Effects of the dopamine D1 receptor antagonist SCH 39166 on the ingestive behaviour of alcohol-preferring rats.

The present study evaluated the effect of the selective and long-acting dopamine D1 receptor antagonist SCH 39166 on several aspects of the ingestive behaviour of genetically selected alcohol-preferring rats, bred from Sardinian alcohol-preferring rats. The effect of subchronic (8 days) subcutaneous drug administration was evaluated on the simultaneous daily intake of 10% ethanol, food and water. SCH 39166, 0.1 mg/kg, did not significantly modify the intake of the three ingesta. The dose of 1 mg/kg differentially modified rat ingestive behaviour, inhibiting intake of 10% ethanol, without modifying total fluid and food intake. The higher dose of 5 mg/kg produced a non-selective suppression of ingestive behaviour, which was accompanied by behavioural impairment. Acute drug injection was tested on 2-h intake of 10% sucrose, 0.1% saccharin, water or food. The doses of 0.1 and 1 mg/kg markedly inhibited the 2-h intake of 10% sucrose and 0.1% saccharin, but they did not modify either the 2-h water intake in water deprived and water sated rats or the 2-h food intake in food deprived rats. These findings suggest an important role of mechanisms mediated by D1 receptors in the control of alcohol and sweet solution intake, but not in water and food intake. Moreover, they indicate that SCH 39166, in relation to its selectivity and long-lasting activity, is an interesting pharmacological tool to investigate further the role of D1 receptor mechanisms in the control of ingestive behaviour.