Department of Physiology and Pathophysiology, Medical School, Xi'an JiaoTong University, Xi'an 710061, Shaanxi, People's Republic of China.
J Muscle Res Cell Motil. 2010 Sep;31(3):155-61. doi: 10.1007/s10974-010-9215-8. Epub 2010 Jul 27.
During hind limb unloading (HU), the soleus is often in a shortened position and the natural physiological stimulus of muscle spindles is altered, such that muscle spindle activity also changes. Using isolated spindle conditions, the present study investigates the electrophysiological activity and ultrastructure of muscle spindles following HU. Results show that muscle spindle discharges fall into either of two main patterns, single spikes or spike clusters in shortened positions, with a steady frequency of 18-38 spikes/s (mean 29.08 +/- 2.45) in an extended position. Following 14-day HU, afferent discharge activity was significantly altered in soleus muscle spindles. Duration of individual spikes was significantly prolonged, from 0.54 +/- 0.05 ms for control rats to 1.53 +/- 0.25 ms for rats in the HU group. In a shortened position, regular rhythm afferent discharges were obviously depressed, and the majority of muscle spindles became silent, while in an extended position, the discharges remained continuous but with decreased frequency. Results also show that the ultrastructure of muscle spindles experience degenerative changes during HU. Altered muscle spindle afference could possibly modify the activity of motor neurons and further affect the activity of extrafusal fibers.
在下肢去负荷(HU)期间,比目鱼肌通常处于缩短的位置,肌肉梭内感受器的自然生理刺激发生改变,肌肉梭内感受器的活动也随之改变。本研究采用分离的梭内器条件,研究了 HU 后肌肉梭内器的电生理活动和超微结构。结果表明,肌肉梭内器的放电分为两种主要模式,缩短位置的单峰或峰簇,在伸展位置的频率稳定在 18-38 个峰/s(平均 29.08 +/- 2.45)。HU 后 14 天,比目鱼肌梭内器传入放电活动明显改变。单个峰的持续时间明显延长,从对照组大鼠的 0.54 +/- 0.05ms 延长至 HU 组大鼠的 1.53 +/- 0.25ms。在缩短位置,规则节律传入放电明显受到抑制,大部分肌肉梭内器变得沉默,而在伸展位置,放电仍然连续,但频率降低。结果还表明,HU 期间肌肉梭内器的超微结构经历退行性变化。肌肉梭内传入的改变可能会改变运动神经元的活动,并进一步影响梭外纤维的活动。