Application of [125I] (S)-5-iodonicotine, a new radioiodinated ligand, in the assay of nicotinic acetylcholine receptor binding in the brain.

125I-5-Iodonicotine was prepared and its application in the assay of nicotinic acetylcholine receptor binding in the brain was studied. 125I-5-Iodonicotine bound to the rat cortical membrane with high affinity (Kd, 15.0 nm). Various nicotinic cholinergic compounds showed competition with 125I-5-iodonicotine for the binding sites in the rats cortical membrane, and the specificity of its binding was correlated well with that of [H3] cytisine (r = 0.98). These findings suggest that 125I-5-iodonicotine binds to the same sites as [H3] cytisine and indicate that 125I-5-iodonicotine can be applied as a brain nicotine receptor binding assay.