The rodent central pattern generator for locomotion

描述(申请人提供)：在新生啮齿动物的脊髓中，5-羟色胺和NMDA的结合足以激活中枢模式生成器(CPG)网络以进行运动，但这些递质组织和激活CPG的细胞和生物物理机制尚不清楚。我们认为，这些神经调节剂重新配置CPG神经元的固有属性和网络突触的强度，将网络组织成功能空闲的状态，从而使下行的谷氨酸或感觉输入可以迅速启动运动。新生小鼠的脊髓是检验这些假说的极好的准备：通过转基因和解剖学方法标记特定的中间神经元类型，已经确定了几个CPG的候选神经元。两类中间神经元被认为在小鼠脊髓运动CPG的组织中发挥重要作用：协调左右运动的连合中间神经元(CINs)和可能参与CPG节律产生成分的HB9中间神经元。按照我们在甲壳类口胃神经节中多年来一直追求的研究方法，我们建议研究这些神经元的固有细胞属性如何在虚构运动中塑造它们的活动模式，以及5-羟色胺和NMDA如何影响这些固有属性。我们的第一个目标是在细胞水平上：结合全细胞记录和钙成像，我们将研究突触分离的中间神经元的内在放电特性，它们被5-羟色胺调制，以及它与NMDA的相互作用。这个目标是为了更好地了解调节器如何改变神经元的活动来激活运动模式。其次，在生物物理水平上，我们将使用电压钳方法来识别5-羟色胺和NMDA对CINs和Hb9中间神经元离子电流的影响，以了解神经元内在放电特性调制变化的生物物理基础。第三，我们将通过研究这些脊髓中间神经元在出生后发育期间、动物学习行走期间以及脊髓损伤后的变化来开始探索这些脊髓中间神经元的内在属性的可塑性。这些项目将阐明神经调节剂用来塑造运动性CPG的一些细胞和分子机制。脊髓损伤不仅会导致用于运动的快速激活信号的丢失，而且还会导致使网络发挥功能的较慢的调制输入信号的丢失。为了学习如何在脊髓损伤后恢复运动，我们必须了解使网络发挥功能的调节机制和运动CPG的快速激活机制。与公共健康相关我们假设5-羟色胺和其他调节剂改变运动网络神经元及其突触的放电特性，使脊髓网络能够产生运动命令。当这些输入在脊髓损伤后丢失时，网络就变得不起作用。我们工作的最终目标是为损伤后的神经调节剂治疗提供合理的基础，帮助维持运动网络的功能状态，直到轴突能够在损伤处再生。

DESCRIPTION (provided by applicant): In the neonatal rodent spinal cord, the combination of serotonin and NMDA is adequate to activate the central pattern generator (CPG) networks for locomotion, but the cellular and biophysical mechanisms by which these transmitters organize and activate the CPG are poorly understood. We propose that these neuromodulators reconfigure the intrinsic properties of the CPG neurons and the strengths of network synapses to organize the network into a functional "idling" state, so that descending glutamatergic or sensory input can rapidly initiate locomotion. The neonatal mouse spinal cord is an excellent preparation to test these hypotheses: several neuronal candidates for the CPG have been identified using transgenic and anatomical methods to label specific interneuron types. Two identified classes of interneurons are thought to play important roles in the organization of the mouse spinal locomotor CPG: commissural interneurons (CINs) which coordinate left-right movements, and the Hb9 interneurons which may participate in the rhythm-generating component of the CPG. Following a research approach we have pursued for many years in the crustacean stomatogastric ganglion, we propose to study how the intrinsic cellular properties of these neurons shape their activity patterns during fictive locomotion, and how serotonin and NMDA affect those intrinsic properties. Our first aim is at the cellular level: using a combination of whole cell recording and calcium imaging, we will study the intrinsic firing properties of synaptically isolated interneurons, their modulation by serotonin, and its interaction with NMDA. The goal of this aim is to better understand how modulators can alter the neurons' activity to activate the motor pattern. Second, at the biophysical level, we will use voltage clamp methods to identify the ionic currents affected by serotonin and NMDA in CINs and Hb9 interneurons, to understand the biophysical basis for modulatory changes in the neurons' intrinsic firing properties. Third, we will begin to explore the plasticity of the intrinsic properties of these spinal interneurons by studying how they change during postnatal development, during the time the animal learns to walk, and following spinal cord injury. These projects will elucidate some of the cellular and molecular mechanisms that neuromodulators use to shape the locomotor CPG. Spinal cord injury causes loss not only of the rapid activating signals for locomotion, but also of the slower modulatory inputs that enable the network to function at all. To learn how to restore movement after spinal cord injury, we must understand both the modulatory mechanisms that enable the network to function and the rapid activating mechanisms in the locomotor CPG. PUBLIC HEALTH RELEVANCE We hypothesize that serotonin and other modulators modify the firing properties of locomotor network neurons and their synapses to enable the spinal network to produce the commands for locomotion. When these inputs are lost following spinal cord lesions, the network becomes non-functional. An eventual goal of our work is to provide a rational basis for post-injury neuromodulator therapy, to help maintain the locomotor networks in a functional state until regrowth of axons can be accomplished across the lesion.