Cyclooxygenase (COX)-1 and COX-2 metabolize arachidonic acid to prostaglandin (PG) H2 that is a common substrate for different prostanoids synthases. Recently we have reported that COX-1-derived PGD2 is involved in neuropathic pain after peripheral nerve injury. Though COX2-derived PGs after peripheral nerve injury are remained unclear. Using spared nerve injury (SNI) model rat, we investigated the expression of COX-2, PGI2 synthase and PGI2 receptor (IP) mRNA in spinal cord. COX-2 and PGIS mRNAs showed the increase from 24 hours and peaked at 48 hours after nerve injury. There was no significant difference in IP mRNA levels in the spinal cord following peripheral nerve injury. COX-2 and PGIS mRNAs were upregulated in endothelial cells and IP receptor mRNA was constitutively expressed in dorsal horn neurons. To examine whether the PGI2 in the endothelial cells is involved in pain mechanisms, we employed the behavioral analysis. COX-2 inhibitor and IP receptor antagonist attenuated pain behavior in early phase of neuropathic pain. Next, we examined the relationship between COX-2 and TNF alpha in the spinal cord of SNI model. TNF alpha mRNA showed the transient increase from 18 hours and peaked at 24 hours in the spinal microglia following SNI. Using double ISHH-immunohistochemistry, TNFR1 and TNFR2 mRNA were co-localized with COX-2. Intrathecal injection of TNF alpha induced COX-2 and PGIS mRNA in endothelial cells. Intrathecal injection of TNF alpha neutralizing antibody attenuated the pain behavior of neuropathic pain and significantly suppressed the upregulation of COX-2 and PGIS following nerve injury. These results revealed that glia-derived TNF alpha induced the COX-2 and PGIS expression in spinal endothelial cells and critical role of endothelial PGI2 via COX-2 in neuropathic pain.