FLAVOR PREFERENCES CONDITIONED BY INTRAGASTRIC SUGAR INFUSIONS IN RATS - MALTOSE IS MORE REINFORCING THAN SUCROSE

Prior research indicates that glucose conditions much stronger flavor preferences in rats than does fructose. This could occur because intes tinal absorption of fructose is much slower than that of glucose and b ecause fructose malabsorption may have aversive consequences. Fructose absorption is facilitated when glucose is also present in the gut. Th e present study therefore compared the flavor conditioning effects of maltose (a glucose + glucose disaccharide) to those of sucrose (a gluc ose + fructose disaccharide). In Experiment 1, rats had different flav ors paired with intragastric infusions of 32% maltose (CS+M), 32% sucr ose (CS+S), and water (CS-) 23 h/day. In subsequent two-bottle tests, both CS + solutions were strongly preferred to the CS-, but the CS+M w as also preferred (78%) to the CS+S. Experiment 2A revealed that the r ats also learned to prefer a CS+M to a CS+S when 16% sugar infusions w ere used. Tn Experiment 2B, the same rats preferred a flavor paired wi th 16% maltose to a flavor paired with 8% maltose. They did not reliab ly prefer a flavor paired with 16% sucrose to a flavor paired with 8% maltose. These results demonstrate that the postingestive actions of m altose are more reinforcing than those of sucrose. This indicates that fructose is less reinforcing than glucose even when malabsorption is not a factor. In contrast to their preference for the CS+M over the CS +S, the rats preferred sucrose to maltose when drinking the sugars by mouth. Therefore, sugar preferences mediated by oral taste receptors d iffer from those conditioned by postoral nutrient detectors. (C) 1998 Elsevier Science Inc.