Anesthesiology
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Ketamine is analgesic in experimental and clinical studies of inflammatory, neuropathic, and postoperative pain. Its role in the treatment of visceral pain is less known. The authors investigated the effect and site of action of ketamine on reflex responses evoked by urinary bladder distension (UBD). The effects of other clinically available N-methyl-d-aspartate (NMDA) receptor antagonists on these responses were also studied. ⋯ Ketamine inhibited, in a dose-dependent fashion, the Delta MAP and EMG responses to UBD, an effect likely caused by actions within the spinal cord. Similar inhibition observed with systemic dextromethorphan and memantine treatments suggests that the analgesic effect of ketamine is caused by antagonism of the NMDA receptor. Pretreatment with ketamine did not have a preventive effect in this model of bladder nociception.
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The effect of ketamine as a treatment of visceral pain is not known. The current study investigated the effect of ketamine on spinal dorsal horn neurons excited by urinary bladder distension (UBD). The effect of other clinically available N-methyl-D-aspartate receptor antagonists on these responses was also studied. ⋯ Intravenous ketamine produces dose-dependent inhibition of the spinal cord neuronal responses evoked by UBD. All three N-methyl-D-aspartate receptor antagonists showed selective effects on spinal cord neurons subject to counterirritation. This neurophysiologic evidence supports a spinally mediated analgesic effect of ketamine in this model of urinary bladder nociception, an effect likely caused by N-methyl-D-aspartate receptor antagonism.
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Xenon, the "inert" gaseous anesthetic, is an antagonist at the N-methyl-D-aspartate (NMDA)-type glutamate receptor. Because of the pivotal role that NMDA receptors play in neuronal injury, the authors investigated the efficacy of xenon as a neuroprotectant in both in vitro and in vivo paradigms. ⋯ Xenon, when coadministered with the injurious agent, exerts a concentration-dependent neuroprotective effect at concentrations below which anesthesia is produced in rodents. Unlike either nitrous oxide or ketamine (other anesthetics with NMDA antagonist properties), xenon is devoid of both neurotoxicity and clinically significant adverse hemodynamic properties. Studies are proposed to determine whether xenon can be used as a neuroprotectant in certain clinical settings.