title: Neuroprotective and neurotoxic properties of the 'inert' gas, xenon.
abstract: BACKGROUND
  Antagonists of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptors have been shown not only to have neuroprotective effects but also to exhibit neurotoxic properties. In this study, we used c-Fos, a protein product of an immediate early gene, as a marker of neuronal injury to compare the neuroprotective effects of xenon and the neurotoxic properties of xenon, nitrous oxide, and ketamine, three anaesthetics with NMDA receptor antagonist properties.
  
  
  METHODS
  We used an in vivo rat model of brain injury in which N-methyl-DL-aspartic acid (NMA) is injected subcutaneously (s.c.) and c-Fos expression in the arcuate nucleus is used as a measure of injury. To examine the neurotoxic potential of each of the three anaesthetics with NMDA receptor antagonist properties, c-Fos expression in the posterior cingulate and retrosplenial (PC/RS) cortices was measured.
  
  
  RESULTS
  Xenon dose-dependently suppressed NMA-induced c-Fos expression in the arcuate nucleus with an IC(50) of 47 (2)% atm. At the highest concentration tested (75% atm) NMA-induced neuronal injury was decreased by as much as that observed with the prototypical NMDA antagonist MK801 (0.5 mg kg(-1) s.c.). Both nitrous oxide and ketamine dose-dependently increased c-Fos expression in PC/RS cortices; in contrast, xenon produced no significant effect. If the dopamine receptor antagonist haloperidol was given before either nitrous oxide or ketamine, their neurotoxic effects were eliminated.
  
  
  CONCLUSIONS
  Uniquely amongst anaesthetics with known NMDA receptor antagonist action, xenon exhibits neuroprotective properties without co-existing neurotoxicity. The reason why ketamine and nitrous oxide, but not xenon, produce neurotoxicity may involve their actions on dopaminergic pathways.
authors.affiliation: Magill Department of Anaesthesia, Chelsea and Westminster Hospital and Biophysics Group, The Blackett Laboratory, Imperial College of Science, Technology and Medicine, London, UK.
authors.forename: D
authors.initials: D
authors.lastname: Ma
authors.forename: S
authors.initials: S
authors.lastname: Wilhelm
authors.forename: M
authors.initials: M
authors.lastname: Maze
authors.forename: N P
authors.initials: NP
authors.lastname: Franks
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000378:metabolism; D015415:Biomarkers / Q000032:analysis; D001921:Brain / Q000187:drug effects* / Q000378:metabolism; D001930:Brain Injuries / Q000378:metabolism; D016291:Dizocilpine Maleate / Q000494:pharmacology; D005260:Female; D015870:Gene Expression / Q000187:drug effects; D006220:Haloperidol / Q000494:pharmacology; D007649:Ketamine / Q000494:pharmacology* / Q000633:toxicity; D023421:Models, Animal; D016202:N-Methylaspartate / Q000378:metabolism; D018696:Neuroprotective Agents / Q000494:pharmacology*; D009609:Nitrous Oxide / Q000494:pharmacology* / Q000633:toxicity; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D014978:Xenon / Q000494:pharmacology* / Q000633:toxicity
chemical_list: D015415:Biomarkers; D018696:Neuroprotective Agents; D016760:Proto-Oncogene Proteins c-fos; D014978:Xenon; D016202:N-Methylaspartate; D007649:Ketamine; D016291:Dizocilpine Maleate; D006220:Haloperidol; D009609:Nitrous Oxide