Sham feeding, flavor associations and diet self-selection as indicators of feeding satiety or aversive effects of peptide hormones

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We have attempted to develop a constellation of behaviors which show differential effects following the administration of putative satiety hormones (CCK-8, BBS, insulin) as opposed to effects seen following a toxin, such as LiCl. In the initial behavior assessed, sham feeding of differently paired, flavored milks (flavor paired with insulin, BBS or saline) was carried out. Male adult Sprague-Dawley rats which sham fed milk flavors paired with 16 μg/kg BBS showed a significant aversion of that flavor in a two-bottle taste test (compared to saline-paired flavors, p<0.001) but a significant preference for flavored milk paired with 0.4 and 0.75 U insulin/rat. Lower dosages of BBS (4 and 8 μg/kg) and insulin (0.1 U/rat) showed no significant aversion or preference when compared to saline. The second behavioral paradigm evaluated the effects of the hormones CCK-8 and BBS and the toxin, LiCl, upon self-selection of pure macronutrients. While CCK-8 reduced intake of calories by significantly lowering ingestion/selection of fats (55%, p<0.01 compared to saline, control injections) and carbohydrates (50%, p<0.01), LiCl and BBS reduced calories by decreasing selection of primarily proteins (LiCl—49%, p<0.03; BBS—63% at 4 μg/kg and 80% at 8 μg/kg, both p<0.025). In both paradigms then, BBS at doses sufficient to significantly reduce sham intake or suppress caloric ingestion in a self-selection paradigm produced behavioral effects most similar to those observed following the injection of a toxin, LiCl, rather than effects seen following other various putative satiety signals.