title: Increase of capsaicin-induced trigeminal Fos-like immunoreactivity by 5-HT(7) receptors.
abstract: OBJECTIVE
  To explore whether pharmacological stimulation of the 5-hydroxytryptamine(7) (5-HT(7) ) receptor modulates Fos-like immunoreactivity in the trigeminal nucleus caudalis of rats.
  
  
  BACKGROUND
  The serotonin 5-HT(7) receptor was proposed to be involved in migraine pathogenesis and evidence suggests it plays a role in peripheral nociception and hyperalgesia through an action on sensory afferent neurons.
  
  
  METHODS
  The potential activating or sensitizing role of 5-HT(7) receptors on trigeminal sensory neurons, as visualized by Fos-like immunoreactivity in the superficial layers of the trigeminal nucleus caudalis in rats, was investigated using the 5-HT(7) receptor agonist, LP-211, in the absence and the presence of intracisternal capsaicin, respectively. The agonist effect was characterized with the 5-HT(7) receptor antagonist, SB-656104. Male Wistar rats received a subcutaneous injection of LP-211, SB-656104, and SB-656104 + LP-211. They were then anesthetized and prepared to receive an intracisternal injection of capsaicin or its vehicle. Animals were perfused and brains removed; sections of the brain stem from the area postrema to the CI level were obtained and processed for Fos immunohistochemistry.
  
  
  RESULTS
  Capsaicin but not its vehicle induced Fos-like immunoreactivity within laminae I and II of trigeminal nucleus caudalis. Pretreatment with LP-211 had no effect on Fos-like immunoreactivity but strongly increased the response produced by capsaicin; this effect was abolished by SB-656104. Interestingly, capsaicin-induced Fos-like immunoreactivity was abolished by SB-656104 pretreatment thus suggesting involvement of endogenous 5-HT.
  
  
  CONCLUSIONS
  Data suggest that 5-HT(7) receptors increase activation of meningeal trigeminovascular afferents and/or transmission of nociceptive information in the brain stem. This mechanism could be relevant in migraine and its prophylactic treatment.
authors.affiliation: Department of Pharmacology, Cinvestav-IPN, Mexico DF, Mexico.
authors.forename: Esther
authors.initials: E
authors.lastname: Martínez-García
authors.forename: Marcello
authors.initials: M
authors.lastname: Leopoldo
authors.forename: Enza
authors.initials: E
authors.lastname: Lacivita
authors.forename: José A
authors.initials: JA
authors.lastname: Terrón
mesh_terms: D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D008297:Male; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000378:metabolism*; D014275:Trigeminal Caudal Nucleus / Q000187:drug effects / Q000378:metabolism*
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D011985:Receptors, Serotonin; C104425:serotonin 7 receptor; D002211:Capsaicin
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