Electroacupuncture Relieves Neuropathic Pain by Suppressing ACC Pyramidal Activity via mGluR5 Inhibition in CCI Mice.

backgroundElectroacupuncture (EA) is widely used for analgesia, but its central mechanisms remain unclear. We investigated whether EA alleviates neuropathic pain by suppressing metabotropic glutamate receptor 5 (mGluR5) signaling in the anterior cingulate cortex (ACC).

methodsIn naïve mice, we manipulated ACC pyramidal neurons using adeno-associated viral (AAV) vectors encoding calcium/calmodulin-dependent protein kinase II (CaMKII)-driven opsins-channelrhodopsin-2 (ChR2) or halorhodopsin (NpHR3.0)-followed by blue- or yellow-light stimulation to assess behavioral responses. In a chronic constriction injury (CCI) model, mice received EA and were evaluated for mechanical and thermal withdrawal thresholds. Western blotting (WB) and immunofluorescence (IF) quantified ACC mGluR5 expression. Then CaMKII-targeted adeno-associated viruses expressing chemogenetic receptors, such as hM3Dq or hM4Di, were injected into the ACC. Two weeks later, CCI was induced, and mice received either EA or intraperitoneal clozapine-N-oxide (CNO) while pain behaviors were monitored. Finally, proteomic profiling of ACC tissue compared CCI and EA groups.

resultsOptogenetic activation of ACC pyramidal neurons in naïve mice reduced both mechanical and thermal withdrawal thresholds, indicating a pronociceptive effect, whereas optogenetic inhibition increased thresholds. In CCI mice, EA significantly attenuated hypersensitivity and downregulated ACC mGluR5 protein levels by WB and IF. Chemogenetic inhibition of ACC pyramidal neurons similarly elevated thresholds in CCI mice, imitating EA. Notably, combining chemogenetic inhibition with EA produced no additional improvement, suggesting convergence on a common ACC mGluR5-dependent pathway.

conclusionsEA relieves neuropathic pain in mice, at least in part, by suppressing ACC pyramidal neuron activity via inhibition of mGluR5 signaling.