Altered orosensory sensitivity to oils in CCK-1 receptor deficient rats

Abstract

CCK-1 receptor deficient Otsuka Long Evans Tokushima Fatty (OLETF) rats are hyperphagic, which leads to subsequent obesity and diabetes. Additionally, they have increased sham intake and enhanced preference for sucrose solutions relative to control, Long Evans Tokushima Otsuka (LETO) rats. To determine the effects of oil on ingestion, we first measured real feeding of various concentrations of oil emulsions (12.5, 25, 50, 75, and 100%) in rats that were fed ad libitum. Secondly, to isolate the orosensory compontent of oils from post-ingestive consequences, as well as determine the contribution of energy status, we measured sham feeding in OLETF and LETO rats using one-bottle acceptance tests while non-deprived and overnight food deprived. Finally, to assess the orosensory effects of nutritive and non-nutritive oils, we used two-bottle preference tests in sham fed OLETF and LETO rats. We found that real feeding resulted in increased intake of high oil concentrations for OLETF rats relative to LETO rats. Similarly, OLETF rats consumed significantly more of higher concentration corn oils than LETO while non-deprived sham feeding. Conversely, OLETF rats overconsumed low concentration corn oil compared to LETO during overnight deprived sham-feeding tests. In two-bottle sham-feeding preference tests, both non-deprived OLETF and LETO rats preferred corn to mineral oil. Collectively, these results show that increased oil intake in OLETF rats is driven by both peripheral deficits to satiation and altered orosensory sensitivity.

Fig. 1

Real feeding of oil in OLETF and LETO rats. OLETF consumed significantly more 50, 75, and 100% oil solutions compared to LETO. There were no strain differences in consumption of 12.5 and 25% oil. Within strains, both OLETF and LETO consumed significantly more 12.5 and 25% oil compared to other concentrations tested (50 – 100%). Data are expressed as means ± SEM. * P < 0.05, *** P < 0.001 denotes statistical significance between strains. ^† denotes statistical significance within strain, P < 0.01.

Fig. 2

Sixty-minute cumulative real feeding in OLETF and LETO rats. OLETF drank significantly more oil at higher concentrations (50 – 100%) than LETO starting at 5 to 15 minutes after presentation of oils. This significant difference was maintained throughout the 60-min feeding test. At 12.5 and 25% oils, OLETF drank significantly more oil than LETO at the beginning of the test session, but this difference was not maintained by the end of the test. Data are expressed as means ± SEM. * P < 0.05, ** < 0.01, *** < 0.001, **** < 0.0001 denotes statistical significance between strains.

Fig. 3

Sham intake of oils in non-deprived OLETF and LETO rats. Compared to LETO rats, OLETF consumed significantly more of the 50 and 75% oil and less of the 12.5 and 25% oil concentrations. Within strain, OLETF consumed significantly more 50 and 75% oil compared to other concentrations while LETO consumed more 25% oil concentration compared to all other concentrations tested. Data are expressed as means ± SEM. * P < 0.05, *** P < 0.001, **** P < 0.0001 denotes differences between strains. ^†P <0 .01 denotes statistical significance within strains.

Fig 4

Sixty-minute cumulative sham intake in non-deprived OLETF and LETO rats. OLETF drank significantly less of the lower oil concentrations (12.5 and 25%) compared to LETO starting within the first 5 to 20 minutes of the test session. The difference between strains remained at a plateau level during the second half of the feeding test. At higher oil concentrations (50 – 75%), OLETF drank significantly more oil than LETO starting at 5 minutes after the test began and consumption remained significantly different throughout the remainder of the 60-min test. Data are expressed as means ± SEM. * P < 0.05, ** < 0.01, *** < 0.001, **** < 0.0001 denotes statistical significance between strains.

Fig. 5

Sham oil intake in overnight food deprived OLETF and LETO rats. OLETF rats consumed significantly more 12.5% oil than LETO. At all other oil concentrations (25 – 100%) there were no significant differences between OLETF and LETO. Both strains consumed significantly more 12.5 and 25% oil compared to all concentrations tested (50 – 100%). Data are expressed as means ± SEM. * P < 0.05 denotes statistical significance between strains. ^† P < 0.01 denotes statistical significance within strains.

Fig 6

Sixty-minute cumulative sham intake in overnight food deprived OLETF and LETO rats. OLETF consumed significantly more 12.5% oil than LETO starting at 15 minutes of the test session. At higher oil concentrations (50 – 75%) OLETF consumed more than LETO during the feeding tests, but the difference between strains was not significant at the completion of the test. During exposure to 100% oil, both strains consumed similar volumes of oil. Data are expressed as means ± SEM. * denotes statistical significance between strains. * P < 0.05.

Fig. 7

Difference in oil intake (% from LETO) across sham feeding conditions. OLETF rats consumed significantly more 75% oil in non-deprived compared to the deprived condition. There was a trend for decreased consumption of low concentration oils (12.5 and 25%) in the non-deprived relative to the deprived condition, but this was not significant. Data are expressed as means ± SEM. * P < 0.05 denotes statistical significance from non-deprived condition,

Fig. 8

Corn and mineral oil preference after brief access two-bottle tests in non-deprived OLETF and LETO rats. Both OLETF and LETO rats preferred corn oil to mineral oil. Data are expressed as means ± SEM. ** P < 0 .01 denotes significant difference from mineral oil.