Summary g-Aminobutyric acid (GABA) is an amino acid found in unpolished rice, chocolate, tea, and other foods. It is an important inhibitory neurotransmitter. However, the influence of GABA on object recognition and working memory is still unknown. In this study, the effects of GABA on novel object recognition (NOR) memory and working memory were examined. The proper retention interval and delay time were also investigated for the NOR test and T-maze test, respectively. Male 3-wk-old Wistar rats were allowed free access to food and water containing 0.5% GABA or 1% GABA for a month. After that, the rats performed the NOR test at a 48 h retention interval and T-maze test at a 900 s delay time to estimate the effects of GABA on learning behavior. The results showed that the object information in the NOR test was stored as long-term memory and the recognition index (RI) was significantly increased after GABA administration. The accuracy rate also significantly increased after GABA administration. These indicate that GABA may be involved in long-term object recognition memory and working memory.

SummaryThe purpose of this study was to determine whether the regulation of brain protein synthesis was mediated through changes in the plasma concentration of growth hormone (GH) when dietary ␥ -aminobutyric acid (GABA) treatment was manipulated in hypophysectomized or sham-operated aged rats. Experiments were done on four groups of hypophysectomized and sham-operated (24-wk-old) male rats given 0% or 0.5% GABA added to a 20% casein diet. The concentrations of plasma GH and fractional rates of protein synthesis in the brains increased significantly with the 20% casein ϩ 0.5% GABA compared with the 20% casein diet alone in the sham-operated rats. However GABA treatment to the basal diet did not affect the rates of protein synthesis in the hypophysectomized rats. In the cerebral cortex and cerebellum, the RNA activity [g protein synthesized/(g RNA·d)] significantly correlated with the fractional rate of protein synthesis. The RNA concentration (mg RNA/g protein) was also related to the fractional rate of protein synthesis in these organs. The results suggest that treatment with GABA is likely to increase the concentrations of GH and the rate of brain protein synthesis in sham-operated rats only, not in hypophysectomized rats, and that the GABA-induced increase in the concentration of GH may be primarily responsible for changes in the brain protein synthesis. The RNA activity is at least partly related to the fractional rate of brain protein synthesis. Key Words ␥ -aminobutyric acid, growth hormone, protein synthesis, brain, ratsThe metabolic response to dietary proteins, age and hormonal factors includes marked changes in protein synthesis, especially in the liver, muscles and intestines ( 1-5 ). Protein synthesis in the brain is also sensitive to the alteration of dietary amino acid composition in young rats ( 6 , 7 ).Many investigators have reported that protein synthesis declines in specific tissues (e.g., liver or muscle) and in the whole body throughout development in mammals after weaning ( 8-10 ). We demonstrated that the rate of protein synthesis in the brain decreases with age in rats after weaning ( 11 ). In many investigations, not only age but also growth hormone (GH) deficiency has been shown to affect many functions related to the central nervous system in mammals ( 12 ). GH is well known as the anabolic hormone in protein metabolism. Several investigators have demonstrated that the protein synthesis in visceral organs, skeletal muscle and brains was increased by GH in rats ( 13 , 14 ).␥ -Aminobutyric acid (GABA) is a kind of amino acid widely distributed over the nature, and is an inhibitory transmitter compound in vertebrates ( 15 , 16 ). Recently, GABA was attracted attention as a functional food for improvement in memory and study capability, bloodpressure reduction and relaxation inducement ( 17 , 18 ). In a previous study, we reported that administration of GABA to young and aged rats increased the concentration of plasma GH and the rate of protein synthesis in the brain, and that a positive c...

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