title: Activation of peripheral NMDA-nitric oxide cascade in formalin test.
abstract: BACKGROUND
  It has been suggested that peripheral glutamate and nitric oxide (NO) released by tissue-damaging stimuli play an important role in peripheral nociceptive transmission. This study was conducted to determine whether NO was released in the periphery after subcutaneous injection of formalin and whether the peripheral N-methyl-d-aspartate (NMDA)-NO cascade was activated.
  
  
  METHODS
  During pentobarbital anesthesia, a microdialysis probe was implanted subcutaneously into the glabrous skin of both hind paws of Sprague-Dawley rats. After sample collection to obtain the basal level of NO metabolites (total amount of nitrite [NO2-] and nitrate [NO3-] [NO2--NO3-]), 5% formalin was injected into the plantar surface of the right hind paw during perfusion of the dialysis catheters with artificial cerebrospinal fluid (ACSF), the NO synthase inhibitor NG-monomethyl-L-arginine acetate, or the NMDA antagonist D,l-2-amino-5-phosphonovaleric acid through a microdialysis probe. Formalin also was injected in the animals that underwent sciatic nerve sectioning. In another series of experiments, NMDA was perfused through one probe. Samples for measurement of NO2--NO3- were collected and immediately analyzed using high-performance liquid chromatography.
  
  
  RESULTS
  Subcutaneous formalin significantly increased the dialysate concentrations of NO2--NO3- (maximum increase 144 +/- 12% of baseline value 30 min after formalin administration; P < 0.05) on the side ipsilateral to the injection. Both NG-monomethyl-l-arginine acetate and D, l-2-amino-5-phosphonovaleric acid significantly (P < 0.05) suppressed the formalin-induced increases in NO2--NO3- concentration. In the rats with denervation of the sensory nerves, formalin did not change the NO2--NO3- concentration. In addition, NMDA perfusion significantly (P < 0.05) increased the concentrations of NO2--NO3-.
  
  
  CONCLUSIONS
  The results of the current study show that subcutaneous formalin injection induces peripheral release of NO, the production of which is mediated by activation of NMDA receptors in the peripheral nervous system.
authors.affiliation: Department of Anesthesiology, Sapporo Medical University School of Medicine, Japan. komote@sapmed.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Omote
authors.forename: T
authors.initials: T
authors.lastname: Kawamata
authors.forename: M
authors.initials: M
authors.lastname: Kawamata
authors.forename: Y
authors.initials: Y
authors.lastname: Nakayama
authors.forename: K
authors.initials: K
authors.lastname: Hazama
authors.forename: A
authors.initials: A
authors.lastname: Namiki
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004202:Disinfectants / Q000008:administration & dosage / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005557:Formaldehyde / Q000008:administration & dosage / Q000494:pharmacology*; D007279:Injections, Subcutaneous; D008297:Male; D017551:Microdialysis; D016202:N-Methylaspartate / Q000378:metabolism / Q000494:pharmacology*; D009569:Nitric Oxide / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors*; D017933:Peripheral Nervous System / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects; D012584:Sciatic Nerve / Q000187:drug effects; D019323:omega-N-Methylarginine / Q000494:pharmacology*
chemical_list: D004202:Disinfectants; D004791:Enzyme Inhibitors; D016194:Receptors, N-Methyl-D-Aspartate; D005557:Formaldehyde; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D016202:N-Methylaspartate; D019001:Nitric Oxide Synthase