Effect of L-theanine on sensorimotor gating in healthy human subjects.

AIM: l-Theanine (N-ethyl-l-glutamine) is an amino acid uniquely found in green tea. Growing evidence has suggested the possible effects of l-theanine on cognition. Previously, we found that l-theanine attenuates MK-801-induced deficit in prepulse inhibition (PPI) in mice. In this study, we examined the effect of l-theanine in increasing the PPI in healthy humans. METHODS: The subjects were 14 healthy adults who underwent PPI testing as a measure of sensorimotor gating 90 min after an oral intake of l-theanine (0, 200, 400, or 600 mg). PPI tests were done by examiners who were blind to the dose. RESULTS: The administration of 200 mg of l-theanine and that of 400 mg, but not 600 mg, significantly increased the % PPI compared to the baseline (0 mg). There was no significant relation between the dose of l-theanine and the startle magnitude or the habituation of startle response. The plasma concentrations of l-theanine correlated with the dose of l-theanine. CONCLUSION: The observed effect with 200-400 mg of l-theanine on PPI suggested that l-theanine at a particular dose range increases sensorimotor gating in humans.