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.

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

“…The CAST mice displayed a somewhat stronger Test 1 preference (74%) than did the FVB and B6 mice (66%), but this difference was not significant and the Test 2 preferences of the three strains were similar (50 – 56%). Although the strains did not differ in their SS-conditioned CS+ flavor preferences, the FVB and CAST mice consumed considerably more CS+/SS during training than did the B6 mice (24.2 and 19.6 vs. 12.0 g/day, F(2,25) = 14.3, P < 0.001) and more unflavored SS in the sweetener vs. water test (20.1 and 18.9 vs. 10.2 g/day, F(2,25) = 26.7, P < 0.001), which confirms prior results [47,48,49]. The elevated SS intakes of the CAST mice are remarkable given their low body weights.…”

“…Yet, both strains appear to be more attracted to SS than are B6 mice. In particular, FVB and CAST mice drink more SS than B6 mice in choice tests vs. water [47,48,49]. However, after separate experience with both sweeteners FVB mice, unlike B6 mice prefer fructose to SS [48].…”

“…This is attributed to the post-oral appetition action of fructose in this strain as documented by the ability of IG fructose infusions to condition a CS+ preference in FVB mice [48]. Fructose also has an IG flavor conditioning action in CAST mice but, unlike FVB mice, CAST mice do not reverse their strong preference for SS over fructose after separate experience with the two sweeteners [47]. Furthermore, unlike B6 and FVB mice, CAST mice do not develop a preference for 8% glucose over SS.…”

“…This was expected because fructose has post-oral appetition effects in FVB and CAST mice unlike in B6 mice [47,48]. Consequently, their preference for the fructose-paired CS+ flavor was reinforced by both the sweet taste and post-oral actions of the sugar.…”

“…B6 mice were studied in all experiments except one that involved FVB/NJ and CAST/EiJ mice. These two strains were of interest because they differ from B6 mice in their oral attraction to non-nutritive sweeteners and their post-oral response to fructose [47,48]. As in most prior studies of preference conditioning by non-nutritive sweeteners [8,10,12,14,18,24,26,53], male animals were primarily used in the current study although the conditioning responses of male and female mice were compared in one experiment.…”