Nav 1.7 expression in trigeminal pain states

Objectives: To evaluate Nav1.7 levels in orofacial pain conditions including toothache, post traumatic lingual nerve injury and Burning Mouth Syndrome. Methods: 17 vital permanent molar teeth scheduled for extraction. 5 patients with painful lingual nerve injury and 10 patients with Burning Mouth Syndrome with matched control patients undergoing third molar surgery were recruited. A pain history was collected. The patients were divided into two groups, those with existing pain and those with no history of or existing pain. The gender distribution of the groups was M: F 1:1. All specimens were immediately snap-frozen at -70oC. Immunohistochemistry and computer image analysis was used to evaluate the relative expressions. The mean values of readings obtained by two independent observers, each blinded, were used for final analysis. Results: A subset of nerve fibres was immunoreactive with the Nav1.7 antibody in both non-painful and painful pulp groups. There was a significant increase of the visual intensity score for Nav1.7 in the painful group compared to controls. Strong Nav1.7 immunoreactivity fibre staining was seen in fascicles in all lingual nerve specimens studied. By image analysis there was a tendency for an increase of Nav1.7 staining in the injured lingual nerve group but was not statistically significant. Strong sub-epithelial Nav1.7 immunoreactive fibre staining was found in all tongue biopsy specimens studied. By image analysis there was no difference between the Burning Mouth Syndrome and control groups. Conclusions: Nav1.7 is significantly increased in association with dental pain. However the increased immunoreactivity of Nav1.7 in lingual tissues in association with neuropathic pain with Burning Mouth Syndrome and post traumatic nerve injury was not significant.