Additivity of taste-specific effects of sucrose and quinine: microstructural analysis of ingestive behavior in rats.

Effects of sweet and bitter tastes on ingestion were studied by timing licking responses. Twelve water-deprived rats were given 15-min access to sucrose (S) solutions (0.00%, 1.25%, 2.50%, and 5.00%) with and without quinine (0.01%) and to quinine (Q) solutions (0.00%, 0.0025%, 0.005%, and 0.01%) with and without sucrose (5.00%). Volume ingested and number of licks increased with S and decreased with Q. In response to S, the number of bursts increased, and interlick intervals lengthened. In response to Q, licks to ingest 1 ml of solution, burst number, and percentage of slow licks increased, and burst size decreased. When Q and S were mixed in the same solution, the pattern of ingestive responses manifested attributes of both tastes. Results suggest 2 separate, parallel systems that operate simultaneously to govern rats' licking behavior. One system expresses the effect of S on the pattern of ingestion and the other expresses the effects of Q.