Alterations in sucrose sham-feeding intake as a function of diet-exposure in rats maintained on calorically dense diets

Abstract

We previously reported that rats increase meal size upon initial presentation of a calorically dense diet. The increase may be attributed to increased orosensory stimulation and/or reduced sensitivity to post-ingestive inhibitory signals. During feeding both types of signals are simultaneously in play; thus here, we compare responses in rats presented a high-energy diet (HE) or 45% high-fat diet (HF) with those of chow-fed controls (CHOW) in a sham-feeding procedure in which post-ingestive feedback is minimized. Measures of sham-feeding to sucrose were taken before diet manipulation (baseline), ~5 days (dynamic phase) and ~6 weeks (static phase) following introduction of the palatable diet, as well as after animals were switched back to standard chow (recovery phase). Some but not all the hypotheses based on our previous findings were confirmed by the outcomes here. Consistent with our hypothesis that enhanced orosensory stimulation during the dynamic phase compared with the static phase would generalize to increased intake of other palatable stimuli, HE rats showed higher sucrose intake during the dynamic phase compared with the static phase. Contrary to what we hypothesized, HE and HF rats did not increase responses to sucrose compared to CHOW rats. In fact, HE rats showed decreased responses compared to CHOW controls. Thus changes in orosensory stimulation do not necessarily generalize to increased intake of other palatable stimuli.

Keywords: High fat; Oral; Palatability; Post-ingestive; Sweet; Taste.

Figure 1

Mean caloric intake ±SE across days for CHOW and HE groups of cohort 1 (CHOW1, HE) and CHOW and HF groups of cohort 2 (CHOW2, HF)

Figure 2

Mean sham-feeding intake ±SE across 60-min sessions of 1.0 M sucrose across four phases of testing (A) CHOW (left panel) and HE (right panel) and (B) CHOW and HF groups

Figure 3

a-parameter (representing asymptotic intake; top panel) and b-parameter (indicating rate of intake; bottom panel) distribution for individual HE rats to 1.0 M sucrose. Means (solid lines) and SE (dashed lines) for each test phase (1, 2, 3, 4). * indicates significant differences after Bonferroni adjustments.

Figure 4

Mean sham-feeding intake ± SE across 60-min sessions of 0.03 (left column), 0.3 (middle column) and 1.0 M sucrose (right column) when tested at baseline (first row), dynamic (second row), static (third row) and recovery (bottom row) test phases in CHOW (solid symbols) and HE (open symbols) groups.

Figure 5

Mean sham-feeding intake of CHOW (solid symbols) and HF (open symbols) groups across 60-min sessions to 0.03 (left column), 0.3 (middle column) and 1.0 M sucrose (right column) when tested at baseline (first row), dynamic (second row), static (third row) and recovery (bottom row) test phases.

Figure 6

Mean ± SE intake of Ensure vs. (A) 0.3 M and (B) 1.0 M sucrose in a 23-h two-bottle intake test in CHOW and HE groups. Percentages denote relative preference of Ensure (E).

Figure 7

Mean ± SE intake of Ensure vs. (A) 0.3 M and (B) 1.0 M sucrose in a 23-h two-bottle intake test in CHOW and HF groups. Percentages denote relative preference of Ensure (E).