Reduced sweet and fatty fluid intake after Roux-en-Y gastric bypass in rats is dependent on experience without change in stimulus motivational potency.

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.

Gastric bypass in rats does not decrease appetitive behavior towards sweet or fatty fluids despite blunting preferential intake of sugar and fat.

After Roux-en-Y gastric bypass (RYGB) surgery, patients report consuming fewer fatty and dessert-like foods, and rats display blunted sugar and fat preferences. Here we used a progressive ratio (PR) task 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 1.0M 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.