Beaumont Eric, Gardiner Phillip
Département de kinésiologie, Université de Montréal, Québec, Canada H3C 3J7.
J Physiol. 2002 Apr 1;540(Pt 1):129-38. doi: 10.1113/jphysiol.2001.013084.
No evidence currently exists that motoneurone adaptations in electrophysiological properties can result from changes in the chronic level of neuromuscular activity. We examined, in anaesthetized (ketamine/xylazine) rats, the properties of motoneurones with axons in the tibial nerve, from rats performing daily spontaneous running exercise for 12 weeks in exercise wheels ('runners') and from rats confined to plastic cages ('controls'). Motoneurones innervating the hindlimb via the tibial nerve were impaled with sharp glass microelectrodes, and the properties of resting membrane potential, spike threshold, rheobase, input resistance, and the amplitude and time-course of the afterhyperpolarization (AHP) were measured. AHP half-decay time was used to separate motoneurones into 'fast' (AHP half-decay time < 20 ms) and 'slow' (AHP half-decay time >/= 20 ms), the proportions of which were not significantly different between controls (58 % fast) and runners (65 % fast). Two-way ANOVA and ANCOVA revealed differences between motoneurones of runners and controls which were confined to the 'slow' motoneurones. Specifically, runners had slow motoneurones with more negative resting membrane potentials and spike thresholds, larger rheobasic spike amplitudes, and larger amplitude AHPs compared to slow motoneurones of controls. These adaptations were not evident in comparing fast motoneurones from runners and controls. This is the first demonstration that physiological modifications in neuromuscular activity can influence basic motoneurone biophysical properties. The results suggest that adaptations occur in the density, localization, and/or modulation of ionic membrane channels that control these properties. These changes might help offset the depolarization of spike threshold that occurs during rhythmic firing.
目前尚无证据表明，神经肌肉活动的慢性水平变化会导致运动神经元电生理特性出现适应性改变。我们研究了在氯胺酮/赛拉嗪麻醉的大鼠中，分别来自在运动轮中进行每日自发跑步运动12周的大鼠（“跑步者”）和饲养在塑料笼中的大鼠（“对照组”）、其轴突位于胫神经的运动神经元的特性。用尖锐的玻璃微电极刺入通过胫神经支配后肢的运动神经元，测量静息膜电位、动作电位阈值、基强度、输入电阻以及超极化后电位（AHP）的幅度和时程等特性。根据AHP的半衰期将运动神经元分为“快”（AHP半衰期<20毫秒）和“慢”（AHP半衰期≥20毫秒）两类，对照组（58%为快运动神经元）和跑步者组（65%为快运动神经元）中这两类运动神经元的比例无显著差异。双向方差分析和协方差分析显示，跑步者和对照组的运动神经元之间的差异仅限于“慢”运动神经元。具体而言，与对照组的慢运动神经元相比，跑步者的慢运动神经元具有更负的静息膜电位和动作电位阈值、更大的基强度动作电位幅度以及更大幅度的AHP。在比较跑步者和对照组的快运动神经元时，这些适应性变化并不明显。这是首次证明神经肌肉活动的生理改变可影响运动神经元的基本生物物理特性。结果表明，控制这些特性的离子膜通道的密度、定位和/或调节发生了适应性变化。这些变化可能有助于抵消节律性放电期间动作电位阈值的去极化。
