Antinociceptive effect of spinally administered cannabinergic and α₂-adrenoceptor drugs on the formalin test in rat: possible interactions.

Khodayar, Mohammad Javad; Shafaghi, Bijan; Naderi, Nima; Zarrindast, Mohammad-Reza

The current experiments were designed to study the antinociceptive effects of intrathecal (i.t.) administration of cannabinoid CB1 receptor and α2-adrenoceptor drugs in the nociceptive processing and also their receptor interactions. Different doses of a cannabinoid receptor agonist, CP 55,940, and an α2-adrenoceptor agonist, clonidine induced a dose-dependent antinociception in both phases of the formalin test. CP 55,940-induced antinociception was reduced by pretreatment of a selective cannabinoid CB1 receptor antagonist, SR 141716A, but not by pretreatment with an α2-adrenoceptor antagonist, yohimbine in both phases of the test. However, yohimbine and SR 141716A attenuated the antinociception induced by clonidine in the early phase but not in the late phase of the test. While SR 141716A by itself did not influence pain behaviour, the reversal effect of clonidine by SR 141716A indicate that clonidine stimulate the release of endocannabinoid(s). In conclusion, our findings may suggest that: (1) spinal cannabinoid and α2-adrenoceptor systems are able to induce antinociception in both phases of formalin test, and (2) the cannabinoid system may be involved in the antinociception induced by adrenoceptors in the early phase.

DRUG administration; ALPHA adrenoceptors; YOHIMBINE; CLONIDINE; PAIN; LABORATORY rats

Journal of Psychopharmacology, 2006, Vol 20, Issue 1, p67

0269-8811

Academic Journal

10.1177/0269881105056996