Attenuation of the effects of cocaine on milk consumption in rats by dopamine antagonists

Abstract

Recent research suggests the both D 1 and D 2 dopamine (DA) receptors play an important role in the behavioral effects of psychomotor stimulants. The present study utilized selective DA antagonists to examine the role of DA receptors in the effects of cocaine on milk intake in rats. Male Sprague-Dawley rats were given access to a milk solution (2:1 tap water:Bordens sweetened condensed milk) for 15 min each day. When milk intake was stable, dose-response functions were determined for cocaine (4.0–32 mg/kg, IP, 10 min presession) administered alone or in combination with the D 1 antagonist SCH 23390 (0.12–0.5 mg/kg, IP, 30 min presession) or the D 2 antagonist raclopride (0.25–1.0 mg/kg, IP, 30 min presession). As a control for the serotonin (5-HT 2) antagonist effects of SCH 23390, the 5-HT 2 antagonist ketanserin (4.o–16 mg/kg) was evaluated as well. To control for nonspecific drug effects on fluid consumption, the effects of cocaine alone on water intake were determined in a separate group of rats. All drugs decreased milk intake when given alone. Both SCH 23390 and raclopride attenuated the effects of at least one dose of cocaine. Ketanserin did not alter the effects of cocaine. These results suggest that stimulation of both D 1 and D 2, but not 5-HT 2, receptors is involved in the effects of cocaine on milk intake in rats.