Introduction: Burning mouth syndrome and atypical odontalgia (BMS/AO) are chronic orofacial pain conditions in the absence of any identifiable odontogenic pathology. The pain is treatment-resistant and frequently causes depressive symptoms. Duloxetine (DLX), a serotonin-noradrenaline reuptake inhibitor, is not only used as therapy for depression, but also for chronic orofacial pain. Since their mechanisms in detail remains unknown, in this study, we focused on serotonin transporter (SERT), one of DLX action site, and investigated association between expression of SERT and effect of DLX on pain in BMS/AO.
Methods: The patients with BMS/AO, were assessed for severity of pain using the visual analog scale (VAS) and for signs of depression using the Hamilton Depression Rating Scale (HDRS). In their platelets before (baseline) and 12 weeks after DLX-treatment, the expression of total and ubiquitinated SERT proteins was confirmed by Western blot. This study was approved by the Ethics Review Committees of Nagoya, Aichi Gakuin, and Meijo Universities.
Results: The expression of total and ubiquitinated SERT protein at baseline in all patients were higher and lower, respectively, compared to those in controls. After the DLX-treatment, there was no difference in the total SERT protein levels between the patients and controls. The mean of VAS and HDRS scores or the expression of total SERT protein were significantly decreased after the treatment, compared to those at baseline. 
Conclusions: These results indicate that DLX relieves chronic orofacial pain in patients with BMS/AO, and such effect may be mediated via SERT downregulation.