Hypothalamic Control of Systemic Glucose Homeostasis: The Pancreas Connection

Resistance Exercise Training Attenuates the Loss of Endogenous GLP-1 Receptor in the Hypothalamus of Type 2 Diabetic Rats

The aim of this study was to investigate the effects of resistance exercise training on hypothalamic GLP-1R levels and its related signaling mechanisms in T2DM. The animals were separated into three groups: a non-diabetic control (CON), diabetic control (DM), and diabetic with resistance exercise (DM + EXE) group. The resistance exercise training group performed ladder climbing (eight repetitions, three days per week for 12 weeks). Body weight was slightly lower in the DM + EXE group than the DM group, but difference between the groups was not significant. Food intake and glucose were significantly lower in the DM + EXE group than in the DM group. The blood insulin concentration was significantly higher and glucagon was significantly lower in the DM + EXE group. The DM + EXE group in the hypothalamus showed significant increases in GLP-1R mRNA, protein kinase A (PKA), glucose transporter 2 (GLUT2), and protein kinase B (AKT) and significant decrease in protein kinase C-iota (PKC-iota). Antioxidant enzymes and apoptosis factors were significantly improved in the DM + EXE group compared with the DM group in the hypothalamus. The results suggest that resistance exercise contributes to improvements the overall health of the brain in diabetic conditions.

Vertical sleeve gastrectomy improves liver and hypothalamic functions in obese mice

Vertical sleeve gastrectomy (VSG) is an effective surgery to treat obesity and diabetes. However, the direct effect of VSG on metabolic functions is not fully understood. We aimed to investigate if alterations in hypothalamic neurons were linked with perturbations in liver metabolism after VSG in an energy intake-controlled obese mouse model. C57BL/6 and hrNPY-GFP reporter mice received HFD for 12 weeks and were then divided into three groups: Sham (ad lib), sham (pair-fed) with VSG, and VSG. Food intake was measured daily, and blood glucose levels were measured before and after the study. Energy expenditure and body composition were determined. Serum parameters, liver lipid and glycogen contents were measured, and gene/protein expression were analyzed. Hypothalamic POMC, AgRP/NPY, and tyrosine hydroxylase expressing neurons were counted. As results, we found that VSG reduced body weight gain and adiposity induced by HFD, increased energy expenditure independent of energy intake. Fed and fasted blood glucose levels were reduced in the VSG group. While serum active GLP-1 level was increased, the active ghrelin and triglycerides levels were decreased along with improved insulin resistance in VSG group. Liver lipid accumulation, glycogen content, and gluconeogenic gene expression were reduced in the VSG group. In the hypothalamus, TH expressing neuron population was decreased, and the POMC-expressing neuron population was increased in the VSG group. Our data suggests that VSG improves metabolic symptoms by increasing energy expenditure and lowering lipid and glycogen contents in the liver. These physiological alterations are possibly related to changes in hypothalamic neuron populations.

Revisiting How the Brain Senses Glucose-And Why

Glucose-sensitive neurons have long been implicated in glucose homeostasis, but how glucose-sensing information is used by the brain in this process remains uncertain. Here, we propose a model in which (1) information relevant to the circulating glucose level is essential to the proper function of this regulatory system, (2) this input is provided by neurons located outside the blood-brain barrier (BBB) (since neurons situated behind the BBB are exposed to glucose in brain interstitial fluid, rather than that in the circulation), and (3) while the efferent limb of this system is comprised of neurons situated behind the BBB, many of these neurons are also glucose sensitive. Precedent for such an organizational scheme is found in the thermoregulatory system, which we draw upon in this framework for understanding the role played by brain glucose sensing in glucose homeostasis.

Sensing Glucose in the Central Melanocortin Circuits of Rainbow Trout: A Morphological Study

In mammals, glucosensing markers reside in brain areas known to play an important role in the control of food intake. The best characterized glucosensing mechanism is that dependent on glucokinase (GK) whose activation by increased levels of glucose leads in specific hypothalamic neurons to decreased or increased activity, ultimately leading to decreased food intake. In fish, evidence obtained in recent years suggested the presence of GK-like immunoreactive cells in different brain areas related to food intake control. However, it has not been established yet whether or not those neuronal populations having glucosensing capacity are the same that express the neuropeptides involved in the metabolic control of food intake. Therefore, we assessed through dual fluorescent in situ hybridization the possible expression of GK in the melanocortinergic neurons expressing proopiomelanocortin (POMC) or agouti-related protein (AGRP). POMC and AGRP expression localized exclusively in the rostral hypothalamus, in the ventral pole of the lateral tuberal nucleus, the homolog of the mammalian arcuate nucleus. Hypothalamic GK expression confined to the ependymal cells coating the ventral pole of the third ventricle but some expression level occurred in the AGRP neurons. GK expression seems to be absent in the hypothalamic POMC neurons. These results suggest that AGRP neurons might sense glucose directly through a mechanism involving GK. In contrast, POMC neurons would not directly respond to glucose through GK and would require presynaptic inputs to sense glucose. Ependymal cells could play a critical role relying glucose metabolic information to the central circuitry regulating food intake in fish, especially in POMC neurons.