Strain differences in sucrose- and fructose-conditioned flavor preferences in mice

Abstract

Genetic factors strongly influence the intake and preference for sugar and saccharin solutions in inbred mouse strains. The present study determined if genetic variance also influences the learned preferences for flavors added to sugar solutions. Conditioned flavor preferences (CFP) are produced in rodents by adding a flavor (CS+) to a sugar solution and a different flavor (CS−) to a saccharin solution (CS−) in one-bottle training trials; the CS+ is subsequently preferred to the CS− when both are presented in saccharin solutions in two-bottle tests. With some sugars (e.g., sucrose), flavor preferences are reinforced by both sweet taste and post-oral nutrient effects, whereas with other sugars (e.g., fructose), sweet taste is the primary reinforcer. Sucrose and fructose were used in three experiments to condition flavor preferences in one outbred (CD-1) and eight inbred strains which have “sensitive” (SWR/J, SJL/J, C57BL/10J, C57BL/6J) or “sub-sensitive” (DBA/2J, BALB/cJ, C3H/HeJ, 129P3/J) sweet taste receptors (T1R2/T1R3). Food-restricted mice of each strain were trained (1 h/day) to drink flavored 16% sucrose (CS+16S, Experiment 1), 16% fructose (CS+16F, Experiment 2) or 8% fructose + 0.2% saccharin (CS+8F, Experiment 3) solutions on five alternate days and a differently flavored saccharin solution (0.05% or 0.2%, CS−) on the other five alternating days. The CS+ and CS− flavors were presented in 0.2% saccharin for two-bottle testing over six days. All strains preferred the CS+16S to CS− although there were significant strain differences in the magnitude and persistence of the sucrose preference. The strains also differed in the magnitude and persistence of preferences for the CS+16F and CS+8F flavors over the CS− with two strains failing to prefer the fructose-paired flavors. Sucrose conditioned stronger preferences than did fructose which is attributed to differences in the taste and post-oral actions of the sugars. These differential training intakes may not have influenced the sucrose-CFP because of the post-oral reinforcing actions of sucrose. Overall, sweet sensitive and sub-sensitive mice did not differ in sucrose-CFP, but unexpectedly, the sub-sensitive mice displayed stronger fructose-CFP. This may be related to differential training intakes of CS+ and CS− solutions: sweet sensitive mice consumed more CS− than CS+ during training while sub-sensitive mice consumed more CS+.

Rapid post-oral stimulation of intake and flavor conditioning by glucose and fat in the mouse

“…The present experiment is the first to report that rodents learn to prefer a sugar-paired flavor over a sucralose-paired flavor, but there are several reports of similar conditioning using saccharin as the nonnutritive sweetener (9,18,27,34,43,61). However, in these earlier studies, the sugar (sucrose, glucose, fructose) was initially preferred to the saccharin so that the conditioned preference could be due to the taste of the sugar, its post-oral actions, or both properties.…”

Fructose- and glucose-conditioned preferences in FVB mice: strain differences in post-oral sugar appetition

“…In a recent study, Pinhas et al (24) investigated preference conditioning by orally consumed flavored sucrose, fructose, and saccharin solutions in nine mouse strains. All strains learned to prefer the sucrose-paired flavor over the saccharinpaired flavor, although they varied in the magnitude of their preferences (FVB mice were not included in the study).…”

“…Conceivably, strain differences in post-oral sugar appetition may contribute to variations in sugar intake in mice, but this has yet to be documented. One study reported mouse strain differences in sugar-conditioned flavor preferences, but because the sugars were orally consumed, the conditioning effects may have been mediated by the taste and/or post-oral actions of the sugars (24). In another study, we compared IG sucrose conditioning in C57BL/6J (B6) and 129 mice, which have the Sac B and Sac D variants of T1r3 receptor and, thus, are sweet sensitive and subsensitive, respectively (35).…”

Dopamine D1 and opioid receptor antagonist-induced reductions of fructose and saccharin intake in BALB/c and SWR inbred mice

“…Correspondingly, marked strain differences occurred in the reduction of fat (Intralipid) following NTX and SCH in 8 inbred strains (Dym et al, 2010). In addition to the intrinsic palatability of sugars, sucrose and fructose elicit conditioned flavor preferences (CFP) that are also subject to marked differences across 8 inbred strains (Pinhas et al, 2012).…”

“…Two of these inbred strains, SWR and BALB/c mice, displayed the most robust and durable sucrose-CFP (Pinhas et al, 2012) and thus Pharmacology, Biochemistry and Behavior 131 (2015) 13-18 were evaluated for DA D1 and opioid antagonist mediation of the expression and acquisition of sucrose-CFP (Dym et al, 2012). Whereas sucrose-CFP expression in both BALB/c and SWR mice was significantly reduced by SCH and NTX, sucrose-CFP acquisition was significantly reduced by NTX, but not SCH in BALB/c mice, and by SCH, but not NTX in SWR mice (Dym et al, 2012).…”