Gardiner P, Dai Y, Heckman C J
Department of Physiology, Spinal Cord Research Center, University of Manitoba, 730 William Ave., Winnipeg, Manitoba, Canada R3E 3J7.
J Appl Physiol (1985). 2006 Oct;101(4):1228-36. doi: 10.1152/japplphysiol.00482.2006. Epub 2006 Jun 15.
Evidence is presented that one locus of adaptation in the "neural adaptations to training" is at the level of the alpha-motoneurons. With increased voluntary activity, these neurons show evidence of dendrite restructuring, increased protein synthesis, increased axon transport of proteins, enhanced neuromuscular transmission dynamics, and changes in electrophysiological properties. The latter include hyperpolarization of the resting membrane potential and voltage threshold, increased rate of action potential development, and increased amplitude of the afterhyperpolarization following the action potential. Many of these changes demonstrate intensity-related adaptations and are in the opposite direction under conditions in which chronic activity is reduced. A five-compartment model of rat motoneurons that innervate fast and slow muscle fibers (termed "fast" and "slow" motoneurons in this paper), including 10 active ion conductances, was used to attempt to reproduce exercise training-induced adaptations in electrophysiological properties. The results suggest that adaptations in alpha-motoneurons with exercise training may involve alterations in ion conductances, which may, in turn, include changes in the gene expression of the ion channel subunits, which underlie these conductances. Interestingly, the acute neuromodulatory effects of monoamines on motoneuron properties, which would be a factor during acute exercise as these monoaminergic systems are activated, appear to be in the opposite direction to changes measured in endurance-trained motoneurons that are at rest. It may be that regular increases in motoneuronal excitability during exercise via these monoaminergic systems in fact render the motoneurons less excitable when at rest. More research is required to establish the relationships between exercise training, resting and exercise motoneuron excitability, ion channel modulation, and the effects of neuromodulators.
有证据表明，“神经对训练的适应性”中的一个适应位点位于α运动神经元水平。随着自主活动的增加，这些神经元表现出树突重构、蛋白质合成增加、蛋白质轴突运输增加、神经肌肉传递动力学增强以及电生理特性改变的证据。后者包括静息膜电位和电压阈值的超极化、动作电位产生速率增加以及动作电位后超极化幅度增加。其中许多变化显示出与强度相关的适应性，并且在慢性活动减少的情况下方向相反。本文使用了一个五室大鼠运动神经元模型，该模型支配快肌纤维和慢肌纤维（在本文中称为“快”和“慢”运动神经元），包括10种活跃的离子电导，试图重现运动训练引起的电生理特性适应性变化。结果表明，运动训练对α运动神经元的适应性可能涉及离子电导的改变，这反过来可能包括构成这些电导的离子通道亚基基因表达的变化。有趣的是，单胺对运动神经元特性的急性神经调节作用，在急性运动期间，由于这些单胺能系统被激活，这将是一个影响因素，其作用方向似乎与耐力训练后静息状态下运动神经元的测量变化相反。可能是运动期间通过这些单胺能系统运动神经元兴奋性的定期增加实际上使运动神经元在静息时兴奋性降低。需要更多的研究来确定运动训练、静息和运动时运动神经元兴奋性、离子通道调节以及神经调节剂作用之间的关系。
