Nociceptive behavior induced by mustard oil injection into the temporomandibular joint is blocked by a peripheral non-opioid analgesic and a central opioid analgesic

The aim of this study was to improve the mustard oil (MO) induced temporomandibular joint (TMJ) nociception model and to investigate the potential analgesic activity of systemic dipyrone and tramadol on the nociceptive behavioral responses induced by injection of low concentrations of the MO into the rat TMJ region. TMJ injection of 2.5% MO produced a significant nociceptive behavior expressed by head flinching and orofacial rubbing. This activity was related to the MO injection since mineral oil (vehicle) did not elicit response. Local application of the lidocaine N-ethyl bromide quaternary salt, QX-314 (2%) and systemic administration of morphine (4 mg/kg) significantly reduced the MO-induced nociceptive responses, validating the nociceptive character of the behaviors. The pretreatment with systemic dipyrone (19, 57 or 95 mg/kg) as well as tramadol (5, 7.5 or 10 mg/kg) was effective in decreasing the nociceptive behavioral responses induced by the injection of MO into the rat TMJ. In conclusion, TMJ injection of low concentrations of MO in rats produces well defined and quantifiable nociceptive behaviors constituting a reliable behavioral model for studying TMJ pain mechanisms and testing analgesic drugs. The results also suggest that dipyrone and tramadol could be effective analgesic options in the management of TMJ pain.