title: CGRP infusion in unanesthetized rats increases expression of c-Fos in the nucleus tractus solitarius and caudal ventrolateral medulla, but not in the trigeminal nucleus caudalis.
abstract: OBJECTIVE
  Calcitonin gene-related peptide (CGRP) and glyceryl trinitrate (GTN) infusion in migraineurs provokes headache resembling spontaneous migraine, and CGRP receptor antagonists are effective in the treatment of acute migraine. We hypothesized that CGRP infusion would increase molecular markers of neuronal activation in migraine-relevant tissues of the rat.
  
  
  METHODS
  CGRP was infused intravenously (i.v.) in freely moving rats to circumvent factors like anesthesia, acute surgery and severe hypotension, the three confounding factors for c-Fos expression. The trigeminal nucleus caudalis (TNC) was isolated at different time points after CGRP infusion. The level of c-Fos mRNA and protein expression in TNC were analyzed by qPCR and immunohistochemistry. c-Fos-stained nuclei were also counted in the nucleus tractus solitarius (NTS) and caudal ventrolateral medulla (CVLM), integrative sites in the brain stem for processing cardiovascular signals. We also investigated Zif268 protein expression (another immediate early gene) in TNC. The protein expression of p-ERK, p-CREB and c-Fos was analyzed in dura mater, trigeminal ganglion (TG) and TNC samples using Western blot.
  
  
  RESULTS
  CGRP infusion caused a significant dose-dependent fall in mean arterial blood pressure. No significant activation of c-Fos in the TNC at mRNA and protein levels was observed after CGRP infusion. A significant increase in c-Fos protein was observed in the NTS and CVLM in the brain stem. Zif268 expression in the TNC was also not changed after CGRP infusion. p-ERK was increased in the dura mater 30 minutes after CGRP infusion.
  
  
  CONCLUSIONS
  CGRP infusion increased the early expression of p-ERK in the dura mater but did not increase c-Fos and Zif268 expression in the TNC. The rats may, thus, differ from migraine patients, in whom infusion of CGRP caused headache and a delayed migraine attack. The rat CGRP infusion model with c-Fos or Zif268 as neuronal pain markers in TNC is unsuitable for antimigraine drug testing.
authors.affiliation: Department of Neurology, Glostrup Hospital, Denmark.
authors.forename: Deepak K
authors.initials: DK
authors.lastname: Bhatt
authors.affiliation: Department of Neurology, Glostrup Hospital, Denmark.
authors.forename: Roshni
authors.initials: R
authors.lastname: Ramachandran
authors.affiliation: Department of Neurology, Glostrup Hospital, Denmark.
authors.forename: Sarah L T
authors.initials: SL
authors.lastname: Christensen
authors.affiliation: Department of Neurology, Glostrup Hospital, Denmark.
authors.forename: Saurabh
authors.initials: S
authors.lastname: Gupta
authors.affiliation: Department of Neurology, Glostrup Hospital, Denmark.
authors.forename: Inger
authors.initials: I
authors.lastname: Jansen-Olesen
authors.affiliation: Department of Neurology, Glostrup Hospital, Denmark jes.olesen@regionh.dk.
authors.forename: Jes
authors.initials: J
authors.lastname: Olesen
mesh_terms: D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000008:administration & dosage*; D005786:Gene Expression Regulation; D007262:Infusions, Intravenous; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017552:Solitary Nucleus / Q000187:drug effects / Q000378:metabolism*; D014275:Trigeminal Caudal Nucleus / Q000187:drug effects / Q000378:metabolism*
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D015740:Calcitonin Gene-Related Peptide
keywords: CGRP; Migraine; c-Fos; neuronal activation; vasodilation; zif268