Reaction chain in feeding behavior ofHydra: Different specificities of three feeding responses

Summary Hydra shows three types of feeding responses to chemostimulants. They are writhing of tentacles, ball-formation of tentacles and mouth-opening.The chemostimulants can be divided into 3 classes on the basis of specificities of the responses they elicit. The first class includes tripeptides glutathione (reduced form) and S-methyl-glutathione. These chemicals evoke all three types of responses. The second class contains dipeptides-glutamylcysteine,-glutamyl-S-methyl-cysteine and-glutamyl--amino butyrate and amino acidl-arginine. These chemicals evoke mouth-opening and writhing of tentacles, but not ball-formation. The third group contains amino acidsl-leucine,l-tryptophan andl-lysine. These chemicals evoke writhing and ball-formation of tentacles but not moutho-pening. These observations indicate the existence of different specificities of the three feeding responses inHydra to chemostimulants.In addition to evoking tentacular movements, the amino acids of the third group also have the capacity to competitively inhibit the mouthopening response induced by S-methyl-glutathione. Evidence exists which suggests thatHydra has different receptors for those amino acids which inhibit mouth-opening and for those which evoke the tentacular movements.Tentacles cut off animals show the typical writhing response to S-methyl-glutathione. The sensitivity of this response is similar to the response of tentacles on intact animals. This suggests that the entire set of receptor-effector system for writhing response is present in individual tentacles. The present results suggest that each feeding response is executed by a different receptor-effector system.Abbreviations GSH reduced glutathione - GSM S-methyl-glutathione - -Glu-CysH -glutamyl-cysteine - -Glu-CysMe -glutamyl-S-methyl-cysteine - -Glu-Abu -glutamyl--aminobutyr-ate