Abstract
Molecular and behavioral studies have identified heterodimers of the T1R family as receptors for detecting the tastes of sweet (T1R2/T1R3) and umami (T1R1/T1R3). Previous studies demonstrated that T1R3-KO mice showed greatly reduced but not abolished behavioral preferences for sweet compounds. It is possible that there may be T1R3-independent sweet-responsive receptor components in mice. In the present study, to further examine behavioral taste responses of T1R3-KO mice, we used a short-term (10s) lick test after conditioning to avoid to each of sucrose, glucose, glycine and D-phenylalanine in T1R3-KO mice. We found that T1R3-KO mice were conditioned to learn to avoid 1.0M sucrose. The aversion generalized to 0.3M sucrose but not to the other various sweet compounds. An aversion conditioned to 0.5M glucose generalized to 1.0M sucrose, 0.5M maltose, 1.0M sorbitol, 0.1M NaCl and 0.1M MSG, whereas an aversion to 0.3M glycine did not generalize the other sweet compounds. Conditioned aversion to 0.1M D-phenylalanine was generalized to 0.5M fructose, 1.0M sorbitol, 0.3M glycine and 30mM D-tryptophan. Our results demonstrate that T1R3-KO mice still possess the ability to learn the conditioned avoidance to various sweet compounds with different generalization patterns. This suggests that there may exist multiple T1R3-independent sweet-responsive components in mice. [J Physiol Sci. 2007;57 Suppl:S225]
