Nakao T
J Comp Neurol. 1976 Jan 1;165(1):1-15. doi: 10.1002/cne.901650102.
The neuromuscular junction in the myotomes of larval and adult lampreys, Lampetra japonica, was studied with the electron microscope. In larval lampreys of 26 days after artificial insemination, the myotome consists of triangular lamellae of muscle cell with their bases laterally and apexes medially oriented and placed one on the other. The lateral aspect of the myotome is covered by a layer of flattened cell, and the other aspect is covered by an external lamina which does not extend into the intercellular space between adjacent cells within a myotome. A bundle of thin axons was found in a depression at the middle of medial edge (apex) of each muscle lamella of the myotome and neuromuscular junction was formed here. No nerve endings were found at the myoseptal ends or at the lateral borders of the muscle lamellae. Enlarged axon terminals contained numerous clear vesicles with a few cored vesicles, mitochondria and neurofilaments. The presynaptic axolemma was separated from the postsynaptic sarcolemma by an interspace (50-55 mmu wide) with an interposed external lamina. In the trunk musculature of adult lampreys, nerve endings were found on the surface of the parietal fibers whereas they were seen on both the myoseptal ends near the myotendinous junction along the medial border of each central fiber. Thickening and enhancement in the electron density and accumulation of filamentous material on the sarcoplasmic surface of the postsynaptic sarcolemma were noted in both the larval and adult lampreys. Any other specific alterations were not found on both the pre- and postsynaptic membrane in the neuromuscular junctions of larval and adult lampreys. A brief comment was made on the relationship in development of the characteristic muscle units and patterns of the motor innervation in the larval and adult lampreys. The significance of the neuromuscular junction in the very young larvae reported here was also discussed in respect to the evolution of the neuromuscular junction, particularly in lower chordates, and it was presumed to be the most primitive pattern of innervation in the vertebrate skeletal muscle.
利用电子显微镜对日本七鳃鳗幼体和成体肌节中的神经肌肉接头进行了研究。在人工授精后26天的幼体七鳃鳗中，肌节由肌肉细胞的三角形薄片组成，其基部朝外侧，顶点朝内侧，相互叠放。肌节的外侧被一层扁平细胞覆盖，另一侧被一层基膜覆盖，该基膜不延伸到肌节内相邻细胞之间的细胞间隙。在肌节每个肌肉薄片内侧边缘（顶点）中部的凹陷处发现一束细轴突，并在此形成神经肌肉接头。在肌隔末端或肌肉薄片的外侧边缘未发现神经末梢。扩大的轴突终末含有许多清亮小泡、少数有芯小泡、线粒体和神经丝。突触前轴膜与突触后肌膜之间有一个间隙（宽50 - 55纳米），间隙中有一层基膜。在成体七鳃鳗的躯干肌肉组织中，在体壁纤维表面发现神经末梢，而在每个中央纤维内侧边缘靠近肌腱连接处的肌隔末端均可见到神经末梢。在幼体和成体七鳃鳗中，均观察到突触后肌膜肌浆表面电子密度增厚增强以及丝状物质的积累。在幼体和成体七鳃鳗的神经肌肉接头的突触前膜和突触后膜上均未发现其他特异性改变。对幼体和成体七鳃鳗中特征性肌肉单位的发育与运动神经支配模式之间的关系进行了简要评论。本文还就神经肌肉接头的进化，特别是在低等脊索动物中的进化，讨论了这里报道的极幼龄幼虫中神经肌肉接头的意义，并推测其为脊椎动物骨骼肌中最原始的神经支配模式。
