Ghrelin is a peptide hormone secreted primarily by endocrine cells that line the stomach and intestine. The most important actions of ghrelin include stimulation of food intake, inhibition of energy expenditure and promotion of adiposity. We have recently shown that ghrelin mediates pleasurable aspects of eating, and in particular, enhances the rewarding value of foods high in fat and increases the motivation to obtain palatable, fatty foods. Despite a substantial literature characterizing ghrelin action in the regulation of the food intake, relatively little is known about the mechanisms responsible for ghrelin's action on hedonic aspects of eating. In the current grant, we propose to better characterize the neuronal circuits mediating ghrelin's action on reward- based eating behaviors. In particular, we will test the hypothesis that corticotrophin releasing factor (CRF)- producing neurons of the central amygdala (CeA) contribute to ghrelin's actions on reward-based eating. We will test this hypothesis as part of three independent, yet related aims. We will determine if rises in ghrelin that occur upon ghrelin injection or naturally upon caloric restriction activate CA CRF neurons. We will determine if ghrelin's ability to enhance the rewarding value of fatty food requires CRF signaling. Also, we will determine if neurons that express the neuropetide orexin mediate ghrelin's effects on CeA CRF neurons. For these studies, we will use a newly developed transgenic mouse line in which green fluorescent protein marks the location of CRF neurons within the brain. These mice will be used together with other mouse models, including those in which CRF or orexin are missing, to elucidate the ghrelin-engaged neuronal circuits of interest. We will also use pharmacologically administered agents, including antagonists to receptors for ghrelin, CRF and orexin, in order to further characterize these pathways. Food reward behaviors will be assessed using a conditioned place preference behavioral task that we have adapted and developed for the specific study of food reward behavior in mouse models. We believe these experiments will yield important insights about behaviors related to eating, and eventually may lead to new therapies for obesity. This research will be performed in collaboration with Mario Perello, as an extension of NIH grant 1R01DA024680-01, 6-1-08 to 4-30- 13. They will be performed both at UTSW Medical Center and in the laboratory of Neurophysiology of the Multidisciplinary Institute of Cell Biology (IMBICE-CONICET/PBA), located in the city of La Plata, Argentina. They are designed to extend and enhance the research interests of both Drs. Zigman and Perello, and will help build the research and research capabilities of Dr. Perello and the IMBICE.
Our group has recently shown that the gastrointestinal tract-derived hormone ghrelin enhances certain pleasurable aspects of eating, such as the rewarding value of fatty food and the motivation to obtain fatty food. The experiments proposed in this study have been designed to investigate the neuronal pathways mediating ghrelin's action on these reward-based eating behaviors, with a particular focus on the role of corticotrophin releasing factor neurons in the central amygdala region of the brain. It is hoped that these fundamental experiments on the mechanism of ghrelin action, which will be performed in a collaborative manner by institutions in the United States and Argentina, will yield important insights about behaviors that control eating, and eventually may lead to new therapies for obesity.
