The Role And Mechanism Of Adrenomedullin-2 In Inflammatory Pain In Rats

Inflammatory pain is a common clinical symptom and widely exists in a variety of acute and chronic diseases.Inflammatory pain mainly caused by tissue damage,chemical stimulation or autoimmune process.Adrenomedullin 2,also known as intermedin,belongs to the Calicitonin gene-related peptide family.AM2 has been found to have a wide range of protective effects in recent studies.And there are many studies that demonstrate the AM2 is involved in neuropathic pain hyperalgesia in rats.However,whether AM2 is particapted in the development of inflammatory pain is unknown.In this study,chronic or acute inflammatory pain models were constructed by injecting CFA in the planter or LPS intraperitoneally.And intrathecal injection of AM2receptor antagongist IMD_17-47into both model rats can inhibit the action of AM2 and its receptor CLR/RAMPs.Behavioral tests,q RT-PCR,WB and IF co-location techniques were applyed to study the effect and mechanism of AM2 in CFA or LPS-induced inflammatory pain in rats.The results showed that:（1）At 48 hours after injection of CFA into the plantar of rats,the paw thermal withdrawal latency decreased and the m RNA expression of AM2 and its receptors CLR or RAMP3 increased in the dorsal root ganglia and spinal dorsal horn.And intrathecal administration of IMD_17-47（10nmol,20nmol,30nmol）can allieviate the CFA-induced hype rsensitivity to heat pain in rats,20nmol intrathecal administration can restore the normal value after intrathecal administration 1.5 hours.Also,the m RNA expression of AM2 and its receptors were down-regulated.At 15 hours afrer intraperitoneal injection of LPS,the threshold of tail flick latency in rats decreased,and the m RNA expression of AM2 and its receptors in dorsal root ganglia and spinal cord dorsal horn increased.Intrathecal administration（5nmol,10nmol,20nmol）could alleviate LPS-induced hypersensitivity to heat pain in rats,and 20 nmol intrathecal administration can recovered to normal value at the intrathecal administration 1.5 hours.At this time,the m RNA levels of AM2 and its receptors decreased.（2）At 48 hours after injection of CFA into the plantar of rats,satellite glial cells in DRG were activated（the expression of GFAP increased）,cytokines TNF-αand CCL5were released,voltage-gated channels Cav3.2,Cav2.2 and Nav1.7 were increased,and signal protein kinase p-ERK1/2 were up-regulated.Intrathecal injection of IMD_17-47inhibited the up-regulation of the expression of these factors.At 15 hours after LPS intraperitoneal injection,satellite glial cells in DRG were activated（GFAP expression increased）,cytokines TNF-αand CCL5 were released,and signal protein kinase p-ERK1/2 was upregulated.Intrathecal injection of IMD_17-47inhibited the upregulated expression of these factors.Meanwhile,AM2 and its receptor element CLR/RAMP3 are co-expressed with GFAP in DRG.（3）At 48 hours after injection of CFA into the plantar of rats,astrocytes in SCDH were activated（the expression of GFAP increased）,cytokines TNF-αand CCL5 were released,voltage-gated sodium channels Cav3.2,Cav2.2 and Nav1.7 were increased,and signal protein kinase p-ERK1/2 was up-regulated.Intrathecal injection of IMD_17-47in rats inhibited the up-regulation of the expression of theses factors.At 15 hours after intraperitoneal injection of LPS,astrocytes in SCDH were activated（the expression of GFAP increased）,cytokines TNF-αand CCL5 were released,and the expression of signal protein kinase p-ERK1/2 was up-regulated.Intrathecal injection of IMD_17-47inhbibited the up-regulation of the expression of these factors.At 15 hours after LPS intraperitoneal injection,astrocytes in SCDH were activated（GFAP expression increased）,cytokines TNF-αand CCL5 were released,and the expression of signal protein kinase p-ERK1/2was up-regulated.Intrathecal injection of IMD_17-47inhibited the up-regulation of the expression of these factors.AM2 and its receptor element CLR/RAMP3 are co-expressed with GFAP in spinal dorsal horn.These results suggest that during the development of CFA or LPS-induced inflammatory pain,blocking AM2 function inhibits the release of cytokines TNF-αand CCL5 by inhibiting the activation of satellite glia in DRG and astrocytes in SCDH,and down-regulated the phosphorylation level of signaling protein kinase p-ERK1/2.Inhibit the increased expression of voltage-gated channels Cav3.2,Cav2.2 and Nav1.7,thus inhibiting inflammatory hyperalgesia.