Alterations in neuromuscular junction morphology during fast-to-slow transformation of rabbit skeletal muscles.
Alterations in neuromuscular junction morphology during fast-to-slow transformation of rabbit skeletal muscles.
复制标题
兔骨骼肌从快到慢的转变过程中神经肌肉接头形态的变化。
DOI：
10.1007/bf02284805
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Reiser,PJ
中科院分区：
文献类型：
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作者：
Somasekhar,T;Nordlander,RH;Reiser,PJ
慢性低频刺激运动神经导致肌纤维表型由快肌纤维向慢肌纤维转变。我们对刺激3周后正常快速收缩肌、胫骨前肌和指长伸肌神经肌肉连接处的光镜和电镜结构进行了观察，以确定在纤维型转化过程中突触结构是否也发生了改变。用罗丹明偶联α-班加罗毒素观察受刺激和未受刺激（对照）的胫骨前肌、指长伸肌和未受刺激的慢抽搐比目鱼肌的神经肌肉连接。对神经肌肉连接点的视频光显微图像进行数字化处理，以便量化它们的表面积、周长、长度和宽度。三周的刺激导致肌纤维缩短的最大速度降低，快速肌肉的线粒体体积增加，证明了刺激方案在改变肌纤维表型方面的有效性。控制性胫前肌和指长伸肌神经肌肉连接点薄、致密、连续，分支形式复杂。相比之下，慢抽动比目鱼肌较厚且不连续。控制性胫前肌和指长伸肌的神经肌肉连接点比比目鱼肌大。刺激三周后，胫前肌和指长伸肌神经肌肉连接的大小明显减小，表现为神经肌肉连接的表面积、长度和宽度明显减小。这些连接的电子显微镜显示，在受刺激的肌肉中，次级突触后折叠的间隔更紧密。此外，受刺激肌肉的轴突末端似乎比对照组含有更密集的突触囊泡和线粒体。神经肌肉连接处尺寸的减小可以部分解释为肌纤维萎缩。然而，两种肌肉中神经肌肉连接处大小的减少比例大于肌纤维直径的减少，这表明除纤维萎缩外的其他因素可能导致受刺激肌肉中神经肌肉连接处大小的减少。受刺激的胫前肌和指长伸肌的神经肌肉连接表现出正常比目鱼神经肌肉连接的一些特征，表明结构适应与改变的肌纤维表型一致。另一方面，受刺激3周的胫前肌和指长伸肌神经肌肉连接及其突触分支与未受刺激的对照组一样薄且连续，这表明神经肌肉连接向慢肌形态特征的转变只是部分的。这些结果表明，冲动活动模式的改变导致成年兔骨骼肌突触重构。
Chronic low frequency stimulation of motor nerves results in transformation of muscle fibre phenotype from fast- to slow-twitch. We examined the light and electron microscopic structure of neuromuscular junctions in normally fast twitch muscles, tibialis anterior and extensor digitorum longus of rabbit after 3 weeks of stimulation to determine whether synaptic structure is also modified during fibre type transformation. Neuromuscular junctions of stimulated and unstimulated (control) tibialis anterior and extensor digitorum longus muscles and unstimulated slow twitch soleus muscle were visualized with rhodamine-conjugated α-bungarotoxin. Video light microscopic images of neuromuscular junctions were digitized to allow quantification of their surface areas, perimeters, lengths and widths. Three weeks of stimulation resulted in a decrease in the maximal velocity of muscle fibre shortening and augmentation of mitochondrial volume in fast muscles, demonstrating the efficacy of the stimulation protocol employed in altering muscle fibre phenotype. Neuromuscular junctions of control tibialis anterior and extensor digitorum longus are thin, compact, and continuous, with complex branching patterns. In contrast, those of slow-twitch soleus are thicker and discontinuous. Neuromuscular junctions in control tibialis anterior and extensor digitorum longus are larger than those in soleus. Three weeks of stimulation causes a marked decrease in the size of neuromuscular junctions in tibialis anterior and extensor digitorum longus, as reflected in the significant reduction in neuromuscular junction surface area, length and width. Electron microscopy of these junctions suggests that secondary postsynaptic folds in stimulated muscles are more closely spaced. Also, axon terminals of stimulated muscles appear to contain more densely packed synaptic vesicles and mitochondria than controls. Decreases in neuromuscular junction dimensions can be partly explained by muscle fibre atrophy. However, the decrease in neuromuscular junction size is proportionately greater than that of muscle fibre diameter in both muscles, indicating that factors other than fibre atrophy may contribute to the reduced neuromuscular junction size in stimulated muscles. Neuromuscular junctions of stimulated tibialis anterior and extensor digitorum longus muscles exhibit some features characteristic of normal soleus neuromuscular junctions, indicating structural adaptations consistent with the altered muscle fibre phenotype. On the other hand, neuromuscular junctions of 3 week stimulated tibialis anterior and extensor digitorum longus and their synaptic branches remain as thin and continuous as those of unstimulated controls, suggesting that the transformation of neuromuscular junctions towards a morphology characteristic of slow muscle, is only partial. These results demonstrate that an altered pattern of impulse activity causes significant synaptic remodelling in adult rabbit skeletal muscles.