Protein phosphatase regulates the phosphorylation of NR2B subunit of NMDA receptors in rat spinal cord following intradermal injection of capsaicin

Abstract

Central sensitization is sensory hypersensitivity in the central nervous system that can be induced by peripheral noxious stimulation. It can be mediated through the activation of several second messenger cascades, such as protein kinase A or protein kinase C. An opposing enzyme to protein kinases, serine/threonine protein phosphatase 2A (PP2A), which catalyzes dephosphorylation reactions, plays an important role in central sensitization. During central sensitization the function of the NMDA receptor is enhanced by increases in channel opening due to its phosphorylation. The effect of a specific inhibitor of PP2A, fostriecin, on the expression of NR2B and phospho-NR2B subunits of NMDA receptors in the spinal cord of rats following capsaicin injection were investigated in this study. After continually perfusing with ACSF or fostriecin (3 M) through a previously implanted microdialysis fiber for 30 minutes, central sensitization was initiated by injection of capsaicin into the plantar surface of the left paw of rats. The spinal cord was removed quickly at different time points (30, 60, 90, 120, 180 min) after intradermal injection of capsaicin. Western blots were performed to examine the expression of NR2B and phospho-NR2B subunits in spinal cord tissue by using specific antibodies. Both NR2B and phospho-NR2B expression were found in ACSFand fostriecintreated groups. At each time point after capsaicin injection, no significant difference was found in NR2B expression in either group. In the ACSF group, phospho-NR2B expression was increased at a time point of 30 minutes and the expression gradually decreased in a time dependent manner. In fostriecin group, phosphoNR2B expression was not significantly reduced until 180 minutes after capsaicin injection. These results suggest that PP2A has a regulatory effect on central sensitization induced by noxious stimuli in the periphery by modulating the phosphorylation state of NMDA receptors. Supported by NIH grant NS09743.