Conditioned taste aversion in rats for a threonine-deficient diet: demonstration by the taste reactivity test

Rats avoid a diet that is deficient in one or more essential amino acids (E AAs). This phenomenon is thought to involve the development of a "learned a version" for the sensory properties or spatial placement associated with th e deficient diet. The dietary self-selection technique has been widely used to show this avoidance of the deficient diet. Because avoidance does not n ecessarily imply taste aversion, we used the Taste Reactivity Test initiall y created by Grill and Norgren (1978) to analyze the affective reactivity p attern of rats that ingested a threonine-deficient diet. The results showed that there was an increase in the aversive responses when ingesting the th reonine-deficient (Thr-Dev) diet, compared to a control diet, without chang es in the hedonic responses. The aversive reactions were mainly gaping, and to a lesser extent chin rubbing and head shaking. This asymmetrical shift in the Thr-Dev diet palatability is consistent with a two-dimensional hypot hesis of palatability, indicating that the aversive palatability of the def icient diet was increased while the positive palatability did not change. F urther evidence indicates that rats do not develop a normal behavioral sati ety sequence after ingesting the threonine-deficient diet. These results in dicate that a true aversion is formed to the taste of a diet that is defici ent in an essential amino acid. (C) 2000 Elsevier Science Inc. All rights r eserved.