The effects of iproniazid and reserpine on the accumulation of granular vesicles and noradrenaline in constricted adrenergic nerves

Axonal transport of adrenaline, noradrenaline and phenylethanolamine-N-methyl transferase (PNMT) in sympathetic neurons of the cod, Gadus morhua

The axonal transport of adrenaline, noradrenaline and phenylethanolamine-N-methyl transferase (PNMT) has been studied in vivo in sympathetic neurons of the splanchnic nerve in the cod, Gadus morhua. Adrenaline and noradrenaline are transported at a mean axonal transport rate of 16 mm/day. After correction for a non-mobile fraction of adrenaline and noradrenaline, which does not contribute to the amine accumulation proximal to a ligature, a maximal rate of transport was calculated to about 45 mm/day for both amines. The increased level of catecholamines in front of a ligature could be depleted by reserpine treatment, which strongly suggests that both amines are stored in granules. PNMT is transported at a slow rate of 2 mm/day. The subcellular distribution of the cod PNMT was exclusively non-particular. The cod PNMT was further characterized by studying substrate specificity, temperature and pH optima. It is concluded that adrenaline and noradrenaline, stored in granules, are transported in a proximo-distal direction at a high rate compared to PNMT.

The effect of tetrabenazine on the accumulation of noradrenaline in constricted postganglionic sympathetic nerves in vitro

The accumulation of noradrenaline proximal to a constriction applied to cat hypogastric nerves in vitro has been studied in preparations treated with tetrabenazine. The accumulation of amine was almost completely abolished by the drug. Evidence is presented which suggests that tetrabenazine exerts a direct noradrenaline-depleting effect on the intraneuronal storage vesicles. Recovery of noradrenaline levels after the removal of the drug was rapid and was effected by the biosynthesis of new noradrenaline within the axon.

Two populations or granular vesicles in constricted post-ganglionic sympathetic nerves

1. A comparative study has been made of the effects of different fixatives on the ultrastructural appearance of granular vesicles accumulated against a constriction in cat hypogastric nerves. 2. After fixation in either osmium tetroxide or in glutaraldehyde followed by post-osmication accumulations of large granular vesicles (65-90 nm in diameter) were observed in profiles of swollen axons. 3. Fixation in acrolein and sodium dichromate revealed a second population of small granular vesicles (mostly 30-50 nm in diameter) in addition to the large vesicles seen after the other fixatives. 4. In reserpinized cats the small granular vesicles were absent. The large granular vesicles were much less numerous, irrespective of the fixative used. 5. It is suggested that either the small vesicles occur in normal noradrenergic axons but are only revealed by catecholamine-sensitive fixatives or they occur as a result of constricting the nerve trunk. Evidence for and against these possibilities is discussed.

Further evidence for the involvement of microtubules in the intra-axonal movement of noradrenaline storage granules

1. Constricted cat hypogastric nerve/inferior mesenteric ganglion preparations maintained in vitro for 48 hr have been used to study the effects of different concentrations of colchicine on axonal microtubules and on the proximo-distal movement of catecholamine containing dense-cored vesicles in non-myelinated axons.2. In low concentrations (0.03-0.3 mug/ml.), colchicine had no effect on the number of microtubules per axon and did not diminish the amount of noradrenaline accumulating proximal to the constriction.3. Higher concentrations of colchicine (1.0-10 mug/ml.) produced a dramatic reduction in the number of microtubules per axon. This was associated with marked reductions in the number of dense-cored vesicles and the amount of noradrenaline accumulating above the constriction.4. There was some morphological evidence for a structural relationship between dense-cored vesicles and microtubules.5. These results further support the view that axonal microtubules are involved in the relatively fast proximo-distal transport of noradrenaline containing dense-cored vesicles in non-myelinated sympathetic axons.