Nav1.7 expression is increased in painful human dental pulp.

ABSTRACT

BACKGROUND: Animal studies and a few human studies have shown a change in sodium channel (NaCh) expression after inflammatory lesions, and this change is implicated in the generation of pain states. We are using the extracted human tooth as a model system to study peripheral pain mechanisms and here examine the expression of the Nav1.7 NaCh isoform in normal and painful samples. Pulpal sections were labeled with antibodies against 1) Nav1.7, N52 and PGP9.5, and 2) Nav1.7, caspr (a paranodal protein used to identify nodes of Ranvier), and myelin basic protein (MBP), and a z-series of optically-sectioned images were obtained with the confocal microscope. Nav1.7-immunofluorescence was quantified in N52/PGP9.5-identified nerve fibers with NIH ImageJ software, while Nav1.7 expression in myelinated fibers at caspr-identified nodal sites was evaluated and further characterized as either typical or atypical as based on caspr-relationships. RESULTS: Results show a significant increase in nerve area with Nav1.7 expression within coronal and radicular fiber bundles and increased expression at typical and atypical caspr-identified nodal sites in painful samples. Painful samples also showed an augmentation of Nav1.7 within localized areas that lacked MBP, including those associated with atypical caspr-identified sites, thus identifying NaCh remodeling within demyelinating axons as the basis for a possible pulpal pain mechanism. CONCLUSION: This study identifies the increased axonal expression and augmentation of Nav1.7 at intact and remodeling/demyelinating nodes within the painful human dental pulp where these changes may contribute to constant, increased evoked and spontaneous pain responses that characterize the pain associated with toothache.