5-HT induces temporomandibular joint nociception in rats through the local release of inflammatory mediators and activation of local β adrenoceptors

The 5-hydroxytryptamine (serotonin, 5-HT) is an important inflammatory mediator found in high levels in the synovial fluid of the temporomandibular joint (TMJ) of patients with inflammatory pain. In this study, we used the nociceptive behavior responses, measured as flinching the head and rubbing the orofacial region, as a nociceptive assay. We demonstrated that the local blockade of the 5-HT3 receptor and β1 or β2-adrenoceptors, the depletion of norepinephrine in the sympathetic terminals and the local inhibition of cyclooxygenase significantly reduced 5-HT-induced TMJ nociception. These results demonstrated that 5-HT induces nociception in the TMJ region by the activation of β1 and β2 adrenoceptors located in the TMJ region and local release of sympathetic amines and prostaglandins. Therefore, the high levels of 5-HT in the synovial fluid of patients with TMJ inflammatory pain may contribute to TMJ pain by similar mechanisms.

► 5-HT induces temporomandibular joint (TMJ) nociception. ► Prostaglandins and sympathetic amines contribute to 5-HT-induced TMJ nociception. ► Activation of TMJ β1 and β2 adrenoceptors contributes to 5-HT-induced TMJ nociception.