title: Opioidergic and adrenergic modulation of formalin-evoked spinal c-fos mRNA expression and nocifensive behavior in the rat.
abstract: Fos protein expression has been used to reflect neuronal activation in pain processing pathways although analgesics may uncouple behavioral and Fos responses. We determine whether formalin-induced spinal c-fos mRNA expression (Northern blotting) correlates with nocifensive behavior following pretreatment with morphine, the alpha2-adrenoceptor agonist dexmedetomidine, or their respective antagonists naloxone and atipamezole. Both opiate and alpha2-adrenoceptor agonists reduced formalin-induced c-fos gene transcription and nocifensive behavior via their cognate receptors. Unexpectedly, blockade of either the opiate or alpha2-adrenergic receptors, alone, caused an increase in formalin-evoked c-fos mRNA; while blocking the opiate receptor had no effect on formalin-induced behavior, alpha2-adrenoceptor block had an analgesic effect, indicating discordance between c-fos message transcription and nocifensive behavior. We concluded that the formalin-induced spinal c-fos signal was a poor predictor of the behavioral response to pharmacological manipulation of pain processing pathways.
authors.affiliation: Department of Anesthesia, Stanford University School of Medicine, CA, USA.
authors.forename: S
authors.initials: S
authors.lastname: Sawamura
authors.forename: M
authors.initials: M
authors.lastname: Fujinaga
authors.forename: W S
authors.initials: WS
authors.lastname: Kingery
authors.forename: N
authors.initials: N
authors.lastname: Belanger
authors.forename: M F
authors.initials: MF
authors.lastname: Davies
authors.forename: M
authors.initials: M
authors.lastname: Maze
mesh_terms: D058669:Adrenergic alpha-2 Receptor Antagonists; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D005557:Formaldehyde / Q000494:pharmacology; D007249:Inflammation / Q000139:chemically induced; D018836:Inflammation Mediators / Q000494:pharmacology; D008297:Male; D009292:Narcotic Antagonists; D010146:Pain / Q000503:physiopathology; D010147:Pain Measurement / Q000187:drug effects*; D016760:Proto-Oncogene Proteins c-fos / Q000187:drug effects* / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology; D011957:Receptors, Opioid / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism
chemical_list: D058669:Adrenergic alpha-2 Receptor Antagonists; D000700:Analgesics; D018836:Inflammation Mediators; D009292:Narcotic Antagonists; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D018341:Receptors, Adrenergic, alpha-2; D011957:Receptors, Opioid; D005557:Formaldehyde