Adolescent obesity is fueling the increase in the prevalence of T2DM in youth. Obese adolescents on their path to developing prediabetes/T2DM present with severe peripheral insulin resistance, marked hyperinsulinemia and relatively low leptin levels. These abnormal adiposity related signals may not only favor the development of peripheral but also central insulin resistance, thereby promoting the perpetuation of obesity and its associated metabolic complications. Dr. Caprio's research is mainly in peripheral insulin and glucose metabolism in obese adolescents. However, there are a number of basic, clinical, physicist and neurobehavioral scientists at Yale actively working in the field of Central Regulation of Energy Metabolism. Our goal is to bring together these various Yale-based investigators to explore whether obese adolescents with insulin resistance and relative low leptin levels exhibit functional alterations of the neuronal circuits involved in the regulation of energy metabolism and food seeking behaviors. We here propose a series of hypotheses-driven studies which will be performed by a multidisciplinary team of investigators from Internal Medicine, Diagnostic Radiology, Psychiatry and Pediatrics, using an integrated team approach. The hypotheses are: 1- The hypothalamic fMRI signal after the ingestion of glucose is attenuated in obese adolescents with insulin resistance, relative low levels of leptin and marked hyperinsulinemia compared to age, gender and puberty matched obese sensitive and lean adolescents. 2- Fructose consumption has differential effects when compared to glucose on the functional connections between the hypothalamus and other brain regions implicated in feeding behavior and that these differential effects are magnified in obese adolescents. 3- Functional connectivity between brain regions of the reward system implicated in the response to specific food cues are altered in the obese adolescents and this is related to hyperinsulinemia/insulin resistance. The team will use functional connectivity fMRI mapping to examine the connections between specific appetitive regions such as the dorsal striatum and caudate nucleus and the hypothalamus. In particular, we will examine how connectivity within these networks changes as a function of brain fuel, and we will look for differential network responses to the fuels between lean and obese adolescents with extreme ends of the insulin resistance spectrum. Understanding the differential response of centers regulating the homeostatic and non-homeostatic neuronal circuits to common highly palatable foods (glucose) in obese adolescents may translate into the development of more effective weight gain and diabetes prevention program in youth.
Much is known in adults regarding how the brain reacts to both ingestion of foods or in response to food cues. In contrast, little investigation has been done in adolescents to understand the neural circuitry underlying hunger and satiation. Even more important, virtually no studies, to our knowledge, have yet been done to understand how these neural circuits might be affected longitudinally by the presence of obesity during this critical period of adolescence. Although a reduced hypothalamic function may well be secondary to the obesity, in the long run it may contribute to the persistence of the obese state and severity of the insulin resistance which, in turn may lead to the development of diabetes and metabolic syndrome. Using fMRI we plan to determine if obese adolescents, with relative low leptin and adiponectin in conjunction with high circulating insulin levels, might also display abnormal neuronal activity in certain regions of the brain, some of which are known to be key regulators of energy homeostasis and food seeking behavior.
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