Pharmacological Reviews, Vol 24, 245-254, Copyright © 1972 by the American Society for Pharmacology and Experimental Therapeutics

Axons of Sympathetic Neurons: Transport of Enzymes in Vivo and Properties of Axonal Sprouts in Vitro

¹ National Institute of Mental Health, Bethesda, Maryland

Enzymes involved in catecholamine synthesis are formed in the cell body and transported to the nerve terminals. DBH, which is present in the vesicles, is rapidly transported by a mechanism involving the neurotubules. The turnover of DBH is more rapid than that of TH.

Axonal damage or interference with integrity of the neurotubules results in diminished synthesis of catecholamine-forming enzymes with a switch to production of structural and membrane components. Levels of DBH and TH in the ganglia decline; however, uptake of NE increases, presumably as a consequence of increased membrane surface.

In vitro, axonal sprouts from cultured ganglia appear to have the properties of nerve endings almost as soon as they form. They avidly take up ³H-NE, and although they contain only large granular vesicles, stimulation induces release of the labeled catecholamine. Thus large granules are sufficient to support adrenergic function.

The granules may be carried directly to the nerve terminal by the neurotubules. When the nerve impulse arrives and the contents of the large granular vesicle are extruded, the residual membranes with adherent proteins may form the smaller granular vesicles concerned with synthesis and storage of the reserve transmitter.