Abstract
Our study addressed the hypothesis that spinal release of endogenous opioids underlies Delta 9-tetrahydrocannabinol (Δ 9-THC)-induced antinociception in Freund's adjuvant-induced arthritic and nonarthritic rats. The paw-pressure test was used to assess the antinociceptive effects of Δ 9-THC versus those of morphine, and opioid and cannabinoid receptor-selective antagonists were used to characterize the involved receptors. Cerebrospinal fluid was collected after Δ 9-THC injection (i.p.) for the measurement of endogenous opioid peptides. Our results indicate that morphine or Δ 9-THC is equally potent and efficacious in both nonarthritic and arthritic rats. Δ 9-THC-induced antinociception is attenuated by the κ opioid receptor antagonist, nor-binaltorphimine, in arthritic rats only. Δ 9-THC induces increased immunoreactive dynorphin A ( idyn A) levels in nonarthritic rats while decreasing idyn A in arthritic rats. We hypothesize that the elevated idyn A level in arthritic rats contributes to hyperalgesia by interaction with N-methyl- d-aspartate receptors, and that Δ 9-THC induces antinociception by decreasing idyn A release.
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