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Differential actions of intrathecal nociceptin on persistent spontaneous nociception, hyperalgesia and inflammation produced by subcutaneous bee venom injection in conscious rats

Sun Yanyan, Luo Ceng, Li Zhen, Chen Jun

Pain Research Center, Institute of Neuroscience, The Fourth Military Medical University. Xi'an 710032, China

Abstract

Nociceptin is an endogenous ligand for the opioid receptor-like 1 (ORL1) receptor. The present study was designed to investigate spinal actions of nociceptin on the spontaneous nociception, hyperalgesia and inflammation induced by subcutaneous bee venom injection.Subcutaneous injection of bee venom into one hindpaw of conscious rat produced a persistent spontaneous nociception followed by a longlasting primary heat and mechanical hyperalgesia as well as local inflammation. Compared with the pre-saline group, pretreatment with intrathecal injection of three doses (3, 10 and 30 nmol) of nociceptin produced significant suppression on the spontaneous paw flinching reflex.The inhibitory rates were 37±7, 43±6 and 57±11%, respectively, which were enhanced with an increase in the concentration of nociceptin. The inhibitory action of nociceptin was completely antagonized by a new selective ORL1 receptor antagonist CompB (30 nmol). Pre-treatment with 10 mol nociceptin prior to bee venom produced no significant effect on the oc currence of primary heat and mechanical hyperalgesia, nor did post-treatment with the same dose again 3 h after bee venom injection. Additionally, pre-treatment with nociceptin had no effect on the bee venom-induced increase in paw thickness and volume and the plasma protein extravasation. These results indicate that intrathecal nociceptin has no effect on primary heat and mechanical hyperalgesia as well as inflammation, but has dose-related anti-nociceptive effect on the bee venom-induced persistent spontaneous nociception via activation of spinal ORL1 receptor.

Key words: Nociceptin;Bee venom test;Persistent spontaneous pain;Hyperalgesia;Inflammation;Anti-nociception;Anti-inflammation

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Citing This Article：

Sun Yanyan, Luo Ceng, Li Zhen, Chen Jun. Differential actions of intrathecal nociceptin on persistent spontaneous nociception, hyperalgesia and inflammation produced by subcutaneous bee venom injection in conscious rats. Acta Physiol Sin 2004; 56 (3): (in Chinese with English abstract).