Amino acid concentrations in rat cochlear nucleus and superior olive

Distributions of 10 amino acids were mapped in the cochlear nucleus and sup erior olive of rats by microdissection of freeze-dried sections combined wi th high performance liquid chromatography. Glutamate concentrations were re latively high in regions containing granule cell bodies, axons and terminal s, whereas aspartate concentrations were higher in the rest of the cochlear nucleus. The distribution of glutamine, a metabolic precursor of glutamate , correlated highly with that of glutamate. In the superior olive, glutamat e concentrations were similar among the nuclei, whereas aspartate concentra tions were higher in the more dorsal nuclei. Glycine concentrations were re latively high in dorsal portions of the cochlear nucleus and superior olive and were much higher in all regions than those of gamma -aminobutyrate (GA BA). Both GABA and taurine showed decreasing gradients from superficial to deep layers of the dorsal cochlear nucleus. Concentrations of serine, threo nine, arginine and alanine were generally lower than those of the other six amino acids. The results support other evidence for prominent roles of glu tamate and glycine as neurotransmitters in the cochlear nucleus and superio r olive. They support a neurotransmitter role also for GABA, especially in the superficial layers of the dorsal cochlear nucleus, but less in the supe rior olive. The literature related to our results is reviewed. (C) 2000 Els evier Science B.V. All rights reserved.