Systemic minocycline differentially influences changes in spinal microglial markers following formalin-induced nociception

In the present study, intraperitoneal administration of minocycline attenuated enhancing nociceptive behaviors in those rats receiving dual formalin injections (5% formalin followed at 7 days later by 1% formalin). The minocycline treatment did not prevent the increase in OX-42 and MHC class I labeling and morphological changes, but significantly attenuated upregulation of phospho-p38 in activated microglia. These results suggest that the later days of microglial activation with upregulated immune markers in the spinal cord contributes to enhancing long-term pain response by a pathway of p38 activation in microglia.