Sucrose-conditioned flavor preferences in sweet ageusic T1r3 and Calhm1 knockout mice

Abstract

The present study compared the ability of sweet ageusic T1r3 knockout (KO) and Calhm1 KO mice to acquire preferences for a sucrose-paired flavor as well as for unflavored sucrose. The KO and wildtype (WT) mice were given 24-h one-bottle access to 8% sucrose containing one flavor CS+, e.g., grape) and to water containing a different flavor (CS-, e.g., cherry) over 4 training days. In subsequent two-bottle tests with the flavors in water only, the T1r3 KO and Calhm1 KO mice, like WT mice, preferred the CS+ to the CS-. After training with flavored solutions, both KO groups also preferred unflavored 8% sucrose to water although Calhm1 KO mice required more sugar experience to match the preference of the T1r3 KO mice. These findings demonstrate that Calhm1 KO mice, like T1r3 KO mice and WT mice, are sensitive to the post-oral preference conditioning actions of sucrose and can discriminate sugar from water. Yet, despite their acquired sucrose preferences, the Calhm1 KO and T1r3 KO mice consumed only half as much sugar per day as did WT mice. Thus, sweet taste signaling elements are not needed in the gut for sugar conditioning, but sweet taste signaling in the mouth is essential for the full expression of sugar appetite.

Keywords: 24-h tests; Oral sugar conditioning; Post-oral sugar reward.

Figure 1

Mean (+sem) 24-h intakes of CS+/Suc and CS- in one-bottle training sessions and CS+ and CS- in two-bottle tests 1-2 (left panels) and of unflavored 8% sucrose and water in two-bottle tests 1-2 and one-bottle training days (right panels) of WT mice (top panels) and T1r3 KO mice (lower panels). Number atop bar represents mean percent preference for the CS+ or sucrose solution. An asterisk indicates a significant difference (P < 0.05) between the data within a pair of bars (CS+/Suc vs. CS-, CS+ vs. CS-, sucrose vs. water); a plus symbol indicates a significant difference between sucrose intake and preference between Test 1 vs. 2; a hash symbol indicates a significant difference between CS+/Suc or sucrose intake between WT and KO mice.

Figure 2

Mean (+sem) 24-h intakes of CS+/Suc and CS- in one-bottle training sessions and CS+ and CS- in two-bottle tests 1-2 (left panels) and of unflavored 8% sucrose and water in two-bottle tests 1-2 and one-bottle training days (right panels) of WT mice (top panels) and Calhm1 KO mice (lower panels). Number atop bar represents mean percent preference for the CS+ or sucrose solution. An asterisk indicates a significant difference (P < 0.05) between the data within a pair of bars (CS+/Suc vs. CS-, CS+ vs. CS-, sucrose vs. water); a plus symbol indicates a significant difference between sucrose intake and preference between Test 1 vs. 2; a hash symbol indicates a significant difference between CS+/Suc or sucrose intake between WT and KO mice.