Neuroleptics block the positive reinforcing effects of amphetamine but not of morphine as measured by place conditioning

The role of dopamine brain systems in mediating the rewarding effects of opiates and stimulants was investigated using the conditioned place preference paradigm. The effects of the neuroleptics alpha-flupentixol (0.8 mg/kg, IP) and haloperidol (1.0 mg/kg, IP) were tested against the place preferences produced by morphine sulphate (1.0 and 5.0 mg/kg, SC), d-amphetamine sulphate (1.0 mg/kg, IP) and cocaine hydrochloride (5.0 mg/kg, IP). Amphetamine place preference was successfully blocked but neuroleptic pretreatment had no effect on the place preferences produced by cocaine and morphine, alpha-Flupentixol alone produced no place conditioning. These results support the hypothesis of dopamine involvement in amphetamine reward. However, morphine reward, as measured by the conditioned place preference paradigm, appears not to be critically dependent on brain dopamine systems.