Article

Food Reinforcement, the Dopamine D 2 Receptor Genotype, and Energy Intake in Obese and Nonobese Humans

Department of Pediatrics, University at Buffalo, State University of New York, Buffalo, NY 14214-3000, USA.
Behavioral Neuroscience (Impact Factor: 2.73). 11/2007; 121(5):877-86. DOI: 10.1037/0735-7044.121.5.877
Source: PubMed

ABSTRACT

The authors measured food reinforcement, polymorphisms of the dopamine D2 receptor (DRD2) and dopamine transporter (DAT1) genes, and laboratory energy intake in 29 obese and 45 nonobese humans 18-40 years old. Food reinforcement was greater in obese than in nonobese individuals, especially in obese individuals with the TaqI A1 allele. Energy intake was greater for individuals high in food reinforcement and greatest in those high in food reinforcement with the TaqI A1 allele. No effect of the DAT1 genotype was observed. These data show that individual differences in food reinforcement may be important for obesity and that the DRD2 genotype may interact with food reinforcement to influence energy intake.

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    • "To date, only few studies have explored obesity-associated alterations in cost-benefit decision-making in humans. Two studies indicate that obese subjects may be willing to invest more effort to obtain high-caloric food than lean individuals (Epstein et al., 2007; Giesen et al., 2010). Both studies used button presses as a measure of physical effort and assessed obesity-associated alterations in cost-benefit decisions solely with respect to food reward. "
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    ABSTRACT: Cost-benefit decision-making entails the process of evaluating potential actions according to the trade-off between the expected benefit (reward) and the anticipated costs (effort). Recent research revealed that dopaminergic transmission within the fronto-striatal circuitry strongly modulates cost-benefit decision-making. Alterations within the dopaminergic fronto-striatal system have been associated with obesity, but little is known about cost-benefit decision-making differences in obese compared with lean individuals. With a newly developed experimental task we investigate obesity-associated alterations in cost-benefit decision-making, utilizing physical effort by handgrip-force exertion and both food and non-food rewards. We relate our behavioral findings to alterations in local grey matter volume assessed by structural MRI. Obese compared with lean subjects were less willing to engage in physical effort in particular for high-caloric sweet snack food. The amount of effort exertion was thereby negatively associated with subjects’ individual levels of chronic stress and punishment sensitivity. Further, self-reported body dissatisfaction negatively correlated with the willingness to invest effort for sweet snacks in obese men. On a structural level, obesity was associated with reductions in grey matter volume in bilateral prefrontal cortex. Nucleus accumbens volume positively correlated with task-induced implicit food craving. Our results challenge the common notion that obese individuals are willing to work harder to obtain high-caloric food and emphasize the need for further exploration of the underlying neural mechanisms regarding cost-benefit decision-making differences in obesity.
    Full-text · Article · Dec 2015 · Frontiers in Behavioral Neuroscience
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    • "As those studies did not directly measure the reinforcing effectiveness of food per se, a behavioral economic analysis could possibly resolve apparent inconsistencies. In addition, using foods high in fat and sugar, one study reported higher rates of food-maintained response in human subjects with genetic markers associated with lower DA D 2 R number (Epstein et al, 2007). Possibly the role of DA D 2 Rs in the reinforcing effects of food varies with the type of food. "
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    ABSTRACT: Previous studies suggest dopamine (DA) D2-like receptor involvement in the reinforcing effects of food. To determine contributions of the three D2-like receptor subtypes, knockout (KO) mice completely lacking DA receptors (D2R, D3R, or D4R KO mice) and their wild-type littermates were exposed to a series of fixed-ratio (FR) food-reinforcement schedules in two contexts: an open economy with additional food provided outside the experimental setting and a closed economy with all food earned within the experimental setting. A behavioral-economic model was used to quantify reinforcer effectiveness with food pellets obtained as a function of price (FR schedule value) plotted to assess elasticity of demand. Under both economies, as price increased, food pellets obtained decreased more rapidly (i.e., food demand was more elastic) in DA D2R KO mice compared to WT littermates. Extinction of responding was studied in two contexts: by eliminating food deliveries and by delivering food independently of responding. A hyperbolic model quantified rates of extinction. Extinction in DA D2R KO mice occurred less rapidly compared to WT mice in both contexts. Elasticity of food demand was higher in DA D4R KO than WT mice in the open, but not closed, economy. Extinction of responding in DA D4R KO mice was not different from that in WT littermates in either context. No differences in elasticity of food demand or extinction rate were obtained in D3R KO mice and WT littermates. These results indicate that the D2R is the primary DA D2-like receptor subtype mediating the reinforcing effectiveness of food.Neuropsychopharmacology accepted article preview online, 24 July 2015. doi:10.1038/npp.2015.223.
    Full-text · Article · Jul 2015 · Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology
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    • "Relative reinforcing value can be studied using laboratory tasks or selfreport questionnaires (e.g., Amlung & MacKillop, 2014; MacKillop et al., 2008, 2010; Rousseau et al., 2011). Relative reinforcing value of food has mainly been studied using laboratory tasks where participants are placed on a concurrent reinforcement schedule and work for access to food vs. a non-food related activity (e.g., Epstein et al., 2007; Temple, Legierski, Giacomelli, Salvy, & Epstein, 2008). Consistent with behavioral economic theory, experiential craving (e.g., in response to cues) increases RRV of a preferred drug (Amlung, Acker, Stojek, Murphy, & Mackillop, 2011; MacKillop et al., 2008, 2010). "
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