Catecholamines and 5-hydroxytryptamine in nervous tissue of cephalopods.

1. Catecholamines and 5-hydroxytryptamine were measured fluorimetrically in nervous tissue of cephalopod molluscs.2. The only catecholamines found present in nervous tissue of Eledone, Octopus and Sepia were dopamine and noradrenaline. The highest concentrations were found in the optic lobes and in the superior buccal lobe. The concentrations of dopamine and noradrenaline were smaller in other regions of the nervous tissue taken.3. 5-Hydroxytryptamine was also found in most of the regions investigated. The highest concentration was found in the inferior buccal ganglia and in the optic lobes.4. The administration of reserpine produced a marked decrease in the concentration of catecholamines and 5-hydroxytryptamine in octopod nervous tissue.5. These findings suggest that dopamine, noradrenaline and 5-hydroxytryptamine may function as neurotransmitters in cephalopod molluscs.