Axoplasmic transport of 14C-noradrenaline and protein in splenic nerves

MOST of the noradrenaline in postganglionic sympathetic neurones is bound within amine granules concentrated in the axon terminals1. These structures, which contain protein, are involved in the synthesis, storage and release of noradrenaline2. When a constriction is placed on the nerve trunk, noradrenaline accumulates proximal to it. This has been ascribed to the arrested distal transport of the granules from their site of manufacture in the cell body3, a view which is supported by electron microscope evidence of a corresponding accumulation of granular vesicles4. Their flow rate in cat sympathetic nerves of 10 mm/h, however, derived from the rate of noradrenaline accumulation3, is about 200 times that obtained for protein movement in somatic nerves (1 to 5 mm/day)5. Because the calculation assumes that no noradrenaline is synthesized, lost to or taken up from the circulation in the movement of the storage granules down the axon and at the site of constriction, an alternative method, labelling both noradrenaline and protein with isotopes, was used on the cat splenic nerves.