Application of [125I] (S)-5-Iodonicotine, a New Radioiodinated Ligand, in the Assay of Nicotinic Acetylcholine Receptor Binding in the Brain

[125I] (S)-5-Iodonicotine was prepared and its application in the assay of nicotinic acetylcholine receptor binding in the brain was studied. [125I] (S)-5-Iodonicotine bound to the rat cortical membrane with high affinity (Kd, 15.0nM). Various nicotinic cholinergic compounds showed competition with [125I] (S)-5-iodonicotine for the binding sites in the rat cortical membrane, and the specificity of its binding was correlated well with that of [3H] cytisine (r=0.98). These findings suggest that [125I] (S)-5-iodonicotine binds to the same sites as [3H] cytisine and indicate that [125I] (S)-5-iodonicotine can be applied as a brain nicotine receptor binding assay.