Study On The Inhibition Of Chronic Morphine-induced Upregulation Of Nociceptive Mediators In Rat DRG Neurons By MrgC Receptor

It has been shown that the activation of Mas-related gene receptors (Mrg receptors) remakly arrenuated the development of morphine tolerance or reversed established morphine tolerance. Studies have shown that matrix metalloproteinase-9 (MMP-9), CX3CL1, CCL2 and interleukin 1β (IL-1β) are implicated in the development of tolerance to morphine-induced analgesia. However, it is not known that the mechanisms underlying the inhibition of morphine tolerance by MrgC receptor involves the suppression on these nociceptive mediators.In this study, the techniques of DRG culture, fluorescent immunohistochemistry and quantitative real-time polymerase chain reaction (qRT-PCR) were used. We examined: (1) Effect of intermittent combination of BAM8-22 and morphine on development of morphine tolerance and the expression of MMP-9, CX3CL1, IL-1β in the rat DRG neurons; (2)Effect of morphine treatment time on the expression of MMP-9 mRNA in DRG and the effect of BAM8-22 treatment time on the expression of MMP-9 mRNA in DRG; (3) Effect of MrgC receptor antibody and BAM8-22 joint action on the expression of MMP-9, CX3CL1, CCL2, IL-1β mRNA in chronic morphine cultured DRG. Results showed that:(1) Intermittent combination of 1nmol BAM8-22 and 20μg morphine inhibited the formation of morphine tolerance and restored the anti- nociceptive effect of morphine. (2) The expression of MMP-9, CX3CL1, IL-1β were increased following morphine tolerance, intrathecal injection BAM8-22 remarkly suppress the expression of MMP-9, CX3CL1, IL-1β. (3) Treatment with BAM8-221 h reversed chronic morphine-induced upregulation of MMP-9, CX3CL1, IL-1β mRNA in DRG. (4) After using the MrgC receptor antibody, reoccupy BAM8-22 was inable to activate MrgC receptor, therefore after chronic morphine application, the expression of MMP-9, CX3CL1, IL-1β increased significantly, which was no significant difference with chronic morphine group. MrgC receptor blockade alone did not alter the effect of chronic morphine.(5) Treatment with BAM8-22 24 h reversed chronic morphine-induced upregulation of MMP-9, CX3CL1, CCL2, IL-1β mRNA in DRG. (6) Treatment with BAM8-22 72 h enhanced chronic morphine-induced upregulation of MMP-9, CX3CL1, CCL2, IL-1β mRNA in DRG. These results show that the activation of MrgC receptor in short time can inhibit the formation of morphine tolerance or resverse established tolerance, but continued activation for a long time will enhance the expression of the nociceptive mediators induced by chronic morphine, the nociceptive mediators MMP-9, CX3CL1, CCL2, IL-lp in DRG are the cellular mechanism of MrgC receptor regulates morphine tolerance. These nociceptive mediators transfer information through intracellular signal pathway to produce tolerance.