Effects of L-theanine on anxiety-like behavior, cerebrospinal fluid amino acid profile, and hippocampal activity in Wistar Kyoto rats

Behavioral tests were performed after 7-10 days of l-theanine (0.4 mg kg(-1) day(-1)) or saline administration, followed by CSF sampling for high-performance liquid chromatography (HPLC) analysis. An independent set of animals was subjected to [F-18]fluorodeoxyglucose positron emission tomography (PET) scanning after the same dose of l-theanine or saline administration for 7 days. In the elevated plus maze test, the time spent in the open arms was significantly longer in the l-theanine group than in the saline group (P = 0.035). In addition, significantly lower CSF glutamate (P = 0.039) and higher methionine (P = 0.024) concentrations were observed in the l-theanine group than in the saline group. A significant increase in the standard uptake value ratio was observed in the hippocampus/cerebellum of the l-theanine group (P < 0.001). These results suggest that l-theanine enhances hippocampal activity and exerts anxiolytic effects, which may be mediated by changes in glutamate and methionine levels in the brain. Further study is required to more fully elucidate the mechanisms underlying the effects of l-theanine.