title: The constitutive activation of extracellular signal-regulated kinase 1 and 2 in periodontal ligament nerve fibers.
abstract: BACKGROUND
  The extracellular signal-regulated kinases 1 and 2 (ERK1/2) have been implicated in the inflammation-dependent sensitization of nociceptors. Because the periodontal ligament (PDL) contains numerous nociceptors and mechanoceptors, phosphorylation of ERK1/2 was investigated in nerve fibers of the PDL to elucidate the role of constitutive local activation of ERK1/2 in peripheral sensitization.
  
  
  METHODS
  Decalcified free-floating sections of rat molars with PDL were incubated using total (t)-ERK1/2 and phosphorylated (p)-ERK1/2 antibodies. For identification of nerve fibers in the PDL, double staining was performed using protein gene product 9.5 (PGP 9.5) with p-ERK1/2. To test whether p-ERK1/2 activated in sensory and mechanoreceptive terminals, double incubations were performed using p-ERK1/2 with calcitonin gene-related peptide (CGRP) and with calretinin. Labeled nerve fibers were quantified by the point-counting method.
  
  
  RESULTS
  In cervical, midroot, and apical zones of the PDL, t-ERK1/2- and p-ERK1/2-labeled nerve fibers were found in close association with blood vessels. The p-ERK1/2-labeled free nerve fibers were often detected in cervical and apical areas of the PDL. In nerve fibers of the PDL, p-ERK1/2 was colocalized with PGP 9.5, CGRP, and calretinin.
  
  
  CONCLUSIONS
  The perivascular distribution of t-ERK1/2 and p-ERK1/2 in nerve fibers in the PDL is compatible with a role for the constitutive activation of ERK1/2 in the neural regulation of blood vessels in the PDL. The colocalizations of p-ERK1/2 with CGRP and calretinin indicate that ERK1/2 is constitutively activated in a subpopulation of sensory and mechanoreceptive nerve terminals in the PDL.
authors.affiliation: Department of Operative and Preventive Dentistry and Endodontics, Heinrich Heine University, Düsseldorf, Germany. yueksel.korkmaz@uni-duesseldorf.de
authors.forename: Yüksel
authors.initials: Y
authors.lastname: Korkmaz
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Bloch
authors.forename: Franz-Josef
authors.initials: FJ
authors.lastname: Klinz
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Kübler
authors.forename: Kurt
authors.initials: K
authors.lastname: Schneider
authors.forename: Stefan
authors.initials: S
authors.lastname: Zimmer
authors.forename: Klaus
authors.initials: K
authors.lastname: Addicks
authors.forename: Wolfgang H-M
authors.initials: WH
authors.lastname: Raab
mesh_terms: D000818:Animals; D064032:Calbindin 2; D015740:Calcitonin Gene-Related Peptide / Q000502:physiology; D004789:Enzyme Activation; D007124:Immunoenzyme Techniques; D008297:Male; D008465:Mechanoreceptors / Q000201:enzymology / Q000502:physiology; D018613:Microscopy, Confocal; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009412:Nerve Fibers / Q000201:enzymology; D009619:Nociceptors / Q000201:enzymology / Q000502:physiology; D010513:Periodontal Ligament / Q000098:blood supply / Q000201:enzymology* / Q000294:innervation*; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D064030:S100 Calcium Binding Protein G / Q000502:physiology
chemical_list: C576512:Calb2 protein, rat; D064032:Calbindin 2; D064030:S100 Calcium Binding Protein G; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D015740:Calcitonin Gene-Related Peptide