An Increase in Synaptic NMDA Receptors in the Insular Cortex Contributes to Neuropathic Pain

Abstract

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.

Phosphorylation of Tyrosine 1070 at the GluN2B Subunit Is Regulated by Synaptic Activity and Critical for Surface Expression of N-Methyl-d-aspartate (NMDA) Receptors

“…5D). Given that the phosphorylation of Tyr-1472 prevents the endocytosis of NMDARs (18), our results were corroborated by a previous report that such stimuli elevate the surface expression of GluN2B (39).…”

A novel phosphorylation site of N-methyl- d -aspartate receptor GluN2B at S1284 is regulated by Cdk5 in neuronal ischemia

“…We wondered whether S1284 was also participated in LTP and learning process. To answer the question, the well-established chemical LTP (cLTP) paradigm (Otmakhov et al, 2004;Qiu et al, 2013;Szepesi et al, 2014) was employed in this study. Chemical LTP was induced in hippocampal cultures by co-application of PKA activators (forskolin and rolipram) and free of Mg 2+ to increase spontaneous neuronal activation and activate NMDA receptors.…”

“…For chemical LTP induction, we followed the protocol reported previously (Qiu et al, 2013;Szepesi et al, 2014). Briefly, the cultures were transferred from Neurobasal medium to extracellular solution (ECS) containing: 150 mM NaCl, 2 mM CaCl 2 , 5 mM KCl, 10 mM HEPES (pH 7.4), 30 mM glucose, 50 μM forskolin, 0.1 μM rolipram, and 50 μM picrotoxin for indicated time and then processed to western blot analysis.…”

Molecular Pharmacology ofδ-Opioid Receptors

“…As a consequence of Raf-1-dependent AC superactivation, cultured sensory neurons display increased PKA activity and enhanced release of CGRP (Yue et al, 2008), which may contribute to the development of analgesic tolerance (Tumati et al, 2010). Other PKA-dependent mechanisms contributing to opioid tolerance as well as pain sensitization include AMPA receptor phosphorylation and targeting of AMPA receptors to the membrane (Asiedu et al, 2011;Zhuo, 2012) as well as PKA-dependent phosphorylation of NMDA receptors (Qiu et al, 2013), which lead to increased neuronal excitability. Thus, in circumstances in which increased tissue levels of cAMP lead to excessive PKA activity and pain sensitization, acute AC inhibition by DOPr ligands may contribute to its analgesic actions .…”