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Aim: To investigate whether activation and translocation of extracellular signalregulated kinase (ERK) is involved in the induction and maintenance of neuropathic pa in, and effects of activation and translocation of ERK on expression of pCREB and Fos in the chronic neuropathic pain.Methods: Lumbar intrathecal catheters were chronically implanted in male Sprague-Dawley rats.The left sciatic nerve was loosely ligated proximal to the sciatica’s trifurcation at approximately 1.0 mm intervals with 4-0 silk sutures.The mitogen-activated protein kinase kinase (MEK) inhibitor U0126 or phosphorothioate-modified antisense oligonucleotides (ODN) were intrathecally administered every 12 h, 1 d pre-chronic constriction injury (CCI) and 3 d post-CCI.Thermal and mechanical nociceptive thresholds were assessed with the paw withdrawal latency (PWL) to radiant heat and yon Frey filaments.The expression of pERK, pCREB, and Fos were assessed by both West blotting and immunohistochemical analysis.Results: Intrathecal injection of U0126 or ERK antisense ODN significantly attenuated CCI-induced mechanical allodynia and thermal hyperalgesia.CCI significantly increased the expression of p-ERK-IR neurons in the ipsilateral spinal dorsal h to injury, not in the contralateral spinal dorsal h.The time courses of pERK expression showed that the levels of both cytosol and nuclear pERK, but not total ERK, were increased at all points after CCI and reached a peak level on postoperative d 5.CCI also significantly increased the expression of pCREB and Fos.Phospho-CREB-positive neurons were distributed in all laminae of the bilateral spinal cord and Fos was expressed in laminae Ⅰ and Ⅱ of the ipsilateral spinal dorsal h.Intrathecal injection of U0126 or ERK antisense ODN markedly suppressed the increase of CCI-induced pERK, pCREB and c-Fos expression in the spinal cord.Conclusion:The activation of ERK pathways contributes to neuropathic pain in CCI rats, and the function of pERK may partly be accomplished via the cAMP response element binding protein (CREB)-dependent gene expression.