Quercetin is a flavonoid compound found in a number of medicinal plants that are often prescribed in Chinese clinics for the treatment of cardiovascular diseases. The present study investigated the effects of quercetin on chronic cerebral ischemia in rats produced through bilateral occlusion of the carotid arteries. Treatment of quercetin (5 mg/kg i.p. for 14 days) was found to improve the performance of learning and memory of ischemic rats in the Morris water maze. Additionally, in electrophysiological experiments, quercetin attenuated the inhibition of long-term potentiation (LTP) in ischemic rats. Also, in acutely isolated rat hippocampal CA1 pyramidal neurons, quercetin (0.3, 3 and 30 microm) decreased the amplitude of voltage-dependent sodium currents in a dose- and voltage-dependent manner. Taken together, these data lend further support for the neuroprotective effects of quercetin and suggest that a therapeutic effect on cerebral ischemia and vascular dementia of quercetin could be due to its inhibition of sodium channels.