Sugiura Miho, Kanda Kenro
The Vocational School of Acupuncture and Judo Therapy, 5 Samoncho, Shinjuku-ku, Tokyo 160-0017, Japan.
J Neurophysiol. 2004 Sep;92(3):1357-65. doi: 10.1152/jn.00947.2003. Epub 2004 Apr 14.
The mechanical properties of individual motor units in the medial gastrocnemius muscle, as well as the whole muscle properties and innervating motor nucleus, were investigated in dietary-restricted, male Fischer 344/DuCrj rats at ages of 4, 7, 12, 21/22, 27, 31, and 36 mo. The tetanic tension of the type S units continuously increased until the age of 36 mo. Those of type FF and FR units declined from 21/22 to 27 mo of age but did not change further while the whole muscle tension decreased greatly. The atrophy of muscle fibers, the decline in motoneuron number and axonal conduction velocity, and the decrease in the posttetanic potentiation of twitch contraction of motor units seemed to start after 21/22 mo of age and were accelerated with advancing age. Prolongation of twitch contraction time was evident for only type S and FR units in 36-mo-old rats. The fatigue index was greatly increased for type FF units in 36-mo-old rats. These findings indicated that the progress of changes in various properties occurring in the senescent muscle was different in terms of their time course and degree and also dependent on the types of motor unit. The atrophy and decrease in specific tension of muscle fibers affected the decline in tension output of motor units. This was effectively compensated for by the capture of denervated muscle fibers over time.
在饮食受限的4、7、12、21/22、27、31和36月龄雄性Fischer 344/DuCrj大鼠中，研究了腓肠肌内侧单个运动单位的力学特性、整块肌肉的特性以及支配运动核。S型运动单位的强直张力持续增加，直至36月龄。FF型和FR型运动单位的强直张力在21/22至27月龄时下降，但此后不再变化，而整块肌肉的张力则大幅下降。肌肉纤维萎缩、运动神经元数量和轴突传导速度下降，以及运动单位单收缩后增强减弱，似乎在21/22月龄后开始，并随年龄增长而加速。在36月龄大鼠中，仅S型和FR型运动单位的单收缩时间延长明显。36月龄大鼠中FF型运动单位的疲劳指数大幅增加。这些发现表明，衰老肌肉中各种特性变化的进程在时间进程和程度上有所不同，并且还取决于运动单位的类型。肌肉纤维萎缩和比张力降低影响了运动单位张力输出的下降。随着时间的推移，失神经支配的肌肉纤维被捕获有效地补偿了这一点。
