Roy Roland R, Matsumoto Akiko, Zhong Hui, Ishihara Akihiko, Edgerton V Reggie
Brain Research Institute, 1320 Gonda Neuroscience and Genetics Building, University of California, Los Angeles, Los Angeles, California 90095-1761, USA.
Muscle Nerve. 2007 Aug;36(2):234-41. doi: 10.1002/mus.20810.
The chronic level of neuromuscular activity, that is, activation and loading, strongly influences the morphological, metabolic, phenotypic, and physiological properties of skeletal muscles. The effects on the innervating motoneurons, however, are less established. We determined and compared the effects of 30 days of decreased activity (induced by a complete mid-thoracic spinal cord transection, ST) or near inactivity (induced by spinal cord isolation, SI) on the soma size and succinate dehydrogenase (SDH) activity of motoneurons innervating a predominantly slow ankle extensor (soleus) and a predominantly fast ankle flexor (tibialis anterior) muscle of adult rats. Soleus and tibialis anterior motoneuron pools were labeled retrogradely using nuclear yellow. The alpha- and gamma-motoneurons were classified based on soma size. Mean number of labeled motoneurons, and mean soma size and SDH activity for both alpha- and gamma-motoneurons were similar in control, ST, and SI rats. Compared to previous reports showing significant decreases in muscle fiber size and adaptations toward a "faster" metabolic profile following ST and SI, the results indicate that, unlike the muscles they innervate, the motoneurons are relatively unresponsive to chronic reductions in neuromuscular activity. The implication of these results is that mean size and SDH activity are independent of the number of action potentials generated by both alpha- and gamma-motoneurons and that even the absence of afferent input to the spinal cord has no influence on size and oxidative metabolic potential of the motoneuron soma.
神经肌肉活动的慢性水平，即激活和负荷，对骨骼肌的形态、代谢、表型和生理特性有强烈影响。然而，对支配运动神经元的影响尚不明确。我们测定并比较了30天活动减少（由胸段脊髓完全横断，即ST诱导）或几乎不活动（由脊髓隔离，即SI诱导）对成年大鼠支配主要为慢肌的踝关节伸肌（比目鱼肌）和主要为快肌的踝关节屈肌（胫骨前肌）的运动神经元的胞体大小和琥珀酸脱氢酶（SDH）活性的影响。使用核黄逆行标记比目鱼肌和胫骨前肌运动神经元池。根据胞体大小对α-和γ-运动神经元进行分类。在对照、ST和SI大鼠中，α-和γ-运动神经元的标记运动神经元平均数量、平均胞体大小和SDH活性相似。与之前报道的ST和SI后肌纤维大小显著减小以及向“更快”代谢特征转变的结果相比，这些结果表明，与它们所支配的肌肉不同，运动神经元对神经肌肉活动的慢性减少相对不敏感。这些结果的意义在于，平均大小和SDH活性与α-和γ-运动神经元产生的动作电位数量无关，甚至脊髓传入输入的缺失对运动神经元胞体的大小和氧化代谢潜能也没有影响。
