Journal Article

Mechanisms Underlying Ectopic Persistent Tooth-Pulp Pain following Pulpal Inflammation

Ohara, Kinuyo, Urata, Kentaro, Iwata, Koichi, Ogiso, Bunnai, Matsuura, Shingo, Shinoda, Masamichi, Sessle, Barry J., Honda, Kuniya, Katagiri, Ayano, Shimizu, Kohei

2013

Overview

In order to clarify the peripheral mechanisms of ectopic persistent pain in a tooth pulp following pulpal inflammation of an adjacent tooth, masseter muscle activity, phosphorylated extracellular signal-regulated protein kinase (pERK) and TRPV1 immunohistochemistries and satellite cell activation using glial fibrillary acidic protein (GFAP) immunohistochemistry in the trigeminal ganglion (TG) were studied in the rats with molar tooth-pulp inflammation. And, Fluorogold (FG) and DiI were also used in a neuronal tracing study to analyze if some TG neurons innervate more than one tooth pulp. Complete Freund's adjuvant (CFA) or saline was applied into the upper first molar tooth pulp (M1) in pentobarbital-anesthetized rats, and capsaicin was applied into the upper second molar tooth pulp (M2) on day 3 after the CFA or saline application. Mean EMG activity elicited in the masseter muscle by capsaicin application to M2 was significantly larger in M1 CFA-applied rats compared with M1 vehicle-applied rats. The mean number of pERK-immunoreactive (IR) TG cells was significantly larger in M1 CFA-applied rats compared with M1 vehicle-applied rats. Application of the satellite cell inhibitor fluorocitrate (FC) into TG caused a significant depression of capsaicin-induced masseter muscle activity and a significant reduction of satellite cell activation. The number of TRPV1-IR TG cells innervating M2 was significantly larger in M1 CFA-applied rats compared with M1 vehicle-applied rats, and that was decreased following FC injection into TG. Furthermore, 6% of TG neurons innervating M1 and/or M2 innervated both M1 and M2. These findings suggest that satellite cell activation following tooth pulp inflammation and innervation of multiple tooth pulps by single TG neurons may be involved in the enhancement of the activity of TG neurons innervating adjacent non-inflamed teeth that also show enhancement of TRPV1 expression in TG neurons, resulting in the ectopic persistent tooth-pulp pain following pulpal inflammation of adjacent teeth.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Analysis / Animals / Biology / Brain-derived neurotrophic factor / Capsaicin / Capsaicin receptors / Carbocyanines - metabolism / Cell activation / Citrates - administration & dosage / Citrates - pharmacology / Dental pulp / Dental Pulp - drug effects / Dental Pulp - pathology / Dentistry / Electromyography / Extracellular Signal-Regulated MAP Kinases - metabolism / Freund's Adjuvant - pharmacology / Glial fibrillary acidic protein / Glial Fibrillary Acidic Protein - metabolism / Immunohistochemistry / Inflammation / Inflammation - complications / Inflammation - enzymology / Inflammation - pathology / Innervation / Intermediate filament proteins / Laboratory animals / Male / Masseter muscle / Masseter Muscle - drug effects / Masseter Muscle - pathology / Medicine / Mental depression / Models, Biological / Molar - drug effects / Molar - pathology / Muscles / Nervous system / Neurons / Neurons - drug effects / Neurons - metabolism / Neurons - pathology / Neurosciences / Pain / Pentobarbital / Phosphorylation / Phosphorylation - drug effects / Physicians / Physiology / Protein kinase / Rats / Rats, Sprague-Dawley / Rodents / Satellite Cells, Skeletal Muscle - drug effects / Satellite Cells, Skeletal Muscle - pathology / Satellites / Stilbamidines - metabolism / Teeth / Toothache - enzymology / Toothache - etiology / Toothache - pathology / Trigeminal ganglion / Trigeminal Ganglion - drug effects / Trigeminal Ganglion - enzymology / Trigeminal Ganglion - pathology / TRPV Cation Channels - metabolism