Studies on the relationships between dietary amino acids and brain neurotransmitters of different aged rats.

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1. Effect of amino acid supplementation to a low-protein diet on brain neurotransmitters and memory-learning ability of rats was investigated. In the brightness-discrimination learning test, the number of total responses of rats fed the amino acid-supplemented diet increased as compared with that of rats fed the nonsupplemented diet.2. By using the method of microdialysis, the release of catecholamines from the striatum of rats administered by tyrosine (the substrate of catecholamine synthesis) was determined. Tyrosine administration caused the significant increase of dopamine release from striatum.3. Effect of several kinds of tea components, such as caffeine, theanine, glutamine and r-aminobutyric acid on brain neurotransmitters or blood pressure was determined. Then, we found that the large dose of theanine decreased the blood pressure of spontaneously hypertensive rats.4. Effects of various kind of fats or fatty acids on brain tryptophan and 5-hydroxyindoles were determined. Accumulation of brain tryptophan in rats after administering various fats or fatty acids was observed.5. Effects of peptide mixture with high Fischer s ratio (branched-chain amino acids/aromatic amino acids) on serum and cerebral cortex amino acids levels and on cerebral cortex monoamines levels in comparison with amino acid mixture with high Fischer s ratio were investigated. The concentrations of amino acids and monoamines in brain were changed by the administration of different kind of peptide.6. The rate of brain protein synthesis of rats fed different kind of protein or different amount of protein was determined. The rate of brain protein synthesis was easily affected by the changes in quality or quantity of dietary protein.