Two types of surface amine receptors modulating the feeding response inHydra japonica: the depressing action of dopamine and related amines

The effect of amines on the feeding response of Hydra japonica was determined using the tentacle ball formation assay. Many aliphatic and aromatic amines depressed the response immediately upon addition to the bathing medium at final concentrations ranging from 1 nmol/l to 100 μmol/l. Examining the depressing effect of various amines, we concluded that two kinds of amine receptors were located on the surface of Hydra . One perceived dopamine and D-noradrenaline, and depressed only the response elicited by weak stimuli. Dopamine depressed the response at 1 nmol/l. D,L-Propranolol was a competitive antagonist against this receptor. The other perceived tyramine and most of the amines examined, and depressed the response elicited by both weak and strong stimuli. Tyramine depressed the response at 1 μmol/l. D,L-Propranolol did not block its action. After the animals were treated with dibenamine, both dopamine and tyramine became ineffective in depressing the response without influence on the response of the animal elicited by S-methylglutathione.