Afferent modulation of rhythm-generating neurons in the spinal locomotor central pattern generator

摘要 有节奏的运动活动，包括步行、跑步和游泳，都是由脊髓回路控制的， 中央模式发生器（CPG）。这些回路整合来自大脑的下行命令信号， 指示肌肉长度和力量的上行反馈信号。产生了行走的基本运动模式 是由位于腰脊髓内的CPG引起的尽管下行命令在脊髓中受到损害， 脊髓损伤，传入感觉信号保留CPG通路，并被认为是在步态康复中招募的 治疗包括跑步机训练和硬膜外刺激。通过以下方式更有效地参与中央人民政府的工作： 传入信号可以改善治疗结果。来自猫和老鼠的大量数据表明， 伸展和踝关节负荷作为站立和摆动相位定时的强调节器。这些传入神经的激活 以在随后的周期中可能或可能不作为相位角偏移持续存在的方式干扰步态周期。这些 结果表明，一个两层的CPG结构，其中的节奏产生（RG）层作为 节拍器和指导模式形成（PF）层，招募运动神经元。RG神经元的感觉输入 会对运动功能产生最深远的影响然而，感官的组织 对CPG内的反馈知之甚少，部分原因是CPG的蜂窝身份和连通性 在最近十年内才开始描述电路元件。最近，一群神经元， Shox 2 +/Chx 10-（Shox 2 RG）被认为是RG层的一部分。建议的目标 一个项目是使用生物学和计算方法的组合来探索感觉传入如何 输入被组织在CPG的RG层内，并对站立/摆动阶段持续时间和开始做出贡献。 我们假设Shox 2 RG神经元的诱发性多突触输入是步态传入调制的基础 时机我们有初步的数据表明，刺激特定的本体感受传入导致 在许多Shox 2神经元的突触后反应。我们将测试来自特定传入的信息的整合， Shox 2 RG神经元通过分别刺激支配髋关节和踝关节屈肌和伸肌的神经 在分离的脊髓制备物中Shox 2 RG神经元的视觉引导膜片钳期间。中间 将测试这些多突触通路中的神经元，以观察传入输入的会聚是否是介导的 在Shox 2 RG神经元的水平或之前。在静态制备中测量的输入模式将是 测试并与虚构运动期间获得的结果进行比较。这些数据将被整合到一个计算 CPG模型，以测试实验数据是否足以解释观察到的感觉调制 CPG的时间和激活结果预计将提供新的见解的基本运作， 影响RG电路的反馈系统，可用于设计有效的治疗方法， 运动CPG在损伤和疾病中的募集。

ABSTRACT Rhythmic motor activities including walking, running and swimming are controlled by spinal circuits known as central pattern generators (CPGs). These circuits integrate descending command signals from the brain and ascending feedback signals indicating muscle length and force. The basic motor pattern for walking is generated by a CPG located within the lumbar spinal cord. Although the descending commands are compromised in spinal cord injury, afferent sensory signals retain CPG access and are thought to be recruited in gait rehabilitation therapies including treadmill training and epidural stimulation. More effective engagement of CPG elements via afferent signaling may improve therapeutic outcomes. Extensive data from the cat and the rat have identified hip extension and ankle load as strong modulators of stance and swing phase timing. Activation of these afferents perturb the gait cycle in ways that may or may not persist as a phase angle shift in subsequent cycles. These results have suggested a two-layer CPG structure in which a rhythm-generating (RG) layer acts as the metronome and directs a pattern-forming (PF) layer that recruits motoneurons. Sensory inputs to the RG neurons are expected to have the most profound effects on locomotor function. However, the organization of sensory feedback within the CPG is poorly understood, in part because the cellular identity and connectivity of CPG circuit elements have only begun to be described within the last decade. Recently, a population of neurons that are Shox2+/Chx10- (Shox2RG) has been putatively identified as part of the RG layer. The goal of the proposed project is to use a combination of biological and computational approaches to explore how sensory afferent inputs are organized within the RG layer of the CPG and contribute to stance/swing phase duration and onset. We hypothesize that evoked polysynaptic inputs to Shox2RG neurons underlie the afferent modulation of gait timing. We have preliminary data showing that stimulation of specific proprioceptive afferents results in postsynaptic responses in many Shox2 neurons. We will test integration of information from specific afferents in Shox2RG neurons by separately stimulating nerves innervating flexor and extensor muscles at the hip and ankle during visually-guided patch clamp of Shox2RG neurons in isolated spinal cord preparations. Intermediate neurons in these polysynaptic pathways will be tested to see whether convergence of afferent input is mediated at the level of Shox2RG neurons or before. The pattern of input measured in the quiescent preparation will be tested and compared to that obtained during fictive locomotion. These data will be integrated into a computational model of the CPG to test for the sufficiency of the experimental data to account for observed sensory modulation of CPG timing and activation. Results are expected to provide new insights into the fundamental operation of feedback systems affecting RG circuits which could be used in the design of effective therapeutics for the recruitment of locomotor CPGs in injury and disease.