Activation Of Microglia By Pain-peptide Adrenomedullin In Vitro-the Study On Morphology And Functions

It has been established that nerve injury in the central and periphery activates glial cells, particularly microglia. Adrenomedullin (AM) belongs to calcitonin gene-related peptide (CGRP) family and has been identified to be a pain neuropeptide. However, it is not known whether AM is involved in the pathogenesis of neuropathic pain. We hypothesized that AM could activate microglia. To test this hypothesis, we first set up the technique to obtain high purity of microglia in vitro. Then, we examined whether AM can activate microglia morphologically and functionally. Finally, we explored whether AM can still exert these effects on microglia following the blockade of AM receptors.The microglial cells were purified from mixed primary cell cultures obtained from the spinal cord of2-day-old rat. Treated with different concentrations of AM, we used immunocytochemistry and real-time quantitative PCR techniques to examine the changes in cell morphology and function of microglia. Then the cultured microglia were treated with AM22-52to block the expression of AM receptors and the changes in the expression of CD11b and IL-1? were determined.After treatment100nM AM for5days, expression of the specific marker of microglia CDllb was significantly higher with changes in cell morphology. Microglia were treated with AM at different concentrations (1-100nM) and only5day-treatment with10nM and100nM AM were shown to increase the expression of inflammatory cytokines IL-1? mRNA and this increase was significantly different from the control group. Following the application of the AM receptor antagonist AM22-52, AM (100nM) induced significantly less increase in the expression of CD11b and IL-1? mRNA compared with AM along group. These results indicate that AM can directly activate microglia mediated via the AM receptors.