Chronic nicotine treatment decreases dopamine D2 agonist binding in the rat basal ganglia

TO elucidate possible actions of nicotine on dopamine D2 receptor binding, the effect of chronic continuous (-)nicotine treatment (osmotic pumps s.c., 0.125 mg kg h, 14 days) was studied in the binding of [H]N-propylnorapomorphine ([H]NPA) and [H]sulpride in coronal cryostat sections in the rat. Quantitative autoradiography showed that nicotine decreased the binding of [H]NPA in the basal ganglia, preferentially in the nucleus accumbens and olfactory tubercle. In contrast, [I]sulpride binding was not affected. Nicotine decreased the KD value of [H]NPA by 27% and decreased the Bmax value by 17%, using filter-wiped sections. These results indicate that chronic continuous nicotine treatment affects the D2 receptor and that this effect may be involved in the development of nicotine dependence.