Nutrients in the circulation play an important role in the regulation of Gl function and eating behavior. Animal and human studies show that hyperglycemia inhibits gastric motility and delays gastric emptying. Other studies indicate that changes in glucose concentration in the portal vein significantly affect feeding behavior. These effects are abolished following selective ablation of vagal and hepatic vagal afferent fibers respectively. We therefore hypothesize glucose sensory neurons responsive to hyper-(GluE) and and hypo-(Glul) glycemia are present in the nodose ganglia. These specialized neurons utilize the product of intracellular glucose metabolism to regulate their activities and transmitter release. In the GluE neurons, uptake and metabolism of glucose lead to closure of the KATP channels, triggering a membrane depolarization, whereas in the Glul neurons the inhibitory effect of hyperglycemia is mediated by an ATP- independent potassium channel related to the IPS signaling pathway. To test this hypothesis we plan to employ a variety of research tools including in vivo and in vitro electrophysiological recording, whole cell patch clamp, single cell RT-PCR, immunocytochemistry, and signal transduction studies using pharmacological tools and small interfering RNA technology. In vivo intracellular recording and labeling technologies will be used to identify GluE and Glul neurons in nodose ganglia. In vitro stomach or liver- vagus preparations will examine whether vagal afferent terminals have the complement of glucosensory components to detect changes in ambient glucose. Calcium-imaging studies will be performed to characterize GluE and Glul nodose neurons innervating the stomach and the portal vein. This study will be complemented by single cell PCR to identify the molecular imprint of signaling molecules and transmitter of the GluE and Glul nodose neurons. Lastly, whole cell voltage or current clamp recordings on dissociated gastric and portal vein projecting nodose neurons will be performed to characterize the intracellular signaling cascade that mediates glucose excited and inhibited activities in these neurons. Understanding glucose sensing as it relates to digestive function and feeding behavior will provide important information on how peripheral glucose can affect nutrient ingestion and metabolism, which ultimately may help in the management of diabetes and obesity. ? ? ? ?
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