In vivo studies on amino acid transmitters in the central auditory system of the guinea pig.

The extracellular concentrations of endogenous amino acids were measured in vivo in the guinea pig cochlear nucleus during sound stimulation. The purpose was to explore whether certain amino acids might be employed as neurotransmitters by the auditory nerve. A dialysis sampling probe was used to collect a dialysate of the cochlear nucleus. The amino acids were determined fluorometrically after precolumn derivation and high-performance liquid chromatography separation. A short pulse of p-chloromercuryphenylsulfonate (p-CMS) was used to reduce the reuptake of amino acids. The concentration of glutamic and aspartic acid increased twofold to threefold during sound stimulation, while gamma-aminobutyric acid was unaffected. The results support a role for glutamic and/or aspartic acids as neurotransmitters in the auditory nerve.