Behavioral responses of the brittle star Ophiura ophiura to chemical stimuli during adaptation of amino acid chemoreceptors

Abstract

Parts of the feeding behavior, the orienting movements and the ‘walking’ behavior pattern in the brittle star Ophiura ophiura are released by several low-molecular-weight compounds. The behavioral responses of this animal were adapted to 10−4 molar concentrations of the following single stimulatory compounds: L(+;)lactic acid, glycine, sarcosine, L-alanine, L-cysteine, L-proline, L-valine, L-leucine, L-arginine and acetylcholine iodide. Complete adaptation of the behavioral response for the entire experimental group of animals occurred for most chemicals within the fifth to the ninth minute after the introduction of the adapting stimulus; however, for acetylcholine iodide, the time to behavioral adaptation was up to 15 min. The same ten and several other compounds were tested during each of the adaptations. Test concentrations were calculated to be below 3 × 10−5 molar at the animals' arms. Narrowly-tuned receptor sites were indicated for L-valine, L-leucine, L-arginine and acetylcholine iodide since behavioral responses to these chemicals were not crossadapted by any of the other amino acid stimuli tested. The ‘walking’ responses to L-proline, L-cysteine and L-alanine, which were the least effective substances tested, were cross-adapted by the majority of the adapting stimuli. Glycine and sarcosine did not cross-adapt the responses to each other which indicated independent receptors for these stimuli. Independent receptor sites located on separate receptor cells were suggested for L-proline, which stimulated the arm coiling response at high concentrations, and for β-alanine and thioglicolic acid, which stimulated the tube feet walking behavior.