Neuroprotective effect of theanine on cerebral ischemia

The present article introduces our study related to the neuroprotective effect of γ-glutamylethylamide (theanine), a component Japanese green tea (Camellia sinensis), on cerebral ischemia. Theanine (1 mg/kg) significantly decreased the size of the cerebral infarcts in a 4 h middle cerebral artery (MCA) occlusion model in mice. However, theanine did not affect the cerebral blood flow, brain temperature and physiological variables (pH, pCO2, pO2 and hematocrit) in this model. Theanine also reduced the alterations of NeuN (neuron), GFAP (astrocyte) and Iba 1 (microglia) expression levels at 24 h after MCA occlusion. This neuroprotective effect of theanine was prevented by bicuculline, γ-aminobutyric acid_A (GABA_A) receptor antagonist, but not 3-mercaptopropionic acid, glutamate decarboxylase inhibitor. Furthermore, theanine (0.3 and 1 mg/kg) significantly prevented the impairment of spatial memory in rats subjected to twice-repeated cerebral ischemia, 7 days after the second reperfusion. In addition, theanine (1 mg/kg) significantly inhibited the decrease in the number of surviving cells in the hippocampal CA1 field in the same rats. These results suggest that theanine directly provides neuroprotection against cerebral ischemia and its neuroprotective effect is mediated, at least in part, by GABAA receptors, and that it may be clinically useful for preventing cerebrovascular disease.