title: Calcitonin gene-related peptide is involved in inflammatory pain but not in postoperative pain.
abstract: BACKGROUND
  The aim of this study was to clarify the roles of calcitonin gene-related peptide (CGRP) in postoperative pain and inflammatory pain.
  
  
  METHODS
  αCGRP knockout mice that the authors have developed and wild-type mice were used. Pain behaviors were assessed after incision and complete Freund's adjuvant (CFA) injection. Changes in CGRP and c-Fos expression in the dorsal horn were also examined.
  
  
  RESULTS
  Guarding pain scores in αCGRP knockout mice were lower than those in wild-type mice at 24 h (3.8 ± 1.6 vs. 6.8 ± 1.5, P = 0.044) and 48 h (1.8 ± 1.7 vs. 6.0 ± 1.5, P = 0.001) after CFA injection (n = 8 to 9). Withdrawal latencies to heat stimulation in αCGRP knockout mice were higher than those in wild-type mice at 24 to 72 h after CFA injection (4.9 ± 1.0 vs. 3.4 ± 0.8 at 24 h, P = 0.04; 5.1 ± 0.3 vs. 3.2 ± 0.9 at 48 h, P = 0.047; and 5.4 ± 1.6 vs. 3.5 ± 0.5 s at 72 h, P = 0.045) (n = 11 to 13), but withdrawal thresholds to mechanical stimulation were comparable. CGRP expression was increased at 24 h after CFA injection in wild-type mice, and the c-Fos-positive profile was increased at 4 h after CFA injection (ipsilateral vs. contralateral: 12.3 ± 4.6 vs. 1.3 ± 1.9, P < 0.0001) and maintained at 24 h (10.0 ± 4.1 vs. 0.8 ± 1.3, P < 0.0001) (n = 4 to 6).
  
  
  CONCLUSIONS
  These results suggest that contribution of the αCGRP system depends on the modality of pain and the stage of inflammation.
authors.affiliation: From the Department of Anesthesiology and Resuscitology, Shinshu University School of Medicine, Matsumoto, Japan (K.I., T.K., S.T., M.K.); and Department of Cardiovascular Research, Shinshu University Graduate School of Medicine, Matsumoto, Japan (T.S.).
authors.forename: Kumiko
authors.initials: K
authors.lastname: Ishida
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Kawamata
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tanaka
authors.forename: Takayuki
authors.initials: T
authors.lastname: Shindo
authors.forename: Mikito
authors.initials: M
authors.lastname: Kawamata
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D015740:Calcitonin Gene-Related Peptide / Q000235:genetics* / Q000502:physiology*; D004487:Edema / Q000473:pathology; D005528:Foot / Q000473:pathology; D007249:Inflammation / Q000150:complications / Q000503:physiopathology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement / Q000187:drug effects; D010149:Postoperative Pain / Q000503:physiopathology*
chemical_list: D015740:Calcitonin Gene-Related Peptide