Extracts from rhizomes of Cyperus articulatus (Cyperaceae) displace [3H]CGP39653 and [3H]glycine binding from cortical membranes and selectively inhibit NMDA receptor-mediated neurotransmission.

The marshland plant Cyperus articulatus (Cyperaceae) is commonly used in traditional medicine in Africa and Latin America to treat a wide variety of human diseases ranging from headache to epilepsy. We tested the hypothesis that the purported anti-epileptic effect of this plant might be due to a functional inhibition of excitatory amino acid receptors. One or several component(s) contained in the extracts inhibited the binding of [3H]CGP39653 to the NMDA recognition site and of [3H]glycine to the strychnine-insensitive glycine site of the NMDA receptor complex from rat neocortex. Water extracts from rhizomes of Cyperus articulatus dose-dependently reduced spontaneous epileptiform discharges and NMDA-induced depolarizations in the rat cortical wedge preparation at concentrations at which AMPA-induced depolarizations were not affected. We conclude that the purported beneficial effects of Cyperus articulatus might at least partially be due to inhibition of NMDA-mediated neurotransmission.

Thalamocortical and corticocortical excitatory postsynaptic potentials mediated by excitatory amino acid receptors in the cat motor cortex in vivo.

Intracellular recordings were made from neurons in the motor cortex of an anaesthetized cat, together with iontophoretic application of excitatory amino acid receptor agonists and antagonists, in order to evaluate the role of such receptors in excitatory postsynaptic potentials evoked from stimulation of afferent and recurrent pathways in vivo. Excitatory postsynaptic potentials which were evoked by stimulation of the ventrolateral thalamus were found to be largely insensitive to antagonism by N-methyl-D-aspartate receptor antagonists, although they were susceptible to blockade by the non-N-methyl-D-aspartate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione. Increasing the ventrolateral thalamus stimulation frequency from 0.5 or 1 to 5 Hz caused an increase of evoked excitatory postsynaptic potential amplitudes and number of action potentials. These augmented excitatory postsynaptic potentials remained insensitive to application of N-methyl-D-aspartate antagonists. In contrast, recurrent excitatory postsynaptic potentials evoked by stimulation of the pyramidal tract were found to be sensitive to N-methyl-D-aspartate receptor antagonists and/or non-N-methyl-D-aspartate receptor antagonists in some neurons. These results demonstrate the involvement of both N-methyl-D-aspartate- and non-N-methyl-D-aspartate receptors in synaptic responses of cat motor cortex neurons in vivo, and that the synaptic pharmacology of the thalamic input may differ from that of the local recurrent pathways.

N-methyl-D-aspartate induces regular firing patterns in the cat lateral habenula in vivo.

The present study was undertaken to elucidate the action of excitatory amino acids in the dorsal diencephalic pathway. Single neurons in the lateral habenula of halothane-anesthetized cats were recorded extracellularly, and excitatory amino acid receptor agonists and antagonists were applied by iontophoresis. Most neurons in the lateral habenula were spontaneously active. This spontaneous firing could be inhibited by kynurenic acid, a broad spectrum antagonist of excitatory amino acid receptors, but not by the selective N-methyl-D-aspartate receptor antagonist 2-amino-7-phosphono-heptanoic acid. Iontophoretic application of alpha-amino-3-hydroxy-5-methyl-5-isoxazolepropionate, quisqualate and kainate mostly elicited a non-burst, regular firing pattern which was sensitive to kynurenic acid. Surprisingly, 116 (96%) out of 121 neurons in the lateral habenula responded to iontophoretic application of N-methyl-D-aspartate with a regular non-burst firing pattern, in contrast to previously published observations from other brain regions where N-methyl-D-aspartate predominantly elicited phasic firing patterns. When cells were recorded with electrode assemblies where one iontophoretic barrel contained MgCl2 or MgSO4, only 10 (43%) out of 23 cells responded with regular firing upon application of N-methyl-D-aspartate, while 13 (57%) now displayed a phasic firing pattern. In these cells iontophoretically applied alpha-amino-3-hydroxy-5-methyl-5-isoxazolepropionate or quisqualate still evoked only regular firing. In a few cases, an initially regular N-methyl-D-aspartate-induced firing pattern could be changed to a phasic pattern following active ejection of Mg2+ ions.(ABSTRACT TRUNCATED AT 250 WORDS)