Amino Acid Content of Nerve Endings (Synaptosomes) in Different Regions of Brain: Effects of Gabaculine and Isonicotinic Acid Hydrazide

Abstract

The amino acid content of synaptosomes was determined in 6 regions of rat brain, and in all regions, the 5 predominant amino acids were glutamate, glutamine, aspartate, taurine and GABA. The proportions of the individual amino acids varied considerably from one region to another, the GABA content being particularly high and the taurine content low in synaptosomes from the diencephalon and mesencephalon. Administration of isonicotinic acid hydrazide to rats lowered the synaptosomal GABA level by similar amounts in all brain regions, but the administration of gabaculine resulted in a particularly long-acting elevation in GABA levels in the nerve endings of the diencephalon and mesenchephalon. The possibility is raised that the high GABA levels in the nerve terminals of the diencephalon may be involved in the gabaculine-induced lowering of the body temperature of the rats. A constancy in the amount of the synaptosomal pool of aspartate + glutamate + glutamine + GABA was observed despite large changes in the relative amounts of the 4-amino acids brought about by gabaculine.