Sex dependency in temporomandibular disorder (TMD) pain is well documented and is thought to be attributable to the influence of reproductive hormones on nociceptive processing. The present study was designed to test the hypotheses that synovial TRPV1 could be involved in TMD pain and estrogen might be through regulating synovial TRPV1 expression to mediate sex-related TMD pain.
Methods:
The rats were randomly divided into 6 groups (6 rats per group), including the control, sham-ovariectomized rats, and ovariectomized rats replaced with 0, 20, 80, and 200 µg of 17-beta-estradiol (E2) per rat, respectively, followed by injection of Complete Freund's Adjuvant (CFA) to induce TMJ arthritis. The effects of estradiol upon the expressions of TRPV1 and NGF were analyzed.
Results:
The injection of CFA into the temporomandibular joint (TMJ) significantly decreased head withdraw threshold. However, the local pretreatment of TRPV1 antagonist, capsaizepine (CPZ), produced up to 50% reversal of mechanical hyperalgesia. Immunoblot demonstrated that synovial TRPV1 and NGF expressions were upregulated by estrogen in a dose-dependent manner. Moreover, in primary cultured synovial cells, TRPV1 transcription was also induced by estrogen but abolished by anti-NGF antiserum and the estrogen receptor antagonist, ICI 182780. Stimulation of cultured synovial cells with the TRPV1 agonist capsaicin led to increased IL-1 mRNA and this induction could be antagonized by CPZ.
Conclusion:
Taken together, our results suggested that synovial TRPV1 might play a role in CFA-induced TMD pain and might mediate nociception induced by estrogen in TMD.