Absolute and relative rewarding properties of fructose, glucose, and saccharin mixtures as reflected in anticipatory contrast

Rats preferred 2% fructose (F) to 2% glucose (G) in daily 5-min two-bottle preference tests, but preferred 8% G to 8% F with the same testing procedur e. In four subsequent experiments brief (3 min) once-per-day sequential pre sentations of two F or two G solutions showed the following results. Antici patory negative contrast (suppressed intake of the initial solution) was gr eater with quantitative variations in fructose (2% F followed by either 8, 16, or 32% Fl than was the case when the same concentrations of G were pair ed. No contrast occurred with qualitative pairings of the two sugars-instea d G enhanced the intake of F whether it was presented before or after F. A solution of 0.15% saccharin produced more suppression (contrast) of 2% gluc ose than of 2% fructose. Also, mixtures of 0.15% saccharin with either suga r (2 or 8% F or G) enhanced absolute intake of the sugars but did not subst antially increase their contrast-producing properties-suggesting a distinct ion between absolute and relative rewarding properties of sugar/saccharin m ixtures. In summary, anticipatory negative contrast can be produced by eith er taste or postingestive factors but the relationship between two-bottle p reference, absolute reward value las reflected in consumption in noncontras t conditions), and relative reward value (measured by the capacity to produ ce contrast) is complex. (C) 1999 Elsevier Science Inc.