Effect of psychosocial stress on intrinsic activation of human motor neurons

描述（由申请人提供）：尽管生物力学和社会心理变量已被确定为肌肉骨骼损伤发展中的独立危险因素，但这些危险因素之间潜在相互作用的生理机制仍然知之甚少。脊髓运动神经元的单胺能输入与生理唤醒水平相关，并产生持续内向电流（PICs），其功能是放大现有的兴奋性突触输入到运动神经元池的来源。这些发现提示了一种与压力相关的肌肉骨骼损伤的新机制，在这种机制中，生理唤醒的增强引起脊髓运动神经元的紧张性兴奋性的增加，这是由持续向内电流的增强激活介导的。三个具体目标将测试这一假设，使用配对运动单元分析技术，通过比较低阈值运动单元（控制单元）在招募和稍高阈值运动单元（测试单元）招募时测量的放电率，来估计人类受试者持续内向电流的大小。目的1将比较当受试者暴露于低水平和高水平的社会心理压力时，持续向内电流对斜方肌上部自愿收缩期间单个运动单元活动的贡献。为了确定持续的内向电流是否有助于增加肌肉骨骼损伤风险的肌肉激活模式，Aim 2将确定PIC估计与暴露于低水平和高水平社会心理压力后间歇性休息期间持续运动单位活动之间的关系。基于一些个体更容易受到社会心理应激对神经肌肉功能的负面影响的研究结果，Aim 3将确定特质和状态焦虑的个体差异对应激诱导的生理唤醒和PIC对运动单位活动的贡献的影响。本研究的发现将提供第一个证据，支持内在机制在人类受试者觉醒变化中调节脊髓运动神经元的紧张性兴奋性的功能作用。

DESCRIPTION (provided by applicant): Although biomechanical and psychosocial variables have been identified as independent risk factors in the development of musculoskeletal injury, physiologic mechanisms that underlie potential interactions among these risk factors remain poorly understood. Monoaminergic inputs to spinal motor neurons are correlated with levels of physiologic arousal and generate persistent inward currents (PICs) that function to amplify existing sources of excitatory synaptic input to the motor neuron pool. These findings suggest a novel mechanism of stress-related musculoskeletal injury in which heightened physiologic arousal is proposed to cause an increase in tonic excitability of spinal motor neurons that is mediated by the enhanced activation of persistent inward currents. Three specific aims will test this hypothesis using the paired motor unit analysis technique to estimate the magnitude of persistent inward currents in human subjects by comparing the discharge rates of a low threshold motor unit (control unit) measured at the time of recruitment and derecruitment of a slightly higher threshold motor unit (test unit). Aim 1 will compare the contribution of persistent inward currents to single motor unit activity during voluntary contractions of the upper trapezius muscle when subjects are exposed to low and high levels of psychosocial stress. To determine whether persistent inward currents contribute to patterns of muscle activation that have been shown to increase the risk of musculoskeletal injury, Aim 2 will determine the association between PIC estimates and sustained motor unit activity during intermittent rest breaks following exposure to low and high levels of psychosocial stress. Based on findings that some individuals are more susceptible to the negative effects of psychosocial stress on neuromuscular function, Aim 3 will determine the effect of individual differences in trait and state anxiety on stress-induced physiologic arousal and PIC contributions to motor unit activity. Findings from this research will provide the first evidence to support a functional role for intrinsic mechanisms in regulating the tonic excitability of spinal motor neurons with changes in arousal in human subjects.