Hepatic glycogenolysis and hypometabolism induced by chemogenetic stimulation of C1 neurons.

The precise regulation of blood glucose levels is indispensable for maintaining physiological functions. C1 neurons determine the outflow of the autonomic nervous and endocrine systems to maintain blood glucose levels in the body. In contrast, activation of C1 neurons induces a decrease in activity, suggesting that hypoactivity also participates in maintaining blood glucose levels. To examine this, we evaluated both glycogenolysis and hypometabolism induced by the selective activation of C1 neurons. We used DbhCre/0 mice expressing receptors for chemogenetic tools in C1 neurons, resulting from microinjection of the viral vector. C1 neurons were activated by intraperitoneal injection of clozapine N-oxide (CNO). The chemogenetic activation of C1 neurons significantly decreased body temperature, oxygen consumption and carbon dioxide production. On the other hand, blood glucose levels were increased by activation of C1 neurons 2 h after CNO administration, even in the fasting state. In this situation, an increase in glucagon and corticosterone levels was observed, while hepatic glycogen content decreased significantly. Plasma insulin levels were not changed by the activation of C1 neurons despite the increase in blood glucose level. Furthermore, adrenal sympathetic nerve activity was significantly increased by the activation of C1 neurons, and plasma catecholamine levels increased significantly. In conclusion, the selective activation of C1 neurons using chemogenetic tools induced an increase in blood glucose levels, probably as a result of hepatic glycogenolysis and hypometabolism. KEY POINTS: Chemogenetic activation of C1 neurons in medulla oblongata decreased body temperature. Oxygen consumption and carbon dioxide production were decreased by chemogenetic activation of C1 neurons in medulla oblongata. Blood glucose levels were increased by chemogenetic activation of C1 neurons in medulla oblongata. Chemogenetic activation of C1 neurons in medulla oblongata increased glucagon, corticosterone and catecholamine levels in plasma. An increase in blood glucose levels by activation of C1 neurons occurred due to the combined effect of hepatic glycogenolysis and hypometabolism.

Repeated activation of C1 neurons in medulla oblongata decreases anti-inflammatory effect via the hypofunction of the adrenal gland adrenergic response.

The immune system is known to be controlled by the autonomic nervous system including sympathetic and parasympathetic (vagus) nerves. C1 neurons in the medulla oblongata, which participate in the control of the autonomic nervous system, are responders to stressors and regulate the immune system. Short-term activation of C1 neurons suppresses inflammation, while the effect of a long-term activation of these neurons on the inflammatory reflex is unclear. We, herein, demonstrate that the coactivation of both the splenic sympathetic nerves and the adrenal gland adrenergic response are indispensable for the prognosis of acute lung injury. The chemogenetic activation of C1 neurons increased plasma catecholamine including adrenaline and noradrenaline levels. The deletion of catecholaminergic cells using local injections of viral vector in the adrenal gland abolished the protective effect against acute lung injury when the C1 neurons were stimulated by either chemogenetic or optogenetic tools. Furthermore, repeated activation of C1 neurons using chemogenetic tool inhibited the adrenal response without affecting the plasma noradrenaline levels, eliminated the protective effect against acute lung injury. This was rescued by the isoprenaline administration. We concluded that the maintenance of an adrenergic response via C1 neurons in the adrenal gland is a prerequisite for the delivery of an effective anti-inflammatory response.

Stimulatory effect of imeglimin on incretin secretion.

AIMS/INTRODUCTION: Imeglimin is a new antidiabetic drug structurally related to metformin. Despite this structural similarity, only imeglimin augments glucose-stimulated insulin secretion (GSIS), with the mechanism underlying this effect remaining unclear. Given that glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) also enhance GSIS, we examined whether these incretin hormones might contribute to the pharmacological actions of imeglimin. MATERIALS AND METHODS: Blood glucose and plasma insulin, GIP, and GLP-1 concentrations were measured during an oral glucose tolerance test (OGTT) performed in C57BL/6JJcl (C57BL/6) or KK-Ay/TaJcl (KK-Ay) mice after administration of a single dose of imeglimin with or without the dipeptidyl peptidase-4 inhibitor sitagliptin or the GLP-1 receptor antagonist exendin-9. The effects of imeglimin, with or without GIP or GLP-1, on GSIS were examined in C57BL/6 mouse islets. RESULTS: Imeglimin lowered blood glucose and increased plasma insulin levels during an OGTT in both C57BL/6 and KK-Ay mice, whereas it also increased the plasma levels of GIP and GLP-1 in KK-Ay mice and the GLP-1 levels in C57BL/6 mice. The combination of imeglimin and sitagliptin increased plasma insulin and GLP-1 levels during the OGTT in KK-Ay mice to a markedly greater extent than did either drug alone. Imeglimin enhanced GSIS in an additive manner with GLP-1, but not with GIP, in mouse islets. Exendin-9 had only a minor inhibitory effect on the glucose-lowering action of imeglimin during the OGTT in KK-Ay mice. CONCLUSIONS: Our data suggest that the imeglimin-induced increase in plasma GLP-1 levels likely contributes at least in part to its stimulatory effect on insulin secretion.

Glucose-dependent insulinotropic polypeptide counteracts diet-induced obesity along with reduced feeding, elevated plasma leptin and activation of leptin-responsive and proopiomelanocortin neurons in the arcuate nucleus.

AIM: To clarify the effects of glucose-dependent insulinotropic polypeptide (GIP) receptor agonists (GIPRAs) on feeding and body weight. MATERIALS AND METHODS: Acute and subchronic effects of subcutaneous GIPFA-085, a long-acting GIPRA, on blood glucose, food intake, body weight, respiratory exchange ratio and plasma leptin levels were measured in diet-induced obese (DIO) mice and/or functional leptin-deficient ob/ob mice. The effects of GIPFA-085 on the hypothalamic arcuate nucleus (ARC) neurons from lean and DIO mice were studied by measuring cytosolic Ca2+ concentration ([Ca2+ ]i ). RESULTS: Single bolus GIPFA-085 (30, 300 nmol/kg) dose-dependently reduced blood glucose in glucose tolerance tests, elevated plasma leptin levels at 0.5-6 hours and inhibited food intake at 2-24 hours after injection in DIO mice. Daily GIPFA-085 (300 nmol/kg) inhibited food intake and increased fat utilization on day 1, and reduced body weight gain on days 3-12 of treatment in DIO, but not ob/ob, mice. GIPFA-085 increased [Ca2+ ]i in the ARC leptin-responsive and proopiomelanocortin (POMC) neurons. GIPFA-085 and leptin cooperated to increase [Ca2+ ]i in ARC neurons and inhibit food intake. CONCLUSIONS: GIPFA-085 acutely inhibits feeding and increases lipid utilization, and sustainedly lowers body weight in DIO mice via mechanisms involving rises in leptin and activation of ARC leptin-responsive and POMC neurons. This study highlights the therapeutic potential of GIPRAs for treating obesity and diabetes.

Galvanic vestibular stimulation-induced activation of C1 neurons in medulla oblongata protects against acute lung injury.

Autonomic nerves, including the sympathetic and parasympathetic nerves, control the immune system along with their physiological functions. On the peripheral side, the interaction between the splenic sympathetic nerves and immune cells is important for the anti-inflammatory effects. However, the central mechanism underlying these anti-inflammatory effects remains unclear. C1 neurons respond to stressors and subsequently determine the outflow of the autonomic nervous system. We have previously shown that C1 neurons protect against acute kidney injury and found a signaling connection between peripheral vestibular organs and C1 neurons. Thus, we hypothesized that hypergravity load or galvanic vestibular stimulation (GVS) might protect against acute lung injury. We showed that C1 neurons are histologically and functionally activated by stimulating the peripheral vestibular organs. Protection against acute lung injury that was induced by a 2 G load disappeared due to vestibular lesions or the deletion of C1 neurons. This GVS-induced protective effect was also eliminated by the deletion of the C1 neurons. Furthermore, GVS increased splenic sympathetic nerve activity in conscious mice, and splenic sympathetic denervation abolished the GVS-induced protection against acute lung injury. Therefore, the activated pathway between C1 neurons and splenic sympathetic nerves is indispensable for GVS-induced protection against acute lung injury.

Hypergravity load-induced hyperglycemia occurs due to hypothermia and increased plasma corticosterone level in mice.

Hypothermia has been observed during hypergravity load in mice and rats. This response is beneficial for maintaining blood glucose level, although food intake decreases. However, saving glucose is not enough to maintain blood glucose level during hypergravity load. In this study, we examined the contribution of humoral factors related to glycolysis in maintaining blood glucose level in a 2 G environment. Increased plasma corticosterone levels were observed in mice with intact peripheral vestibular organs, but not in mice with vestibular lesions. Plasma glucagon levels did not change, and decrease in plasma adrenaline levels was observed in mice with intact peripheral vestibular organs. Accordingly, it is possible that increase in plasma corticosterone level and hypothermia contribute to prevent hypoglycemia in a 2 G environment.

Dietary Gamma-Aminobutyric Acid (GABA) Induces Satiation by Enhancing the Postprandial Activation of Vagal Afferent Nerves.

Gamma-aminobutyric acid (GABA) is present in the mammalian brain as the main inhibitory neurotransmitter and in foods. It is widely used as a supplement that regulates brain function through stress-reducing and sleep-enhancing effects. However, its underlying mechanisms remain poorly understood, as it is reportedly unable to cross the blood-brain barrier. Here, we explored whether a single peroral administration of GABA affects feeding behavior as an evaluation of brain function and the involvement of vagal afferent nerves. Peroral GABA at 20 and 200 mg/kg immediately before refeeding suppressed short-term food intake without aversive behaviors in mice. However, GABA administration 30 min before refeeding demonstrated no effects. A rise in circulating GABA concentrations by the peroral administration of 200 mg/kg GABA was similar to that by the intraperitoneal injection of 20 mg/kg GABA, which did not alter feeding. The feeding suppression by peroral GABA was blunted by the denervation of vagal afferents. Unexpectedly, peroral GABA alone did not alter vagal afferent activities histologically. The coadministration of a liquid diet and GABA potentiated the postprandial activation of vagal afferents, thereby enhancing postprandial satiation. In conclusion, dietary GABA activates vagal afferents in collaboration with meals or meal-evoked factors and regulates brain function including feeding behavior.

Gastrointestinal Distension by Pectin-Containing Carbonated Solution Suppresses Food Intake and Enhances Glucose Tolerance via GLP-1 Secretion and Vagal Afferent Activation.

Diet-induced gastrointestinal distension is known to evoke satiation and suppress postprandial hyperglycemia; however, the underlying mechanisms remain poorly understood. This study explored how gastrointestinal distension regulates energy homeostasis by using inflating stomach formulation (ISF), the carbonated solution containing pectin that forms stable gel bubbles under acidic condition in the stomach. Here we show that, in mice, oral administration of ISF induced distension of stomach and proximal intestine temporarily, stimulated intestinal glucagon-like peptide-1 (GLP-1) secretion, and activated vagal afferents and brainstem. ISF suppressed food intake and improved glucose tolerance via enhancing insulin sensitivity. The anorexigenic effect was partially inhibited, and the beneficial glycemic effect was blunted by pharmacological GLP-1 receptor blockade and chemical denervation of capsaicin-sensitive sensory nerves. In HFD-fed obese mice showing arrhythmic feeding and obesity, subchronic ISF treatment at the light period (LP) onset for 10 days attenuated LP hyperphagia and visceral fat accumulation. These results demonstrate that gastrointestinal distension by ISF stimulates GLP-1 secretion and the vagal afferent signaling to the brain, thereby regulating feeding behavior and glucose tolerance. Furthermore, subchronic ISF treatment ameliorates HFD-induced visceral obesity. We propose the diet that induces gastrointestinal distension as a novel treatment of hyperphagic obesity and diabetes.