Methyllycaconitine and (+)-anatoxin-a differentiate between nicotinic receptors in vertebrate and invertebrate nervous systems.

Specific high-affinity binding sites for 125I-alpha-bungarotoxin and (-)-[3H]nicotine have been measured in rat brain and locust (Schistocerca gregaria) ganglia. The binding sites for 125I-alpha-bungarotoxin had similar Kd values of 1.5 x 10(-9) and 0.8 x 10(-9) M for rat and locust preparations, respectively; the corresponding values for the (-)-[3H]nicotine-binding site were 9.3 x 10(-9) and 1.7 x 10(-7) M. Methyllycaconitine (MLA) potently inhibited 125I-alpha-bungarotoxin binding in both rat and locust. MLA was a less effective inhibitor of (-)-[3H]nicotine binding whereas (+)-anatoxin-a was a very potent inhibitor at this site in the rat but not in the locust. These data suggest that (+)-anatoxin-a is a useful probe for the high-affinity nicotine-binding receptor in vertebrate brain, whereas MLA is a preferential probe for the subclass of receptor that binds alpha-bungarotoxin.