PROJECT SUMMARY / ABSTRACT Diabetes is one of the leading causes of death, affecting more than 30 million people in the U.S., with one in four individuals over 65 years suffering from its debilitating symptoms. Economically, diabetes represents an enormous burden due to associated healthcare cost and loss of productivity. Insulin is the most effective treatment used by many diabetic patients. However, achieving euglycemic balance can be a challenge since therapeutic insulin often leads to unintended sharp drop in blood glucose level, causing severe hypoglycemia which, if not addressed, may result in coma and death. Frequent hypoglycemia is one of the most reliable predictor of malignant disease course and mortality in diabetes. Normally, hypoglycemia is averted by counterregulary response pathway in the brain, which coordinates a series of physiological measures, along with hunger, to restore blood glucose. However, recurrent hypoglycemic episodes, due to intensive insulin therapy and daily activities, impairs these brain pathways, leaving diabetic patients vulnerable to subsequent hypoglycemia. Efforts to identify the central counterregulatory pathways revealed essential role of brainstem catecholamine neurons. We and others have shown that these neurons project extensively to hypothalamus, and these projections are essential for their counterregulatory actions. However, hypothalamic target(s) of these neurons and the mechanism(s) underlying their impairment by repeated hypoglycemia has not been determined. The overall goal of this proposal is to identify the neural circuit(s) mediating counterregulatory actions of brainstem catecholamine neurons. The aims of this grant are to 1) determine the direct neuronal target(s) of medullary catecholamine neurons in the hypothalamus mediating counterregulation, and 2) determine how repeated hypoglycemic episodes desensitize communication in this pathway. To accomplish these aims, we will use axons of medullary catecholamine neurons as a map to downstream circuits. These studies will provide new fundamental insights into the central counterregulatory pathways. In addition, by identifying mechanism of impaired counterregulation, these studies may lead to novel therapeutic targets for the treatment of hypoglycemia associated autonomic failure and hypoglycemia unawareness.