Erysodine, a competitive antagonist at neuronal nicotinic acetylcholine receptors

Erysodine, an erythrina alkaloid related to dihydro-beta-erythroidine, was found to be a more potent inhibitor of [3H]cytisine binding at neuronal nicotinic acetylcholine receptors but a less potent inhibitor of [125I]alpha-bungarotoxin binding at muscle-type nicotinic acetylcholine receptors than dihydro-beta-erythroidine. Erysodine was a competitive, reversible antagonist of (-)-nicotine-induced dopamine release from striatal slices and inhibited (-)-nicotine-induced 86Rb+ efflux from IMR-32 cells. Erysodine was equipotent with dihydro-beta-erythroidine in the dopamine release assay but 10-fold more potent in the 86Rb+ efflux assay, suggesting differential subtype selectivity for these two antagonists. Erysodine, systemically administered to mice, entered the brain and significantly attentuated nicotine's hypothermic effects and its anxiolytic-like effects in the elevated plus-maze test. There was greater separation between antagonist and toxic doses for erysodine than for dihydro-beta-erythroidine, perhaps because of erysodine's greater selectivity for neuronal receptors. In rats, erysodine prevented both the early developing decrease and the late-developing increase in locomotor activity produced by (-)-nicotine. The potent and competitive nature of erysodine's antagonism together with its ability to enter the brain after systemic administration suggest that erysodine may be a useful tool in characterizing neuronal nicotinic acetylcholine receptors.