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[Activation of spinal MrgC receptors inhibits hyperalgesia in rats.] [Article in Chinese]

JIANG Jian-Ping, FU Yan, HU Fen-Juan, HONG Yan-Guo

College of Life Sciences, Fujian Normal University, Fujian Key Laboratory of Developmental and Neuro Biology, Fuzhou 350117, China； Daqinjia Animal Husbandry and Veterinary Station, Zhaoyuan 265408, China

Abstract

This study was aimed to investigate the mechanisms of the modulation effect of activation of spinal Mas-related gene C (MrgC) receptors on hyperalgesia induced by intraplantar (i.pl.) injection of (Tyr6)-γ2-MSH-6–12 (MSH) or complete Freund’s adjuvant (CFA). Paw withdrawal latency test and immunohistochemistry were used to observe the effect of intrathecal (i.t.) administration of MSH or BAM8-22, two selective agonists of MrgC receptor, in hyperalgesia in rats. The results showed that i.t. administration of MSH inhibited acute hyperalgesic response induced by i.pl. application of MSH, while did not change thermal nociceptive threshold in naïve rats. The i.t. administration of MSH also attenuated CFA-induced inflammatory hyperalgesia. However, i.t. administration of the μ-opioid receptor (MOR) antagonist CTAP blocked the induction of delayed anti-hyperalgesia by MSH. The i.t. injection of BAM8-22 at a dose of 30 nmol evidently reduced the number of CFA-evoked nitric oxide synthase (NOS)-positive neurons and the expression of calcitonin gene-related peptide (CGRP)-immunoreactivity positive nerve fibers at L3–L5 segments of the spinal cord. These results suggest that the activation of MrgC receptor in CFA-induced inflammation reduces inflammatory hyperalgesia through inactivation of NOS neurons and down-regulation of CGRP expressions, and generates delayed but long-lasting anti-nociception through the endogenous activation of MOR via indirect mechanisms. Agonists for MrgC receptors may, therefore, represent a new class of antihyperalgesics for treating inflammatory pain because of the highly specific expression of their targets.

Key words: Mas-related gene C receptors; hyperalgesia; (Tyr6)-γ2-MSH-6-12; bovine adrenal medulla 8-22

Received: 2015-01-14　　Accepted: 2015-02-26

Corresponding author: 江剑平　　E-mail: jjp@fjnu.edu.cn

Citing This Article：

JIANG Jian-Ping, FU Yan, HU Fen-Juan, HONG Yan-Guo. [Activation of spinal MrgC receptors inhibits hyperalgesia in rats.] [Article in Chinese]. Acta Physiol Sin 2015; 67 (4): 413-422 (in Chinese with English abstract).