The Constitutive Activation of Extracellular Signal‐Regulated Kinase 1 and 2 in Periodontal Ligament Nerve Fibers

• Published in: Journal of periodontology (1970) 2009-05, Vol.80 (5), p.850-859
• Main Authors: Korkmaz, Yüksel, Bloch, Wilhelm, Klinz, Franz‐Josef, Kübler, Alexander C., Schneider, Kurt, Zimmer, Stefan, Addicks, Klaus, Raab, Wolfgang H.‐M.
• Format: Article
• Language: English
• Subjects: Animals; Biological and medical sciences; Calbindin 2; Calcitonin Gene-Related Peptide - physiology; Dentistry; Enzyme Activation; Extracellular signal‐regulated kinases; Immunoenzyme Techniques; Male; Mechanoreceptors - enzymology; Mechanoreceptors - physiology; Medical sciences; Microscopy, Confocal; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; mitogen‐activated protein kinase; Nerve Fibers - enzymology; nociception; Nociceptors - enzymology; Nociceptors - physiology; Otorhinolaryngology. Stomatology; periodontal ligament; Periodontal Ligament - blood supply; Periodontal Ligament - enzymology; Periodontal Ligament - innervation; Phosphorylation; Rats; Rats, Wistar; S100 Calcium Binding Protein G - physiology
• ISSN: 0022-3492; 1943-3670
• DOI: 10.1902/jop.2009.080550

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.