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Abstract
Free amino acids were quantitatively estimated in intact tissues and isolated synaptosome
and synaptic vesicle fractions of the bovine brain regions with the aid of a sensitive
amino acid analyzer. The brain areas studied were frontal, parietal and occipital
cerebral cortices, cerebellar cortex, caudate and lenticular nuclei, superior colliculi,
thalamus, pons and medulla. The most abundant amino acid in tissue samples and synaptosome
fractions was glutamic acid, followed by glutamine, aspartic acid, GABA and taurine.
The dominatating amino acid in all isolated synaptic vesicle fractions was taurine.
The concentrations of glutamic acid, glutamine, GABA and aspartic acid were generally
much lower. The 5 transmitter candidates, viz. GABA, glycine, glutamic acid, as particaid
and taurine, comprised about one-half of the total amino acids in all samples. Taurine
was the only amino acid highly enriched in the vesicle fractions. This enrichment
was discernible in all brain areas. It is suggested therefore that taurine is rather
a ubiquitous associate of synaptic membrane structures than a specific inhibitory
transmitter.