Effects of dopamine D1 and dopamine D2 antagonists on the free feeding and drinking patterns of rats.

In male rats with food and water freely available, the specific dopamine D2 antagonist YM-09151-2 had little effect on total food or water intake across a 24-hr period. However, it produced a substantial dose-related decrease in feeding rate during meals and an enhancement of both meal size and duration. The equivalent parameters for water intake were affected to a much lesser extent. A second dopamine D2 antagonist, remoxipride, had similar effects on feeding patterns and, in addition, raised food intake during the 2 hr after drug administration. A third dopamine D2 antagonist, raclopride, produced a short-lived rise in food intake and a slowing of feeding rate with a nonsignificant increase in meal size at intermediate doses. Higher doses increased the latency to feed and drink. The specific D1 antagonist SCH 23390 had small effects on both total food intake and feeding patterns. Water intake was substantially reduced in the first 2-4 hr after drug administration by an increased latency to drink. The results are interpreted, first of all, in terms of two separate effects of dopamine D2 receptors on feeding behavior: the first mediating positive feedback processes important at meal initiation and the second mediating the preabsorptive effects of food on meal termination. D1 receptors, in contrast, are of greater importance in controlling water intake.