The Role Of Neuregulin In Neuropathic Pain In Rats

Objective: To study the effect of NRG1in the development and maintenance ofneuropathic pain model on ratsMethods：1. Investigate the contribution of exogenous NRG1on neuropathic pain relatedbehavior and molecular changes by intrathecal injection on rats.male SD rats (180g-200g) were randomly divided into the two groups (n=30),control group and experimental group. After Three days of intrathecal catheterization,the control group received20μ l0.9%saline and the experimental group were treatedwith exogenous neuregulin20μ l (1ng/μ l), twice a day. We assessed MWT(mechanical withdrawal threshold) the day before Drug injection, and after Drugdilivery1day、2day、3day、4day、5day、6day、7day、14day、21day. Onthe3day、7day、14day、21day,The expression of endogenous neuregulin and GFAPwere detected by Western-blot; The transcription level of IL-1/TNFα were detectedby R-PCR; The morphology changes of astrocytes were detected by GFAPimmunofluorescence stain on14day.2. To explore the effect of NRG1receptor antagonist on neuropathic pain model on rats.75male SD rats (180g-200g) were randomly divided into three groups (n=25), SNL group,SNL+DMSO group and SNL+Inhibitor group. SNL group, the left L5,6spinal nerve was ligatedand transected. There was no other treatment for Group SNL. Group SNL+DMSO and groupSNL+inhibitor respectively suffered Catheterization from foramen magnum7days after SNL.group SNL+DMSO were given5%DMSO,The group SNL+Inhibitor were given neuregulin/erbBsignaling pathway inhibitor AG1478(which dissolved in5%DMSO)20μ l (1ug/μ l). Weassessed MWT (mechanical withdrawal threshold) the day before Drug injection, and after Drugdilivery. On the14day,The expression of endogenous neuregulin and GFAP were detected byWestern-blot; The transcription level of IL-1/TNFα were detected by Realtime-PCR; Themorphology changes of astrocytes were detected by GFAP immunofluorescence stain.Results:1. On the first day after administration exogenous neuregulin, compared with thecontrol group, the mechanical withdraw threshold of experiment group decreasedsignificantly (p<0.05); Western blot analysis reveals the expression of GFAP andneuregulin was higher than control group (p<0.05); compared with controlgroup,Real-time PCR showes IL-1β, TNF α mRNA expression up-regulated; comparewith control group,Immunofluorescence shows increased number of astrocyte with anactivated morphology.2. After delivered intrathecally inhibitor, compared with the SNL group andSNL+DMSO group,the mechanical withdraw threshold of SNL+inhibitor group wasincreased significantly (p<0.05). Western blot analysis reveals the expression ofGFAP and neuregulin was lower than SNL group and SNL+DMSO group (p<0.05);compare with the other two groups,Real-time quantitative determination showsSNL+inhibitor group IL-1, TNF-α mRNA expression down-regulated; compare withthe other two groups,Immunofluorescence shows reduced number of astrocyte with anactivated morphology in SNL+inhibitor group. Conclusion:Intrathecal administration neuregulin resulted in the dorsal horn astrocyte with anactivated morphology and also produced mechanical pain-related hypersensitivity. Atthe same time, Western blot analysis reveals the expression of GFAP and neuregulinwas higher than control group, IL-1β, TNF α mRNA expression up-regulated.Incontrast to the results before,sequestration of endogenous NRG after SNL reduced thenumber of astrocyte with an activated morphology,and Western blot analysis revealsthe expression of GFAP and neuregulin was lower than others, IL-1β, TNF α mRNAexpression down-regulated.Furyhermore,consequent to such changes,the mechanicalpain-related hypersensitivity was reduced.So we can draw a conclusion that the NRGmay contributes to neuropathic pain by medidate IL-1β，TNF-relaese fromastrocyte.