Extracts from rhizomes of Cyperus articulatus L. (Cyperaceae) used in Africa and Amazonia to treat many diseases has been shown to possess sedative and anticonvulsant properties. The aim of this study is to determine the mechanism of action of Cyperus articulatus extracts. In Xenopus oocytes expressing receptors, using electrophysiological measurement, extracts of rhizomes of Cyperus articulatus (300 microg/ml) inhibited 50% of the EC(50) and EC(80) of glutamate (1.3 and 2.9 microM, respectively) induced inward current through hNMDAR1A/2A receptors. Extracts induced very small current through rGluR3 receptors. The largest current induced by the extract (30 mg/ml) represents 128% of the EC(100) of glutamate induced inward current, through rGluR3 receptors. The excess 28% current could be induced by aspartate and/or glutamate in the extracts. The effect on Xenopus oocytes expressing heteromeric GABA(B)R1b/R2 receptors and rectifying potassium channels (Kir3) is clear. A decoction and water extract of Cyperus articulatus induced a large inward current that represented 71 and 57% (respectively) of the EC(100) of gaba (30 microM) induced inward current. The water extract induced also a large current through rectifying potassium channels (Kir3). Part of the current induced through GABA(B) receptors could be related to rectifying potassium channels and GABA(B) site receptors. Cyperus articulatus extracts possessed components that could decrease excitation (NMDA receptor antagonists) and increase inhibition (GABA(B) receptor agonists) in the central nervous system.