Selective Demonstration of a Type of Synaptic Vesicle by Phosphotungstic Acid Staining

Fine structural analyses of nerve terminals in both the central and in the peripheral nervous systems have demonstrated the presence of synaptic vesicles, which were postulated to be the storage sites of neurotransmitters . Several different types of synaptic vesicles have been described (see ref . 6) . Electron-lucent vesices, 400-500 A in diameter, constitute the most commonly occurring type in central and in peripheral synapses . Because they are consistently found in cholinergic nerve terminals, these vesicles were postulated to constitute the site of acetylcholine storage, an assumption confirmed by isolation studies (8) . Granulated vesicles, 300-500 A in diameter, with an electronopaque core are characteristic of peripheral adrenergic terminals (7) . Combined pharmacological and electron microscopical studies have shown that these vesicles contain norepinephrine (NE) (19, 20) and also, in nerve endings of rat pineal gland, 5-hydroxytryptamine (5-HT) (16) . The presence of another type of vesicle, a larger one (800-1000 A in diameter) which possesses an internal content of variable density, has been also observed . These large granulated vesicles (LGV) occur in terminals which also contain electron-lucent or granulated vesicles, e.g . postganglionic sympathetic terminals, endings in the sphincter pupillae, preganglionic cholinergic fibers to sympathetic ganglia, preganglionic terminals supplying the adrenal medulla, parasympathetic ganglia, endings and neuronal perikarya of the central nervous system (CNS) of areas rich or poor in monoamines in both vertebrates and invertebrates, stumps of injured peripheral nerves or central tracts, etc . (for bibliography see ref. 12) . There is not yet general agreement concerning the significance of the LGV . When phosphotungstic acid is added to the absolute ethanol (E-PTA) during the dehydration of glutaraldehyde-fixed tissue, the dense cores of the LGV in the CNS seem to be specifically stained (1) . In order to determine the relationship between the LGV in peripheral nerve endings and those of CNS terminals, the reactivity of the former to E-PTA was studied . The possible participation of biogenic amines in the reaction was also analyzed .