Stephen C. Benoit - US grants

Obesity is a health problem of grave concern in western nations and the search for effective treatments has yet to come to fruition. The control of food intake and body weight involves peripheral (hormonal) and central (neural) mechanisms. One peripheral hormone that satisfies the criteria for being a signal of body fat is the pancreatic hormone, insulin. Insulin is released in proportion to fat mass, and when administered into the brain, reduces food intake and body weight. In the brain, the hypothalamic melanocortin family of peptides is thought to play an important role in the control of food intake. Administration of MC antagonists produce robust increases in food intake, while agonists lead to decreased intake. The present experiments are proposed to investigate the role of hypothalamic MC in the mediation of insulin's effects. The first series of studies will incorporate double-labeling in-situ hybridization techniques to assess whether neurons which produce MC peptides also contain receptors for insulin. The second series will assess whether there is a functional relationship between hypothalamic insulin receptors and MC neurons. This will be accomplished with in-situ hybridization and c-fos immunocytochemistry techniques. It is hypothesized that central administration of insulin will lead to changes in activation of MC neurons. Finally, the third set of studies will assess whether MC neurons mediate the effects of insulin on food intake. It is hypothesized that MC antagonists will block the hypophagic effects of central insulin administration

DESCRIPTION (provided by applicant):The prevalence of neurodegenerative diseases is escalating at an alarming rate as life expectancy increases. During the next quarter century, the number of individuals suffering from neurodegenerative cognitive deficits is expected to rise at an alarming rate. One important goal for neuroscience is the elucidation of physiological mechanisms underlying or otherwise contributing to these pathologies. Considerable evidence suggests that the pancreatic hormone, insulin, is a key factor. Secreted in response to increased blood glucose, insulin's best-known systemic action is to facilitate uptake of energy by peripheral tissues. Recent research has focused on insulin's actions in the central nervous system as well. Receptors for insulin are selectively expressed in several brain areas, with high concentrations in the hippocampus, a brain area important for formation of certain memories. Importantly, disease states related to systemic insulin insensitivity, such as diabetes mellitus, are associated with cognitive deficits in humans and animals, and administration of insulin either peripherally or directly into the brain, can alleviate symptoms of these cognitive deficits in animal subjects. These and other data encourage the hypothesis that insulin plays an important role in normal neural function and that disruptions in insulin signaling may contribute to neurological pathologies. The long-term goal of our proposal is to elucidate the roles for central insulin receptors, particularly in the hippocampus, in cognitive processes. To accomplish this, we will investigate learning abilities in mice with selective genetic deletion of a critical region of the insulin receptor gene. Importantly, these deletions will be limited to the central nervous system or only to the hippocampus. Previous work has attempted to study the role of insulin using systemic manipulations, which can cause serious side effects and confounds. Utilization of this new transgene technology will help us eliminate those confounds and side effects, to more fully understand the role of insulin signaling in learning and memory. Ultimately, this line of investigation may offer novel therapeutic strategies for treating individuals with cognitive disorders such as Alzheimer' s disease.

DESCRIPTION (provided by applicant): Obesity is a health problem of grave concern in western nations and the search for effective treatments has yet to come to fruition. The control of food intake and body weight involves peripheral (hormonal) and central (neural) mechanisms. In the brain, the hypothalamic melanocortin (MC) family of peptides is thought to play an important role in the control of food intake. Administration of MC antagonists produce[s] robust increases in food intake, while agonists lead to decreased intake. In addition, central expression of the precursor molecule, pro-opiomelanocortin (POMC), for these peptides is regulated by signals of energy balance, including the adipocyte hormone, leptin. Finally, genetic knockout mice, which lack a specific receptor subtype for these brain melanocortins, overeat and become obese. Together, these data suggest that the melanocortin system plays an important role in the CNS control of food intake and are critical to the maintenance of energy balance. Yet, virtually no analysis [has focused on] the behavioral mechanisms through which the MC peptides might alter food intake. The goal of this proposal is to assess the effects of melanocortins in several categories of ingestive behaviors. In one series of experiments, we will assess whether MC peptides influence pre-ingestive stimuli or appetitive behavior using sophisticated behavioral paradigms. In some studies, we will train rats to make conditioned responses under a food deprivation state and assess whether administration of central MCs lead[s] to similar sensory consequences. In addition, we will assess if MC peptides modulate rats' conditioned responses for stimuli that predict food, in ways similar to food deprivation. In a separate series of experiments, we will assess whether administration of central MCs alters the hedonic value of food. In one experiment, we will measure rats' appetitive responses during oral infusion of sweet solutions. In another experiment, we will assess whether MC peptides influence the ability of a sweet flavor to support conditioned place preference. In a final series of experiments, we will assess whether MC peptides [affect] food intake by influencing post-ingestive learning. We will test whether exposure to foods after central administration of MC peptides changes subsequent conditioned responding to cues that predicted the exposed food. Finally, we will assess whether such changes are post-ingestive, rather than orosensory, by infusing nutritive or nonnutritive solutions directly into the stomachs of the rats. These results will expand our understanding of this critical system for the regulation of food intake and body weight and, hopefully, provide insight into important structures and systems that are downstream of the melanocortins.

DESCRIPTION (provided by applicant): Obesity is a health problem of grave concern in western nations and the search for effective treatments has yet to come to fruition. The control of food intake and body weight involves peripheral (hormonal) and central (neural) mechanisms. In the brain, the hypothalamic melanocortin (MC) family of peptides is thought to play an important role in the control of food intake. Administration of MC antagonists produces robust increases in food intake, while agonists lead to decreased intake. In addition, central expression of the precursor molecule, pro-opiomelanocortin (POMC), for these peptides is regulated by signals of energy balance, including the adipocyte hormone, leptin. Importantly, recent reports have identified a novel co-receptor, called syndecan-3, which facilitates the action of melanocortin antagonists. Because POMC is critically involved in the regulation of several physiological processes (e.g., stress), syndecan-3 may represent a way to modulate melanocortin control of body weight without disrupting POMC involvement in other systems. We propose to examine the mechanisms that regulate the function of this novel syndecan-3 co-receptor and the specific ways through which it interacts with melanocortin control of food intake and body weight. First, we will assess the anatomical specificity of syndecan-3 and melanocortin receptor expression. Second, we will use pharmacological techniques to identify the enzymes responsible for syndecan-3 function. Additional experiments will assess whether drugs that influence food intake can influence syndecan-3 function, and vice-versa. Finally, we will use genetic approaches to assess the degree of syndecan-3 and melanocortin interaction in the control of energy balance. Specifically, we will cross mice with genetic disruptions of syndecan-3 function and mice that have mutant genes for melanocortin antagonists. Collectively, these experiments are designed to identify the mechanisms of syndecan-3 function as well as syndecan-3 interaction with melanocortins in the control of food intake and body weight. The results may provide important, basic insights into the control of body weight by the central melanocortin system and its recently identified co-receptor, syndecan-3.

Project Summary (Behavioral and Cognitive Core) Metabolic disorders, including diabetes, are characterized by abnormalities in circulating substrates (glucose, lipids) as well as their causes and consequences vis-à-vis peripheral tissues including the endocrine pancreas, liver, adipose tissue, and others. While this peripheral focus has been vital for developing current therapeutic approaches, recent years have seen a steady progression in understanding the importance of the central nervous system (CNS) in terms of receiving signals from these peripheral organs, integrating them with circulating nutrients and diverse non-homeostatic factors, and then coordinating activity among diverse systems to optimally control glycemia and other parameters. An important component of this activity is the CNS control of behavior. Recognizing the importance of the interplay between the CNS and peripheral metabolism, NIDDK modified the RFP for the current round of MMPC applications by explicitly naming behavioral assays as key phenotypic endpoints to be offered. This innovation is timely and nicely fits with a successful internal behavioral core that has historically served UC's MDI and Obesity Research Center. Although this internal core wasn't explicitly advertised, investigators in other institutions and industry learned of it and utilized it on a limited basis; however, we have been unable to make these services widely available to non-UC investigators due to funding limitations. We are proposing that this already-existing core become an official Behavior and Cognitive Core of the UC-MMPC, thereby making its services and considerable behavioral expertise broadly available to non-UC investigators. By doing so, we are also taking advantage of the extremely well-established MMPC core structure and its mechanism for the retrieval of service fees. There are four broad, long-range aims of this Core: Specific Aim 1: To provide sophisticated state-of-the-art behavioral assays that allow investigators to better characterize mouse models of metabolic disorders. Specific Aim 2: To advise investigators on the most appropriate behavioral tests, as well as the optimal sequence to be used when performing different assays. Specific Aim 3: To train investigators in the execution and analysis of specialized behavioral procedures established and routinely practiced in the Core. Specific Aim 4: To continuously improve current paradigms and develop new ones, including methods to enhance the efficiency and accuracy of behavioral assessments in mice.