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There is evidence that gonadal hormones may affect the perception of painful stimulation, although the underlying mechanisms remain unclear.This investigation was undertaken to determine whether the adenosine 5-triphosphate (ATP) receptor subunit, P2X3, is involved in the modulatory action of estrogen in peripheral pain signal transduction in dorsal root ganglion (DRG).The mechanical pain behavior test, real-time quantitative reverse transcription-polymerase chain reaction analysis (QT-RT-PCR), and Western blot methods were used to determine the mean relative concentrations and functions of P2X3 receptors in DRG in sham, ovariectomized (OVX) and estradiol replacement (OVX+E2) female rats and in sham and orchiectomized male rats.The mechanical hyperalgesia appeared after ovariectomy, which was subsequently reversed after estradiol replacement, whereas it was not observed after orchiectomy in male rats.Plantar injection of 2(3)-O-(2,4,6-trinitrophenyl) ATP (TNP-ATP), a P2X3 and P2X2/3 receptor antagonist, resulted in an increase of the pain threshold force in OVX rats while had no effect on sham rats.Further, A-317491, a selective P2X3/P2X2/3 receptor antagonist, significantly reversed the hyperalgesia of OVX rats.