Based on previous work, we hypothesized that activation of spinal NMDA-receptor initiates activation of the p38 mitogen-activated protein kinase (p38 MAPK) pathway, leading to spinal release of prostaglandins and hyperalgesia. Accordingly, we examined the effect of intrathecal SD-282, a selective p38 MAPK inhibitor, on NMDA-induced release of prostaglandin E(2) (PGE(2)) and thermal hyperalgesia. Inhibition of spinal p38 MAPK attenuated both NMDA-evoked release of PGE(2) and thermal hyperalgesia. NMDA injection led to increased phospho-p38 MAPK immunoreactivity in superficial (I-II) dorsal laminae. Co-labeling studies revealed co-localization of activated p38 MAPK predominantly with microglia but also with a small subpopulation of neurons. Taken together these data suggest a role for p38 MAPK in NMDA-induced PGE(2) release and hyperalgesia, and that microglia is involved in spinal nociceptive processing.