In this study, [3H]hemicholinium−3([3H]HC−3)binding, which labels the presynaptic high affinity−choline transport sites, was examined in two brain regions, cerebral cortex and midbrain, of nicotine−treated and −untreated rat neonates.In nicotine−untreated neonates, [3H]HC−3 binding sites of cerebral cortex increased from 64 fmol/mg protein at postnatal day 7 to 142 fmol/mg protein at postnatal day 35.In nicotine−treated neonates, the development of [3H]HC−3 binding sites in cerebral cortex was significantly retarded, compared with control neonates on the 7th, 14th and 21st postnatal days.In parallel with this, the development of muscarinic receptor in cerebral cortex, which was detected by [3H]quinuclidinyl benzylate([3H]QNB)binding, was also retarded by nicotine treatment.However, in midbrain, neither [3H]HC−3 nor [3H]QNB binding sites at postnatal day 14 was affected by nicotine treatment.These results strongly suggest that perinatal treatment with nicotine inhibits presynaptic and postsynaptic development of the cholinergic pathway in cerebral cortex but not in midbrain of rat neonate.
