| The hormones leptin and ghrelin are important contributors to the body's process of homeostasis, or balancing of energy intake and expenditure to maximize metabolic efficiency. Metabolic syndrome (MetS) is characterized by risk factors that also influence this balance including: high blood pressure, high triglyceride levels, low HDL cholesterol levels, raised fasting glucose, and abdominal obesity. This study examined the unique contribution of leptin and ghrelin to brain activation of taste, beyond that explained by MetS symptoms, and how this relationship between hormones and activation differs among age groups. A sample of 43 young, middle-aged, and older adults, 21 with MetS and 22 healthy controls, participated. fMRI and blood sample data were collected under conditions of hunger and satiety. Participants had their first (hunger) blood draw after fasting overnight, followed by a preload, second (satiety) blood draw, and scan. While in the scanner, participants were administered a sweet taste solution and brain activation was recorded while they rated its pleasantness. Using hypothalamic and orbitofrontal cortex (OFC) activation as the dependent variables, separate multiple regressions were run for young, middle-aged, and older adults for each brain area, with leptin levels, ghrelin levels, and number of MetS symptoms included as the predictor variables.;For young and middle-aged, leptin and ghrelin levels during hunger did not significantly predict hypothalamus activation during satiety, however, in the old, as leptin levels increased, right hypothalamus activation increased (p=.028 eta2=.79), and as ghrelin levels increased, left hypothalamus activation decreased (p=.028, eta 2=.76). When treating age as a continuous variable, ghrelin was a significant predictor of left OFC activation during hunger ( p=.028, eta2=.17) and satiety (p=.028, eta 2=.15).;The findings of the current study suggest that when evaluating sweet taste during satiety, the hypothalamus shows greater activation with higher levels of leptin, a signal of satiety, and lower activation with higher levels of ghrelin, a signal of hunger. Ghrelin's influence may be more relevant to the OFC which evaluates the reward value of food cues. Understanding more about the biological underpinnings of food evaluation and selection is an important foundation for advancing treatment plans for individuals at risk for metabolic and neurodegenerative disorders. |
