Intra-articular induction of µ-opioid-receptor ameliorates temporomandibular joint pain and dysfunction

Temporomandibular joint (TMJ) pain and dysfunction are often debilitating symptoms associated with orofacial pain (OP). Current treatments for OP produce variable and often inadequate results. Objectives: To examine the anti-nociceptive (pain-killer) effect of local induction of human μ-opioid receptor (HuMOR) in the TMJ of the transgenic Col1-IL-1β^xat mouse model of arthritis. Methods: This model uses somatic mosaic analysis in a transgenic mouse with an inducible IL-1β gene. Transgene activation was induced by Cre recombinase in the TMJ, resulting in nociceptive orofacial behavior, as measured by increased orofacial grooming, and jaw dysfunction, as measured by decreased resistance to mouth opening. Results: Local pre-treatment with the feline immunodeficiency virus (FIV) vector encoding HuMOR attenuated the nociceptive behavior and jaw dysfunction (ANOVA, p<0.05) via over-expression of HuMOR in the trigeminal neurons innervating TMJ tissues. In addition, it ameliorated the arthritic TMJ pathology and reversed the expression of c-fos and murine IL-1β as well as the astroglia activation in the trigeminal subnucleus caudalis (p<0.05). Conclusions: Over-expression of HuMOR attenuates experimentally-induced nociceptive orofacial behavior, joint dysfunction and arthritic pathology providing the base for the development of novel treatments for the management of TMJ disorders.