Objective       To determine the effects of intrathecal injection of P2X

7

receptor agonist

3′-O-(4-Benzoyl)benzoyl ATP (BzATP) and antagonist

Brilliant Blue G (BBG) on the activation of spinal dorsal horn microglia and pain related behaviors.        Methods        Totally 48 SD rats with intrathecal catheterization were

randomly divided into 4 groups

control

BzATP group

BBG+BzATP group and BBG group (n=12). The rats of above groups received an intrathecal administration of phosphorylate buffer solution (PBS)

BzATP

BBG+BzATP

and BBG

respectively since 3 d after catheterization for 7 continuous days. Pain threshold was assessed by thermal radiation and von Frey filament in 0

1

3

5

7

11

and 14 d after administration. Expression of OX42 and P2X

7

receptor in spinal dorsal horn of L

4

  to L

6

was measured by immunofluoresence staining.       Results       After administration of BzATP

thermal hyperalgesia and mechanical allodynia appeared in the rats. The thermal withdrawl latency (TWL) and 50% paw withdrawl threshold (PWT) were decreased obviously from 1 d after injection and descended to the lowest at 7 d (

P

0.01)

then returned to the level of normal control slowly. And these results were reversed by the treatment of P2X

7

receptor antagonist

BBG. The double labeled immunofluorescence results showed that the OX42 positive microglia expressed P2X

7

receptor. Immunohistological assay showed that the reaction of OX42 was obviously increased after injection of 7 days’ treatment of BzATP (

P

0.01)

and then declined to the baseline after the end of administration.       Conclusion        Activation of spinal dorsal horn microglial P2X

7

receptor plays essential roles in the incidence and progress of neuropathic pain.