Representative fEPSPs evoked by HFS in PP-DG area in vivo. fEPSPs were continuously recorded and normalized prior to HFS as baseline and 1 h after HFS as the LTP (A). Values are expressed as percentage of change relative to baseline. Magnitude of LTP, determined as responses between 30 and 60 min after HFS (B) were represented as the mean ± SEM. There are significant differences in different groups (P < 0.05).