Objective To observe the effects of phenolic alkaloids of Menispermum dauricum (PAMd) on synaptic transmission in hippocampus CA3 region in ischemic rats.Methods The evoked population spike (PS) was recorded in hippocampus CA3 region of normal rats in vivo. Transient incomplete global brain ischemia was caused by occluding both carotid arteries, and the change of PS amplitudes were observed. PAMd were injected intraperitoneally at 5, 10, 20 mg/kg respectively before ischemia and their effects on PS amplitudes were observed in ischemic rats. Different doses of glutamic acid(Glu) were injected locally in microdose and their effects on PS amplitudes were observed.Results After both carotid arteries had been occluded to cause incomplete global brain ischemia, the amplitudes of PS were decreased significantly. After the animals were subjected to a Glu intrahippocampal infusion of 5, 10, and 20 mmol/L, respectively, there was an increase of the amplitude of PS at all measured time points (5, 10, 20, 30, 40, 50, 60 min), but Glu 50 mmol/L significantly decreased the amplitudes of PS. Administration of PAMd (20 mg/kg) before ischemia could significantly increase the PS amplitudes after ischemia and PAMd significantly ameliorated the depressive effects of 50 mmol/L Glu on synaptic transmission in hippocampus CA3 region too.Conclusion Administration of PAMd (20 mg/kg) before ischemia significantly improved the weakened synaptic transmission in hippocampus CA3 region induced by brain ischemia, and significantly ameliorate the depressive effects of higher dose Glu.