Electron-dense Particle in Cholinergic Synaptic Vesicles

Abstract

SINCE the initial descriptions of synaptic vesicles^1,2 and their hypothesized relationship with the secretory and electrophysiological phenomena associated with synaptic transmission³, many workers have attempted to distinguish different types of vesicles in different nerve terminals. Known adrenergic terminals contain vesicles approximately 400 and 1000 Å in diameter, both of which may have large dense, granular cores⁴. Similar vesicles of diameter 1400 Å have been described in a mammalian sympathetic interneurone⁵ and are thought to contain noradrenaline⁶. Vesicles of diameter 1400 Å with a large granular core of low electron density have been described in nerve terminals in Auerbach's plexus; these are thought to release ATP on stimulation⁷. Electron micrographs of known cholinergic nerve terminals at mammalian neuromuscular⁸ and torpedine neuroelectroplaque⁹ junctions show large populations of synaptic vesicles having diameters of about 400 and 800 Å respectively but with no evidence of a core structure.