title: Are NMDA or AMPA/kainate receptor antagonists more efficacious in the delayed treatment of excitotoxic neuronal injury?
abstract: At which time-point and to what extent do N-methyl-D-aspartate (NMDA) receptors, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptors and L-type voltage-sensitive Ca2+ channels (VSCC) contribute to glutamate-induced neuronal injury? To address this question, we induced glutamate neurotoxicity in two neuronal culture systems, chick telencephalic neurons and rat hippocampal neurons, and tested selective antagonists for their neuroprotective activity when administered either during the excitotoxic insult (acute treatment) or during the recovery period (posttreatment). In cultured chick telencephalic neurons exposed to 1 mM L-glutamate for 60 min, both the NMDA receptor antagonist dizocilpine (MK-801; 0.1 microM) and the AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 1 microM) completely blocked glutamate-induced neuronal injury when applied concomitantly with glutamate. If the antagonists were applied during the recovery period, dizocilpine at concentrations up to 10 microM only moderately increased cell viability, whereas CNQX showed a neuroprotective activity comparable to that observed in the case of the acute treatment. In cultured rat hippocampal neurons, excitotoxic injury was induced by a 30-min exposure to 1 microM glutamate. Treatment with dizocilpine during the glutamate exposure could rescue the hippocampal neurons from the excitotoxic insult, whereas acute treatment with the AMPA/kainate receptor antagonist 2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)-quinoxaline (NBQX) or the L-type VSCC blocker nimodipine showed no protection. In contrast, all three drugs showed neuroprotective activity when applied 30, 60 or 120 min after the glutamate exposure. Surprisingly, when the onset of the treatment was delayed for even 240 min, only NBQX and nimodipine led to a reduction in excitotoxic neuronal injury. We conclude that activation of AMPA/kainate receptors and L-type VSCC is critically involved in a late stage of glutamate neurotoxicity, thereby allowing pharmacological intervention at a time when blockade of NMDA receptors becomes less efficacious.
authors.affiliation: Institut für Pharmakologie und Toxikologie, Philipps-Universität, Marburg, Germany.
authors.forename: J H
authors.initials: JH
authors.lastname: Prehn
authors.forename: K
authors.initials: K
authors.lastname: Lippert
authors.forename: J
authors.initials: J
authors.lastname: Krieglstein
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000187:drug effects; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D002560:Cerebrovascular Circulation / Q000187:drug effects; D002642:Chick Embryo; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D018846:Excitatory Amino Acids / Q000633:toxicity*; D018698:Glutamic Acid / Q000633:toxicity; D006624:Hippocampus / Q000166:cytology; D007427:Intracranial Pressure / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D051381:Rats; D011916:Rats, Inbred F344; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors*; D018092:Kainic Acid Receptors / Q000037:antagonists & inhibitors*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D013687:Telencephalon / Q000166:cytology
chemical_list: D015220:Calcium Channels; D018691:Excitatory Amino Acid Antagonists; D018846:Excitatory Amino Acids; D018698:Glutamic Acid; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate