The Cholinergic System and Nociception in the Primate: Interactions with Morphine.
Technical rept. Jul 72-Sep 73,
EDGEWOOD ARSENAL ABERDEEN PROVING GROUND MD
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In experiment 1, the shock titration task was used to evaluate the antinociceptive properties of five different classes of cholinergic compounds in the Rhesus monkey. It was found that only scopolamine and high doses of physostigmine were effective in elevating the shock threshold. The apparent antinociceptive effect of physostigmine, however, was difficult to separate from its nonspecific behavioral depressant effect and was probably not related to an increase in cholinergic tone. Experiment 2 examined the interaction of morphine with arecoline, scopolamine, and physostigmine. Only scopolamine 0.05 and 0.1 mgkg and high doses of physostigmine 0.1 mgkg interacted with morphine in the shock titration paradigm. The multiplicative interaction of morphine with scopolamine was confirmed in experiment 3 over a wider range of doses. It was concluded that morphine and the cholinergic compounds produce antinociceptive effects through different mechanisms of the pain system.