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NMDA receptor antagonists are a class of anesthetics that work to antagonize, or inhibit the action of, the ''N''-Methyl-D-aspartate receptor (NMDAR). They are used as anesthetics for animals and for humans; the state of anesthesia they induce is referred to as dissociative anesthesia. There is evidence that NMDA receptor antagonists can cause a certain type of neurotoxicity or brain damage referred to as Olney's Lesions in rodents, although such damage has never been conclusively observed in adult primates like humans. Recent research conducted on primates suggests that, while very consistent and long-term ketamine use may be neurotoxic, acute use is not. Several synthetic opioids function additionally as NMDAR-antagonists, such as pethidine, methadone, dextropropoxyphene, tramadol and ketobemidone. Some NMDA receptor antagonists, such as ketamine, dextromethorphan (DXM), phencyclidine (PCP), methoxetamine (MXE), and nitrous oxide (N2O), are popular recreational drugs used for their dissociative, hallucinogenic, and euphoriant properties. When used recreationally, they are classified as dissociative drugs. ==Uses and effects== NMDA receptor antagonists induce a state called dissociative anesthesia, marked by catalepsy, amnesia, and analgesia. Ketamine is a favored anesthetic for emergency patients with unknown medical history and in the treatment of burn victims because it depresses breathing and circulation less than other anesthetics. Dextrorphan, a metabolite of dextromethorphan (one of the most commonly used cough suppressants in the world), is known to be an NMDA receptor antagonist. Depressed NMDA receptor function is associated with an array of negative symptoms. For example, NMDA receptor hypofunction that occurs as the brain ages may be partially responsible for memory deficits associated with aging. Schizophrenia may also have to do with irregular NMDA receptor function (the glutamate hypothesis of schizophrenia). Increased levels of another NMDA antagonist, kynurenic acid, may aggravate the symptoms of schizophrenia, according to the "kynurenic hypothesis". NMDA receptor antagonists can mimic these problems; they sometimes induce "psychotomimetic" side effects, symptoms resembling psychosis. Such side effects caused by NMDA receptor inhibitors include hallucinations, paranoid delusions, confusion, difficulty concentrating, agitation, alterations in mood, nightmares, catatonia, ataxia, anaesthesia, and learning and memory deficits. Because of these psychotomimetic effects, NMDA receptor antagonists, especially phencyclidine, ketamine, and dextromethorphan, are used as recreational drugs. At subanesthetic doses, these drugs have mild stimulant effects and, at higher doses, begin inducing dissociation and hallucinations, though these effects and the strength thereof vary from drug to drug. Most NMDA receptor antagonists are metabolized in the liver. Frequent administration of most NMDA receptor antagonists can lead to tolerance, whereby the liver will more quickly eliminate NMDA receptor antagonists from the bloodstream. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「NMDA receptor antagonist」の詳細全文を読む スポンサード リンク
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