Flavor preferences conditioned by nutritive and non-nutritive sweeteners in mice

Abstract

Recent studies suggest that preferences are conditioned by nutritive (sucrose) but not by non-nutritive (sucralose) sweeteners in mice. Here we compared the effectiveness of nutritive and non-nutritive sweeteners to condition flavor preferences in three mouse strains. Isopreferred sucrose and sucralose solutions both conditioned flavor preferences in C57BL/6J (B6) mice but sucrose was more effective, consistent with its post-oral appetition action. Subsequent experiments compared flavor conditioning by fructose, which has no post-oral appetition effect in B6 mice, and a sucralose+saccharin mixture (SS) which is highly preferred to fructose in 24-h choice tests. Both sweeteners conditioned flavor preferences but fructose induced stronger preferences than SS. Training B6 mice to drink a flavored SS solution paired with intragastric fructose infusions did not enhance the SS-conditioned preference. Thus, the post-oral nutritive actions of fructose do not explain the sugar's stronger preference conditioning effect. Training B6 mice to drink a flavored fructose solution containing SS did not reduce the sugar-conditioned preference, indicating that SS does not have an off-taste that attenuates conditioning. Although B6 mice strongly preferred flavored SS to flavored fructose in a direct choice test, they preferred the fructose-paired flavor to the SS-paired flavor when these were presented in water. Fructose conditioned a stronger flavor preference than an isopreferred saccharin solution, indicating that sucralose is not responsible for the limited SS conditioning actions. SS is highly preferred by FVB/NJ and CAST/EiJ inbred mice, yet conditioned only weak flavor preferences. It is unclear why highly or equally preferred non-nutritive sweeteners condition weaker preferences than fructose, when all stimulate the same T1r2/T1r3 sweet receptor. Recent findings support the existence of non-T1r2/T1r3 glucose taste sensors; however, there is no evidence for receptors that respond to fructose but not to non-nutritive sweeteners.

Keywords: C57BL/6J mice; CAST/EiJ mice; FVB/NJ mice; Flavor-preference conditioning; Fructose; Saccharin; Sucralose; Sucrose.

Figure 1

Experiment 1. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in the Sucrose (left panel) and Sucralose (right panel) B6 groups. (Order of training and testing is from left to right in the panels.) During training the CS+ flavor was added to the sweetener solution (CS+/Sweetener), which was 8% sucrose for the Sucrose group and 0.8% sucralose for the Sucralose group. During testing the CS+ flavor was in water (CS+/H2O); the CS− flavor was always in water (CS−/H2O). Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 2

Experiment 2. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in the Fructose (left panel) and SS (right panel) B6 groups. (Order of training and testing is from left to right in the panels.) During training the CS+ flavor was added to the sweetener solution (CS+/Sweetener), which was 8% fructose for the Fructose group and 0.1% sucralose + 0.1% saccharin (SS) for the SS group. During testing the CS+ flavor was in water (CS+/H2O); the CS− flavor was always in water (CS−/H2O). In the Sweetener vs. water Test, the Fructose group was given unflavored 8% fructose and the SS group unflavored SS. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 3

Experiment 3. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in B6 mice. (Order of training and testing is from left to right in the panel.) During training, the CS+ flavor was added to 0.1% sucralose + 0.1% saccharin (SS) and was paired with matched IG infusions of 16% fructose (CS+/SS -> IG fructose). During testing the CS+ flavor was in water (CS+/H2O) and was not paired with IG infusions. The CS− flavor was always in water (CS−/H2O) and during training, but not testing it was paired with matched IG water infusions. In the Sweetener Test the mice were given unflavored SS vs. water without IG infusions. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 4

Experiment 4. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in B6 mice. (Order of training and testing is from left to right in the panel.) During training the CS+ flavor was added to an 8% fructose solution that also contained 0.1% sucralose + 0.1% saccharin (CS+/FRU+SS) and during testing the CS+ flavor was in water (CS+/H2O). The CS− flavor was always in water (CS−/H2O). In the Sweetener Test the mice were given unflavored 8% fructose mixed with SS (FRU+SS) vs. water. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 5

Experiment 5. Mean intakes (+sem) of CS+ solutions during two-bottle tests and one-bottle training in B6 mice. (Order of training and testing is from left to right in the panel.) In the initial and final Sweetener CS Tests and during one-bottle training, the CS+F flavor was added to an 8% fructose solution (CS+F/FRU) and the CS+SS flavor was added to an 0.1% sucralose + 0.1% saccharin (SS) solution (CS+SS/SS). During two-bottle CS tests the CS+F and CS+SS flavors were in water. In the Sweetener Test, the mice were given unflavored 8% fructose vs. unflavored SS. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 6

Experiment 6. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in B6 mice. (Order of training and testing is from left to right in two panels.) During training the CS+ flavor was added to 0.2% saccharin (CS+/SAC) and during testing it was in water (CS+/H2O). The CS− flavor was always in water (CS−/H2O). During the first Sweetener Test, the mice were given unflavored 0.2% saccharin (SAC) vs. water (left panel). In two subsequent tests (right panel) the mice were given the choice of unflavored 0.2% saccharin (SAC) vs. 8% fructose and 0.2% saccharin vs. 0.1% sucralose + 0.1% saccharin (SS). Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 7

Experiment 7. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in the Fructose (left panel) and SS (right panel) FVB groups. (Order of training and testing is from left to right in the panels.) During training the CS+ flavor was added to the sweetener solution (CS+/Sweetener) which was 8% fructose for the Fructose group and 0.1% sucralose + 0.1% saccharin (SS) for the SS group. During testing the CS+ flavor was in water (CS+/H2O); the CS− flavor was always in water (CS−/H2O). In the Sweetener vs. water test the Fructose group was tested with unflavored 8% fructose and the SS group with unflavored SS. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 8

Experiment 7. Mean intakes (+sem) of CS+ and CS− during one-bottle training and two-bottle Tests 1 and 2 in the Fructose (left panel) and SS (right panel) CAST groups. (Order of training and testing is from left to right in the panels.) During training the CS+ flavor was added to the sweetener solution (CS+/Sweetener) which was 8% fructose for the Fructose group and 0.1% sucralose + 0.1% saccharin (SS) for the SS group. During testing the CS+ flavor was in water (CS+/H2O); the CS− flavor was always in water (CS−/H2O). In the Sweetener vs. water test the Fructose group was tested with unflavored 8% fructose and the SS group with unflavored SS. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).

Figure 9

Experiment 7. Mean intakes (+sem) of 8% fructose (FRU) vs. water, 0.1% sucralose + 0.1% saccharin (SS) vs. water, and fructose vs. SS. The Fructose group was tested with fructose vs. water followed by SS vs. water; the SS group was tested in the reverse order. All mice were given fructose vs. SS in the final test. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and two-bottle tests are indicated by an asterisk (*).