[Free amino acids in the central nervous system of skates (Batomorpha)].

The distribution of free amino acids in strongly and weakly electric fishes (skates and rays) varies in relation to species, brain region and functional peculiarities. In comparison to the weakly electric fishes (Raja clavata and Myliobatis aquila) a number of brain regions of the strongly electric species (Torpedo marmorata and T. ocellata) show considerably higher concentrations of arginine, glycine and tyrosine, and lower concentrations of aspartic acid. The electric organ of the strongly electric fishes was characterized by the lack of tyrosine and glycine, by traces of GABA, and by considerably higher concentrations of alanine, serine, cysteine, and histidine than in the brain of the same species. The electromotor center Lobus electricus of the stronlgy electric fishes, in contrast to other brain regions, shows exceptionally high concentrations of tyrosine and alanine. In comparison to the mammalian brain, levels of brain alanine, glycine, cysteine and cystine are higher in the four fish species studied. The results are discussed in relation to the morphophysiological organization of the fish central nervous system and of the mechanisms of electrogenesis.