title: Flavor preference conditioning by different sugars in sweet ageusic Trpm5 knockout mice.
abstract: Knockout (KO) mice missing the taste signaling protein Trpm5 have greatly attenuated sweetener preferences but develop strong preferences for glucose in 24-h tests, which is attributed to post-oral sugar conditioning. Trpm5 KO mice express mild preferences for galactose but no preferences for fructose in 24-h tests, which suggests that these sugars differ in their post-oral reinforcing effects. Here we investigated sugar-conditioned flavor preferences in Trpm5 KO and C57BL/6J wildtype (B6) mice. The mice were trained to consume a flavored (CS+, e.g. grape) 8% sugar solution and flavored (CS-, e.g., cherry) water on alternating days followed by two-bottle choice tests with CS+ vs. CS- flavors in water and with unflavored sugar vs. water. The KO mice displayed strong preferences (>80%) for the CS+ glucose and CS+ galactose but not for the CS+ fructose flavor. They also preferred glucose and galactose, but not fructose to water. In contrast, the B6 mice preferred all three CS+ flavors to the CS- flavor, and all three sugars to water. In tests with the non-metabolizable sugar α-methyl-d-glucopyranoside (MDG), the KO and B6 mice preferred 8% MDG to water but did not prefer the CS+ 8% MDG to CS-. However, they preferred a CS+ flavor mixed with 4% MDG over the CS- flavor. Trpm5 KO mice also preferred galactose and MDG to fructose in direct choice tests. The Trpm5 KO data indicate that glucose and, to a lesser extent, galactose and MDG have post-oral reinforcing actions that stimulate intake and preference while fructose has a much weaker effect. The CS+ flavor and sugar preferences of B6 mice may be mediated by the sweet taste and/or post-oral actions of the various sugars. Glucose, galactose, and MDG, but not fructose, are ligands for the sodium-glucose transporter 1 (SGLT1) which is implicated in post-oral sugar conditioning in B6 mice.
authors.affiliation: Brooklyn College and the Graduate School, City University of New York, Brooklyn, NY 11210, USA. Electronic address: ASclafani@gc.cuny.edu.
authors.forename: Anthony
authors.initials: A
authors.lastname: Sclafani
authors.affiliation: Brooklyn College and the Graduate School, City University of New York, Brooklyn, NY 11210, USA.
authors.forename: Karen
authors.initials: K
authors.lastname: Ackroff
mesh_terms: D000818:Animals; D002241:Carbohydrates / Q000008:administration & dosage* / Q000145:classification; D003214:Conditioning, Classical / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004435:Eating / Q000187:drug effects / Q000235:genetics; D005260:Female; D005421:Flavoring Agents / Q000008:administration & dosage* / Q000145:classification; D005518:Food Preferences / Q000187:drug effects*; D008297:Male; D008757:Methylglucosides / Q000008:administration & dosage; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D050053:TRPM Cation Channels / Q000172:deficiency* / Q000235:genetics; D013649:Taste / Q000187:drug effects / Q000235:genetics*
chemical_list: D002241:Carbohydrates; D005421:Flavoring Agents; D008757:Methylglucosides; D050053:TRPM Cation Channels; C498617:Trpm5 protein, mouse; C027020:methylglucoside
keywords: C57BL/6J mice; Flavor-nutrient learning; Flavor-taste learning; Fructose; Galactose; Glucose