Influence of running exercise on γmotoneuron activity

很长时间以来，人们在经验上都知道，通过所谓的“训练”，重复有关的动作，可以完成身体的表现。近年来，许多研究报道了对训练引起的骨骼肌和神经肌肉接头适应性变化的科学分析。然而，关于中枢神经系统中诱导的适应性变化的神经机制的报道很少。γ运动神经元-肌梭系统通过其反馈回路调节肌肉的收缩，对于建立肌肉收缩的精确的特殊和时间控制所特别需要的物理性能是必不可少的。本研究旨在探讨运动训练对γ运动神经元-肌梭系统的影响，通过记录大鼠比目鱼肌初级终末的Gia纤维和次级终末的GII纤维的放电活动，分析肌梭终末对肌肉牵拉的传入反应。以40 m/min的速度在跑台上进行间歇跑负荷，并对训练组大鼠和未训练组大鼠（CR）进行比较。在纺锤体末端的每个传入反应中，通过检测各自的瞬时频率来测量伸展结束时的峰值频率（P）、0.5秒后的静态频率和动态指数（DI），P和S之间的差异。结果表明，在GIa纤维上，TR的P和DI显著大于CR，而在GII纤维上，TR的P、S和DI显著大于CR。没有反应模式，如减少P伴随着增加S在GIa纤维中遇到。结果提示，跑步运动可引起运动神经元动态激活等适应性变化。

It has been experietially well known for a long time that a physical performance can be accomplished by so-called 'training', repeating of the movement concerned. Recently, many studies have been reported on the scientific analysis of the training-induced adaptive changes in skeletal muscles and nueuromuscular junctions. However, there are a few reports on the neural mechanism for the adaptive changes induced in the central nervous system. γ motoneuron-muscle spindle system to modulate via its feed back circuit the contraction of the muscle could be essential for the establishment of the physical performance particularly required for an accurate special- and temporal-control of muscle contraction. In the present study, to examine whether or not γ motoneuron-muscle spindle system is influenced by physical training, the afferent responses of the muscle spindle endings to stretch of the muscle were analysed by recording the discharge activities of the Gia fibers from the primary endings as well as the GII fibers from the secondary endings in the soleus muscles of the rats (TR) which were loaded by the interval running on a treadmill at the speed of 40 m/min, and a comparison was made between trained rats and untrained rats (CR). In each afferent response of the spindle ending, peak frequency (P) at the end of stretch, static frequency 0.5 sec later and the dynamic index (DI), the difference between P and S were measured by detecting the respective instantaneous frequency. It was found that on the GIa fibers P and DI in TR were significantly greater than those in CR while on the GII fibers P, S and DI in TR than those in CR. No response pattern such a decreased P accompanied by an increased S in the GIa fiber was encountered. The results suggest that the adaptive changes such as the activated dynamic γ motoneuron are induced by running exercise.