Elsevier

Neuroscience Letters

Volume 237, Issues 2–3, 21 November 1997, Pages 136-138
Neuroscience Letters

Partial loss of tolerance liability to morphine analgesia in mice lacking the nociceptin receptor gene

https://doi.org/10.1016/S0304-3940(97)00832-XGet rights and content

Abstract

In mice lacking the nociceptin (or orphanin FQ) receptor gene, when 10 mg/kg of morphine was subcutaneously given, a potent analgesia in the tail pinch test was observed. The analgesic effect of morphine was equivalent among wild-type, heterozygous and homozygous mutant mice. When morphine was given to such mice in a dose of 10 mg/kg once per day for 5 days, wild-type and heterozygous mice showed marked tolerance or reduction in the morphine analgesia on the 5th day, while homozygous mice showed only 50% reduction in the peripheral analgesia of morphine. These findings suggest that nociceptin or its receptor plays important roles in the in vivo mechanism for the development of morphine tolerance.

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Acknowledgements

Parts of this study were supported by Grants-in-Aid from the Ministry of Education, Science, Culture and Sports of Japan, grants from The Japan Health Sciences Foundation, The Uehara Foundation and The Takeda Science Foundation.

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