Kidokoro Y, Yeh E
Proc Natl Acad Sci U S A. 1982 Nov;79(21):6727-31. doi: 10.1073/pnas.79.21.6727.
The excellent visibility of cultured cells allows the early events during formation of the neuromuscular junction to be suitably studied. It has been shown in various culture systems that synaptic transmission occurs early after nerve-muscle contact. Early synaptic potentials are small in amplitude and slow in time course reflecting a low acetylcholine receptor density at the site of nerve contact. Acetylcholine receptors accumulate later at the contact region. We have examined initial synaptic transmission at the growth cone-muscle contact in Xenopus nerve-muscle cultures. The approaching growth cone was observed under a phase-contrast microscope while the membrane potential of its target muscle cell was continuously monitored by using an intracellular microelectrode. The innervating neuron was stimulated extracellularly at the cell body. No synaptic potential was evoked when the growth cone was contacting the muscle only at the tip of filopodia. However, as soon as the main portion of the growth cone contacted the muscle membrane, nerve-evoked synaptic potentials were detected after stimulation of the nerve. This immediate appearance of synaptic potentials raises the possibility that acetylcholine could be released at the growth cone even prior to contact with muscle cells. As the area of contact enlarged during the observation period the amplitude of end-plate potentials also increased. Spontaneous synaptic potentials (miniature end-plate potentials) were rarely observed in these early growth cone-muscle contacts. Although there were several inherent difficulties, quantal analysis of the end-plate potentials was attempted by using binomial statistics. This analysis suggests that nerve-evoked transmitter release at the growth cone occurs in a quantal fashion.
培养细胞具有出色的可视性，这使得神经肌肉接头形成过程中的早期事件能够得到恰当的研究。在各种培养系统中已经表明，神经与肌肉接触后早期就会发生突触传递。早期的突触电位幅度小且时程慢，这反映出神经接触部位的乙酰胆碱受体密度较低。乙酰胆碱受体随后会在接触区域聚集。我们已经在非洲爪蟾神经肌肉培养物中研究了生长锥与肌肉接触处的初始突触传递。在相差显微镜下观察接近的生长锥，同时使用细胞内微电极持续监测其靶肌肉细胞的膜电位。在细胞体处对支配神经元进行细胞外刺激。当生长锥仅通过丝状伪足尖端与肌肉接触时，不会诱发突触电位。然而，一旦生长锥的主要部分接触到肌肉膜，在刺激神经后就会检测到神经诱发的突触电位。突触电位的这种即时出现增加了一种可能性，即乙酰胆碱甚至可能在与肌肉细胞接触之前就在生长锥处释放。在观察期内，随着接触面积的扩大，终板电位的幅度也增加。在这些早期的生长锥与肌肉接触中很少观察到自发突触电位（微小终板电位）。尽管存在一些固有的困难，但仍尝试使用二项式统计对终板电位进行量子分析。该分析表明，生长锥处神经诱发的递质释放是以量子方式发生的。
