Estrogen upregulates hippocampus NGF and TRPV1 in TMJ arthritis rats

Objectives: Pain is the chief complaint of Temporomandibular disorders (TMD) and female is predominant in TMD patients. All those factors suggest estrogen may play an important role in the TMD related pain. The purpose of this study was to evaluate the effects of estrogen on expression of hippocampus nerve growth factor (NGF) and Transient receptor potential vanilloid 1 (TRPV1) in the experimental arthritis rats. Methods: Thirty rats were included in this study, twenty five rats were underwent ovariectomized (OVX). The OVX animals received estrogen replacement through daily subcutaneous injection of 17-beta estradiol (E2) at doses of 0, 20, 80, and 200 ug/kg for 12 days. Following E2 treatment, the rats were given an intra-articular TMJ injection of saline or complete Freund's adjuvant (CFA) and sacrificed one day later. Hippocampus samples were collected for RNA extraction, followed by RT-PCR, sequencing, restriction enzyme analysis and real-time PCR. Results: The PCR products of NGF were verified by the restriction enzyme analysis. The PCR products of TRPV1 were verified by sequencing. Real-time PCR demonstrated that expression of hippocampus NGF and TRPV1 mRNA was upregulated by estrogen in a dose dependent manner in the experimental arthritis model. Conclusions: The expression of hippocampus NGF and TRPV1 was upregulated by estrogen in the experimental arthritis model, suggesting that estrogen might play a role in TMD related pain by influencing the expression of pain related genes in the central nervous system. Further experiments were needed to define the mechanism underlying the induction of NGF and TRPV1 and enhancement of pain by estrogen.