GAMMA-AMINOBUTYRIC ACID AND OTHER BLOCKING COMPOUNDS IN CRUSTACEA: III. THEIR RELATIVE CONCENTRATIONS IN SEPARATED MOTOR AND INHIBITORY AXONS

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Abstract
Peripheral nervous systems of lobsters and crabs were surveyed for compounds that block transmission at the crayfish neuromuscular junction. Ten such substances were isolated. Gamma-aminobutyric acid (GABA), taurine, and betaine contributed most of the blocking activity of the extracts. Other compounds were: beta-alanine, alanine, homarine, glutamine, aspartic acid and two unidentified substances. These materials were separated by electrophoretic and paper chromatographic techniques and GABA was further identified by a specific enzyme assay procedure. GABA had the strongest blocking activity. The only excitatory substance in the extracts was glutamic acid. GABA does not appear to be produced by destruction of a larger molecule during extraction. The GABA content of peripheral nervous tissues increased together with the proportion of known inhibitory axons.