Meal Patterns and Food Choices of Female Rats Fed a Cafeteria-Style Diet Are Altered by Gastric Bypass Surgery

After Roux-en-Y gastric bypass surgery (RYGB), rats tend to reduce consumption of high-sugar and/or high-fat foods over time. Here, we sought to investigate the behavioral mechanisms underlying these intake outcomes. Adult female rats were provided a cafeteria diet comprised of five palatable foodstuffs varying in sugar and fat content and intake was monitored continuously. Rats were then assigned to either RYGB, or one of two control (CTL) groups: sham surgery or a nonsurgical control group receiving the same prophylactic iron treatments as RYGB rats. Post-sur-gically, all rats consumed a large first meal of the cafeteria diet. After the first meal, RYGB rats reduced intake primarily by decreasing the meal sizes relative to CTL rats, ate meals more slowly, and displayed altered nycthemeral timing of intake yielding more daytime meals and fewer nighttime meals. Collectively, these meal patterns indicate that despite being motivated to consume a cafeteria diet after RYGB, rats rapidly learn to modify eating behaviors to consume foods more slowly across the entire day. RYGB rats also altered food preferences, but more slowly than the changes in meal patterns, and ate proportionally more energy from complex carbohydrates and protein and proportionally less fat. Overall, the pattern of results suggests that after RYGB rats quickly learn to adjust their size, eating rate, and distribution of meals without altering meal number and to shift their macronutrient intake away from fat; these changes appear to be more related to postingestive events than to a fundamental decline in the palatability of food choices

Meal Patterns and Food Choices of Female Rats Fed a Cafeteria-Style Diet Are Altered by Gastric Bypass Surgery

After Roux-en-Y gastric bypass surgery (RYGB), rats tend to reduce consumption of high-sugar and/or high-fat foods over time. Here, we sought to investigate the behavioral mechanisms underlying these intake outcomes. Adult female rats were provided a cafeteria diet comprised of five palatable foodstuffs varying in sugar and fat content and intake was monitored continuously. Rats were then assigned to either RYGB, or one of two control (CTL) groups: sham surgery or a nonsurgical control group receiving the same prophylactic iron treatments as RYGB rats. Post-sur-gically, all rats consumed a large first meal of the cafeteria diet. After the first meal, RYGB rats reduced intake primarily by decreasing the meal sizes relative to CTL rats, ate meals more slowly, and displayed altered nycthemeral timing of intake yielding more daytime meals and fewer nighttime meals. Collectively, these meal patterns indicate that despite being motivated to consume a cafeteria diet after RYGB, rats rapidly learn to modify eating behaviors to consume foods more slowly across the entire day. RYGB rats also altered food preferences, but more slowly than the changes in meal patterns, and ate proportionally more energy from complex carbohydrates and protein and proportionally less fat. Overall, the pattern of results suggests that after RYGB rats quickly learn to adjust their size, eating rate, and distribution of meals without altering meal number and to shift their macronutrient intake away from fat; these changes appear to be more related to postingestive events than to a fundamental decline in the palatability of food choices

T1R2 and T1R3 subunits are individually unnecessary for normal affective licking responses to polycose: implications for saccharide taste receptors in mice

The T1R2 and T1R3 proteins are expressed in taste receptor cells and form a heterodimer binding with compounds described as sweet by humans. We examined whether Polycose taste might be mediated through this heterodimer by testing T1R2 knockout (KO) and T1R3 KO mice and their wild-type (WT) littermate controls in a series of brief-access taste tests (25-min sessions with 5-s trials). Sucrose, Na-saccharin, and Polycose were each tested for three consecutive sessions with order of presentation varied among subgroups in a Latin-Square manner. Both KO groups displayed blunted licking responses and initiated significantly fewer trials of sucrose and Na-saccharin across a range of concentrations. KO mice tested after Polycose exposure demonstrated some degree of concentration-dependent licking of sucrose, likely attributable to learning related to prior postingestive experience. These results are consistent with prior findings in the literature, implicating the T1R2+3 heterodimer as the principal taste receptor for sweet-tasting ligands, and also provide support for the potential of postingestive experience to influence responding in the KO mice. In contrast, T1R2 KO and T1R3 KO mice displayed concentration-dependent licking responses to Polycose that tracked those of their WT controls and in some cases licked midrange concentrations more; the number of Polycose trials initiated overall did not differ between KO and WT mice. Thus, the T1R2 and T1R3 proteins are individually unnecessary for normal concentration-dependent licking of Polycose to be expressed in a brief-access test. Whether at least one of these T1R protein subunits is necessary for normal Polycose responsiveness remains untested. Alternatively, there may be a novel taste receptor(s) that mediates polysaccharide taste

Extensive lesions in rat insular cortex significantly disrupt taste sensitivity to NaCl and KCl and slow salt discrimination learning.

While studies of the gustatory cortex (GC) mostly focus on its role in taste aversion learning and memory, the necessity of GC for other fundamental taste-guided behaviors remains largely untested. Here, rats with either excitotoxic lesions targeting GC (n = 26) or sham lesions (n = 14) were assessed for postsurgical retention of a presurgically LiCl-induced conditioned taste aversion (CTA) to 0.1M sucrose using a brief-access taste generalization test in a gustometer. The same animals were then trained in a two-response operant taste detection task and psychophysically tested for their salt (NaCl or KCl) sensitivity. Next, the rats were trained and tested in a NaCl vs. KCl taste discrimination task with concentrations varied. Rats meeting our histological inclusion criterion had large lesions (resulting in a group averaging 80% damage to GC and involving surrounding regions) and showed impaired postsurgical expression of the presurgical CTA (LiCl-injected, n = 9), demonstrated rightward shifts in the NaCl (0.54 log10 shift) and KCl (0.35 log10 shift) psychometric functions, and displayed retarded salt discrimination acquisition (n = 18), but eventually learned and performed the discrimination comparable to sham-operated animals. Interestingly, the degree of deficit between tasks correlated only modestly, if at all, suggesting that idiosyncratic differences in insular cortex lesion topography were the root of the individual differences in the behavioral effects demonstrated here. This latter finding hints at some degree of interanimal variation in the functional topography of insular cortex. Overall, GC appears to be necessary to maintain normal taste sensitivity to NaCl and KCl and for salt discrimination learning. However, higher salt concentrations can be detected and discriminated by rats with extensive damage to GC suggesting that the other resources of the gustatory system are sufficient to maintain partial competence in these tasks, supporting the view that such basic sensory-discriminative taste functions involve distributed processes among central gustatory structures

The Influence of Roux-en-Y Gastric Bypass and Diet on NaCl and Sucrose Taste Detection Thresholds and Number of Circumvallate and Fungiform Taste Buds in Female Rats

Roux-en-Y gastric bypass (RYGB) in rats attenuates preference for, and intake of, sugar solutions. Additionally, maintenance on a high-fat diet (HFD) reportedly alters behavioral responsiveness to sucrose in rodents in short-term drinking tests. Due to the fact that the behavioral tests to date rely on the hedonic value of the stimulus to drive responsiveness, we sought to determine whether taste detection thresholds to sucrose and NaCl are affected by these manipulations as measured in an operant two-response signal detection paradigm. Female rats were maintained on HFD or chow for 10 weeks, at which point animals received either RYGB or SHAM surgery followed by a gel-based diet and then powdered chow. Upon recovery, half of the rats that were previously on HFD were switched permanently to chow, and the other rats were maintained on their presurgical diets (n = 5–9/diet condition × surgery group for behavioral testing). The rats were then trained and tested in a gustometer. There was a significant interaction between diet condition and surgery on NaCl threshold that was attributable to a lower value in RYGB vs. SHAM rats in the HFD condition, but this failed to survive a Bonferroni correction. Importantly, there were no effects of diet condition or surgery on sucrose thresholds. Additionally, although recent evidence suggests that maintenance on HFD alters taste bud number in the circumvallate papillae (CV) of mice, in a subset of rats, we did not find that diet significantly influenced taste pores in the anterior tongue or CV of female rats. These results suggest that any changes in sucrose responsiveness in intake/preference or hedonically oriented tests in rats as a function of HFD maintenance or RYGB are not attributable to alterations in taste sensitivity

The z-scores for individual GCX rats relative to the SHAM distribution for different behavioral tests.

<p>The z-scores calculated are relative to SHAM-LiCl mean and SD for Taste/Water Ratios to 0.1 M sucrose (CS; top), and relative to the full SHAM group for detection testing and discrimination training. Dashed line indicates a z-score of 1.96 (or -1.96 for discrimination phases), the criterion for being classified as impaired on a task. Red bars indicate rats with lesions meeting the inclusion criteria for behavioral analyses (≥50% of GC and ≥70% of the GC “core” containing a lesion).</p

Overlap Map for lesions of rats included in behavioral analyses.

<p>A graphic depiction of compiled Symmetry Maps of those rats meeting the inclusion criteria for behavioral analyses (left panel; ≥50% of GC and ≥70% of the GC “core” containing a lesion; n = 17) and lesions too small for inclusion (right panel; n = 9). The lesions for the included rats encompassed 80% of GC and 91% of GC “core” on average. Each color represents the average lesion score for the group in each cell, as shown in the color key to the right of the Overlap Map. Each row represents a single 50 μm section. Solid horizontal lines (at 2.3, 0.2) indicate anterior and posterior boundaries of the conventionally defined GC. Long-dashed horizontal lines (at 1.8, 0.6) indicate anterior and posterior boundaries of GC “core”. Short-dashed horizontal line (at 1.2) indicates the approximate center of GC. Subdivisions representing the dorsal/ventral axis are divided vertically by solid line; D: cortical areas dorsal to granular insular cortex. GI: Granular insular cortex. DI: Dysgranular insular cortex. AI: Agranular insular cortex, dorsal to the rhinal fissure. V: cortical tissue ventral to the rhinal fissure. Each column of the map within eachdorsal/ventral subdivisions represents a portion of tissue from the lateral (L) to medial (M) direction.Scale bar = 1 mm.</p

Pearson correlations between behavioral tests.

<p>Significant values indicated in bold.</p><p>¹: These correlations were conducted with LiCl-injected GCX rats.</p><p>²: These correlations were conducted with all GCX rats.</p><p>Pearson correlations between behavioral tests.</p