Effects of P2X4 receptor in spinal microglia on rrTNF-induced pathological pain

AIM: To investigate the effects of P2X₄ receptor on peri-sciatic administration of recombinant rat TNF-α (rrTNF)-induced mechanical allodynia. METHODS: Male Sprague-Dawley rats (180~200 g) were used in the experiments. The levels of P2X₄ receptor on day 3, day 7 and day 14 after peri-sciatic administration of rrTNF were examined by Western blot, and the location of P2X₄ receptor in the spinal dorsal horn was observed by double immunofluorescence staining. The changes of 50% paw-withdrawal thresholds of the rat were detected by behavioral test, and the level of TNF-α in the spinal dorsal horn was also examined by Western blot when TNP-ATP was intrathecally injected before the administration of rrTNF. RESULTS: Compared with control group, the expression of P2X₄ receptor in the spinal dorsal horn on the ipsilateral side significantly increased on day 3, day 7 and day 14 (P<0.01) after rrTNF (100 ng/L) administration. P2X₄ receptor was co-localized only with microglia, but not with neurons or astrocytes. Intrathecal injection of TNP-ATP before rrTNF administration prevented mechanical allodynia induced by rrTNF and inhibited the upregulation of TNF-α in the spinal dorsal horn. CONCLUSION: P2X₄ receptors in microglia may be involved in rrTNF-induced mechanical allodynia by the upregulation of TNF-α in the spinal dorsal horn.