BEHAVIORAL-RESPONSES OF THE BRITTLE STAR OPHIURA-OPHIURA TO AMINO-ACIDS, ACETYLCHOLINE AND RELATED LOW-MOLECULAR-WEIGHT COMPOUNDS

Feeding behavior of the brittle star Ophiura ophiura includes orienting posture, orienting movements, arm 'walking', changing the direction of 'walking' arm coiling and ingestion. All sequential behavior patterns were released or enhanced by single low-molecular-weight compounds. Stimuli which released 'walking' behavior at high concentrations (10(-4) M) in all the test animals are listed in decreasing order of sensitivity: sarcosine, glycine, urea, L-valine, L-leucine, L-methionine, L-homocysteine, L-norvaline, L-norleucine, L-threonine, L-serine, S-methyl-L-cysteine, L-proline. Threshold values for single amino acids were as much as 100 times different in different individuals and ranged from 3 x 10(-9) to 3 x 10(-7) M for the most effective stimulus, sarcosine, and from 10(-6) to 10(-4) M for proline. Above 10(-5) M, only L-proline regularly released a second behavior pattern, the arm coiling response, which temporarily inhibited the 'walking' behavior Behavioral thresholds for the 'walking' behavior for L(+)-lactate and L-alanine were higher than those for the orienting movements. Thyoglycolic acid and beta-alanine released tube feet walking, which is not part of the feeding behavior. Structure - activity comparisons were studied at estimated 10(-5) M concentrations. Gycline, sarcosine, L-valine, L-norvaline, L-leucine, L-isoleucine, DL-norleucine and DL-homocysteine released arm 'walking' behavior in more than 75% of all the tests. With the exceptions of S-methyl- and S-ethyl-cysteine, and glycine methylester, derivatives of amino acids were not effective behavioral stimuli in Ophiura ophiura. L-Isomers of valine and leucine regularly stimulated the 'walking' behavior while their D-isomers were effective in some tests and ineffective in others. Acetylcholine iodide, acetyl-beta-methyl choline chloride and choline phosphate chloride regularly released 'walking' behavior at concentrations above 10(-5) M.