Influence of running exercise on γmotoneuron activity

长期以来，根据经验众所周知，身体表现可以通过所谓的“训练”、重复相关动作来完成。最近，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，关于中枢神经系统适应性变化的神经机制的报道很少。 γ运动神经元-肌肉纺锤体系统通过其反馈回路调节肌肉的收缩对于建立身体性能至关重要，特别是对肌肉收缩进行精确的特殊和时间控制所必需的。在本研究中，为了检查γ运动神经元-肌梭系统是否受到体育训练的影响，通过记录大鼠比目鱼肌（TR）初级末梢Gia纤维和次级末梢GII纤维的放电活动来分析肌梭末梢对肌肉拉伸的传入反应，并在跑步机上以40 m/min的速度进行间歇跑步负荷，并在训练过的大鼠和未训练过的大鼠之间进行比较大鼠（CR）。在纺锤体末端的每个传入反应中，拉伸结束时的峰值频率（P）、0.5秒后的静态频率和动态指数（DI），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，Gla 纤维上 TR 中的 P 和 DI 显着大于 CR 中的 P 和 DI，而 GII 纤维上 TR 中的 P、S 和 DI 显着大于 CR 中的。在Gla纤维中没有遇到诸如P降低伴随S增加的响应模式。结果表明，跑步运动会诱发适应性变化，例如激活动态γ运动神经元。

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.