Dopamine D1 receptor and dopamine D2 receptor binding activity changes during chronic administration of nicotine in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice.

The effect of nicotine on MPTP-induced changes in striatal dopamine receptors binding activity was investigated. Dopamine D1 and D2 receptors were labeled with [3H]SCH-23390 and [3H]spiperone respectively in BALB/cBy mice. With administration of only MPTP, which caused more than an 80% decrease in striatal dopamine level, binding of 0.15 nM [3H]spiperone was increased by 37%; whereas 0.3 nM [3H]SCH-23390 binding was unchanged. With chronic nicotine treatment (0.4 mg/kg twice daily for 7-9 days), [3H]SCH-23390 binding activity was increased by 27% and [3H]spiperone binding activity was unchanged. When nicotine was administered after MPTP, their separate effects could be seen in that both the D1 and D2 dopamine receptor ligand binding activities were increased and that nicotine elevated the ratio of D1/D2 receptor binding activities in MPTP-treated mice.