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

神经末梢是生长或形成芽的部位，也是释放递质的部位。因此，神经末梢有望具有不同于神经纤维的离子机制。然而，由于神经末梢的微小结构，离子机制的分析是困难的。本研究试图用松弛膜片钳技术记录运动神经末梢的局部离子电流，并通过形成终末芽来扩张神经末梢。在本研究过程中，偶然发现降钙素基因相关肽(CGRP)抑制运动神经末梢发芽的形成。因此，这项研究进一步扩展到分析神经肌肉接头的可塑性变化的机制。这些实验是在成年大鼠身上进行的。在Nomarski光学视觉控制下，将微电极固定在…延伸部运动神经末梢的表面从后肢解剖出更多或更多的趾肌。对神经刺激的反应，运动神经末梢表现为河豚毒素敏感的内向钠电流和外向钾电流。当钾电流被阻断时，内向钙电流也被揭开。当坐骨神经慢性传导阻滞在运动神经末梢形成芽时，在末梢也检测到类似的内向钠电流。顶芽的传导速度约为0.2m/s。用降钙素基因相关肽治疗坐骨神经传导阻滞10天后，瘫痪的后肢肌肉所期望的末梢芽的形成几乎完全被抑制。据我们所知，CGRP是第一个被发现抑制顶芽形成的物质。在过去，瘫痪肌肉中递质释放的增加被认为是由于末端芽的形成。然而，CGRP不能阻止瘫痪肌肉中转氨酶释放的增加，而肌肉中末端芽的形成被阻止。结论：在慢性麻痹肌肉中观察到递质释放的增加和末端芽的形成是两个独立的过程。较少

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