The Expression And Related Mechanisms Of Metabotropic Glutamate Receptor 5 In A Chronic Migraine Rat Model

Background: The pathogenesis of chronic migraine(CM)is complex,and central sensitization is considered to be one of its pathological mechanisms.Metabotropic glutamate receptor 5(mGluR5)mediates pain by activating various intracellular pathways.However,whether mGluR5 contributes to central sensitization in CM and the exact mechanism remains unclear.Therefore,the purpose of this study was to explore the expression of mGluR5 in the trigeminal nucleus caudalis(TNC)and the role of mGluR5 in the central sensitization of CM rats.Methods:1.Male Wistar rats were repeatedly infused with inflammatory soup(IS)for 7 days to simulate the activation of dural nociceptors to establish CM model,and the mechanical and thermal thresholds were used to evaluate model.2.The expression of mGluR5 was detected by quantitative polymerase chain reaction(q-PCR)and Western blot,and the localization of mGluR5 in TNC was detected by double immunofluorescence staining.3.mGluR5 agonist CHPG and antagonist MPEP,were injected into the lateral ventricle of CM rats.The mechanical pain thresholds and thermal pain thresholds were measured.The expressions of calcitonin gene-related peptide(CGRP),mammalian rapamycin target protein(mTOR)phosphorylation,microtubule-associated protein 1 light chain 3(LC3),p62 and substance P(SP)were detected.4.Rapamycin(Rap),an inhibitor of mTOR signal pathway,was injected into the lateral ventricle of CM rats.The mechanical pain thresholds and thermal pain thresholds were measured.The expressions of inflammatory cytokines IL-1β(IL-1β),CGRP,LC3,p62 and SP were detected.5.After intracerebroventricular administration of mGluR5 agonist CHPG in CM rats,Rap,an inhibitor of mTOR signal pathway,was given to CM rats.The mechanical pain thresholds and thermal pain thresholds were measured.The protein level of IL-1β,CGRP and SP were detected.Results:1.After repeated dural infusion of IS for 7 days,the pain thresholds significantly decreased,indicating that the CM model was established successfully.2.The results of q-PCR and Western blot showed that the expression of mGluR5 in TNC was significantly increased,and mGluR5 was expressed in the cytoplasm and nuclear membrane of neurons in TNC.3.Intracerebroventricular administration of mGluR5 antagonist MPEP,significantly relieved the mechanical and thermal pain in CM rats,increased the protein expression of LC3,decreased the protein level of CGRP,p-mTOR and p62,and decreased the average fluorescence intensity of SP.However,intracerebroventricular administration of mGluR5 agonist CHPG had the opposite effect.4.Intracerebroventricular administration of Rap,an inhibitor of mTOR signal pathway,significantly relieved mechanical and thermal pain in CM rats,increased the protein level of LC3,decreased the protein level of CGRP and IL-1β in TNC,and decreased the average fluorescence intensity of p62 and SP.5.After intracerebroventricular administration of mGluR5 agonist CHPG in CM rats,Rap,an inhibitor of mTOR signal pathway,could relieve mechanical and thermal pain and decrease the protein expression of IL-1β and CGRP and the average fluorescence intensity of SP in CM rats induced by CHPG.Conclusion:The downregulation of mGluR5 in CM rat model reduces the expression of IL-1β and central sensitization-related proteins CGRP and SP by inhibiting mTOR pathway to activate autophagy.This study identified a new strategy for the treatment of CM.