The Journal of pharmacy and pharmacology
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J. Pharm. Pharmacol. · Aug 2010
Involvement of kappa opioid receptors in the formalin-induced inhibition of analgesic tolerance to morphine via suppression of conventional protein kinase C activation.
Repeated morphine treatment results in a decreased analgesic effect or the development of analgesic tolerance. However, we reported that some inflammatory chronic pain may inhibit morphine tolerance via kappa opioid receptor (KOR) activation. In this study, we further investigated the role of KOR in the inhibition of morphine tolerance in a chronic pain condition with a focus on the regulation of protein kinase C (PKC) activity. ⋯ These results indicate that KOR plays an important role in the inhibition of repeated morphine-induced cPKC up-regulation under chronic pain condition. Furthermore, this may result in the increase of MOR activity and in the inhibition of morphine tolerance under chronic pain condition.