( super(3)H)Acetylcholine and ( super(3)H)(-)nicotine label the same recognition site in rat brain

High affinity binding sites for ( super(3)H)acetylcholine and ( super(3)H)(-)nicotine in rat brain were compared with respect to key characteristics. The density of binding sites for each ligand varied approximately 4-fold in five areas of rat forebrain, but in each of these areas and in human cerebral cortex as well, the densities of ( super(3)H)acetylcholine- and ( super(3)H)(-)nicotine-binding sites were indistinguishable. The binding of ( super(3)H)acetylcholine and ( super(3)H)(-)nicotine was decreased to the same extent by preincubation of tissues with dithiothreitol. Treatment of rats with nicotine for 10 days increased the density of binding sites for both ligands. The results indicate that ( super(3)H)acetylcholine and ( super(3)H)(-)nicotine bind to the same nicotinic cholinergic recognition site in rat brain.