Monoamine transport in theOctopus posterior salivary gland nerves

Summary Noradrenaline (NA) and 5-hydroxytryptamine (5-HT) accumulated on the proximal side of a ligature to the posterior salivary gland (PSG) nerves in the octopus PSG duct. The NA concentration continued to increase proximally up to 18 days after ligation when a level of 59 g/g was reached compared with 12 g/g distally and 16–18 g/g for the corresponding portions of the normal duct. The concentration of 5-HT after the same period was 8.5 g/g proximally and 0.7 g/g distally compared to 4–7 g/g for normal duct. Dopamine (DM) was undetectable either after ligation or in the non-ligated duct. Accumulations of dense-core synaptic vesicles were observed by electron microscopy in some of the axons on both sides of the ligature.The NA concentration in the gland shows a decrease 6–8 days post-ligation and by 16–18 days had fallen to 50% of the normal value. No change in the DM or 5-HT concentrations had occurred by this time. When the nerves had been ligated for 40 days the 5-HT level in the gland had also decreased but the DM concentration was comparable to control values. It is concluded that NA is the predominant aminergic neurotransmitter in the PSG nerves and that its transport from the brain to the gland is a continuous process.Ligating or cutting the PSG duct caused a decrease in diameter of the distal nerve bundles but many axons did not degenerate even after 40 days ligation. The continued existence of some of the axons may explain the slow depletion of monoamines from the gland. Morphological changes in the secretory cells of the glandular tubules were observed by light microscopy 40 days after interruption of the nerve supply. It is suggested that the PSG nerves are required for the maintenance of the glandular tubules.