No abstract

After Roux-en-Y gastric bypass surgery (RYGB), patients report consuming fewer fatty and dessert-like foods, and rats display blunted sugar and fat preferences. Here we used a progressive ratio task (PR) in our rat model to explicitly test whether RYGB decreases the willingness of rats to work for very small amounts of preferred sugar- and/or fat-containing fluids. In each of two studies, two groups of rats - one maintained on a high-fat diet (HFD) and standard chow (CHOW) and one given CHOW alone - were trained while water-deprived to work for water or either Ensure or 1.0 M sucrose on increasingly difficult operant schedules. When tested before surgery while nondeprived, HFD rats had lower PR breakpoints (number of operant responses in the last reinforced ratio) for sucrose, but not for Ensure, than CHOW rats. After surgery, at no time did rats given RYGB show lower breakpoints than SHAM rats for Ensure, sucrose, or when 5% Intralipid served postoperatively as the reinforcer. Nevertheless, RYGB rats showed blunted preferences for these caloric fluids versus water in 2-bottle preference tests. Importantly, although the Intralipid and sucrose preferences of RYGB rats decreased further over time, subsequent breakpoints for them were not significantly impacted. Collectively, these data suggest that the observed lower preferences for normally palatable fluids after RYGB in rats may reflect a learned adjustment to altered postingestive feedback rather than a dampening of the reinforcing taste characteristics of such stimuli as measured by the PR task in which postingestive stimulation is negligible.

Here we assessed how intake reductions induced by Roux-en-Y gastric bypass surgery (RYGB) occur within and across access periods by examining drinking microstructure. After training, RYGB (n = 8-10) or sham-operated (SHAM, n = 12) rats were given 60-min access first to 0.3 M sucrose, then to 5% Intralipid, and finally to milk-chocolate Ensure Plus across 5 days each. Initially, total licks taken during the first meal of sucrose and Intralipid by RYGB and SHAM rats did not differ, but, across subsequent test periods, RYGB rats licked less than SHAM rats. First Ensure meal size also did not differ between RYGB and SHAM rats, but SHAM rats increased licking across test periods while the behavior of RYGB rats remained stable. The intake differences between the surgical groups, when they occurred, were most often due to smaller burst sizes in RYGB rats. Importantly, the surgical-group difference in sucrose and Intralipid intakes could not be explained by altered palatability of these solutions because, throughout testing, both groups had similar early meal licking behavior thought to represent the motivational potency of stimulus orosensory features. Although, overall, RYGB rats displayed lower early meal licking of Ensure relative to the SHAM rats, this appeared to be driven primarily by increases in the latter group across test periods; the RYGB group stayed relatively stable. Collectively, these results suggest that some level of postoral experience with these stimuli and/or their components is necessary before intake differences emerge between surgical groups, and, even when differences occur, often immediate taste-motivated ingestive behavior remains unaltered.

Roux-en-Y gastric bypass (RYGB) surgery has been shown to decrease consummatory responsiveness of rats to high sucrose concentrations, and genetic deletion of glucagon-like peptide-1 receptors (GLP-1R) has been shown to decrease consummatory responsiveness of mice to low-sucrose concentrations. Here we assessed the effects of RYGB and pharmacological GLP-1R modulation on sucrose licking by chow-fed rats in a brief-access test that assessed consummatory and appetitive behaviors. Rats were tested while fasted presurgically and postsurgically and while nondeprived postsurgically and 5 h after intraperitoneal injections with the GLP-1R antagonist exendin-3(9-39) (30 μg/kg), agonist exendin-4 (1 μg/kg), and vehicle in 30-min sessions during which a sucrose concentration series (0.01-1.0 M) was presented in 10-s trials. Other rats were tested postsurgically or 15 min after peptide or vehicle injection while fasted and while nondeprived. Independent of food-deprivation state, sucrose experience, or GLP-1R modulation, RYGB rats took 1.5-3× as many trials as sham-operated rats, indicating increased appetitive behavior. Under nondeprived conditions, RYGB rats with presurgical sucrose experience licked more to sucrose relative to water compared with sham-operated rats. Exendin-4 and exendin-3(9-39) impacted 0.3 M sucrose intake in a one-bottle test, but never interacted with surgical group to affect brief-access responding. Unlike prior reports in both clearly obese and relatively leaner rats given RYGB and in GLP-1R knockout mice, we found that neither RYGB nor GLP-1R blockade decreased consummatory responsiveness to sucrose in our less obese chow-fed rats. Collectively, these results highlight the fact that changes in taste-driven motivated behavior to sucrose after RYGB and/or GLP-1R modulation are very model and measure dependent.

Mathes CM, Letourneau C, Blonde GD, le Roux CW, Spector AC. Roux-en-Y gastric bypass in rats progressively decreases the proportion of fat calories selected from a palatable cafeteria diet. Am J Physiol Regul Integr Comp Physiol 310: R952-R959, 2016. First published February 10, 2016 doi:10.1152/ajpregu.00444.2015.-Roux-en-Y gastric bypass surgery (RYGB) decreases caloric intake in both human patients and rodent models. In long-term intake tests, rats decrease their preference for fat and/or sugar after RYGB, and patients may have similar changes in food selection. Here we evaluated the impact of RYGB on intake during a "cafeteria"-style presentation of foods to assess if rats would lower the percentage of calories taken from fat and/or sugar after RYGB in a more complex dietary context. Male Sprague-Dawley rats that underwent either RYGB or sham surgery (Sham) were presurgically and postsurgically given 8-days free access to four semisolid foods representative of different fat and sugar levels along with standard chow and water. Compared with Sham rats, RYGB rats took proportionally fewer calories from fat and more calories from carbohydrates; the latter was not attributable to an increase in sugar intake. The proportion of calories taken from protein after RYGB also increased slightly. Importantly, these postsurgical macronutrient caloric intake changes in the RYGB rats were progressive, making it unlikely that the surgery had an immediate impact on the hedonic evaluation of the foods and strongly suggesting that learning is influencing the food choices. Indeed, despite these dietary shifts, RYGB, as well as Sham, rats continued to select the majority of their calories from the high-fat/high-sugar option. Apparently after RYGB, rats can progressively regulate their intake and selection of complex foods to achieve a seemingly healthier macronutrient dietary composition. supermarket diet; bariatric surgery; diet-induced obesity; conditioned avoidance ROUX-EN-Y GASTRIC BYPASS (RYGB) is an effective means by which to reduce excess body weight in the morbidly obese (e.g., 28). While many physiological changes induced by the operation may contribute to weight loss, there is strong evidence that patients eat less and have reduced appetite (e.g., 1, 13, 35). In some studies, RYGB patients report less frequent consumption of high-fat foods, like cheeses and red meats (e.g., 14); sweets, like soda and candy (e.g., 7, 11, 31); and other palatable mixtures of sugar and fat, such as ice cream (e.g., 2, 10, 30). While self-report measures in humans are vulnerable to inaccuracies (e.g., 9, 15, 23, 24, 33; also see 19), these results are mirrored in rat models of RYGB. After RYGB, rats lose body weight, consume fewer overall calories, and show blunted preferences for high-fat laboratory diets, as well as for sucrose solutions, the soybean oil emulsion Intralipid, and dietary supplements like Ensure that are high in fat and sugar (e.g., 3,5,14,16,22,26,27,36,37).Although these data from rodent models of RYGB are compelling, t...