Abstract: AIM: To investigate the antinociceptive effect of choline on inflammatory pain.METHODS: Formalin and hot-plate tests were used to study the antinociceptive effect of choline, and observe the synergetic antinociceptive effects of choline and its combination with aspirin or morpine.RESULTS: Early phase (0-5 min) response was induced by an immediate and intense increase in the spontaneous activity of afferent C fibers. Late phase (15-30 min) response was thought to be inflammatory response induced by the release of inflammatory factors after formalin administration.Choline (4, 8, 16, 32, and 64mg°kg^-1, iv) obviously shortened the paw licking time in phase Ⅱ in the formalin test.The conjoint administration of choline 2 mg°kg^-1 and aspirin 9.4 mg°kg^-1 produced a synergistic antinociception effect compared with that administration of choline 2 mg°kg^-1 or aspirin 9.4 mg°kg^-1, respectively.And the phenomenon was also observed on the conjoint administration of choline 2 mg°kg^-1 and morpine 0.165 mg°kg^-1 compared with that administration of morpine 0.165 mg°kg^-1 singly, but synergistic effect on the conjoint administration of choline 4 mg°kg^-1 and aspirin 23.5 mg°kg^-1 did not show obvious significance compared with that administration of choline 4 mg°kg^-1 or aspirin 23.5 mg°kg^-1, respectively.CONCLUTION: Choline can inhibit inflammatory pain induced by formalin.Co-administrations of choline and aspirin, or morpine have prominent synergetic antinociceptive effects.

Key words: nAchR agonist, choline, synergistic antinociception, formalintest