title: Intrathecal co-administration of NMDA antagonist and NK-1 antagonist reduces MAC of isoflurane in rats.
abstract: BACKGROUND
  Intravenous administration of N-methyl-D-aspartate (NMDA) receptor antagonists and alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor antagonists reportedly reduce the minimum alveolar anaesthetic concentration (MAC) for inhalation anaesthetics. If pain perception can be prevented by the intrathecal administration of antinociceptive receptor antagonists, these agents may reduce the requirements for inhalation anaesthetics. We studied the effect of intrathecal administration of an AMPA/kainate receptor antagonist, a metabotropic glutamate (mGlu) receptor antagonist and co-administration of NMDA and a neurokinin-1(NK-1) receptor antagonist drugs at low doses on the MAC.
  
  
  METHODS
  After Wistar rats (n=36) were fitted with indwelling intrathecal catheters, the MAC of isoflurane was determined following intrathecal administration of a non-NMDA receptor antagonist (CNQX) at 10 microg, a mGlu receptor antagonist (AP3) at 10 microg, or a combination of NMDA receptor antagonist (APV) at 0.01 microg to 1 microg with NK-1 receptor antagonist (CP96345, CP) at 0.1 microg to 10 microg. Subsequently, a reversal dose of intrathecal NMDA with substance P (SP) was administered, and the MAC of isoflurane was redetermined. Conscious rats (n=15) were also examined for the presence of locomotor dysfunction following the intrathecal co-administration of APV and CP.
  
  
  RESULTS
  Neither CNQX nor AP3 reduced the MAC of isoflurane. APV at 0.01 microg plus CP at 1 microg, as well as APV at 0.1 microg plus CP at 10 microg, reduced the MAC of isoflurane, with respective reductions of 7.6% and 14%; (P<0.05). Co-administration of NMDA plus SP reversed the decrease in the MAC of isoflurane. Locomotive activity was not changed.
  
  
  CONCLUSIONS
  The NMDA receptor and the NK-1 receptor are important determinants of the MAC of isoflurane, exerting this influence by inhibition of pain transmission in the spinal cord, while mGlu and AMPA receptors have no effect on the MAC of isoflurane.
authors.affiliation: Department of Anesthesiology and Reanimatology, Gunma University School of Medicine, Maebashi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ishizaki
authors.forename: M
authors.initials: M
authors.lastname: Sasaki
authors.forename: S
authors.initials: S
authors.lastname: Karasawa
authors.forename: H
authors.initials: H
authors.lastname: Obata
authors.forename: T
authors.initials: T
authors.lastname: Nara
authors.forename: F
authors.initials: F
authors.lastname: Goto
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000008:administration & dosage / Q000494:pharmacology; D000409:Alanine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D001713:Biphenyl Compounds / Q000008:administration & dosage / Q000494:pharmacology; D002408:Catheters, Indwelling; D004338:Drug Combinations; D018691:Excitatory Amino Acid Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D007278:Injections, Spinal; D007530:Isoflurane / Q000008:administration & dosage*; D008124:Locomotion / Q000187:drug effects; D008297:Male; D064729:Neurokinin-1 Receptor Antagonists; D009619:Nociceptors / Q000187:drug effects; D010146:Pain / Q000503:physiopathology; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000037:antagonists & inhibitors*; D018092:Kainic Acid Receptors / Q000037:antagonists & inhibitors*; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*; D013116:Spinal Cord / Q000187:drug effects / Q000503:physiopathology; D013373:Substance P / Q000008:administration & dosage / Q000037:antagonists & inhibitors; D009435:Synaptic Transmission / Q000187:drug effects; D014633:Valine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000409:Alanine; D018685:Anesthetics, Inhalation; D001713:Biphenyl Compounds; D004338:Drug Combinations; D018691:Excitatory Amino Acid Antagonists; D007530:Isoflurane; D064729:Neurokinin-1 Receptor Antagonists; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D016194:Receptors, N-Methyl-D-Aspartate; D013373:Substance P; D014633:Valine; C000211:2-amino-3-phosphonopropionic acid; C056639:2-amino-5-phosphopentanoic acid; C066892:CP 96345