A comparison of the antinociceptive actions of cholinomimetic and morphine‐like drugs

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Abstract
1 . The antinociceptive activity of morphine, nalorphine, oxotremorine and eserine has been examined in mice in electroshock and phenylbenzoquinone writhing tests. 2 . The effectiveness of these drugs alone, in combination with each other, and in combination with the muscarinic antagonist atropine sulphate, and with the narcotic antagonist naloxone has also been investigated. 3 . In both tests morphine was effective and antagonized by naloxone. 4 . Nalorphine was active in the phenylbenzoquinone test but only slightly active in the electroshock test: it was antagonized by naloxone in both tests. 5 . Morphine was potentiated by nalorphine in the phenylbenzoquinone test. but antagonized by it in the electroshock test. 6 . Oxotremorine was effective in both tests, and was antagonized by atropine sulphate. 7 . Eserine was active only in the phenylbenzoquinone test, and was antagonized by atropine sulphate. 8 . Oxotremorine was potentiated by eserine in the phenylbenzoquinone test. but antagonized by it in the electroshock test. 9 . Crossed agonist and partial agonist experiments produced enhancement. 10 . No antagonism was seen in the crossed antagonist experiments. 11 . The similarities between the effects of the two classes of drugs are discussed, and the conclusion drawn that they act by separate mechanisms.