Intensive therapy is essential to optimize glucose control in insulin- dependent diabetes mellitus (IDDM). However, avoiding hypolglycemia is a major challenge for the management of IDDM. The central nervous system monitors glucose levels and coordinates a counter regulatory response during periods of hypoglycemia. However, the mechanism(s) and central pathways that underlie the counter regulatory response are not understood. Our preliminary findings suggest central glucagon-like peptide 1 (GLP-1) systems regulate sympathetic outflow and are involved in regulating CNS responses to insulin-induced hypoglycemia. We hypothesis that the action of GLP-1 systems are fundamental in the coordinated endocrine and autonomic counter regulatory responses during hypoglycemia. In this proposal, we outline experiments designed to characterize the neuroanatomic mechanisms by which leptin and serotonin systems interact to regulate food intake. First, we will determine the effect of peripheral and central injections of GLP-1R agonists and antagonists on activating the sympathoadrenal and blood pressure responses. Next, using retrograde tracing and in situ hybridization, we will determine if subpopulations of GLP-1 sensitive neurons in hypothalamus and brainstem innervate sympathetic preganglionic neurons in the interomedial lateral cell column in the (IML) spinal cord. Third, using micro injections into selected brain regions, we will determine the sites in the brain that respond to GLP-1 resulting in increased blood pressure and activation of adrenal catecholamine secretion. Fourth, using central injections of GLP-1 receptor antagonists we will determine the effect of central antagonism of GLP-1Rs on the counter regulatory responses to hypoglycemia. Finally, using GLP-1R-/- mice and mine over expressing GLP-1 receptor agonists, we will determine the effects on the coordinated counter regulatory responses following insulin-induced hypoglycemia in GLP-1R knockout mice and EXN-4 over expressing transgenic mice.
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