Effects Of Intrathecal Injection Of AM22-52 On Nerve Injury-induced Alterations In Spinal Cord And DRG In Rats

Background and objective:Adrenomedullin(AM)was originally isolated from human pheochromocytoma cells and was identified by its ability to generate cAMP in platelets[1].AM is produced in vascular smooth muscle cells and endothelial cells.A number of studies showed that AM and its receptors are distributed in spinal dorsal horn and dorsal root ganglion which suggests us to pay attention to the relationship between AM and pain.And the previous studies in our lab have shown that AM plays a role in neuropathic pain.Based on the previous research in our laboratory and other previous studies,this study intends to further explore the mechanism of adrenomedullin and its receptors in chronic neuropathic pain.Methods:(1)After setting up the spinal nerve ligation(SNL)of neuropathic pain model in rats,the experimental group was given AM22-52(the receptor antagonist of AM)for 7 days,which was compared with Sham group and SNL control group by behavioral method.Then,observe and analysis the paw withdrawal mechanical threshold(PWMT)in rats with mechanical foot contraction.(2)The experiment was divided into three groups:Sham+Saline,SNL+Saline,SNL+AM22-52.Using Western Blotting to detect and compare the expression of GFAP、Interleukin-1beita(IL-1β),neuronal Nitric Oxide Synthase(nNOS)in dorsal horn of spinal cord in ipsilateral lumbar enlargement.(3)Quantitative real-time polymerase chain reaction(qRT-PCR)was used to detect and compare the expression of GFAP,IL-1β,nNOS in ipsilateral L5 dorsal root ganglion of rats.Results:(1)After the establishment of rats’ SNL model,AM22-52 was given for 7 days,which made the rats’ PWMT flip on the 5th day;(2)WB technique showed that the expression of GFAP、IL-1β、nNOS in the ipsilateral dorsal horn of spinal cord of rats which treated with AM22-52 was significantly lower than that in the Saline+SNL group,but there had no significant difference with the Sham group.(3)The mRNA expression of GFAP、IL-1β、nNOS in rats’L5 DRG was significantly lower than that in Saline+SNL group,but there had no significant difference with the Sham group.In summary:(1)Blockade of AM receptor inhibited mechanical allpdynia that caused by peripheral nerve injury.(2)After SNL rats were given AM receptor antagonist,the expression of GFAP in the ipsilateral dorsal horn of spinal cord decreased.The results suggest that AM22-52 can activate astrocytes after peripheral nerve injury.(3)That chronic application of AM22-52 can inhibit the increase of IL-1β,nNOS in spinal dorsal horn and DRG which are induced by SNL.These results suggest that AM can induce neuropathic pain by the cellular mechanism:activating spinal astrocytes,up-regulating nNOS,IL-1β in spinal cord and activating satellite glial cells in DRG,up-regulating the expression of nNOS and IL-1β.