Ishihara A, Oishi Y, Roy R R, Edgerton V R
Laboratory of Neurochemistry, Faculty of Integrated Human Studies, Kyoto University, Japan.
Aviat Space Environ Med. 1997 May;68(5):421-5.
Chronic unloading of the hindlimbs of rats results in atrophy and a shift in the metabolic and mechanical properties of the soleus muscle a predominantly slow postural muscle, towards those observed in faster muscles.
We hypothesized that the spinal motoneurons innervating the soleus muscle would also atrophy and show adaptations in their metabolic properties following a period of unloading.
For 2 weeks, 10-week-old male Wistar rats were hindlimb suspended and the mean soma size and succinate dehydrogenase activity of motoneurons innervating the soleus muscle were examined. Retrograde labeling with nuclear yellow injected in the soleus muscle was used to identify the soleus motor pool. The mean fiber size and fiber type distribution from a central region of each soleus muscle was determined.
The soma size distribution, mean soma cross-sectional area and mean succinate dehydrogenase activity of motoneurons in the soleus motor pool were similar in control and hindlimb suspended rats. In contrast, compared to control the mean fiber size of each fiber type and the percentages of Type I fibers decreased and of Type IIa fibers increased in the soleus muscle following hindlimb suspension.
The results indicate that significant alterations in the phenotype and size of muscle fibers can occur without concomitant adaptations in the innervating motoneurons usually associated with motor unit types (i.e., soma size and oxidative capacity).
大鼠后肢的长期卸载会导致比目鱼肌萎缩，并使其代谢和机械特性发生变化，比目鱼肌是一种主要的慢肌，负责维持姿势，其特性逐渐向快肌转变。
我们假设，在一段时间的卸载后，支配比目鱼肌的脊髓运动神经元也会萎缩，并在代谢特性上表现出适应性变化。
将10周龄雄性Wistar大鼠后肢悬吊2周，然后检测支配比目鱼肌的运动神经元的平均胞体大小和琥珀酸脱氢酶活性。通过向比目鱼肌注射核黄进行逆行标记，以识别比目鱼肌运动神经元池。测定每块比目鱼肌中央区域的平均纤维大小和纤维类型分布。
对照组和后肢悬吊组大鼠比目鱼肌运动神经元池的胞体大小分布、平均胞体横截面积和平均琥珀酸脱氢酶活性相似。相比之下，后肢悬吊后，比目鱼肌中每种纤维类型的平均纤维大小以及I型纤维的百分比下降，IIa型纤维的百分比增加。
结果表明，肌肉纤维的表型和大小发生显著改变时，支配它们的运动神经元（通常与运动单位类型相关，即胞体大小和氧化能力）并不会随之发生适应性变化。
