AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 2 320-R325, Copyright © 1993 by American Physiological Society
Intragastric glucose but not fructose conditions robust flavor preferences in rats
A. Sclafani, C. Cardieri, K. Tucker, D. Blusk and K. Ackroff
Department of Psychology, Brooklyn College and Graduate School, City University of New York 11210.
Prior work indicates that glucose and fructose differ in their
postingestive reinforcing effects. The present study investigated this
phenomenon by training rats to associate the intake of flavored water with
intragastric (IG) infusions of 16% sugar solutions. In experiment 1, rats
had one flavor [conditional stimulus (CS)] paired with IG sugar infusions
(CS+; e.g., cherry) and another flavor paired with IG water (CS-; e.g.,
grape) 23 h/day; Chow was available ad libitum. In subsequent choice tests,
rats infused with glucose displayed a strong preference (89%) for the CS+
flavor, whereas rats infused with fructose showed only a small and
nonreliable CS+ flavor preference (62%). When next trained to associate one
flavor (e.g., orange) with IG glucose and another flavor (e.g., strawberry)
with IG fructose, rats in both groups developed a significant preference
(81%) for the glucose-paired flavor. In experiment 2, food-deprived rats
were trained 2 h/day to associate a CS+ flavor with IG sugar and a CS-
flavor with IG water infusions. The glucose-reinforced rats displayed a
near-total preference (95%) for the CS+ flavor, whereas fructose-reinforced
rats showed a much smaller CS+ preference (67%). The preference findings
indicate that the postingestive consequences of glucose are much more
reinforcing than those of fructose. It appears that food conditioning is
mediated by chemospecific actions of nutrients rather than their general
satiating or energy repleting effects.
