Effects of experimentally induced inflammation on temporomandibular joint nociceptors in rats

Response properties of nociceptors in the temporomandibular joint (TMJ) and surrounding area under experimental inflammation were investigated using an in vitro TMJ-nerve preparation in the rat. Nociceptive units (receptor and innervating nerve fiber) were classified into the following subtypes: Adelta-high-threshold mechanonociceptor (HTM), Adelta-polymodal nociceptor (POLY), C-HTM and C-POLY. In the inflamed joint, mechanical thresholds tended to be lower; however, the reaction to bradykinin was not identified as clearly as in control. Experimentally induced inflammation increased the proportion of heat-sensitive units and lowered heat threshold significantly. These results suggest that inflammation may sensitize nociceptors in the temporomandibular joint, and cause hyperalgesia and allodynia.