Strain differences in muscarinic cholinergic receptor antagonism of fat intake and acquisition and expression of fat-conditioned flavor preferences in male BALB/c, C57BL/6 and SWR mice

A systematic review of the biological mediators of fat taste and smell

Taste and smell play a key role in our ability to perceive foods. Overconsumption of highly palatable energy-dense foods can lead to increased caloric intake and obesity. Thus there is growing interest in the study of the biological mediators of fat taste and associated olfaction as potential targets for pharmacologic and nutritional interventions in the context of obesity and health. The number of studies examining mechanisms underlying fat taste and smell has grown rapidly in the last 5 years. Therefore, the purpose of this systematic review is to summarize emerging evidence examining the biological mechanisms of fat taste and smell. A literature search was conducted of studies published in English between 2014 and 2021 in adult humans and animal models. Database searches were conducted using PubMed, EMBASE, Scopus, and Web of Science for key terms including fat/lipid, taste, and olfaction. Initially, 4,062 articles were identified through database searches, and a total of 84 relevant articles met inclusion and exclusion criteria and are included in this review. Existing literature suggests that there are several proteins integral to fat chemosensation, including cluster of differentiation 36 (CD36) and G protein-coupled receptor 120 (GPR120). This systematic review will discuss these proteins and the signal transduction pathways involved in fat detection. We also review neural circuits, key brain regions, ingestive cues, postingestive signals, and genetic polymorphism that play a role in fat perception and consumption. Finally, we discuss the role of fat taste and smell in the context of eating behavior and obesity.

Acquisition and expression of fat conditioned flavor preferences following dopamine D1, opioid and NMDA receptor antagonism in C57BL/6 mice

Objectives: Inbred mouse strains differ in the pharmacology mediating sugar and fat intake and conditioned flavor preferences (CFP). C57BL/6, BALB/c and SWR inbred mice are differentially sensitive to dopamine (DA) D1, opioid and muscarinic receptor antagonism of sucrose, saccharin or fat intake, and to DA, opioid, muscarinic and N-methyl-D-aspartate (NMDA) receptor antagonism of acquisition of sucrose-CFP. DA D1, opioid and NMDA receptor antagonists differentially alter fat (Intralipid)-CFP in BALB/c and SWR mice. The present study examined whether naltrexone, SCH23390 or MK-801 altered acquisition and expression of Intralipid-CFP in C57BL/6 mice.Methods: In acquisition, groups of male food-restricted C57BL/6 mice received vehicle, naltrexone (1, 5 mg/kg), SCH23390 (50, 200 nmol/kg) or MK-801 (100, 200 μg/kg) before 10 training sessions in which mice alternately consumed two novel-flavored 5% (CS+) and 0.5% (CS-) Intralipid solutions. Six two-bottle CS choice tests followed with both flavors mixed in 0.5% Intralipid without injections. In expression, C57BL/6 mice underwent the 10 training sessions without injections followed by two-bottle CS choice tests 30 min following vehicle, naltrexone (1, 5 mg/kg), SCH23390 (200, 800 nmol/kg) or MK-801 (100, 200 μg/kg).Results: Fat-CFP acquisition in C57BL/6 mice was significantly though marginally reduced following naltrexone, SCH23390 and MK-801. Fat-CFP expression was similarly reduced by naltrexone, SCH23390 and MK-801 in C57BL/6 mice. Discussion: C57BL/6 mice were more sensitive to DA D1, opioid and NMDA antagonists in the expression of fat-CFP relative to sugar-CFP, but were less sensitive to DA D1 and NMDA antagonists in the acquisition of fat-CFP relative to sugar-CFP.