The Effect And Mechanism Of Adrenomedullin Mediates SNL-induced Neuropathic Pain In Rats

Neuropathic pain is a chronic pain caused by peripheral or central nervous system dysfunction,which is usually associated with allodynia,hyperalgesia,and spontaneous pain.In the case of noxious stimuli or nerve injury,the synthesis and release of cytokines is increased at the injury site,and activation of the intracellular signaling pathway leads to the development of pain.Adrenomedullin(AM),one of the members of the calcitonin gene-related peptide(CGRP)superfamily,is a pro-pain neuropeptide with biological activity.AM is activated to mediate the development of pain.Previous experiments in our laboratory have preliminarily confirmed that AM is involved in SNL-induced neuropathic pain.However,the role and mechanism of AM in the early and late stages of SNL-induced neuropathic pain is unclear.In this study,the model of SNL were established in rats.Behavioral,Real-time quantitative PCR,Western Blot and Immunofluorescence double labeling were used to investigate the effect and mechanism of AM in early and late SNL-induced neuropathic pain.The result show that:(1)On the second and tenth day of SNL,intrathecal injection of AM22-52 reduced mechanical hyperalgesia.Indicating that AM is involved in the development and maintenance of neuropathic pain induced by SNL.(2)On the second day of SNL,the expression of nNOS,TRPV1 in DRG,and IBA-1,IL-1?,TNF-?,CX3CL1,and phosphorylation p38 increased in spinal dorsal horn.Intrathecal injection of AM22-52 inhibits the expression of above cytokines.It is indicated that AM can mediate pain molecules in DRG neurons and the activity of spinal microglia involved in the development of early neuropathic pain.(3)On the tenth day of SNL,the expression of nNOS,TRPV1 in DRG,as well as GFAP,IL-1?,TNF-?,MCP-1,and phosphorylation JNK of spinal dorsal horn are increased.But the expression of these cytokines decreased significantly after intrathecal injection of AM22-52.It is shown that AM regulates the activity of DRG neuron pain molecules and spinal astrocytes in late neuropathic pain.(4)The immunofluorescence double label showed that AM and its receptor elements CLR and RAMP2 could be co-located and expressed with nNOS and TRPV1 in DRG,respectively.It provides anatomical basis for AM to regulate the expression of both of them and participate in neuropathic pain.In conclusion,the purpose of this study was to investigate the effect and mechanism of AM in early and late SNL-induced neuropathic pain.The results showed that AM regulates the activity of cytokines such as nNOS and TRPV1 in DRG neurons to regulate the changes of cytokines and signaling pathways in glial cells(microglia and astrocytes),which were involved in the development and maintenance of neuropathic pain.It provides an experimental basis and lays a theoretical foundation for elucidating that AM participated in the early and late stages of neuropathic pain.