Intragastric carbohydrate exerts both intake-stimulating and intake-suppressing effects

Ingestion-contingent infusions of 6% carbohydrate did not affect saccharin intake during the first ingestive bout, but later they greatly stimulated ingestion, slowed the rate of decline of ingestion during bouts, and increased the average bout size. This suggests that the intake-stimulating effect of carbohydrate infusions is partly attributable to conditioned desatiation. Satiation can also be conditioned because more concentrated infusions (24% carbohydrate) did not increase daily intake or average bout size, even though both concentrations stimulated ingestion during the first 0.5-6.0 min of a test session, as well as during extinction tests when only water was infused. Increased intake may be partly mediated by a hedonic mechanism because naloxone, an opioid antagonist, decreased intake in rats infused with carbohydrate to a greater degree than it decreased intake in rats infused with water.