Development of the technique for recording ionic currents at motor nerve terminals

神经末梢是生长或芽形成的部位，也是递质释放的部位。因此，神经末梢可能具有与神经纤维不同的离子机制。然而，由于神经末梢的微小结构，离子机制的分析是困难的。本研究尝试用松片钳技术记录运动神经末梢的局部离子电流，并通过形成末梢芽来扩展神经末梢。在研究过程中，偶然发现运动神经末梢芽的形成受到降钙素基因相关肽（CGRP）的抑制。因此，本研究进一步扩展到分析神经肌肉连接处可塑性改变的机制。实验是在大鼠身上进行的。在诺玛斯基光学系统的视觉控制下，将微电极牢固地放置在运动神经末梢的表面，从后肢解剖更多的指趾肌。在神经刺激下，运动神经末端表现出对河豚毒素敏感的向内钠电流和向外钾电流。当钾电流被阻断时，底层向内的钙电流也被打开。当坐骨神经慢性传导阻滞在运动神经末梢形成芽时，在末梢芽中也检测到类似的向内钠电流。顶芽处的传导速度约为0.2 m/s。在坐骨神经传导阻滞10 d期间，CGRP每天给药，几乎完全抑制了瘫痪后肢肌肉中预期的末梢芽的形成。据我们所知，CGRP是第一个被确定可以抑制末端芽形成的物质。过去，麻痹肌肉中递质释放的增加被认为是由于末梢芽的形成。然而，CGRP并不能阻止瘫痪肌肉中递质释放的增加，而肌肉中末端芽的形成被阻断。由此可见，在慢性瘫痪肌肉中观察到的递质释放增加和末端芽的形成是两个独立的过程。少

Nerve terminals are the site of growth or the formation of sprouts as well as the site of transmitter release. Therefore, nerve terminals are expected to have different ionic mechanisms from those for nerve fibers. However, the analysis of ionic mechanisms is difficult at nerve terminals because of their minute structure. In the present study, attempts were made to record local ionic currents from motor nerve terminals by the technique of loose-patch clamp and to expand the nerve terminal by the formation of terminal sprouts. During the course of this study, it was accidentally found that the formation of sprouts in motor nerve terminals is inhibited by calcitonin gene-related peptide (CGRP). Consequently, the study was further extended to analyze the mechanisms opf plastic changes at neuromuscular junctions. The experiments were made in abult rats. Under the visual control with Nomarski's optics, a microelectrode was firmyl placed on the surface of a motor nerve terminal in the extens … More or digitorum muscle dissected from the hind limb. In response to nerve stimulation, the motor nerve terminal showed a tetrodotoxin-sensitive inward sodium current followed by an outward potassium current. When the potassium current was blocked, the umderlying inward calcium current was also unmasked. When sprouts were formed in motor nerve terminals by chronic conduction block of the sciatic nerve, a similar inward sodium current was also detected in the terminal sprouts. The conduction velocity at terminal sprouts was about 0.2 m/sec. When CGRP was daily applied to the snimal curing the 10-day-period of conduction block of the sciatic nerve, the formation of terminal sprouts expected in the paralyzed hind limb muscle was almost completely inhibited. To our knowledge, CGRP is the first substance which is identified to inhibit the formation of terminal sprouts. In the past, an increase of transmitter release in the paralyzed muscle has been assumed to be due to the formation of terminal sprouts. However,CGRP did not prevent increased transnitter release in the paralyzed muscle, while the formation of terminal sprouts was blocked in the muscle. It is concluded that an increase in transmitter release and the formation of terminal sprouts observed in chronically paralyzed muscle are two independent processes. Less