateral network interactions in regulating locomotor frequency, and determine the operation of these pathways during afferent-evoked locomotion. Together, our multidisciplinary study will reveal mechanisms of rhythm generation, establish the first mammalian locomotor neural network model based on “real” rhythm generating cellular and network properties, and determine the ways by which afferent stimulation may influence the locomotor rhythm and pattern generated in the spinal cord. The results of these studies will identify specific neural targets for the future devices and strategies aimed at restoration of locomotion following injury or motor disorders.