EGCG Ameliorates the Suppression of Long-Term Potentiation Induced by Ischemia at the Schaffer Collateral-CA1 Synapse in the Rat

The function of Epigallocatechin gallate (EGCG), a main component of green tea, has been widely investigated, amelioration of synaptic transmission and neuroprotective effects against ischemia-induced brain damage among others. However, the mechanism underlying is still unveiled. We investigated the effects of EGCG on high frequency stimulation-induced long-term potentiation (LTP) in the Schaffer collateral-CA1 synapse with or without cerebral ischemia injury induced by middle cerebral artery occlusion (MCAO) in vivo to examine the possible relations between EGCG and synaptic transmission. Application of EGCG modulated synaptic transmission and produced a dose-dependent improvement of the induction of LTP. However, relative high-dose EGCG can block the induction of LTP at the Schaffer collateral-CA1 synapse in normal rat in vivo. In addition, the effects of EGCG were observed on the infarct volume and neurological deficit in rats subjected to MCAO; furthermore, the cell viability of primary cultured rat hippocampal and cortical neurons suffered from oxygen-glucose deprivation were evaluated with MTT and LDH assay, which showed significant neuroprotective properties in vitro. Surprisingly, the contents of the glutamate (Glu), glycine (Gly), and gamma-aminobutyric acid amino acids were totally dis-equilibrated before and after cerebral ischemia injury and could be rebalanced to original level by application of EGCG. Our results suggest that EGCG is able to improve the efficiency of synaptic transmission in cerebral ischemia injury with attenuated effect related to the neuroprotection of EGCG through regulating excitatory and inhibitory amino acid balance.