Distribution and metabolism of neuroexcitatory amino acids in aquatic organisms

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Contents of three neuroexcitatory amino acids, N-methyl-D,L-aspartic acid (NMA), kainic acid (KA) and domoic acid (DA) were investigated in 47 marine algae species and various tissues of 28 marine animals. In marine algae, NMA was detected in very small amounts in several marine algae belonging to Chlorophyceae and Rhodophyceae, but not in algae belonging to Phaeophyceae. KA was detected in three species and DA was detected in four species all belonging to the family Rhdomelaceae (Ceramiales, Rhodophyceae). Among rhodomelacean algae, as far as investigated in this study, KA and DA were detected only in the several particular species collected only in South West Islands of Japan (Tokunoshima Island and Okinawa Main Island). It is noteworthy that the distribution of both KA and DA was strictly restricted within some algae of limited species of limited subtropical area. In marine animals, NMA was found in four species of marine bivalves all belonging to the family Arcidae, DA was found in only one crab collected in Tokyo bay, but KA was not detected in all animal species analyzed. Effect of long term dose of low excitatory amino acids should be investigated from hygienic view point.Concerning the physiological roll of NMDA in blood shell Scapharca broughtonii, the relation of NMDA and physiological and environmental condition was investigated. NMDA did not change by starvation, osmotic pressure, anaerobic condition, but drastically decreased during light and dark circumstance. This would be indicated that NMDA have some important roll as a neurotransmitter in the Arcidae bivalves.Biosynthetic pathway of NMDA from D-aspartic acid was not confirmed by tracer experiment of blood shell. We should therefore check another biosynthetic pathway.