Antinociception induced by SM 32 depends on a central cholinergic mechanism

The antinociceptive effect of SM 32 was examined in mice by using the hot-plate (10-40 mg kg(-1) i.p; 3-30 microg per mouse i.c.v.) and abdominal constriction (10-30 mg kg(-1) i.p) tests. In the antinociceptive dose-range, SM 32 did not impair mouse spontaneous motility and motor coordination evaluated respectively by the Animex and rota-rod tests. The increase in the pain threshold produced by SM 32 was prevented by dicyclomine, pirenzepine and hemicholinium-3 but not by naloxone and CGP 35348. In vitro experiments showed that the SM 32 amplified electrically- and nicotine-evoked guinea-pig ileum contractions. On the basis of the above data, it can be postulated that SM 32 exerts its antinociceptive effect through a potentiation of central cholinergic transmission.