Estrogen altered facial mechanical pain threshold and trigeminal P2X3 receptor expression.

Objectives: P2X3 receptors are expressed in trigeminal ganglia (TG) and participate in the transduction of facial pain. However, the mechanisms underlying P2X receptor-mediated nociception at different estrogen levels has not been examined.

Methods: In this study, female rats were randomly divided into sham-operated (sham), ovariectomized (OVX), and estrogen-treated groups. In each group, the facial mechanical pain threshold was tested and the TG were harvested for a real-time PCR analysis of P2X3 receptor mRNA and western blot analysis of protein level.

Results: In OVX rats we found that the mechanical pain threshold was significantly decreased compared with that in sham rats. Estrogen replacement reversed the decrease. The expression of P2X3 mRNA level in TG from OVX rats was significantly increased, consistent with the enhanced P2X3 receptor in protein level. Estrogen replacement could decrease the expression of P2X3 receptor in both mRNA and protein level.

Conclusion: These results indicate that estrogen might modulate the transduction of facial pain by inhibiting P2X3 receptor in TG.