Incretins and Amylin: Neuroendocrine Communication Between the Gut, Pancreas, and Brain in Control of Food Intake and Blood Glucose
Annual Review of Nutrition (Impact Factor: 8.36). 04/2014; 34(1). DOI: 10.1146/annurev-nutr-071812-161201
Arguably the most fundamental physiological systems for all eukaryotic life are those governing energy balance. Without sufficient energy, an individual is unable to survive and reproduce. Thus, an ever-growing appreciation is that mammalian physiology developed a redundant set of neuroendocrine signals that regulate energy intake and expenditure, which maintains sufficient circulating energy, predominantly in the form of glucose, to ensure that energy needs are met throughout the body. This orchestrated control requires cross talk between the gastrointestinal tract, which senses the incoming meal; the pancreas, which produces glycemic counterregulatory hormones; and the brain, which controls autonomic and behavioral processes regulating energy balance. Therefore, this review highlights the physiological, pharmacological, and pathophysiological effects of the incretin hormones glucagon-like peptide-1 and gastric inhibitory polypeptide, as well as the pancreatic hormone amylin, on energy balance and glycemic control. Expected final online publication date for the Annual Review of Nutrition Volume 34 is July 17, 2014. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
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- "NTS, VTA, NAc, PBN, CeA, PVH, ARH), only a subset of these GLP-1R-expressing nuclei has also been directly linked with mediating behaviors indicative of visceral malaise, emesis, nausea, and/or aversion (e.g. NTS, CeA)  "
ABSTRACT: While chemotherapy-induced nausea and vomiting is clinically controlled in the acute (<24h) phase following treatment, the anorexia, nausea, fatigue, and other illness-type behaviors during the delayed phase (>24h) of chemotherapy are largely uncontrolled. As the hindbrain glucagon-like peptide-1 (GLP-1) system contributes to energy balance and mediates aversive and stressful stimuli, here we examine the hypothesis that hindbrain GLP-1 signaling mediates aspects of chemotherapy-induced nausea and reductions in feeding behavior in rats. Specifically, hindbrain GLP-1 receptor (GLP-1R) blockade, via 4th intracerebroventricular (ICV) exendin-(9-39) injections, attenuates the anorexia, body weight reduction, and pica (nausea-induced ingestion of kaolin clay) elicited by cisplatin chemotherapy during the delayed phase (48hr) of chemotherapy-induced nausea. Additionally, the present data provide evidence that the central GLP-1-producing preproglucagon neurons in the nucleus tractus solitarius (NTS) of the caudal brainstem are activated by cisplatin during the delayed phase of chemotherapy-induced nausea, as cisplatin led to a significant increase in c-Fos immunoreactivity in NTS GLP-1-immunoreactive neurons. These data support a growing body of literature suggesting that the central GLP-1 system may be a potential pharmaceutical target for adjunct anti-emetics used to treat the delayed-phase of nausea and emesis, anorexia, and body weight loss that accompany chemotherapy treatments.
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- "notion as VTA amylin receptor activation with sCT did not change blood glucose levels in an oral glucose tolerance test, suggesting that other CNS site(s) mediate the ability of amylin to regulate glycemia (Hayes et al, 2014). "
ABSTRACT: Amylin acts in the CNS to reduce feeding and body weight. Recently, the ventral tegmental area (VTA), a mesolimbic nucleus important for food intake and reward, was identified as a site-of-action mediating the anorectic effects of amylin. However, the long-term physiological relevance and mechanisms mediating the intake-suppressive effects of VTA amylin receptor activation are unknown. Data show that the core component of the amylin receptor, the calcitonin receptor (CTR), is expressed on VTA dopamine neurons and that activation of VTA amylin receptors reduces phasic dopamine in the nucleus accumbens core (NAcC). Suppression in NAcC dopamine mediates VTA amylin-induced hypophagia, as combined NAcC D1/D2 receptor agonists block the intake-suppressive effects of VTA amylin receptor activation. Knockdown of VTA CTR via AAV-shRNA resulted in hyperphagia and exacerbated body weight gain in rats maintained on high-fat diet. Collectively, findings show that VTA amylin receptor signaling controls energy balance by modulating mesolimbic dopamine signaling.Neuropsychopharmacology accepted article preview online, 18 July 2014; doi:10.1038/npp.2014.180.
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ABSTRACT: Glucagon-like peptide-1 (GLP-1) is produced in the small intestines and in nucleus tractus solitarius (NTS) neurons. Activation of central GLP-1 receptors (GLP-1Rs) reduces feeding and body weight. The neural circuits mediating these effects are only partially understood. Here we investigate the inhibition of food intake and motivated responding for food in rats following GLP-1R activation in the ventral hippocampal formation (HPFv), a region only recently highlighted in food intake control. Increased HPFv GLP-1R activity following exendin-4 administration potently reduced food intake (both chow and Western diet) and body weight, whereas HPFv GLP-1R blockade increased food intake. These hypophagic effects were based on reduced meal size, and likely do not involve nausea as HPFv exendin-4 did not induce a conditioned flavor avoidance. HPFv GLP-1R activation also reduced effort-based responding for food under an operant progressive ratio reinforcement schedule, but did not affect food conditioned place preference expression. To investigate possible routes of HPFv GLP-1 signaling, immunohistochemical analysis revealed the absence of GLP-1 axon terminals in the HPFv, suggesting volume transmission as a mechanism of action. Consistent with this, the presence of active GLP-1 was detected in both the cerebral spinal fluid (CSF) and the HPFv. The source of CSF GLP-1 may be NTS GLP-1-producing neurons, as, 1) ~30% of NTS GLP-1 neurons colocalized with the retrograde tracer fluorogold following lateral ventricle fluorogold injection, and 2) GLP-1-immunoreactive axon terminals were observed adjacent to the ventricular ependymal layer. Collectively these findings illuminate novel neuronal and behavioral mechanisms mediating food intake reduction by GLP-1.Neuropsychopharmacology accepted article preview online, 18 July 2014; doi:10.1038/npp.2014.175.
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