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Previously, we revealed that theanine, a green tea component, induced phospholipase C (PLC)-b b1 and -g g1, stress-responsible molecules, in primary cultured rat cerebral cortical neurons, suggesting its protective effect on oxidative stress in neurons. In this study, we investigated whether the same favorable effect occurs in vivo. On the oral administration of theanine (10 mmol (1.74 g)/kg, once a day) to rats via gastric intubation for 2 weeks, there was no change in the weight of the body or the cerebral cortex (Cx), cerebellum (Cb), or hippocampus (Hip) in the brain. On assessment of oxidation levels in the brain with thiobarbiturate reactive substances as a marker, the levels were found to be 20% lower in the Cx of theanine-treated rats than in that of control ones. The protein expression levels of PLC-b b1 and -g g1 were significantly increased in the Cx on theanine administration and the same tendency was observed in the Cb, but not the Hip. In addition, the protein expression level of PLC-d d1, which plays an opposite role to the other two isozymes, was not affected in any brain regions on theanine administration. Overall, it was demonstrated that theanine is a safe compound and its repeated oral administration reduces oxidation levels in the brain, especially the Cx, by increasing PLC-b b1 and -g g1 protein expression, suggesting its favorable effect on the brain in vivo.

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ment, the expression level of PLC-b b1 decreased dose-dependently. On the other hand, there was no difference in the PLC-g g1 protein expression level between control and ER stress-loaded neurons. Overall, we demonstrated that ER stress decreases the expression of PLC-b b1, but not -g g1, in neurons.