Impact of T1r3 and Trpm5 on Carbohydrate Preference and Acceptance in C57BL/6 Mice

Knockout (KO) mice missing the sweet taste receptor subunit T1r3 or the signaling protein Trpm5 have greatly attenuated sweetener preferences but learn to prefer sucrose in 24-h tests. Here, we examined 24-h preferences of T1r3 KO, Trpm5 KO, and C57BL/6J wild-type (WT) mice for glucose, fructose, galactose, and corn starch. Unlike glucose, fructose has little postoral reward effect in WT mice, whereas conflicting data have been obtained with galactose. Nave KO mice were initially indifferent to dilute glucose solutions (0.54%) but exhibited strong preferences for 832% concentrations. In a second test, they strongly preferred (similar to 90%) all glucose concentrations although they drank less sugar than WT mice. Nave KO mice were indifferent to 0.58% fructose and avoided 1632% fructose. However, the glucose-experienced KO mice displayed significant preferences for all fructose solutions. Nave KO mice preferred only 8% galactose, whereas WT mice preferred 416% galactose, and all mice avoided 32% galactose. Galactose experience enhanced the preference for this sugar in KO and WT mice. Nave T1r3 KO and WT mice displayed similar preferences for 0.532% corn starch, which were enhanced by starch experience. Nave Trpm5 KO mice did not prefer starch but did so after 1-bottle starch experience. The results confirm the sweet taste deficits of T1r3 KO and Trpm5 KO mice but demonstrate their ability to develop strong glucose and milder galactose preferences attributed to the postoral actions of these sugars. The acquired preference for the non-sweet flavor properties of glucose generalized to those of fructose. The findings further demonstrate that although Trpm5 (but not T1r3) signaling is essential for starch preference, Trpm5 KO mice can learn to prefer starch based on its postoral effects.