Amino Acid Nutrition and Brain Function

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Tryptophan and tyrosine are the amino acids to build blocks of protein, and are present in most foods. The composition and function of the brain can be altered by tryptophan and tyrosine because they are the precursors of neurotransmitters: substances that are released from a neuron, or nerve cen, when it fires. The neurotransmitter thereby conveys the nerve impulse across a synapse to either another neuron, a muscle cell or secretary cell. Tryptophan is converted in the terminals of certain neurons into the neurotransmitter serotonin. Tyrosine serves as the precursor of dopamine, norepinephrine and epinephrine, which are collectively called the catecholamine transmitters. The synthesis and release of neurotransmitters may regulate some important behavioral mechanisms (such as the control of pain, appetite, sleep, mood and performance). So, relationships between neurochemical changes caused by amino acid supplementation to low protein diet and a brightness-discrimination learning test … More were investigated.1. The concentrations of brain tryptophan, serotonin and 5-hydroxyindole acetic acid(5HIAA) significantly increased by the addition of 0.1% of tryptophan to corn diet, then the learning ability was improved. Especially the frequency of R-(incorrect response) decreased.2. When rats were fed a 10% soy protein isolate diet supplemented with methionine and threonine(supplemented levels fulfill two-fold of each amino acid requirement), the concentrations of brain tryptophan, serotonin and 5HIAA sharply decreased. By the brightness-discrimination learning test, the total response(R^+; correct + R^-; incorrect) of rats fed amino acid supplemented group increased as compared with those of rats fed non-supplemented basal diet. Correct response ratios of primary learning test did not change, but in reverse learning test, its response ratios of rats fed amino acid supplemented diet increased. Therefore, it may be considered that the activities of serotoninergic neurons(such as the concentrations of 5-hydroxyindoles, or the synthesis and release of neurotransmitters) and some behavioral activities(such as memory-learning) are correlated with the nut ritional stages, so these neurochemical and neuropharmacological parameters may be considered as possible measures for the nutritional and safety evaluation of diets. Less