Ultracytochemical identification of catecholamine-containing vesicles in the ligated sciatic nerve of the rat. Comparison with sympathetic nerve terminals.

Using the fixation procedure of Tranzer, three kinds of granular vesicles were identified in certain unmyelinated fibres of rat sciatic nerves proximal to a ligature: (1) small vesicles (SGV:30-60 nm in diameter), (2) large vesicles (LGV:60-100 nm in diameter), and (3) large elongated vesicles (LEV:60-100 nm in diameter). A comparative study concerning the distribution of these granular vesicles was carried out using a cytopharmacological method (reserpine) and employing different fixatives (aldehydes + OSO4, or OSO4 alone) in periarterial nerve plexus of the femoral artery, vas deferens and the pineal organ. Use of Tranzer's method allows preservation in almost all granular vesicles of a strongly electron-dense core, while with the other fixatives mainly small, eccentric dense cores occur in the vesicles. Two main features were observed in ligated sciatic nerves: (i) a clear increase in the number of LGV, and (ii) the presence of LEV, considered as a variety of LGV rather than a new population of granular vesicles. Reserpine caused the cores of SGV to disappear almost completely, while LGV and LEV remained only partly depleted. The original method combining Tranzer's fixation procedure with radioautography revealed radioautographic labelling only in the unmyelinated fibres of ligated sciatic nerves and mainly superimposed over SGV, LGV and LEV. It is suggested that (i) SGV, LGV and also LEV represent possible storage sites of catecholamines, and (ii) a local morphogenesis of SGV from the large vesicles occurs in ligated sympathetic nerve fibres.