title: Rat odontoblasts may use glutamate to signal dentin injury.
abstract: Accumulating evidence indicates that odontoblasts act as sensor cells, capable of triggering action potentials in adjacent pulpal nociceptive axons, suggesting a paracrine signaling via a currently unknown mediator. Since glutamate can mediate signaling by non-neuronal cells, and peripheral axons may express glutamate receptors (GluR), we hypothesized that the expression of high levels of glutamate, and of sensory receptors in odontoblasts, combined with an expression of GluR in adjacent pulpal axons, is the morphological basis for odontoblastic sensory signaling. To test this hypothesis, we investigated the expression of glutamate, the thermo- and mechanosensitive ion channels transient receptor potential vanilloid 1 (TRPV1), transient receptor potential ankyrin 1 (TRPA1), and TWIK-1-related K+channel (TREK-1), and the glutamate receptor mGluR5, in a normal rat dental pulp, and following dentin injury. We also examined the glutamate release from odontoblast in cell culture. Odontoblasts were enriched with glutamate, at the level as high as in adjacent pulpal axons, and showed immunoreactivity for TRPV1, TRPA1, and TREK-1. Pulpal sensory axons adjacent to odontoblasts expressed mGluR5. Both the levels of glutamate in odontoblasts, and the expression of mGluR5 in nearby axons, were upregulated following dentin injury. The extracellular glutamate concentration was increased significantly after treating of odontoblast cell line with calcium permeable ionophore, suggesting glutamate release from odontoblasts. These findings lend morphological support to the hypothesis that odontoblasts contain glutamate as a potential neuroactive substance that may activate adjacent pulpal axons, and thus contribute to dental pain and hypersensitivity.
authors.affiliation: Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 700-412, Republic of Korea.
authors.forename: Yi Sul
authors.initials: YS
authors.lastname: Cho
authors.affiliation: Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 700-412, Republic of Korea.
authors.forename: Chang Hyun
authors.initials: CH
authors.lastname: Ryu
authors.affiliation: Pain Cognitive Function Research Center, Dental Research Institute of Neurobiology and Physiology, School of Dentistry, Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea.
authors.forename: Jong Hwa
authors.initials: JH
authors.lastname: Won
authors.affiliation: Pain Cognitive Function Research Center, Dental Research Institute of Neurobiology and Physiology, School of Dentistry, Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea.
authors.forename: Hue
authors.initials: H
authors.lastname: Vang
authors.affiliation: Pain Cognitive Function Research Center, Dental Research Institute of Neurobiology and Physiology, School of Dentistry, Department of Brain and Cognitive Sciences, College of Natural Sciences, Seoul National University, Seoul, Republic of Korea.
authors.forename: Seog Bae
authors.initials: SB
authors.lastname: Oh
authors.affiliation: Department of Neural and Pain Sciences, University of Maryland School of Dentistry, Baltimore, USA.
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Ro
authors.affiliation: Department of Anatomy and Neurobiology, School of Dentistry, Kyungpook National University, Daegu 700-412, Republic of Korea. Electronic address: ycbae@knu.ac.kr.
authors.forename: Yong Chul
authors.initials: YC
authors.lastname: Bae
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D003782:Dental Pulp / Q000293:injuries / Q000378:metabolism*; D003804:Dentin / Q000293:injuries*; D018698:Glutamic Acid / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009804:Odontoblasts / Q000378:metabolism*; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism; D017207:Rats, Sprague-Dawley; D011984:Sensory Receptor Cells / Q000378:metabolism; D050916:TRPV Cation Channels / Q000378:metabolism
chemical_list: D009419:Nerve Tissue Proteins; D024683:Potassium Channels, Tandem Pore Domain; D050916:TRPV Cation Channels; C103742:potassium channel protein TREK-1; D018698:Glutamic Acid
keywords: electron microscopy; glutamate; glutamate receptor; neuroactive substance; odontoblast; signaling