Adrenomedullin mediates tumor necrosis factor-α-induced responses in dorsal root ganglia in rats

Adrenomedullin (AM), a member of the calcitonin gene-related peptide (CGRP) family, has been demonstrated to be a pain peptide. This study investigated the possible involvement of AM in tumor necrosis factor-alpha (TNF-alpha)-induced responses contributing to neuronal plasticity in the dorsal root ganglia (DRG). Exposure of the DRG explant cultures to TNF-alpha (5 nM) for 48 h upregulated the expression of AM mRNA. The treatment with TNF-alpha also increased the level of CGRP, CCL-2 and MMP-9 mRNA in the cultured DRG. This increase was attenuated by the co-treatment with the selective AM receptor antagonist AM(22-52) (2 mu M). The blockade of AM receptors inhibited TNF-alpha-induced increase of the glial fibrillary acidic protein (GFAP), interleukin-1 beta (IL-1 beta, phosphorylated cAMP response element binding protein (pCREB) and nuclear factor kappa B (pNF-kappa B) proteins. On the other hand, the treatment with the AM receptor agonist AM(1-50) (10 nM) for 96 h induced an increase in the level of GFAP, IL-1 beta, pCREB and pNF-kappa B proteins. The inhibition of AM activity did not change TNF-a-induced phosphorylation of extracellular signal-related kinase (pERK) while the treatment with AM(1-50) still increased the level of pERK in the cultured DRG. Immunofluorescence assay showed the colocalization of AM-like immunoreactivity (IR) with TNF-alpha-IR in DRG neurons. The present study suggests that the increased AM receptor signaling mediated the many, but not all, TNF-alpha-induced activities, contributing to peripheral sensitization in neuropathic pain. (C) 2016 Elsevier B.V. All rights reserved.