The chronic disease course of obesity reflects interactions between etiological traits and factors involved in maintenance, of which stress-induced hyperphagia offers unique prognostic value. Although occasional intake of high-calorie foods in response to stress does not directly cause obesity, for some, repeated exposure to stress triggers hyperphagic behaviors such that homeostatic pathways are overridden in favor of mesolimbic reward signaling, culminating in weight gain and obesity. In its most severe state, stress-induced hyperphagia may manifest as hyperphagic depression (or chronic stress-induced hyperphagia; increased appetite/weight gain in an episode). Stress-induced hyperphagic behaviors stem, in part, from disruption in mesolimbic regions governing reward. Despite data on abnormal dopamine (DA) signaling in obesity and mood disorders, the pathophysiology of chronic stress-induced hyperphagia remains poorly understood. Preclinical work supports involvement of ghrelin, a gut peptide primarily recognized for its orexigenic properties, in modulating DA transmission and reward signaling - a role recently corroborated in human obesity. We showed, in women with chronic stress-induced hyperphagia, that ghrelin was significantly related to self-reported reward capacity and stress-related eating, and to ventral tegmental area and nucleus accumbens activity in response to food reward. We hypothesize that chronic stress-induced hyperphagia is promoted by ghrelinergic signaling in response to psychosocial stress, and that these ghrelin-specific effects are significantly associated with differential reward activity in and connectivity between mesolimbic regions. This proposal will address the following Specific Aims: 1. To assess relationships between ghrelin and BOLD activity/connectivity related to food reward after psychosocial stress in chronic stress-induced hyperphagia, chronic stress-induced hypophagia, euphagic depression, and healthy controls; 2. To examine associations between ghrelin and BOLD activity/connectivity related to monetary reward in mesolimbic circuitry during reward anticipation/receipt after psychosocial stress in chronic stress-induced hyperphagia, chronic stress-induced hypophagia, euphagic depression, and healthy controls. We will study mesolimbic circuitry using functional MRI to measure BOLD activity and connectivity during food and non-food reward tasks following psychosocial stress in individuals with chronic stress-induced hyperphagia, chronic stress-induced hypophagia, euphagic depression, and healthy controls. Our study will identify acute and chronic effects of stress on relationships between ghrelin and brain reward circuitry, determine specificity of ghrelin-related reward potentiation to food or generalization beyond food-related reward, and explore associations between these variables and intake during ad libitum access to palatable foods. Understanding these effects will provide a mechanistic explanation for the maintenance of obesity in the context of triggers such as psychosocial stress, potentially informing the design of behavioral and pharmacologic treatments.
Difficulty losing weight and maintaining weight loss may be due in part to biological factors which favor increased intake of palatable foods in response to stress, including hormones such as ghrelin which act on brain reward regions to signal food reward sensitivity and attainment. In the proposed study, we plan to determine whether, following short-term psychosocial stress, ghrelin is associated with brain activity in response to palatable food and to monetary reward in individuals with chronic stress-related overconsumption of palatable foods. An improved mechanistic explanation for the relationship between stress and overeating will potentially inform the design of more effective intervention.