Chow I, Cohen M W
J Physiol. 1983 Jun;339:553-71. doi: 10.1113/jphysiol.1983.sp014733.
The acquisition and distribution of nerve fibres and of acetylcholine (ACh) receptors were examined in the myotomes of Xenopus laevis during normal development. This muscle is well-suited for investigating temporal relationships during neuromuscular synaptogenesis because the age of the Xenopus embryo at the onset of innervation can be assessed with an accuracy of about one hour. Myotomal nerve fibres were visualized after staining them with nitroblue tetrazolium and ACh receptors were examined after exposure to alpha-bungarotoxin labelled with 125I or fluorescent dye. Nerve fibres were seen in the myotomes of some embryos as early as stage 19 (20 . 75 hr) and in virtually all embryos by stage 24 (26 . 25 hr). From the outset they were located mainly at the ends of the myotomes, but some myotomes also exhibited nerve fibres in more central regions. ACh receptors were already present in myotomes by stage 19 (20 . 75 hr) and initially had a widespread, uniform distribution. The density of extrajunctional ACh receptors increased until stage 36 (50 hr) and then declined less than 3-fold over the next 10 days of development. Discrete patches of high ACh receptor density began to appear at the ends of the myotomes at stage 22 (24 hr) and were seen in almost all embryos by stage 26 (29 . 5 hr). ACh receptor patches were also seen in central regions of some myotomes and these were usually aligned in patterns which resembled the course of nerve fibres. The present findings suggest that myotomal muscle cells in Xenopus embryos begin to acquire ACh receptors shortly before the arrival of nerve fibres and that discrete patches of ACh receptors begin to form at presumptive synaptic sites on the average about 3 hr after the arrival of the nerve fibres. The latter delay is considerably shorter than that in developing rat muscle. The temporal and spatial relationships between nerve fibres and the development of ACh receptor patches in Xenopus myotomes in vivo are consistent with findings in Xenopus cell cultures which indicate that nerve fibres can rapidly induce ACh receptor localization at sites of nerve--muscle contact.
在非洲爪蟾正常发育过程中，对其肌节中神经纤维和乙酰胆碱（ACh）受体的获取与分布进行了研究。这种肌肉非常适合用于研究神经肌肉突触形成过程中的时间关系，因为在神经支配开始时，非洲爪蟾胚胎的年龄可以精确到大约1小时来评估。用硝基蓝四氮唑对肌节神经纤维进行染色后可观察到神经纤维，用125I标记的α - 银环蛇毒素或荧光染料处理后可检测ACh受体。早在第19期（20.75小时），在一些胚胎的肌节中就可见神经纤维，到第24期（26.25小时）时，几乎所有胚胎的肌节中都能看到神经纤维。从一开始，它们主要位于肌节的末端，但一些肌节在更中央的区域也有神经纤维。早在第19期（20.75小时），ACh受体就已存在于肌节中，最初分布广泛且均匀。接头外ACh受体的密度一直增加到第36期（50小时），然后在接下来的10天发育过程中下降不到3倍。在第22期（24小时），在肌节末端开始出现离散的高ACh受体密度斑块，到第26期（29.5小时）时，几乎在所有胚胎中都能看到。在一些肌节的中央区域也可见ACh受体斑块，并且这些斑块通常排列成类似于神经纤维走向的模式。目前的研究结果表明，非洲爪蟾胚胎中的肌节肌细胞在神经纤维到达前不久就开始获取ACh受体，并且在神经纤维到达后平均约3小时，在假定的突触部位开始形成离散的ACh受体斑块。后一种延迟比发育中的大鼠肌肉中的延迟要短得多。非洲爪蟾体内肌节中神经纤维与ACh受体斑块发育之间的时间和空间关系与非洲爪蟾细胞培养中的发现一致，这些发现表明神经纤维可以迅速诱导ACh受体在神经 - 肌肉接触部位定位。
