Role Of Pka In Nmda Receptor-induced Nmda Receptor Synaptic Accumulation In Spinal Dorsal Horn During Inflammatory Pain

The hyperfunction of NMDA (N-methyl-D-aspartate) subtype glutamate receptor in spinal dorsal horn plays a critical role in the initiation and development of chronic pathological pain. However, the intracellular signaling cascades triggered by peripheral tissue injury to upregulate NMDA receptor function are still elusive. Previous studies have demonstrated that Ca2+ influx via NMDA receptor is able to evoke a series of signaling pathways in nociceptive neurons to enhance the neuronal excitability and its responsiveness to noxious stimuli. The present study, therefore, systematically investigated the contribution of NMDA receptor per se to NMDA receptor hyperfunction and inflammatory pain. Our data showed that:(1) Intrathecal application of NMDA to stimulate spinal NMDA receptors elicited pronounced mechanical allodynia in naive mice; (2) NMDA operated to increase the accumulation of NMDA receptor at synapses in spinal dorsal horn of naive mice, a key event that led to NMDA receptor hyperfunction; (3) NMDA induced the synaptic accumulation of NMDA receptors by activating spinal cAMP-dependent protein kinase (PKA), because inhibition of PKA activity totally eliminated the regulatory effects of NMDA on NMDA receptor synaptic expression and direct activation of spinal PKA in naive mice mimicked the action of NMDA; (4) Peripheral inflammation also boosted the synaptic localization of spinal NMDA receptors and more importantly, such an effect could be readily ruled out by inhibition of either NMDA receptor or PKA, suggesting that peripheral tissue injury induced NMDA receptor hyperfunction and pain states via "NMDA receptor/PKA" pathways; (5) Activation of spinal NMDA receptors dramatically enhanced the synaptic concentration of PKA targeting protein--- A kinase-anchoring protein 150 (AKAP150), suggesting that NMDA receptor might activate PKA by promoting AKAP150-mediated PKA synaptic anchoring; (6) Intrathecal administration of Ht31 peptide to disrupt AKAP150-mediated PKA synaptic anchoring effectively alleviated inflammatory pain; (7) Ht31 served to decrease the synaptic concentration of NMDA receptors in spinal dorsal horn induced by peripheral inflammation.Taken together, these data suggested that activation of spinal NMDA receptors enhanced the distribution of NMDA receptors at synapses by promoting AKAP150-mediated PKA synaptic targeting to facilitate the regulatory effects of PKA on synaptic NMDA receptors.