Abstract
This study evaluated the contribution of supraspinal opioid receptors to the production of antinociception, in the rat. I.c.v. administration of a selective μ-(DAMGO) and a selective δ-(DPDPE), but not a selective κ- (U50,488H) opioid receptor agonist, produced significant dose-dependent increases in mechanical nociceptive thresholds. ICI 174,864, a δ-opioid receptor antagonist, completely blocked the antinociceptive effects produced by DPDPE ([D-Pen 2,D-Pen 5]enkephalin) at a dose that had no effect on the increases in nociceptive thresholds produced by DAMGO ([D-Ala 2,N-MePhe 4,Gly 5-ol]enkephalin). The simultaneous i.c.v. administration of a low-antinociceptive dose of DAMGO or DPDPE given in combination with sequentially increasing doses of the other cpioid agonist, produced synergy (i.e., a more than additive antinociceptive effect), at the lower doses tested. The results of these experiments provide evidence to support the suggestion that both supraspinal μ- and δ-opioid receptors contribute to the production of antinociception, in the rat.
Published Version
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