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

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.