Objective  To investigate the expression change of P2X

3

receptor in spinal dorsal horn and dorsal root ganglion (DRG) in rats with experimental inflammatory pain. Methods  Totally 30 SD rats received a subcutaneous  injection of carrageenan in the right paw to establish inflammatory pain model

and then divided randomly and equally into 5 groups

that is 6

12

24

72 and 168 h after injection. Another 6 rats undergoing a subcutaneous injectio

n of normal saline in the right paw served as control. Pain threshold was assayed by thermal radiation and von Frey filament in 2

4

6

12

24

72 and 168 h after injection. Expression of P2X

3

receptor in spinal dorsal horn and DRG of every group was measured by immunohistochemical staining (IHC). Results  After injection of carrageenan

thermal hyperalgesia and mechanical allodynia appeared in the rats. The thermal withdrawl latency (TWL) and 50% paw withdrawl threshold (PWT) were decreased obviously from 2 h

descended to the lowest at 12 h

then returned to the normal level after 72 h. The expression of P2X

3

receptor in spinal dorsal horn was increased obviously from 24 h，while that at DRG was increased obviously from 12 h. Both of the expressions lasted for 72 h

and returned to the normal level at 168 h after injection. Conclusion  Thermal hyperalgesia and mechanical allodynia appear in the rats after carrageenan injection

and the P2X

3

receptor is activated and up-regulated in the DRG and spinal cord

suggesting that P2X

3

receptor may play an important role in the incidence and development of inflammatory pain.