6-cyano-7-nitroquinoxaline-2-3-dione and Neuralgia

Chronic pain is a serious debilitating disease for which effective treatment is still lacking. Acid-sensing ion channel 1a (ASIC1a) has been implicated in nociceptive processing at both peripheral and spinal neurons. However, whether ASIC1a also contributes to pain perception at the supraspinal level remains elusive. Here, we report that ASIC1a in ACC is required for thermal and mechanical hypersensitivity associated with chronic pain. ACC-specific genetic deletion or pharmacological blockade of ASIC1a reduced the probability of cortical LTP induction and attenuated inflammatory thermal hyperalgesia and mechanical allodynia in male mice. Using cell type-specific manipulations, we demonstrate that ASIC1a in excitatory neurons of ACC is a major player in cortical LTP and pain behavior. Mechanistically, we show that ASIC1a tuned pain-related cortical plasticity through protein kinase C λ-mediated increase of membrane trafficking of AMPAR subunit GluA1 in ACC. Importantly, postapplication of ASIC1a inhibitors in ACC reversed previously established nociceptive hypersensitivity in both chronic inflammatory pain and neuropathic pain models. These results suggest that ASIC1a critically contributes to a higher level of pain processing through synaptic potentiation in ACC, which may serve as a promising analgesic target for treatment of chronic pain.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Acid Sensing Ion Channels; Animals; Cells, Cultured; Gyrus Cinguli; Isoenzymes; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Microinjections; Neuralgia; Neuronal Plasticity; Organ Culture Techniques; Pain Measurement; Protein Kinase C

Long-term potentiation of glutamatergic transmission has been observed after physiological learning or pathological injuries in different brain regions, including the spinal cord, hippocampus, amygdala, and cortices. The insular cortex is a key cortical region that plays important roles in aversive learning and neuropathic pain. However, little is known about whether excitatory transmission in the insular cortex undergoes plastic changes after peripheral nerve injury. Here, we found that peripheral nerve ligation triggered the enhancement of AMPA receptor (AMPAR)-mediated excitatory synaptic transmission in the insular cortex. The synaptic GluA1 subunit of AMPAR, but not the GluA2/3 subunit, was increased after nerve ligation. Genetic knock-in mice lacking phosphorylation of the Ser845 site, but not that of the Ser831 site, blocked the enhancement of the synaptic GluA1 subunit, indicating that GluA1 phosphorylation at the Ser845 site by protein kinase A (PKA) was critical for this upregulation after nerve injury. Furthermore, A-kinase anchoring protein 79/150 (AKAP79/150) and PKA were translocated to the synapses after nerve injury. Genetic deletion of adenylyl cyclase subtype 1 (AC1) prevented the translocation of AKAP79/150 and PKA, as well as the upregulation of synaptic GluA1-containing AMPARs. Pharmacological inhibition of calcium-permeable AMPAR function in the insular cortex reduced behavioral sensitization caused by nerve injury. Our results suggest that the expression of AMPARs is enhanced in the insular cortex after nerve injury by a pathway involving AC1, AKAP79/150, and PKA, and such enhancement may at least in part contribute to behavioral sensitization together with other cortical regions, such as the anterior cingulate and the prefrontal cortices.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Cerebral Cortex; Disease Models, Animal; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; GABA Antagonists; In Vitro Techniques; Male; Membrane Potentials; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Neuralgia; Phosphorylation; Picrotoxin; Receptors, AMPA; Sodium Channel Blockers; Subcellular Fractions; Synaptic Transmission; Tetrodotoxin

Neuropathic pain is a common cause of pain after nerve injury, but its molecular basis is poorly understood. In a post-gene chip microarray effort to identify new target genes contributing to neuropathic pain development, we report here the characterization of a novel neuropathic pain contributor, thrombospondin-4 (TSP4), using a neuropathic pain model of spinal nerve ligation injury. TSP4 is mainly expressed in astrocytes and significantly upregulated in the injury side of dorsal spinal cord that correlates with the development of neuropathic pain states. TSP4 blockade by intrathecal antibodies, antisense oligodeoxynucleotides, or inactivation of the TSP4 gene reverses or prevents behavioral hypersensitivities. Intrathecal injection of TSP4 protein into naive rats is sufficient to enhance the frequency of EPSCs in spinal dorsal horn neurons, suggesting an increased excitatory presynaptic input, and to cause similar behavioral hypersensitivities. Together, these findings support that injury-induced spinal TSP4 may contribute to spinal presynaptic hypersensitivity and neuropathic pain states. Development of TSP4 antagonists has the therapeutic potential for target-specific neuropathic pain management.

Topics: 6-Cyano-7-nitroquinoxaline-2,3-dione; Analysis of Variance; Animals; Antibodies; Disease Models, Animal; Excitatory Amino Acid Antagonists; Green Fluorescent Proteins; Humans; Hyperalgesia; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Injections, Spinal; Male; Mice; Mice, Transgenic; Motor Activity; Neuralgia; Oligodeoxyribonucleotides, Antisense; Pain Measurement; Pain Threshold; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Spinal Cord; Spinal Nerves; Tetrodotoxin; Thrombospondins; Up-Regulation; Valine

In this study, we sought to characterize the effects of focal GABA(A) receptor antagonism on spontaneous and evoked activity in dorsal horn neurons of the alpha-chloralose anesthetized cat. Bicuculline (0.5, 1.0 mM) applied near the neurons through a transparenchymal dialysis fiber resulted in increased evoked activity in nociceptive dorsal horn neurons. Hair deflection was the stimulus most affected, followed by both low and high threshold tonic mechanical stimulation of the receptive field. In addition, neurons displayed increased background discharge and a subpopulation developed an increased afterdischarge to noxious mechanical stimulation. This is in contrast to our previous work with glycine receptor antagonism where only the evoked response to hair follicle activation was significantly enhanced. Subsequent co-administration of an NMDA receptor antagonist (AP-7, 2.0 mM) was without any apparent effect on either basal or bicuculline-enhanced responses. Co-administration of a non-NMDA excitatory amino acid receptor antagonist (CNQX, 1.0 mM) with the bicuculline non-selectively blocked both low and high threshold mechanical input. The inability of AP-7 to reverse the bicuculline-associated hyperreactivity also contrasts with the AP-7 reversal of the strychnine-associated hyperreactivity. These results point out that, while GABA and glycine are frequently co-localized in cells of the spinal dorsal horn and both appear to mediate tonic inhibitory control systems, they are not at all equivalent and are subject to different modulatory pharmacologies. Removal of each influence may model a different component of neuropathic pain.

Topics: 2-Amino-5-phosphonovalerate; 6-Cyano-7-nitroquinoxaline-2,3-dione; Animals; Bicuculline; Blood Pressure; Cats; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Glycine Agents; Microdialysis; Neuralgia; Neurons, Afferent; Nociceptors; Pain Threshold; Receptors, GABA-A; Receptors, N-Methyl-D-Aspartate; Spinal Cord; Stimulation, Chemical; Strychnine