Blockade of D-1 receptors by SCH 23390 antagonizes morphine- and amphetamine-induced place preference conditioning.

Morphine (0.5 mg/kg s.c.) and amphetamine (1 mg/kg s.c.) used in a two-compartment place preference test induced strong place preference when paired to the non-preferred environments. They did not modify preference under basal conditions but completely reversed morphine- and amphetamine-induced place preference. Pairing of haloperidol (0.2 mg/kg s.c.) to both environments also abolished the morphine-induced place preference.