CAST/EiJ and C57BL/6J Mice Differ in Their Oral and Postoral Attraction to Glucose and Fructose

Abstract

A recent study indicated that CAST/EiJ and C57BL/6J mice differ in their taste preferences for maltodextrin but display similar sucrose preferences. The present study revealed strain differences in preferences for the constituent sugars of sucrose. Whereas B6 mice preferred 8% glucose to 8% fructose in 2-day tests, the CAST mice preferred fructose to glucose. These preferences emerged with repeated testing which suggested post-oral influences. In a second experiment, 2-day choice tests were conducted with the sugars versus a sucralose + saccharin (SS) mixture which is highly preferred in brief access tests. B6 mice strongly preferred glucose but not fructose to the non-nutritive SS whereas CAST mice preferred SS to both glucose and fructose even when food restricted. This implied that CAST mice are insensitive to the postoral appetite stimulating actions of the 2 sugars. A third experiment revealed, however, that intragastric glucose and fructose infusions conditioned significant but mild flavor preferences in CAST mice, whereas in B6 mice glucose conditioned a robust preference but fructose was ineffective. Thus, unlike other mouse strains and rats, glucose is not more reinforcing than fructose in CAST mice. Their oral preference for fructose over glucose may be related to a subsensitive maltodextrin receptor or glucose-specific receptor which is stimulated by glucose but not fructose. The failure of CAST mice to prefer glucose to a non-nutritive sweetener distinguishes this strain from other mouse strains and rats.

Keywords: flavor conditioning; fructose; glucose; saccharin; strain differences; sucralose.

Figure 1.

Experiment 1. Mean intakes (+SEM) of sugar and water in 2-day, 2-bottle tests in CAST (left panel) and B6 mice (right panel). (Order of testing is from left to right in the panels.) In Tests 1 and 4, the mice were given the choice of 8% fructose versus 8% glucose. In Test 2, the choice was glucose versus water and in Test 3, it was fructose versus water. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences within the 2-bottle tests are indicated by an asterisk (*).

Figure 2.

Experiment 2, Test series 1. Mean intakes (+SEM) of 8% fructose, 0.1% sucralose + 0.1% saccharin (SS), and water in 2-day, 2-bottle tests in CAST (left panel) and B6 mice (right panel). (Order of testing is from left to right in the panels.) In Tests 1 and 4, the mice were given the choice of fructose versus SS. In Test 2, the choice was fructose versus water and in Test 3, it was SS versus water. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences within the 2-bottle tests are indicated by an asterisk (*).

Figure 3.

Experiment 2, Test series 2. Mean intakes (+SEM) of 8% glucose, 0.1% sucralose + 0.1% saccharin (SS), and water in 2-day, 2-bottle tests in CAST (left panel) and B6 mice (right panel) maintained on ad libitum food. (Order of testing is from left to right in the panels.) In Tests 1 and 4, the mice were given the choice of glucose versus SS. In Test 2, the choice was glucose versus water and in Test 3, it was SS versus water. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences within the 2-bottle tests are indicated by an asterisk (*).

Figure 4.

Experiment 2, Test series 3. Mean intakes (+SEM) of 8% glucose, 0.1% sucralose + 0.1% saccharin (SS), and water in 2-day, 2-bottle tests in CAST (left panel) and B6 mice (right panel) maintained on restricted food rations. (Order of testing is from left to right in the panels.) In Test 1, the choice was glucose versus water, in Test 2, it was SS versus water, and in Test 3, it was glucose versus SS. Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences within the 2-bottle tests are indicated by an asterisk (*).

Figure 5.

Experiment 3. Mean total oral and IG intakes (+SEM) of the conditioned stimulus (CS+G) paired with IG infusion of 16% glucose, (CS+F) paired with IG 16% fructose, and (CS−) paired IG water during 1-bottle training sessions (train) and 2-bottle test sessions. Data from CAST and B6 mice are presented in the upper and lower panels, respectively. In Part 1, the mice were trained 3 days each with the CS+G and CS− and then given a 2 day, 2-bottle test with CS+G versus CS− (left panels). In Part 2, they were trained 3 days each with the CS+F and CS− and then given a 2-day, 2-bottle test with CS+F versus CS− (middle panels). In Part 3, they were trained 2 days each with the CS+G and CS+F and then given a 2-bottle test with the CS+G versus CS+F (right panels). Numbers atop bars represent mean percent preference for that solution. Significant (P < 0.05) intake differences in the training and 2-bottle tests are indicated by an asterisk (*).