Era Increases Following Adjuvant-Induced Inflammation in the Female Rat Tmj

OBJECTIVES: Estrogen is known to play role in this hormonal influence and estrogen effects can be mediated by ERa and ERb present in the temporomandibular joint (TMJ). Here we hypothesize that ERa and ERb expression will increase during inflammation and that estrogen will modulate this expression.

METHODS: Sixteen ovariectomized female rats were divided into two groups such that one group received 17b estradiol (E2) and the other was given vehicle (VEH). Groups were then subdivided further, one received injections of saline and the other received Complete Freund's adjuvant (CFA) within the superior joint space of the TMJ. Thus the four groups include VEH/saline, VEH/CFA, E2/saline and E2/CFA. The animals were sacrificed. TMJ tissues sections were immunohistochemically stained or the protein was isolated for western blot analysis. Positive stained cells were counted using a Nikon epifluorescent microscope.

RESULTS: Confocal microscopy analysis demonstrated that ERa was located primarily within the retrodiscal tissue, the anterior tissue and synovium. Combined cell counts in these tissues indicated that ERa significantly increased in the VEH/CFA and E2/CFA as compared to the E2/saline group. In the synovium, higher levels of ERa were observed in the VEH/saline in comparison to the VEH/CFA group and also in VEH/saline in comparison to the E2/saline group. Combining cell counts from the retrodiscal tissue and synovium demonstrated a significant difference between E2/saline and VEH/saline. Significant differences were also seen in the anterior tissue between the VEH/saline and VEH/CFA as well as between the VEH/saline and E2/saline group. Consistent with this result, ERa protein expression in the E2/saline group was significantly elevated as compared to VEH/saline.

CONCLUSIONS: These data suggest that ERa but not ERb expression increased during inflammation and that estrogen can modulate ERa expression in the TMJ. These results support the hypothesis that ERa plays a role in temporomandibular joint disorder.