Possible mediation of catecholaminergic pathways in the antinociceptive effect of an extract of Cannabis sativa L.

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Abstract
An extract of cannabis (5 and 15 mg/kg expressed as Δ9-THC) orally administered to rats caused an elevation of the nociceptive threshold (tail-flick latency and vocalization tests). Naloxone and naltrexone (blockers of μ-type opiate receptors) as well as MR 1452 (blocker of κ opiate receptors) did not prevent the antinociceptive effect of cannabis when used at the dose of 2 mg/kg SC; only a high dose (10 mg/kg SC) of these narcotic antagonists partially blocked cannabis antinociception. ICI 154, 129, an antagonist of δ-type opiate receptors, failed to prevent the cannabis-induced rise in nociceptive threshold when used at a dose of 2 mg/kg SC but produced a significant effect at 10 mg/kg SC. While the role of opiate receptors does not seem fundamental to cannabis antinociception, the clear-cut effectiveness shown by 6-hydroxydopamine (a neurotoxin which causes a degeneration of catecholamine-containing terminals) in reducing cannabis antinociception is indicative of a participation of catecholamines in the phenomenon.