Influence of running exercise on γmotoneuron activity

体能表现可以通过所谓的“训练”，即相关动作的重复来完成，这在经验上是众所周知的。近年来，许多研究报道了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，关于中枢神经系统适应性改变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电路调节肌肉收缩，肌肉收缩可能是建立身体性能所必需的，特别是准确、特殊和暂时控制肌肉收缩所必需的。为探讨γ运动神经元-肌梭系统是否受运动训练的影响，通过记录大鼠比目鱼肌(Tr)以40m/min的速度间歇跑负荷时，肌梭末梢的GIA纤维和二级末梢的GII纤维的放电活动，分析了肌梭末梢对肌肉拉伸的传入反应，并比较了训练大鼠和非训练大鼠(CR)的差异。在纺锤体末端的每个传入反应、拉伸结束时的峰值频率(P)、0.5s后的静态频率(P)和动态指数(DI)中，通过检测各自的瞬时频率来测量P和S之间的差异。结果发现，TR组Gia纤维上的P和DI显著高于CR组，而GII纤维上的P、S和DI显著高于CR组。在Gia纤维中未见P降低伴随S升高的反应模式。结果提示，跑步运动可引起动态γ运动神经元的激活等适应性变化。

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.