title: Effect of dextromethorphan on antinociception and tolerance induced by swim-stress in the formalin test.
abstract: BACKGROUND
  In the present study, the effect of dextromethorphan on antinociception and tolerance induced by water swim-stress in the formalin test was investigated.
  
  
  METHODS
  Swim-stress at 8 masculineC induces antinociception in both phases of the formalin test. Intraperitoneal administration of dextromethorphan (60 mg/kg) also induces antinociception in the second phase of the formalin test. The lower doses of dextromethorphan (1.25, 2.5, and 5 mg/kg) which did not induce antinociception alone, but did so in combination with swim- stress (40 second), showed antinociceptive effect in both phases of the test. Exposure to water swimming stress with a period of 20 sec, once daily for three days, altered swim- stress- induced antinociception in the formalin test, when tested on the fourth day.
  
  
  RESULTS
  In these animals, exposure to either water swimming stress alone or water swimming stress in combination with dextromethorphan showed potentiation of antinociception induced by swim- stress up to 20 second and decreased the response induced by 40 and 60 second swim- stress, indicating a tolerance induction. Dextromethorphan (20 mg/kg) did not alter the changes induced by three days exposure to swim- stress.
  
  
  CONCLUSIONS
  The results may indicate a possible involvement of n-methyl-d-aspartate receptor mechanism in the antinociception but not tolerance induced by swim- stress at 8 masculineC.
authors.affiliation: Research Laboratory, Tehran Medical Unit, Azad University, Tehran, Iran.
authors.forename: Soheila
authors.initials: S
authors.lastname: Fazli-Tabaei
authors.forename: Amir
authors.initials: A
authors.lastname: Maghsoudi
authors.forename: Navid
authors.initials: N
authors.lastname: Bazaz
authors.forename: Azadeh
authors.initials: A
authors.lastname: Modirzadeh
authors.forename: Mohammad-Reza
authors.initials: MR
authors.lastname: Zarrindast
mesh_terms: D000698:Analgesia; D000818:Animals; D003915:Dextromethorphan / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D008297:Male; D051379:Mice; D010147:Pain Measurement / Q000187:drug effects*; D013312:Stress, Physiological; D013550:Swimming; D013997:Time Factors
chemical_list: D018691:Excitatory Amino Acid Antagonists; D003915:Dextromethorphan