Klemm M F, Van Helden D F, Luff S E
Zoology Department, University of Melbourne, Parkville, Victoria, Australia.
J Comp Neurol. 1993 Aug 1;334(1):159-67. doi: 10.1002/cne.903340113.
This study reports on the detailed ultrastructure of sympathetic postganglionic varicose axon terminals on mesenteric veins leading from the ileum of the guinea pig and in particular the structural arrangement of the varicosities with venous smooth muscle cells. The response to nerve stimulation in veins has a long time course and it has been suggested that this reflects a wide separation between the site of transmitter release and the receptors on the effector cell membrane. The aim of this study was to determine the distance between individual sympathetic varicosities and smooth muscle cells in mesenteric veins. Fluorescent histochemical preparations of the sympathetic innervation of the different branches of mesenteric veins indicate the branching network of varicose axons around the vessel to be relatively dense. Electron micrographs show the innervation to be confined to the adventitia close to the medio-adventitial border and to be predominantly catecholaminergic. A serial section ultrastructural analysis of the relationship of the varicosities with the outer smooth muscle cells showed that almost all (98%) of the exposed axon varicosities in the adventitia formed neuromuscular junctions. Three-dimensional reconstructions from serial sections of individual varicosities have shown that the junctions have structural specialisations identical to neuromuscular junctions described on arterial vessels and similar to those found at skeletal neuromuscular junctions. The density of neuromuscular junctions on the veins was found to be similar to that on the corresponding artery in the same animal. We suggest that in veins, noradrenaline is released focally at neuromuscular junctions.
本研究报告了豚鼠回肠引出的肠系膜静脉上交感节后曲张轴突终末的详细超微结构，特别是曲张体与静脉平滑肌细胞的结构排列。静脉对神经刺激的反应具有较长的时程，有人认为这反映了递质释放部位与效应细胞膜上受体之间的广泛分离。本研究的目的是确定肠系膜静脉中单个交感曲张体与平滑肌细胞之间的距离。肠系膜静脉不同分支的交感神经支配的荧光组织化学制剂表明，血管周围曲张轴突的分支网络相对密集。电子显微镜照片显示，神经支配局限于靠近中膜外膜边界的外膜，且主要是儿茶酚胺能的。对曲张体与外平滑肌细胞关系的连续切片超微结构分析表明，外膜中几乎所有（98%）暴露的轴突曲张体都形成了神经肌肉接头。从单个曲张体的连续切片进行的三维重建表明，这些接头具有与动脉血管上描述的神经肌肉接头相同的结构特化，并且与骨骼肌神经肌肉接头处发现的结构特化相似。发现静脉上神经肌肉接头的密度与同一动物相应动脉上的密度相似。我们认为，在静脉中，去甲肾上腺素在神经肌肉接头处局部释放。
