The Effect And Mechanism Of Cerebral Cortex Adrenomedullin Involved In Pathological Pain In Rats

Pathologic pain refers to pain caused by multiple diseases or syndromes,manifested as spontaneous pain and evoked pain.Pathologic pain is a confounding sensory state,and its pathogenesis is not clinically understood,causing great distress to people’s physical and mental health and quality of life.Adrenomedullin(AM),a member of the calcitonin generelated peptide,is a pain neuropeptide composed of 52 amino acids,which acts through the complex of calcitonin receptor-like receptor(CLR)/receptor activating modified protein 2(RAMP2).Previous work by our research group demonstrated that AM is involved in the development of pathological pain,but the mechanism of action is unclear.In this study,spinal nerve ligation(SNL)neuropathic pain model and lipopolysaccharide(LPS)inflammatory pain model were constructed,and LPS was used to treat cerebral cortex of rats in vitro,and applied AM22-52,an AM receptor antagonist,by lateral ventricular injection or ex vivo.Behavioral,Western Blot,Real-time fluorescence quantitative PCR,immunofluorescence co-location techniques were used to explore the role and mechanism of AM involvement in pathologic pain.The experimental results showed that:(1)Lateral ventricular injection of AM22-52(1 nmol)alleviated LPS-induced thermal hyperalgesia and SNL-induced mechanical hyperalgesia and was most effective after 1 h of administration.The expression of AM and its receptor components CLR and RAMP2 were upregulated in the cerebral cortex of animals when LPS was injected intraperitoneally to induce inflammatory pain or SNL to induce neuropathic pain;in vitro LPS(15 μg/m L)treatment of the cerebral cortex for 2 h also caused upregulation of AM and its receptors.After lateral ventricular injection or ex vivo application of AM22-52,AM,CLR,and RAMP2 in the cerebral cortex of the animals returned to their original levels.(2)When LPS was injected intraperitoneally to induce inflammatory pain or SNL to induce neuropathic pain,astrocytes in the cerebral cortex of the animals were activated(GFAP expression was upregulated)and cytokine(TNF-α,IL-1β,IL-6,IL-10 and CX3CL1)expression in the cerebral cortex of LPS-inflammatory pain rats was upregulated.2 h of LPS(15 μg/m L)treatment of the cerebral cortex,the same changes occurred in GFAP and cytokines.Lateral ventricle injection or ex vivo application of AM22-52 inhibited astrocyte activation and cytokine release.Histological experiments confirmed the expression of AM and its receptor components CLR and RAMP2 in astrocytes in the cerebral cortex.(3)Intraperitoneal injection of LPS induced inflammatory pain or in vitro LPS(15μg/m L)treated the cerebral cortex for 2 h.P2X7 R,NMDAR1 expression was upregulated and BDNF expression was decreased in the cerebral cortex.Inhibition of AM activity by lateral ventricular injection or in vitro application of AM22-52 reversed the expression of P2X7 R,BDNF and NMDAR1.Histological experiments confirmed that P2X7 R and BDNF were expressed in astrocytes in the cerebral cortex.Conclusion: Increased AM expression in the cerebral cortex and activation of astrocytes contribute to cytokine release,inducing upregulation of P2X7 R,NMDAR1 and decreased BDNF expression,mediating the development of inflammatory pain or neuropathic pain.