How the brain maintains energy homeostasis is not well understood making it a critical area of research. Agouti-related peptide (AgRP) neurons located in the arcuate nuclei (ARC) of the hypothalamus are essential for the regulation of energy balance. Specific activation of these neurons through pharmacogenetic stimulation produces intense hunger as well as a rapid decrease in energy expenditure. Remarkably, little attention has been paid to the mechanisms producing suppression of energy expenditure by AgRP neurons, leaving the downstream circuitry mediating this effect unknown. This is due, in part, to the complex circuitry that exists within the ARC, where AgRP neurons exist among other neurons of opposite or unrelated function that also share partial overlap in circuitry. To unravel the process by which AgRP neurons function to decrease metabolism, there must first be an understanding of the circuitry mediating the physiological response to AgRP neuron activation. Traditional tract tracing methods are incapable of cell-specific targeting and assessment of functional connectivity, however, recent development of innovative optogenetic and pharmacogenetic technologies now permit the study of complex circuits controlling feeding behavior and metabolism. By utilizing Cre-dependent gene-targeting approaches in transgenic mice, this application proposes to map sites downstream to AgRP neurons and identify the specific neuronal population responsible for AgRP- mediated suppression of energy expenditure. Subsequently, a combination of pharmacogenetic and optogenetic tools will allow for isolated manipulation of specific AgRP synapses to reveal the necessary and/or sufficient efferent targets that mediate suppression of energy expenditure. The findings generated from these studies will provide a wiring diagram for AgRP-mediated suppression of energy expenditure, which could provide insight into potential contributions to a wide range of metabolic diseases, ranging from eating disorders to obesity.

Public Health Relevance

In order to combat the increasing prevalence of obesity and other related disorders, we must gain a better understanding of the hypothalamic neurocircuitry that regulates both feeding and metabolism. Hypothalamic AgRP neurons are essential to the control of body weight and are primarily considered to be hunger neurons, however, these neurons not only drive hunger, but also suppress energy expenditure. This proposal aims to isolate the AgRP neurocircuitry that regulates energy expenditure using cell-type specific functional circuit mapping technologies.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Postdoctoral Individual National Research Service Award (F32)
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Special Emphasis Panel (ZDK1)
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Castle, Arthur
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Beth Israel Deaconess Medical Center
United States
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