Elsevier

Neuroscience Letters

Volume 223, Issue 1, 14 February 1997, Pages 49-52
Neuroscience Letters

Lack of cross-tolerance between the antinociceptive effect of intrathecal orphanin FQ and morphine in the rat

https://doi.org/10.1016/S0304-3940(97)13401-2Get rights and content

Abstract

We assessed whether tolerance develops to the antinociceptive effect of intrathecal (i.t.) orphanin FQ, the endogenous ligand of the orphan opioid-like receptor, and whether there is a cross-tolerance between the antinociceptive effect of i.t. orphanin FQ and the mu opioid receptor agonist morphine. Orphanin FQ administered i.t. at 10 μg induced strong thermal antinociception as assessed with the tail flick test without inducing motor impairment or sedation. Tolerance developed in 4 days to the antinociceptive effect of orphanin FQ upon twice daily injections. However, rats rendered tolerant to orphanin FQ did not exhibit cross-tolerance to morphine. Moreover, in rats made tolerant to morphine, orphanin FQ induced similar antinociceptive effect as in morphine naive rats. The present results are the first to show that there is no cross-tolerance between orphanin FQ and morphine in eliciting spinal antinociception, supporting the notion that orphanin FQ produced spinal antinociception through a site which is different from classical opioid receptors.

Section snippets

Acknowledgements

We would like to thank Dr. Wei Yu for her help during the experiments. This study was supported by Swedish Medical Research Council (07913). the Biomed II Programme of the European Commission (project BMH4-CT95-0172), Astra Pain Control AB and research funds of the Karolinska Institute.

References (17)

There are more references available in the full text version of this article.

Cited by (0)

View full text