T1R3 taste receptor is critical for sucrose but not Polycose taste

Abstract

In addition to their well-known preference for sugars, mice and rats avidly consume starch-derived glucose polymers (e.g., Polycose). T1R3 is a component of the mammalian sweet taste receptor that mediates the preference for sugars and artificial sweeteners in mammals. We examined the role of the T1R3 receptor in the ingestive response of mice to Polycose and sucrose. In 60-s two-bottle tests, knockout (KO) mice preferred Polycose solutions (4-32%) to water, although their overall preference was lower than WT mice (82% vs. 94%). KO mice also preferred Polycose (0.5-32%) in 24-h two-bottle tests, although less so than WT mice at dilute concentrations (0.5-4%). In contrast, KO mice failed to prefer sucrose to water in 60-s tests. In 24-h tests, KO mice were indifferent to 0.5-8% sucrose, but preferred 16-32% sucrose; this latter result may reflect the post-oral effects of sucrose. Overall sucrose preference and intake were substantially less in KO mice than WT mice. However, when retested with 0.5-32% sucrose solutions, the KO mice preferred all sucrose concentrations, although they drank less sugar than WT mice. The experience-induced sucrose preference is attributed to a post-oral conditioned preference for the T1R3-independent orosensory features of the sugar solutions (odor, texture, T1R2-mediated taste). Chorda tympani nerve recordings revealed virtually no response to sucrose in KO mice, but a near-normal response to Polycose. These results indicate that the T1R3 receptor plays a critical role in the taste-mediated response to sucrose but not Polycose.

Fig. 1.

Saccharide licks (± SE) (top) and percent saccharide preference over water (bottom) in T1R3 KO and B6 WT mice during 60-s two-bottle tests. Licks of water are not shown. Significant (P < 0.05) differences between KO and WT genotypes are indicated by an asterisk (*). Overall genotype difference is denoted by a number sign (#).

Fig. 2.

Polycose solution intake (± SE) (top), percent Polycose preference over water (middle) and Polycose energy intake (bottom) in T1R3 KO and B6 WT mice during 24-h two-bottle Polycose vs. water tests 1 and 2. Water intakes are not shown. Significant (P < 0.05) genotype differences at individual concentrations are indicated by an asterisk (*) and significant overall genotype differences are indicated by number sign (#). The lowest concentration at which Polycose was significantly (P < 0.05) preferred to water is indicated by a plus sign (+).

Fig. 3.

Sucrose solution intake (± SE) (top), percent sucrose preference over water (middle), and sucrose energy intake (bottom) in T1R3 KO and B6 WT mice during 24-h two-bottle sucrose vs. water tests 1 and 2. Water intakes are not shown. Significant (P < 0.05) genotype differences at individual concentrations are indicated by an asterisk (*). The lowest concentration at which sucrose was significantly (P < 0.05) preferred to water is indicated by a plus sign (+).

Fig. 4.

Saccharin solution intake (± SE) (top) and percent saccharin preference (bottom) over water in T1R3 KO and B6 WT mice during 24-h two-bottle saccharin vs. water tests. Water intakes are not shown. Significant (P < 0.05) differences genotype differences are indicated by an asterisk (*).

Fig. 5.

Chorda tympani nerve responses (normalized to 100 mM NH₄Cl) of T1R3 KO and WT mice to a range of concentrations of sucrose (A), Polycose (B), and NaCl (C). Values are means ± SE; n = 8 or 9 per strain.