Kwong W H, Gauthier G F
Department of Anatomy, University of Massachusetts Medical School, Worcester 01605.
Anat Rec. 1987 Dec;219(4):409-19. doi: 10.1002/ar.1092190412.
Functional changes that occur just before hatching in future fast muscles of the chicken are thought to be influenced by the pattern of innervation. We have compared the neuromuscular junctions of two fast muscles, the posterior latissimus dorsi (PLD) and the pectoralis, which differ in their myosin composition at 18 days in ovo. We have also presented new information on the neuromuscular junctions of the adult fast muscles and an adult slow muscle, the anterior latissimus dorsi (ALD). Both categories of adult muscles were heterogeneous, and there was little difference between endplates of the two fast muscles or between the fast and slow muscles. In contrast, there were significant structural differences between the two fast muscles during embryonic development. In early embryonic muscle fibers, which synthesize embryonic forms of myosin, individual motor endplates were contacted by multiple axon terminals. At 18 days in ovo, the majority of the neuromuscular junctions in the pectoralis continued to be multiterminal, whereas all but one of the terminals had been withdrawn from each endplate in the PLD. This single terminal had a unique form that distinguished it from the embryonic pectoralis and also from the two adult muscles. By 7 days after hatching, the neuromuscular junctions of both muscles had single terminals. They were different from the embryonic terminals, though not necessarily equivalent to adult terminals. The results show that multiple terminals persist at 18 days in ovo in the muscle that continues to express an embryonic myosin, but they have been withdrawn from the muscle that has lost this myosin. It is concluded, from combined data on the two muscles, that maturation of the neuromuscular junction during embryonic and late posthatch development is correlated with transitions in the myosin pattern and in contractile properties.
人们认为，鸡未来的快肌在孵化前发生的功能变化受神经支配模式的影响。我们比较了两块快肌，即背阔肌后部（PLD）和胸肌的神经肌肉接头，这两块肌肉在胚胎发育18天时肌球蛋白组成有所不同。我们还提供了关于成年快肌和一块成年慢肌，即背阔肌前部（ALD）神经肌肉接头的新信息。两类成年肌肉都是异质的，两块快肌的终板之间或快肌与慢肌的终板之间几乎没有差异。相比之下，在胚胎发育过程中，这两块快肌之间存在显著的结构差异。在合成胚胎型肌球蛋白的早期胚胎肌纤维中，单个运动终板与多个轴突终末接触。在胚胎发育18天时，胸肌中的大多数神经肌肉接头仍是多终末的，而PLD中每个终板除一个终末外，其余终末都已退缩。这个单一终末具有独特的形态，使其有别于胚胎期的胸肌以及两块成年肌肉。到孵化后7天时，两块肌肉的神经肌肉接头都只有单个终末。它们与胚胎期的终末不同，不过不一定等同于成年期的终末。结果表明，在胚胎发育18天时，继续表达胚胎型肌球蛋白的肌肉中存在多个终末，但在已失去这种肌球蛋白的肌肉中，这些终末已退缩。综合这两块肌肉的数据得出结论，胚胎期和孵化后期神经肌肉接头的成熟与肌球蛋白模式及收缩特性的转变相关。
