Abstract

Mas oncogene-related G-protein-coupled receptor C (MrgC) is unequally expressed in primary sensory ganglia and has been shown to modulate pathological pain. This study determined the mechanism underlying effect of MrgC receptors on inflammatory pain. Intrathecal (i.t.) administration of the selective MrgC receptor agonist bovine adrenal medulla 8-22 (BAM8-22, 30 nmol) inhibited CFA-evoked hyperalgesia. This was accompanied by the inhibition of protein kinase C-gamma (PKCγ) and phosphorylated extracellular signal-regulated protein kinase (pERK) in the spinal cord and/or dorsal root ganglia (DRG). The CFA injection in the hindpaw induced an increase in Gq, but not Gi and Gs, protein in the spinal dorsal horn. This increase was inhibited by the i.t. administration of BAM8-22. The exposure of DRG cultures to bradykinin (BK, 10 μM) and prostaglandin E2 (PGE2, 1 μM) increased the expression of CGRP and nNOS in small- and medium-sized neurons as well as the levels of CGRP, aspartate and glutamate in the cultured medium. The BK/PGE2-induced alterations were absent in the presence of BAM8-22 (10 nM). These results suggest that the activation of MrgC receptors can modulate the increase in the expression of CGRP and nNOS as well as the release of CGRP and excitatory amino acids in DRG associated with inflammatory pain. This modulation may result in the inhibition of peripheral and central sensitization via suppressing the expression of Gq protein and PKCγ and ERK signaling pathways in the spinal cord and/or DRG. The present study suggests that MrgC receptors may be a novel target for relieving inflammatory pain.