Single Sympathetic Varicosities and Their Receptor Clusters
The autonomic ground plexus of Hillarp1 consists of postganglionic nerves which terminate in systems of collateral branches each of which possesses in the order of one hundred varicosities.2 Single strings of varicosities of these collateral systems can be found on occasion at the surface of smooth muscles after their labelling by orthograde transport of rhodamine coupled to dextran into the varicosities and their subsequent identification with confocal microscopy.3 Labelling the synaptic vesicles in these varicosities in the vas deferens with fluorescent coupled antibodies to the vesicle proteoglycan SV2 shows that the vesicles are concentrated in a volume about one-third that of the varicosity and in close apposition to one of its membranes.4 The clump of synaptic vesicles apposes a site on the vesicle membrane that possesses a high concentration of syntaxin, necessary for vesicle docking.4 Each varicosity in a single string possesses vesicles, together with their associated proteins synaptobrevin and SNAP25, accumulated at a site which is defined by the high concentration of syntaxin, whether the string of varicosities occurs at the surface of the muscle or in its media.5 The observations described below are our most recent attempts to determine the properties of individual varicosites in Hillarp’s ground plexus, principally using the vas deferens as the experimental preparation.
KeywordsTransmitter Release Receptor Cluster Single String Nerve Varicosity Postganglionic Nerve
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