Nav1.7 sodium channel expression in human lingual nerve neuromas

ObjectivePeripheral branches of the trigeminal nerve are often damaged during the removal of lower third molar teeth, and a small proportion of patients who sustain an injury develop persistent chronic pain. The cause of the pain is not clear and there are no satisfactory methods of treatment. The aim of the present study was to examine the expression of the sodium channel subtype Nav1.7 in damaged human lingual nerves, and to identify any association between Nav1.7 expression and reported symptoms of dysaesthesia.MethodsEleven neuromas-in-continuity (NICs) and 11 nerve-end neuromas (NENs) were studied, and were all obtained at the time of surgical repair of the damaged lingual nerve. Specimens were categorised as being obtained from patients with symptoms or without symptoms, according to the degree of pain, tingling or discomfort that had been experienced. The tissue was prepared and processed for indirect immunofluorescence, and image analysis was used to quantify the percentage area of PGP 9.5-labelled tissue that also contained Nav1.7.ResultsThe results demonstrated that sodium channel Nav1.7 was expressed in human lingual nerve neuromas. There was no direct relationship between the level of expression of Nav1.7 and the patients’ symptoms of dysaesthesia. However, in NICs there was found to be an inverse correlation between Nav1.7 and macrophage expression, and in symptomatic NICs a direct correlation was found between Nav1.7 expression and axonal apposition.ConclusionsThese data suggest that Nav1.7 expression alone does not play a primary role in initiating the painful symptoms of dysaesthesia. The development of neuropathic pain may involve complex interactions including changes in ultrastructure and ion channel density.