APPLICATION OF [I-125] (S)-5-IODONICOTINE, A NEW RADIOIODINATED LIGAND, IN THE ASSAY OF NICOTINIC ACETYLCHOLINE-RECEPTOR BINDING IN THE BRAIN

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