The effect of d-amphetamine and haloperidol alone and in combination on milk drinking in rats

Abstract

The effects of d-amphetamine (0.5–4.0 mg/kg IP) and haloperidol (0.015–1.0 mg/kg IP) alone and in combination on intake of a sweetened milk solution were determined in rats. Experimental sessions consisted of a 15-min access to the milk solution once a day, 7 days a week. d-Amphetamine was administered 15 min prior to the session. The interaction of these compounds was determined by repeated determination of the dose-response function for d-amphetamine in combination with different doses of haloperidol. When given alone, each drug produced a dose-dependent decrease in milk intake. In combination with haloperidol, the decrement caused by d-amphetamine was shifted to lower doses in a dose-dependent manner. Isobolographic analysis of the interaction indicates that the intermediate doses (0.03–0.06 mg/kg) of haloperidol were additive and the highest doses (0.12–0.25 mg/kg) of haloperidol were infraadditive with d-amphetamine. Dose-dependent neuropharmacological actions of these compounds may account for dose-dependent interactions.