Obesity is a major health problem in the United States and is a leading contributor to cardiovascular disease, diabetes mellitus and stroke. One of the less well understood areas of obesity research are the mechanisms by which neurons respond to, integrate and pass on central and peripheral signals about energy state and how these signaling pathways are altered in obesity. Our long-range goal is to understand the molecular and cellular mechanisms by which neurons in the nucleus of the solitary tract (NTS) of the brainstem control body- weight and how these mechanisms are altered in obesity. Visceral afferents, including gastric afferents, carrying information about satiety terminate in the NTS. As such, NTS neurons act as gates, determining what information contained in afferents is passed onto other brain regions. Ablation of NTS neurons expressing catecholamines (NTS-CA neurons) disrupts control of food intake by several hormones, including ghrelin and cholecystokinin (CCK). The overall objective of this proposal is to identify the mechanisms by which NTS-CA neurons respond to appetite-regulating inputs under normal and obese conditions. Our central hypothesis is that the output of NTS-CA neurons is an integration of afferent and hormonal inputs and that it is altered by different energy states, such as fasting or obesity. We will test this hypothesis with the following three specific aims. (1) Determine how afferent inputs regulate NTS-CA neurons. Our working hypothesis for this aim is that the firing rate of NTS-CA neurons is controlled by visceral afferents, including gastric afferents, both through direct and indirect inputs. (2) Identify mechanism(s) by which key hormonal appetite modulators regulate NTS- CA neurons. Our working hypothesis for this aim is that CCK, which inhibits food intake and ghrelin, which stimulates food intake, regulate the output of NTS-CA neurons. (3) Determine how NTS-CA neurons adapt to different energy states. Our working hypothesis for this aim is that NTS-CA neurons adapt to prolonged exposure to hormones or conditions of altered energy states. We are well prepared to undertake the proposed research because we have developed a mouse horizontal brain slice that allows us to selectively stimulate visceral afferents while recording from identified NTS-CA neurons using electrophysiological patch clamp techniques. This is an extremely powerful system to address the cellular and molecular mechanisms by which NTS-CA neurons integrate neuronal and hormonal responses and how these mechanisms are altered in obesity. In addition, we will use labeling techniques to specifically identify NTS-CA neurons receiving gastric afferent inputs, pharmacology to dissect out molecular signaling pathways and behavioral paradigms to examine how these pathways/mechanisms are altered in different energy states. The contribution of this work is expected to be significant, because increasing our understanding of the molecular mechanisms underlying appetite control and how these mechanisms are altered in different energy states, will lead to more precisely targeted approaches for the prevention treatment of obesity.
The proposed research is relevant to public health because obesity is a major health problem in the United States and is a leading contributor to cardiovascular disease, diabetes mellitus and stroke. The expected contribution of these studies will be the identification of molecular mechanisms by which one group of critical neurons control weight regulation and how these are altered in obesity. The belief is that increasing our understanding of these mechanisms will lead to more precisely targeted approaches for the prevention and treatment of obesity.
