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

AbstractSpecific high-affinity binding sites for 125I-α-bungarotoxin and (−)-[3H]nicotine have been measured in rat brain and locust (Schistocerca gregaria) ganglia. The binding sites for 125I-α-bungarotoxin had similar Kd values of 1.5 × 10−9 and 0.8 × 10−9 M for rat and locust preparations, respectively; the corresponding values for the (−)-[3H]nicotine-binding site were 9.3 × 10−9 and 1.7 × 10−7 M. Methyllycaconitine (MLA) potently inhibited 125I-α-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 α-bungarotoxin