Inhibiting effects of theanine on caffeine stimulation evaluated by EEG inthe rat

In this study, the inhibiting action of theanine on the excitation by caffe ine at the concentration regularly associated with drinking tea was investi gated using electroencephalography (EEG) in rats. First, the stimulatory ac tion by caffeine i.v. administration at a level higher than 5 mu mol/kg (0. 970 mg/kg) b.w. was shown by means of brain wave analysis, and this level w as suggested as the minimum dose of caffeine as a stimulant. Next, the stim ulatory effects of caffeine were inhibited by an i.v. administration of the anine at a level higher than 5 mu mol/kg (0.781 mg/kg) b.w., and the result s suggested that theanine has an antagonistic effect on caffeine's stimulat ory action at an almost equivalent molar concentration. On the other hand, the excitatory effects were shown in the rat i.v. administered 1 and 2 mu m ol/kg (0.174 and 0.348 mg/kg) b.w. of theanine alone. These results suggest ed two effects of theanine, depending on its concentration.