• Tomoe Kanbara, Atsushi Nakamura, Masahiro Shibasaki, Tomohisa Mori, Tsutomu Suzuki, Gaku Sakaguchi, and Toshiyuki Kanemasa.
• Pain & Neurology, Discovery Research Laboratories, SHIONOGI Co., Ltd., 1-1, 3-chome, Futaba-cho, Toyonaka 561-0825, Osaka, Japan; Department of Toxicology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, 2-4-41 Ebara, Shinagawa-ku, Tokyo 142-8501, Japan.
• Neurosci. Lett. 2014 Sep 19;580:119-24.

AbstractIt has begun to be understood that μ-opioid receptor (MOR) produces ligand-biased agonism, which contributes to differential physiological functions of MOR agonists. We previously demonstrated that in oxaliplatin-induced neuropathy in rats, morphine and oxycodone exhibited antinociceptive effects while antinociception of fentanyl was partial, and such different efficacies might result from the different level of Gi/o protein activation. Based on our background, to reveal further mechanism, we focused on the role of Gi/o protein-related downstream signaling, the G-protein inwardly rectifying K(+)1 (GIRK1) channel. The GIRK1 channel blocker tertiapin-Q (30pmol) was intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administered to rats with oxaliplatin-induced neuropathy. The antinociception of systemic morphine (3mg/kg, subcutaneously (s.c.)) was suppressed only by pretreatment of i.t. tertiapin-Q, while supraspinal tertiapin-Q suppressed only the antinociception of systemic oxycodone (0.56mg/kg, s.c.). Partial antinocicpetion of fentanyl (0.017mg/kg, s.c.) was neither affected by i.c.v nor i.t. tertiapin-Q. These results demonstrated that GIRK1 channels differentially contribute to antinociceptive effects of MOR agonists, and that action site of GIRK1 channels is also different between morphine and oxycodone in oxaliplatin model. This study suggests the possibility that GIRK1 channels have a crucial role for antinociception of MOR agonists in oxaliplatin-induced neuropathy.Copyright © 2014 Elsevier Ireland Ltd. All rights reserved.

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