Neuronal Plasticity and Signaling in Neuropathic Pain Project Summary Activity-dependent synaptic plasticity at the spinal cord level is fundamentally important to the development of neuropathic pain caused by traumatic nerve injury and surgery. N-methyl-D-aspartate (NMDA) receptors in the spinal dorsal horn are critically involved in central sensitization and maintenance of neuropathic pain. However, the mechanisms of potentiated NMDA receptor activity in the spinal cord after nerve injury remain poorly understood. Although increased phosphorylation of NMDA receptors after nerve injury is known, the upstream mechanisms of increased NMDA receptor activity in neuropathic pain remain to be determined. In our preliminary studies, we found that inhibition of the protein kinase CK2 in the spinal cord completely reversed increased NMDA receptor activity and produced long-lasting attenuation of allodynia caused by nerve injury. In this application, we will use an animal model of neuropathic pain to test the central hypothesis that nerve injury increases CK2 activity in the spinal cord, which facilitates phosphorylation of the NR1 subunit of NMDA receptors and potentiates NMDA-mediated synaptic transmission in neuropathic pain.
The specific aims of this application are to (1) define the role of imbalance between the CK2(phosphorylation) and calcineurin(de-phosphorylation) activities in augmented NMDA-mediated synaptic transmission at the spinal cord level and neuropathic pain; (2) determine the level of CK2 activity and its role in increased phosphorylation of the NR1 subunit of NMDA receptors in the spinal cord after nerve injury; and (3) identify the protein interaction between NR1 and CK2 subunits, the CK2 phosphorylation sites on the NMDA receptor, and their roles in regulation of increased NMDA receptor activity in neuropathic pain. The role of CK2 in the development of synaptic plasticity in the spinal cord induced by nerve injury has not been recognized previously. We expect that new findings from this proposal will be critical not only to the significant improvement of our understanding of the molecular mechanisms of neuropathic pain but also to the development of new strategies to treat neuropathic pain. Because directly blocking NMDA receptors produces intolerable side effects, targeting CK2 and its specific NMDA receptor phosphorylation sites could represent novel strategies for reducing the NMDA receptor activity and neuropathic pain.
Neuropathic pain remains a major clinical problem because available pain medications are less effective and possess serious side effects. This application seeks to define the mechanisms involved in the maintenance of chronic neuropathic pain caused by nerve injury. Findings from this proposal not only are critical to significantly improve our understanding of the cellular and molecular mechanisms of neuropathic pain but also are important to the development of new strategies to treat neuropathic pain.
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