Learned preference and aversion for complete and isoleucine-devoid diets in rats

Choice tests using flavored solutions were conducted to demonstrate a learned preference or aversion in rats fed replete (complete) or isoleucine (ILE)-devoid diets. In the first learning trial, rats demonstrated a preference for the flavored solutions paired with the replete diet at 6 and 24 h (p < 0.001), and an aversion for the solutions paired with the ILE-devoid diet at 6 h (p < 0.05). In the second trial, using a different concentration of tastant, rats ingested significantly more of the flavored solution paired with the replete diet at 24 h (11.4 ± 3.0 g vs. 5.4 ± 1.0 g, respectively; p < 0.05), and significantly more of a novel flavored solution than of the solution paired with the ILE-devoid diet at 24 h (12.4 ± 2.4 g vs. 1.7 ± 0.6 g, respectively; p < 0.001). These results suggest that learning contributes to the rat's ability to self-select diets that promote growth, and that a learning paradigm pairing flavored solutions with complete and indispensible amino acid-devoid diets may be used to demonstrate learned preferences and aversions for such diets in rats.