Local Circuit Properties of Mouse Corticospinal Neurons

描述（由申请人提供）：影响初级运动皮层（M1）的神经病理学导致主要的神经损伤，包括瘫痪/截瘫、癫痫和运动障碍，包括肌萎缩侧索硬化症（ALS），一种影响上运动神经元的疾病。初级运动皮层（M1）主要参与自主运动和其他方面的运动控制。M1中的皮质脊髓神经元的局部回路——从皮层到脊髓的神经元——介导了控制身体运动的关键输出通路。尽管皮质脊髓神经元的输出已被广泛研究，但对任何物种皮质脊髓神经元的局部输入知之甚少。超极化激活的环核苷酸门控（HCN）通道在超极化时激活，产生h电流（Ih），可通过多种信号转导途径调节。在体感觉皮层和内嗅皮层的L5神经元中观察到Ih。目前尚未对Ih及其对M1皮质脊髓神经元局部电路特性的影响进行评估。由于Ih抵抗膜电位的变化，预计皮质脊髓神经元局部输入的时空整合窗口会很窄。阐明这一点对于详细了解M1如何控制身体运动至关重要，并有可能揭示许多影响运动控制的神经系统疾病（如ALS）的新治疗靶点。肌萎缩侧索硬化症是一种迟发性神经退行性疾病，可导致进行性瘫痪，导致过早死亡。ALS患者的皮质亢进性已被证实，然而，对ALS患者的皮质脊髓回路知之甚少。这些研究的总体目标是利用高分辨率激光扫描光刺激（LSPS）、切片电生理学、药理学和解剖标记策略来研究小鼠皮质脊髓神经元的体外电路水平特性。初步数据表明，小鼠皮质脊髓回路(1)接受来自第2/3层的强兴奋性突触输入，(2)具有以高表达超极化激活电流（Ih）为主的内在电生理，(3)在超氧化物歧化酶1 （SOD1-693A）突变小鼠（ALS小鼠模型）中发生改变。因此，这一提议的假设是，Ih在皮质脊髓神经元中产生特定类别的突触整合特性，推论是，这些特性在ALS小鼠模型中被破坏。本研究结果将揭示M1皮质脊髓神经元局部突触回路生理学的基本机制，为今后运动控制障碍中皮质功能障碍的研究提供新的基础。

DESCRIPTION (provided by applicant): Neuropathology affecting primary motor cortex (M1) causes major neurological impairment including paralysis/paraplegia, epilepsy, and movement disorders including amyotrophic lateral sclerosis (ALS), a disease affecting upper motor neurons. Primary motor cortex (M1) is centrally involved in voluntary movement and other aspects of motor control. Local circuits of corticospinal neurons -- neurons projecting from cortex to the spinal cord -- in M1 mediate the key output pathway controlling movement of the body. Although the output of corticospinal neurons has been studied extensively, little is known about the local inputs to corticospinal neurons in any species. Hyperpolarization- activated cyclic nucleotide-gated (HCN) channels activate upon hyperpolarization, generating h-current (Ih) which can be regulated by multiple signal transduction pathways. Ih has been observed in L5 neurons of somatosensory cortex, and entorhinal cortex. Evaluation of Ih and its effects on local circuit properties in corticospinal neurons of M1 has yet to be done. Since Ih resists changes in membrane potential, a narrow spatio-temporal integration window would be expected for local inputs to corticospinal neurons. Elucidating this will be critical for a detailed understanding of how M1 controls movement of the body, and holds the potential to reveal new therapeutic targets in the many neurological diseases that affect motor control such as ALS. ALS is a late onset neurodegenerative disease that results in progressive paralysis leading to premature death. Cortical hyperexcitability has been shown in ALS patients, however, little is known about corticospinal circuits in ALS. The overall goal of these studies is to investigate in vitro circuit-level properties of mouse corticospinal neurons using use high-resolution laser scanning photostimulation (LSPS), slice electrophysiology, pharmacology, and anatomical labeling strategies. Preliminary data suggests that mouse corticospinal circuits (1) receive strong excitatory synaptic input from layer 2/3, (2) have intrinsic electrophysiology that is dominated by high expression of hyperpolarization-activated current (Ih), and (3) become altered in superoxide dismutase 1 (SOD1-693A) mutant mice, a mouse model of ALS. Thus the hypothesis for this proposal is that Ih produces class-specific synaptic integration properties in corticospinal neurons, and a corollary is that these properties are disrupted in a mouse model of ALS. The results of the proposed research will reveal fundamental mechanisms of local synaptic circuit physiology in M1 corticospinal neurons, providing a new basis for future studies of cortical dysfunction in disorders of motor control. PUBLIC HEALTH RELEVANCE: Amyotrophic lateral sclerosis (ALS) is a late onset neurodegenerative disease affecting corticospinal neurons that results in progressive paralysis leading to premature death. Local circuits of corticospinal neurons -- neurons projecting from cortex to the spinal cord -- mediate the key output pathway controlling movement of the body by integrating diverse inputs from multiple sensory and motor-related systems. The results of the proposed research will reveal fundamental mechanisms of local synaptic circuit physiology in M1 corticospinal neurons, providing a new basis for future studies of cortical dysfunction in ALS.