Axoplasmic flow of adrenaline and monoamine oxidase in amphibian sympathetic nerves

Summary The accumulation of both A and MAO proximal to a ligature on toad spinal nerves has been shown to occur at a slower rate than in mammals. As in mammals, there are two components of axonal transport in amphibian nerves, with the accumulation of A reaching a peak at between 4 and 7 days (cf. 2–4 days for NA in mammals), while MAO accumulation does not reach its maximum before 9 days (cf. 7 days in mammals). No accumulation occurs after sympathectomy, providing evidence for localization of MAO within amphibian sympathetic adrenergic nerves. Distal accumulation of MAO occurs in toad sympathetic nerves; this has not been reported to occur in mammalian nerves. Distal accumulation reaches a peak at 2–4 days, which suggests either a fast retrograde flow of MAO or that induction of MAO is occurring. These results are discussed in relation to differences between mammalian and amphibian sympathetic nerves and to the events occurring following ligation of these nerves.We wish to thank Judy Lenk, Vivienne Einhorn and Barbara Peachey for their assistance with the initial MAO histochemical work. This work was supported by grants from the National Heart Foundation of Australia and the Australian Research Grants Committee.