An increase in synaptic NMDA receptors in the insular cortex contributes to neuropathic pain.

Neurons in the insular cortex are activated by acute and chronic pain, and inhibition of neuronal activity in the insular cortex has analgesic effects. We found that in a mouse model in which peripheral nerve injury leads to the development of neuropathic pain, the insular cortex showed changes in synaptic plasticity, which were associated with a long-term increase in the amount of synaptic N-methyl-d-aspartate receptors (NMDARs), but not that of extrasynaptic NMDARs. Activation of cyclic adenosine monophosphate (cAMP)-dependent signaling enhanced the amount of synaptic NMDARs in acutely isolated insular cortical slices and increased the surface localization of NMDARs in cultured cortical neurons. We found that the increase in the amount of NMDARs required phosphorylation of the NMDAR subunit GluN2B at Tyr(1472) by a pathway involving adenylyl cyclase subtype 1 (AC1), protein kinase A (PKA), and Src family kinases. Finally, injecting NMDAR or GluN2B-specific antagonists into the insular cortex reduced behavioral responses to normally nonnoxious stimuli in the mouse model of neuropathic pain. Our results suggest that activity-dependent plasticity takes place in the insular cortex after nerve injury and that inhibiting the increase in NMDAR function may help to prevent or treat neuropathic pain.