Elsevier

Neuroscience Letters

Volume 242, Issue 1, 6 February 1998, Pages 33-36
Neuroscience Letters

Cannabinoid receptor-mediated inhibition of the rat tail-flick reflex after microinjection into the rostral ventromedial medulla

https://doi.org/10.1016/S0304-3940(98)00044-5Get rights and content

Abstract

Systemic administration of cannabinoids produce profound antinociception in rodents. The purpose of this study was to examine the contribution of the rostral ventromedial medulla (RVM) to cannabinoid-mediated inhibition of the tail-flick reflex. Rats received direct injections of two selective cannabinoid agonists, WIN55,212-2 and HU210, into the RVM. Both compounds significantly elevated tail-flick latencies by over 50%. WIN55,212-3, the inactive enantiomer, was without effect. Furthermore, co-administration of the selective cannabinoid receptor antagonist, SR141716A greatly attenuated the antinociception produced by HU210. Finally, injections of WIN55,212-2 outside the region of the RVM did not affect tail-flick latencies. These results demonstrate that the cannabinoid receptor system participates in the descending control of nociception and raise the possibility that actions of endogenous cannabinoids in the RVM may modulate nociceptive responsiveness.

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Acknowledgements

This work was supported by National Institute on Drug Abuse (DA10043). W.J.M. was supported by graduate fellowships from the National Science Foundation and the National Institute on Drug Abuse (F31DA05617). J.M.W. is grateful for the financial support provided by the Public Health Service/National Institutes of Health (KO2-MH01083, NS33247).

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Present address: Department of Anatomy, University of California, Box 0452, San Francisco, CA 94143-0452, USA.

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