Figlewicz DP, Bennett JL, Aliakbari S, Zavosh A, Sipols AJ. Insulin acts at different CNS sites to decrease acute sucrose intake and sucrose self-administration in rats. Am J Physiol Regul Integr Comp Physiol 295: R388 -R394, 2008. First published June 4, 2008 doi:10.1152/ajpregu.90334.2008.-Findings from our laboratory and others have demonstrated that the hormone insulin has chronic effects within the CNS to regulate energy homeostasis and to decrease brain reward function. In this study, we compared the acute action of insulin to decrease intake of a palatable food in two different behavioral tasks-progressive ratios sucrose self-administration and mu opioidstimulated sucrose feeding-when administered into several insulinreceptive sites of the CNS. We tested insulin efficacy within the medial hypothalamic arcuate (ARC) and paraventricular (PVN) nuclei, the nucleus accumbens, and the ventral tegmental area. Administration of insulin at a dose that has no chronic effect on body weight (5 mU) into the ARC significantly suppressed sucrose self-administration (75 Ϯ 5% of paired control). However, although the mu opioid DAMGO, [D-Ala2,N-MePhe4,Gly5-ol]-enkephalin acetate salt, stimulated sucrose intake at all four CNS sites, the ventral tegmental area was the only sensitive site for a direct effect of insulin to antagonize acute (60 min) mu opioid-stimulated sucrose feeding: sucrose intake was 53 Ϯ 8% of DAMGO-induced feeding, when insulin was coadministered with DAMGO. These findings demonstrate that free feeding of sucrose, and motivated work for sucrose, can be modulated within unique sites of the CNS reward circuitry. Further, they support the interpretation that adiposity signals, such as insulin, can decrease different aspects of ingestion of a palatable food, such as sucrose, in an anatomically specific manner. food reward; ventral tegmental area; arcuate nucleus WE HAVE PREVIOUSLY REPORTED that insulin can act within the central nervous system (CNS) to decrease food reward, in addition to providing an energy regulatory signal at the medial hypothalamus (3,11,14,31). Intraventricular (IVT) insulin administration prevents the expression of a place preference conditioned to a high-fat food treat (11), decreases initial lick rates for preferred sucrose solutions in a lickometer task (42), and decreases sucrose self-administration (13) in rats that are not food deprived. Further, IVT insulin decreases performance in the lateral hypothalamic self-stimulation task, such that there is an increase in the electrical frequency threshold required to sustain the behavior (7). Collectively, these findings support the hypothesis that insulin can blunt brain reward activity, including the rewarding attributes of food. However, the specific CNS sites that mediate the actions of insulin in different behavioral paradigms evaluating food reward have not been determined.Both the caloric and the motivating aspects of a palatable food such as sucrose might contribute to its ingestion, or overingestion, and the CNS circuitries i...

Rats and humans avidly consume flavored foods that contain sucrose and fat, presumably due to their rewarding qualities. In this study, we hypothesized that the complex mixture of corn oil, sucrose, and flavor is more reinforcing than any of these components alone. We observed a concentrationdependent increase in reinforcers received of sucrose solutions (0, 3, 6.25, and 12.5%) in both fixed ratio and progressive ratio procedures, but with equicaloric corn oil solutions (0, 1.4, 2.8, and 5.6%) this finding was replicated only in the fixed ratio procedure. Likewise, addition of 1.4% oil to 3% or 12.5% sucrose increased fixed ratio, but not progressive ratio, reinforcers received relative to those of sucrose alone. Finally, addition of 3% vanilla flavoring did not change self-administration of 3% sucrose or 3% sucrose + 1.4% oil solutions. These data suggest that, calorie-for-calorie, sucrose is the dominant reinforcing component of novel foods that contain a mixture of fat, sucrose, and flavor.

Camels with cannulas in the small intestine were used to study the "digestive-absorptive" capacities of the small intestine. Solutions of different carbohydrates were infused through the cannulas and the responses in blood glucose levels were measured. Monosaccharides were readily absorbed from the camel small intestine. The pattern of disaccharide absorption indicated that there was high lactase activity and low maltase and sucrase activity, in the camel small intestinal mucosa.