Role of Central Nervous System Glucagon-Like Peptide-1 Receptors in Enteric Glucose Sensing

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Abstract
OBJECTIVE-Ingested glucose is detected by specialized sensors in the enteric/hepatoportal vein, which send neural signals to the brain, which in turn regulates key peripheral tissues. Hence, impairment in the control of enteric-neural glucose sensing could contribute to disordered glucose homeostasis. The aim of this study was to determine the cells in the brain targeted by the activation of the enteric glucose-sensing system. RESEARCH DESIGN AND METHODS-We selectively activated the axis in mice using a low-rate intragastric glucose infusion in wild-type and glucagon-like peptide-1 (GLP-1) receptor knockout mice, neuropeptide Y- and proopiomelanocortingreen fluorescent protein-expressing mice, and high-fat diet diabetic mice. We quantified the whole-body glucose utilization rate and the pattern of c-Fos positive in the brain. RESULTS-Enteric glucose increased muscle glycogen synthesis by 30% and regulates c-Fos expression in the brainstem and the hypothalamus. Moreover, the synthesis of muscle glycogen was diminished after central infusion of the GLP-1 receptor (GLP-1Rc) antagonist Exendin 9-39 and abolished in GLP-1Rc knockout mice. Gut-glucose-sensitive c-Fos-positive cells of the arcuate nucleus colocalized with neuropeptide Y-positive neurons but not with proopiomelanocortin-positive neurons. Furthermore, high-fat feeding prevented the enteric activation of c-Fos expression. CONCLUSIONS-We conclude that the gut-glucose sensor modulates peripheral glucose metabolism through a nutrient-sensitive mechanism, which requires brain GLP-1Rc signaling and is impaired during diabetes.