ABSTRACT
Neural injury due to ischemia and related insults is thought to involve the action of excitatory amino acids at N-methyl-D-aspartate receptors, which results in the influx of extracellular Ca2+ and the generation of nitric oxide. Because ethanol inhibits physiologic responses to excitatory amino acids, we examined its effect on toxicity induced by N-methyl-D-aspartate and by the nitric oxide donor sodium nitroprusside in neuron-enriched cultures prepared from rat cerebral cortex. Both N-methyl-D-aspartate and sodium nitroprusside were cytotoxic, as measured by the release of lactate dehydrogenase and by microfluorescent determination of cell viability. Ethanol (3-1,000 mM) protected cultures from N-methyl-D-aspartate but not sodium nitroprusside toxicity, and the ability of a series of n-alkanols to reproduce the effect of ethanol was related to carbon-chain length. Neuroprotection by ethanol was accompanied by a decrease in the N-methyl-D-aspartate-evoked elevation of free intracellular Ca2+ and did not appear to involve gamma-aminobutyric acid- or cyclic GMP-mediated mechanisms. These findings suggest that ethanol inhibits excitotoxicity at an early step in the N-methyl-D-aspartate signaling pathway, probably by reducing Ca2+ influx, and not by interfering with the action of nitric oxide.
Subject(s)
Cerebral Cortex/cytology , Cerebral Cortex/physiology , Ethanol/pharmacology , N-Methylaspartate/toxicity , Neurons/physiology , Nitroprusside/toxicity , Animals , Calcium/metabolism , Cell Death/drug effects , Cells, Cultured , Cerebral Cortex/embryology , Drug Interactions , L-Lactate Dehydrogenase/metabolism , Neurons/metabolism , Neurons/ultrastructure , Nitric Oxide/metabolism , Rats , Rats, Sprague-Dawley , Receptors, N-Methyl-D-Aspartate/analysis , Receptors, N-Methyl-D-Aspartate/drug effects , Receptors, N-Methyl-D-Aspartate/physiologyABSTRACT
Excessive release of glutamate has been implicated in the pathogenesis of excitotoxic neurologic disorders, such as stroke. BW 1003C87, an inhibitor of glutamate release and a putative Na+ channel antagonist, reduced veratridine-stimulated, tetrodotoxin- and dizocilpine-sensitive toxicity (measured by lactate dehydrogenase efflux) in neuron-enriched cortical cultures (IC50 = 5 microM). In contrast, BW 1003C87 (300 microM) had no effect on toxicity induced by direct application of 1 mM glutamate or 1 mM N-methyl-D-aspartate, or by depolarization with 50 mM KCl. Glutamate release inhibitors such as BW 1003C87 may provide a novel approach to protection from excitotoxicity.
Subject(s)
Glutamates/toxicity , Neurons/drug effects , Neurotoxins/antagonists & inhibitors , Pyrimidines/pharmacology , Animals , Cells, Cultured , Cerebral Cortex/cytology , Cerebral Cortex/embryology , Dizocilpine Maleate/pharmacology , Glutamates/metabolism , Glutamic Acid , N-Methylaspartate/antagonists & inhibitors , N-Methylaspartate/toxicity , Potassium Chloride/pharmacology , Rats , Rats, Sprague-Dawley/embryology , Sodium Channels/drug effects , Sodium Channels/physiology , Tetrodotoxin/pharmacology , Veratridine/antagonists & inhibitors , Veratridine/toxicityABSTRACT
N-Methyl-D-aspartate (NMDA) receptor activation generates nitric oxide (NO) and cyclic GMP (cGMP) and produces 'excitotoxic' neuronal injury. To examine the possible role of cGMP in excitotoxicity, we evaluated the effects of agents that stimulate or inhibit cGMP activity on the release of lactate dehydrogenase from neuron-enriched cortical cultures. cGMP analogs exhibited no toxicity, and inhibitors of guanylate cyclase or of cGMP-dependent enzymes failed to protect cultures from the toxic effects of NMDA or the NO donor sodium nitroprusside. These findings argue against a role for cGMP in the pathogenesis of excitotoxic neuronal injury.
