Search

Objective The ventromedial nucleus of the hypothalamus (VMH) is a critical component of the forebrain pathways that regulate energy homeostasis. It also plays an important role in the metabolic response to fasting. However, the mechanisms contributing to these physiological processes remain elusive. Autophagy is an evolutionarily conserved mechanism that maintains cellular homeostasis by turning over cellular components and providing nutrients to the cells during starvation. Here, we investigated the importance of the autophagy-related gene Atg7 in Sf1-expressing neurons of the VMH in control and fasted conditions. Methods We generated Sf1-Cre; Atg7loxP/loxP mice and examined their metabolic and cellular response to fasting. Results Fasting induces autophagy in the VMH, and mice lacking Atg7 in Sf1-expressing neurons display altered leptin sensitivity and impaired energy expenditure regulation in response to fasting. Moreover, loss of Atg7 in Sf1 neurons causes alterations in the central response to fasting. Furthermore, alterations in mitochondria morphology and activity are observed in mutant mice. Conclusion Together, these data show that autophagy is nutritionally regulated in VMH neurons and that VMH autophagy participates in the control of energy homeostasis during fasting., Graphical abstract Image 1, Highlights • Fasting induces autophagy in the ventromedial nucleus of the hypothalamus. • Genetic loss of Atg7 in the VMH impairs metabolic response to fasting. • Mice lacking Atg7 in the VMH display impaired mitochondria morphology and activity.

Objective Hypothalamic glucose sensing (HGS) initiates insulin secretion (IS) via a vagal control, participating in energy homeostasis. This requires mitochondrial reactive oxygen species (mROS) signaling, dependent on mitochondrial fission, as shown by invalidation of the hypothalamic DRP1 protein. Here, our objectives were to determine whether a model with a HGS defect induced by a short, high fat-high sucrose (HFHS) diet in rats affected the fission machinery and mROS signaling within the mediobasal hypothalamus (MBH). Methods Rats fed a HFHS diet for 3 weeks were compared with animals fed a normal chow. Both in vitro (calcium imaging) and in vivo (vagal nerve activity recordings) experiments to measure the electrical activity of isolated MBH gluco-sensitive neurons in response to increased glucose level were performed. In parallel, insulin secretion to a direct glucose stimulus in isolated islets vs. insulin secretion resulting from brain glucose stimulation was evaluated. Intra-carotid glucose load-induced hypothalamic DRP1 translocation to mitochondria and mROS (H2O2) production were assessed in both groups. Finally, compound C was intracerebroventricularly injected to block the proposed AMPK-inhibited DRP1 translocation in the MBH to reverse the phenotype of HFHS fed animals. Results Rats fed a HFHS diet displayed a decreased HGS-induced IS. Responses of MBH neurons to glucose exhibited an alteration of their electrical activity, whereas glucose-induced insulin secretion in isolated islets was not affected. These MBH defects correlated with a decreased ROS signaling and glucose-induced translocation of the fission protein DRP1, as the vagal activity was altered. AMPK-induced inhibition of DRP1 translocation increased in this model, but its reversal through the injection of the compound C, an AMPK inhibitor, failed to restore HGS-induced IS. Conclusions A hypothalamic alteration of DRP1-induced fission and mROS signaling in response to glucose was observed in HGS-induced IS of rats exposed to a 3 week HFHS diet. Early hypothalamic modifications of the neuronal activity could participate in a primary defect of the control of IS and ultimately, the development of diabetes., Graphical abstract Image 1, Highlights • Only three weeks of HFHS diet consumption impairs hypothalamic glucose sensing. • HFHS consumption alters central glucose-induced vagal control of insulin secretion. • Glucose-induced ROS production and mitochondrial fission are decreased in HFHS rats. • Impaired translocation of DRP1in HFHS rats does not involve its phosphorylation.

International audience; During the last 20 years, studies have revealed the important role of the central nervous system (CNS) in the regulation of homeostatic mechanisms, including food intake, energy expenditure, and glucose, lipid and protein homeostasis. Brain regions involved in the regulation of energy balance, such as the arcuate (ARC), the ventromedial nuclei of the hypothalamus (VMN), and the hindbrain, have the ability to monitor the amount of available fuel in the body, to modulate energy intake and expenditure, and to modify peripheral tissue/organ function via alteration of neuronal firing. For that, they must be informed about the level of nutrients. Within specific brain sites, neuronal populations have been described as able to sense all types of nutrients, enabling proper peripheral tissue adaptations to the fluctuating nutrient environment. Therefore, when glucose or fatty acids rise in the blood because of food consumption, specific brain circuits promote cessation of feeding (satiety), insulin secretion, and glucose use by peripheral tissues while inhibiting hepatic glucose production. When the level of glucose decreases between meals, however, another set of neurons is activated to promote hunger and appropriate changes in peripheral glucose and lipid metabolisms.

Glucose, fructose, and sucrose are important carbohydrates in Western diets with particular sweetness intensity and metabolisms. No study has compared their cerebral detection and their taste perception. Gustatory evoked potentials (GEPs), taste detection thresholds, intensity perception, and pleasantness were compared in response to glucose, fructose, and sucrose solutions at similar sweetness intensities and at identical molar concentrations. Twenty-three healthy subjects were randomly stimulated with 3 solutions of similar sweetness intensity (0.75 M of glucose, 0.47 M of fructose and 0.29 M of sucrose – sit. A), and with an identical molar concentration (0.29 M – sit. B). GEPs were recorded at gustatory cortex areas. Intensity perception and hedonic values of each solution were evaluated as were gustatory thresholds of the solutions. No significant difference was observed concerning the GEP characteristics of the solutions according to their sweetness intensities (sit. A) or their molar concentration (sit. B). In sit. A, the 3 solutions were perceived to have similar intensities and induced similar hedonic sensations. In sit. B, the glucose solution was perceived to be less intense and pleasant than the fructose and the sucrose solutions (P < 0.001) and the fructose solution was perceived to be less intense and pleasant than the sucrose (P < 0.001). Since GEP recordings were similar for glucose, fructose, and sucrose solutions whatever the concentrations, activation of same taste receptor induces similar cortical activation, even when the solutions were perceived differently. Sweet taste perception seems to be encoded by a complex chemical cerebral neuronal network.

International audience; Epidemiological studies indicate that insulin resistance (IR), a hallmark of type 2 diabetes, is associated with an increased risk of major depression. Here, we demonstrated that male mice fed a high-fat diet (HFD) exhibited peripheral metabolic impairments reminiscent of IR accompanied by elevated circulating levels of branched-chain amino acids (BCAAs), whereas both parameters were normalized by chronic treatment with metformin (Met). Given the role of BCAAs in the regulation of tryptophan influx into the brain, we then explored the activity of the serotonin (5-HT) system. Our results indicated that HFD-fed mice displayed impairment in the electrical activity of dorsal raphe 5-HT neurons, attenuated hippocampal extracellular 5-HT concentrations and anxiety, one of the most visible and early symptoms of depression. On the contrary, Met stimulated 5-HT neurons excitability and 5-HT neurotransmission while hindering HFD-induced anxiety. Met also promoted antidepressant-like activities as observed with fluoxetine. In light of these data, we designed a modified HFD in which BCAA dietary supply was reduced by half. Deficiency in BCAAs failed to reverse HFD-induced metabolic impairments while producing antidepressant-like activity and enhancing the behavioral response to fluoxetine. Our results suggest that Met may act by decreasing circulating BCAAs levels to favor serotonergic neurotransmission in the hippocampus and promote antidepressant-like effects in mice fed an HFD. These findings also lead us to envision that a diet poor in BCAAs, provided either alone or as add-on therapy to conventional antidepressant drugs, could help to relieve depressive symptoms in patients with metabolic comorbidities. SIGNIFICANCE STATEMENT Insulin resistance in humans is associated with increased risk of anxiodepressive disorders. Such a relationship has been also found in rodents fed a high-fat diet (HFD). To determine whether insulin-sensitizing strategies induce anxiolytic- and/or antidepressant-like activities and to investigate the underlying mechanisms, we tested the effects of metformin, an oral antidiabetic drug, in mice fed an HFD. Metformin reduced levels of circulating branched-chain amino acids, which regulate tryptophan uptake within the brain. Moreover, metformin increased hippocampal serotonergic neurotransmission while promoting anxiolytic- and antidepressant-like effects. Moreover, a diet poor in these amino acids produced similar beneficial behavioral property. Collectively, these results suggest that metformin could be used as add-on therapy to a conventional antidepressant for the comorbidity between metabolic and mental disorders.

International audience; AIMS: GLP-1 analogues decrease food intake and have great promise for the fight against obesity. Little is known about their effects on food hedonic sensations and taste perception in poor controlled patients with type 2 diabetes (T2D). MATERIALS AND METHODS: Eighteen T2D patients with BMI >/=25kg/m(2) and poor controlled glycemia were studied before and after 3 months of treatment with Liraglutide. Detection thresholds for salty, sweet and bitter tastes, optimal preferences, olfactory liking, wanting and recalled liking for several food items were assessed. Subjects also answered questionnaires to measure their attitudes to food. RESULTS: T2D patients had a significant decrease in bodyweight and HbA1c after treatment with Liraglutide. Liraglutide improved gustative detection threshold of sweet flavors, and decreased wanting for sweet foods and recalled liking for fatty foods. It also led to a decrease in feelings of hunger. CONCLUSIONS: Liraglutide increases sensitivity to sweet tastes and decreases pleasure responses for fatty foods in poor controlled T2D patients, and is of particular interest in the understanding of the mechanisms of weight loss. CLINICAL TRIAL: NCT02674893.

Resume Notre rythme de vie actuel a entraine une diminution progressive du temps alloue au sommeil. En France, une personne sur 3 dormirait moins de 7 heures par nuit. Dans le meme temps, le nombre de patients souffrant d’obesite a augmente. De nombreuses etudes epidemiologiques soulignent le lien entre la faible duree du temps de sommeil et la prise de poids. En parallele, les etudes experimentales ont observe que la privation de sommeil modifiait le comportement alimentaire en augmentant la sensation de faim et la prise alimentaire. Le cycle nycthemeral induit par l’alternance lumiere–obscurite a une influence majeure sur le sommeil mais aussi sur le comportement alimentaire : la lumiere agit sur les noyaux suprachiasmatiques, puis secondairement sur les noyaux preoptiques et les noyaux lateraux de l’hypothalamus d’ou l’augmentation des orexines. Plusieurs theories tentent d’expliquer l’augmentation de la prise alimentaire : la premiere, phylogenetique, serait liee aux variations de la duree du sommeil au cours des saisons ; la deuxieme concernerait l’adaptation anticipatoire face a l’eveil ; la derniere serait liee a une modification du controle hedonique de la prise alimentaire. De nombreuses pathologies alterent la relation physiologique sommeil–comportement alimentaire, comme par exemple le syndrome d’apnee du sommeil. Il est donc necessaire de mieux comprendre cette relation pour ameliorer la prise en charge des personnes obeses et pour prevenir le developpement du surpoids par le respect d’un rythme du sommeil adapte a l’enfant.

BACKGROUND AND PURPOSE The link between type 2 diabetes mellitus (T2DM) and depression is bidirectional. However, the possibility that metabolic disorders may elicit anxiogenic-like/depressive-like symptoms or alter the efficacy of antidepressant drugs remains poorly documented. This study explored the influence of T2DM on emotionality and proposed a therapeutic strategy that might be used in depressed diabetic patients. EXPERIMENTAL APPROACH Mice were fed a high-fat diet (HFD) and subjected to a full comprehensive metabolic and behavioural analysis to establish correlations between metabolic and psychiatric disorders. In vivo intra-hippocampal microdialysis was also applied to propose a mechanism underpinning the phenotype of mice fed the HFD. Finally, we tested whether chronic administration of the selective 5-HT reuptake inhibitor escitalopram or HFD withdrawal could reverse HFD-induced metabolic and behavioural anomalies. KEY RESULTS The increased body weight, hyperglycaemia and impaired glucose tolerance in response to HFD were correlated with anxiogenic-like/depressive-like symptoms. Moreover, this phenotype was associated with decreased extracellular 5-HT levels in the hippocampus which may result from increased sensitivity of the dorsal raphe 5-HT1A autoreceptor. Interestingly, the beneficial effect of prolonged administration of escitalopram was abolished in HFD-fed mice. On the contrary, HFD withdrawal completely reversed metabolic impairments and positively changed symptoms of anxiety, although some behavioural anomalies persisted. CONCLUSIONS AND IMPLICATIONS Our data provide clear-cut evidence that both pathologies are finely correlated and associated with impaired 5-HT mediated neurotransmission in the hippocampus. Further experiments are warranted to define the most adequate strategy for the treatment of such co-morbidity.

Aims: We have previously demonstrated that central apelin is implicated in the control of peripheral glycemia, and its action depends on nutritional (fast versus fed) and physiological (normal versus diabetic) states. An intracerebroventricular (icv) injection of a high dose of apelin, similar to that observed in obese/diabetic mice, increase fasted glycemia, suggesting (i) that apelin contributes to the establishment of a diabetic state, and (ii) the existence of a hypothalamic to liver axis. Using pharmacological, genetic, and nutritional approaches, we aim at unraveling this system of regulation by identifying the hypothalamic molecular actors that trigger the apelin effect on liver glucose metabolism and glycemia. Results: We show that icv apelin injection stimulates liver glycogenolysis and gluconeogenesis via an over-activation of the sympathetic nervous system (SNS), leading to fasted hyperglycemia. The effect of central apelin on liver function is dependent of an increased production of hypothalamic reactive oxygen species (ROS). These data are strengthened by experiments using lentiviral vector-mediated over-expression of apelin in hypothalamus of mice that present over-activation of SNS associated to an increase in hepatic glucose production. Finally, we report that mice fed a high-fat diet present major alterations of hypothalamic apelin/ROS signaling, leading to activation of glycogenolysis. Innovation/Conclusion: These data bring compelling evidence that hypothalamic apelin is one master switch that participates in the onset of diabetes by directly acting on liver function. Our data support the idea that hypothalamic apelin is a new potential therapeutic target to treat diabetes. Antioxid. Redox Signal. 20, 557–573.

Supplementary Information accompanies the paper on the Journal of Cerebral Blood Flow & Metabolism website; Hypothalamic glucose detection participates in maintaining glycemic balance, food intake, and thermogenesis. Although hypothalamic neurons are the executive cells involved in these responses, there is increasing evidence that astrocytes participate in glucose sensing (GS); however, it is unknown whether astroglial networking is required for glucose sensitivity. Astroglial connexins 30 and 43 (Cx30 and Cx43) form hexameric channels, which are apposed in gap junctions, allowing for the intercellular transfer of small molecules such as glucose throughout the astroglial networks. Here, we hypothesized that hypothalamic glucose sensitivity requires these connexins. First, we showed that both Cxs are enriched in the rat hypothalamus, with highly concentrated Cx43 expression around blood vessels of the mediobasal hypothalamus (MBH). Both fasting and high glycemic levels rapidly altered the protein levels of MBH astroglial connexins, suggesting cross talk within the MBH between glycemic status and the connexins' ability to dispatch glucose. Finally, the inhibition of MBH Cx43 (by transient RNA interference) attenuated hypothalamic glucose sensitivity in rats, which was demonstrated by a pronounced decreased insulin secretion in response to a brain glucose challenge. These results illustrate that astroglial connexins contribute to hypothalamic GS.

International audience; Hormones such as leptin and ghrelin can rapidly rewire hypothalamic feeding circuits when injected into rodent brains. These experimental manipulations suggest that the hypothalamus might reorganize continually in adulthood to integrate the metabolic status of the whole body. In this study, we examined whether hypothalamic plasticity occurs in naive animals according to their nutritional conditions. For this purpose, we fed mice with a short-term high-fat diet (HFD) and assessed brain remodeling through its molecular and functional signature. We found that HFD for 3 d rewired the hypothalamic arcuate nucleus, increasing the anorexigenic tone due to activated pro-opiomelanocortin (POMC) neurons. We identified the polysialic acid molecule (PSA) as a mediator of the diet-induced rewiring of arcuate POMC. Moreover, local pharmacological inhibition and genetic disruption of the PSA signaling limits the behavioral and metabolic adaptation to HFD, as treated mice failed to normalize energy intake and showed increased body weight gain after the HFD challenge. Altogether, these findings reveal the existence of physiological hypothalamic rewiring involved in the homeostatic response to dietary fat. Furthermore, defects in the hypothalamic plasticity-driven adaptive response to HFD are obesogenic and could be involved in the development of metabolic diseases.

Besides adipocytes, specialized in lipid handling and involved in energy balance regulation, white adipose tissue (WAT) is mainly composed of other cell types among which lymphocytes represent a non-negligible proportion. Different types of lymphocytes (B, alphabetaT, gammadeltaT, NK and NKT) have been detected in WAT of rodents or humans, and vary in their relative proportion according to the fat pad anatomical location. The lymphocytes found in intra-abdominal, visceral fat pads seem representative of innate immunity, while those present in subcutaneous fat depots are part of adaptive immunity, at least in mice. Both the number and the activity of the different lymphocyte classes, except B lymphocytes, are modified in obesity. Several of these modifications in the relative proportions of the lymphocyte classes depend on the degree of obesity, or on leptin concentration, or even fat depot anatomical location. Recent studies suggest that alterations of lymphocyte number and composition precede the macrophage increase and the enhanced inflammatory state of WAT found in obesity. Lymphocytes express receptors to adipokines while several proinflammatory chemokines are produced in WAT, rendering intricate crosstalk between fat and immune cells. However, the evidences and controversies available so far are in favour of an involvement of lymphocytes in the control of the number of other cells in WAT, either adipocytes or immune cells and of their secretory and metabolic activities. Therefore, immunotherapy deserves to be considered as a promising approach to treat the endocrino-metabolic disorders associated to excessive fat mass development.

OBJECTIVE Recent data demonstrated that glucose sensing in different tissues is initiated by an intracellular redox signaling pathway in physiological conditions. However, the relevance of such a mechanism in metabolic disease is not known. The aim of the present study was to determine whether brain glucose hypersensitivity present in obese Zücker rats is related to an alteration in redox signaling. RESEARCH DESIGN AND METHODS Brain glucose sensing alteration was investigated in vivo through the evaluation of electrical activity in arcuate nucleus, changes in reactive oxygen species levels, and hypothalamic glucose-induced insulin secretion. In basal conditions, modifications of redox state and mitochondrial functions were assessed through oxidized glutathione, glutathione peroxidase, manganese superoxide dismutase, aconitase activities, and mitochondrial respiration. RESULTS Hypothalamic hypersensitivity to glucose was characterized by enhanced electrical activity of the arcuate nucleus and increased insulin secretion at a low glucose concentration, which does not produce such an effect in normal rats. It was associated with 1) increased reactive oxygen species levels in response to this low glucose load, 2) constitutive oxidized environment coupled with lower antioxidant enzyme activity at both the cellular and mitochondrial level, and 3) overexpression of several mitochondrial subunits of the respiratory chain coupled with a global dysfunction in mitochondrial activity. Moreover, pharmacological restoration of the glutathione hypothalamic redox state by reduced glutathione infusion in the third ventricle fully reversed the cerebral hypersensitivity to glucose. CONCLUSIONS The data demonstrated that obese Zücker rats' impaired hypothalamic regulation in terms of glucose sensing is linked to an abnormal redox signaling, which originates from mitochondria dysfunction.

OBJECTIVE Insulin plays an important role in the hypothalamic control of energy balance, especially by reducing food intake. Emerging data point to a pivotal role of reactive oxygen species (ROS) in energy homeostasis regulation, but their involvement in the anorexigenic effect of insulin is unknown. Furthermore, ROS signal derived from NADPH oxidase activation is required for physiological insulin effects in peripheral cells. In this study, we investigated the involvement of hypothalamic ROS and NADPH oxidase in the feeding behavior regulation by insulin. RESEARCH DESIGN AND METHODS We first measured hypothalamic ROS levels and food intake after acute intracerebroventricular injection of insulin. Second, effect of pretreatment with a ROS scavenger or an NADPH oxidase inhibitor was evaluated. Third, we examined the consequences of two nutritional conditions of central insulin unresponsiveness (fasting or short-term high-fat diet) on the ability of insulin to modify ROS level and food intake. RESULTS In normal chow-fed mice, insulin inhibited food intake. At the same dose, insulin rapidly and transiently increased hypothalamic ROS levels by 36%. The pharmacological suppression of this insulin-stimulated ROS elevation, either by antioxidant or by an NADPH oxidase inhibitor, abolished the anorexigenic effect of insulin. Finally, in fasted and short-term high-fat diet–fed mice, insulin did not promote elevation of ROS level and food intake inhibition, likely because of an increase in hypothalamic diet-induced antioxidant defense systems. CONCLUSIONS A hypothalamic ROS increase through NADPH oxidase is required for the anorexigenic effect of insulin.

OBJECTIVE—Rosiglitazone displays powerful antidiabetes benefits but is associated with increased body weight and adipogenesis. Keeping in mind the concept of selective peroxisome proliferator–activated receptor (PPAR)γ modulator, the aim of this study was to characterize the properties of a new PPARγ ligand, S 26948, with special attention in body-weight gain. RESEARCH DESIGN AND METHODS—We used transient transfection and binding assays to characterized the binding characteristics of S 26948 and GST pull-down experiments to investigate its pattern of coactivator recruitment compared with rosiglitazone. We also assessed its adipogenic capacity in vitro using the 3T3-F442A cell line and its in vivo effects in ob/ob mice (for antidiabetes and antiobesity properties), as well as the homozygous human apolipoprotein E2 knockin mice (E2-KI) (for antiatherogenic capacity). RESULTS—S 26948 displayed pharmacological features of a high selective ligand for PPARγ with low potency in promoting adipocyte differentiation. It also displayed a different coactivator recruitment profile compared with rosiglitazone, being unable to recruit DRIP205 or PPARγ coactivator-1α. In vivo experiments showed that S 26948 was as efficient in ameliorating glucose and lipid homeostasis as rosiglitazone, but it did not increase body and white adipose tissue weights and improved lipid oxidation in liver. In addition, S 26948 represented one of the few molecules of the PPARγ ligand class able to decrease atherosclerotic lesions. CONCLUSIONS—These findings establish S 26948 as a selective PPARγ ligand with distinctive coactivator recruitment and gene expression profile, reduced adipogenic effect, and improved biological responses in vivo.

Four types of responses to glucose changes have been described in the arcuate nucleus (ARC): excitation or inhibition by low glucose concentrations 5 mmol/l (high glucose–excited and –inhibited neurons). However, the ability of the same ARC neuron to detect low and high glucose concentrations has never been investigated. Moreover, the mechanism involved in mediating glucose sensitivity in glucose-inhibited neurons and the neurotransmitter identity (neuropeptide Y [NPY] or pro-opio melanocortin [POMC]) of glucosensing neurons has remained controversial. Using patch-clamp recordings on acute mouse brain slices, successive extracellular glucose changes greater than and less than 5 mmol/l show that glucose-excited, high glucose–excited, glucose-inhibited, and high glucose–inhibited neurons are different glucosensing cell subpopulations. Glucose-inhibited neurons directly detect decreased glucose via closure of a chloride channel. Using transgenic NPY–green fluorescent protein (GFP) and POMC-GFP mice, we show that 40% of NPY neurons are glucose-inhibited neurons. In contrast, 5 mmol/l. In vivo results confirm the lack of glucose sensitivity of POMC neurons. Taken together, hypo- and hyperglycemia are detected by distinct populations of glucosensing neurons, and POMC and NPY neurons are not solely responsible for ARC glucosensing.

Adiponectin (ApN) is an adipokine whose expression and plasma levels are inversely related to obesity and insulin-resistant states. Chronic repercussions of ApN treatment or overexpression on adiposity and body weight are still controversial. Here, we generated a transgenic (Tg) mouse model allowing persistent and moderate overexpression of native full-length ApN targeted to white adipose tissue. Adipose mass and adipocyte size of Tg mice were reduced despite preserved calorie intake. This reduction resulted from increased energy expenditure and up-regulation of uncoupling proteins, and from abrogation of the adipocyte differentiation program, as shown by the loss of a key lipogenic enzyme and of adipocyte markers. Adipose mass remodeling favors enhanced insulin sensitivity and improved lipid profile of Tg mice. Alteration of the adipocyte phenotype was likely to result from increased expression of the preadipocyte factor-1 and from down-regulation of the transcription factor, CCAAT/enhancer binding protein-alpha, which orchestrates adipocyte differentiation. We further found that recombinant ApN directly stimulated pre- adipocyte factor-1 mRNA and attenuated CCAAT/enhancer binding protein-alpha expression in cultured 3T3-F442A cells. Conversely, opposite changes in the expression of these genes were observed in white fat of ApN-deficient mice. Thus, besides enhanced energy expenditure, our work shows that impairment of adipocyte differentiation contributes to the anti-adiposity effect of ApN.

The ability for the brain to sense peripheral fuel availability is mainly accomplished within the hypothalamus, which detects ongoing systemic nutrients and adjusts food intake and peripheral metabolism as needed. Here, we hypothesized that mitochondrial reactive oxygen species (ROS) could trigger sensing of nutrients within the hypothalamus. For this purpose, we induced acute hypertriglyceridemia in rats and examined the function of mitochondria in the hypothalamus. Hypertriglyceridemia led to a rapid increase in the mitochondrial respiration in the ventral hypothalamus together with a transient production of ROS. Cerebral inhibition of fatty acids–CoA mitochondrial uptake prevented the hypertriglyceridemia-stimulated ROS production, indicating that ROS derived from mitochondrial metabolism. The hypertriglyceridemia-stimulated ROS production was associated with change in the intracellular redox state without any noxious cytotoxic effects, suggesting that ROS function acutely as signaling molecules. Moreover, cerebral inhibition of hypertriglyceridemia-stimulated ROS production fully abolished the satiety related to the hypertriglyceridemia, suggesting that hypothalamic ROS production was required to restrain food intake during hypertriglyceridemia. Finally, we found that fasting disrupted the hypertriglyceridemia-stimulated ROS production, indicating that the redox mechanism of brain nutrient sensing could be modulated under physiological conditions. Altogether, these findings support the role of mitochondrial ROS as molecular actors implied in brain nutrient sensing.

Objectives:\ud The corticotrophin-releasing factor (CRF)/urocortin system is expressed in the adipose tissue of mammals, but its functional role in this tissue remains unknown.\ud \ud Methods:\ud Pharmacological manipulation of the activity of CRF receptors, CRF1 and CRF2, was performed in 3T3L1 white pre-adipocytes and T37i brown pre-adipocytes during in vitro differentiation. The expression of genes of the CRF/urocortin system and of markers of white and brown adipocytes was evaluated along with mitochondrial biogenesis and cellular oxygen consumption. Metabolic evaluation of corticosterone-deficient or supplemented Crhr1-null (Crhr1−/−) mice and their wild-type controls was performed along with gene expression analysis carried out in white (WAT) and brown (BAT) adipose tissues.\ud \ud Results:\ud Peptides of the CRF/urocortin system and their cognate receptors were expressed in both pre-adipocyte cell lines. In vitro pharmacological studies showed an inhibition of the expression of the CRF2 pathway by the constitutive activity of the CRF1 pathway. Pharmacological activation of CRF2 and, to a lesser extent, inhibition of CRF1 signaling induced molecular and functional changes indicating transdifferentiation of white pre-adipocytes and differentiation of brown pre-adipocytes. Crhr1−/− mice showed increased expression of CRF2 and its agonist Urocortin 2 in adipocytes that was associated to brown conversion of WAT and activation of BAT. Crhr1−/− mice were resistant to diet-induced obesity and glucose intolerance. Restoring physiological circulating corticosterone levels abrogated molecular changes in adipocytes and the favorable phenotype of Crhr1−/− mice.\ud \ud Conclusions:\ud Our findings suggest the importance of the CRF2 pathway in the control of adipocyte plasticity. Increased CRF2 activity in adipocytes induces browning of WAT, differentiation of BAT and is associated with a favorable metabolic phenotype in mice lacking CRF1. Circulating corticosterone represses CRF2 activity in adipocytes and may thus regulate adipocyte physiology through the modulation of the local CRF/urocortin system. Targeting CRF receptor signaling specifically in the adipose tissue may represent a novel approach to tackle obesity.

Brain plays a central role in energy homeostasis continuously integrating numerous peripheral signals such as circulating nutrients, and in particular blood glucose level, a variable that must be highly regulated. Then, the brain orchestrates adaptive responses to modulate food intake and peripheral organs activity in order to achieve the fine tuning of glycemia. More than fifty years ago, the presence of glucose-sensitive neurons was discovered in the hypothalamus, but what makes them specific and identifiable still remains disconnected from their electrophysiological signature. On the other hand, astrocytes represent the major class of macroglial cells and are now recognized to support an increasing number of neuronal functions. One of these functions consists in the regulation of energy homeostasis through neuronal fueling and nutrient sensing. Twenty years ago, we discovered that the glucose transporter GLUT2, the canonical “glucosensor” of the pancreatic beta-cell together with the glucokinase, was also present in astrocytes and participated in hypothalamic glucose sensing. Since then, many studies have identified other actors and emphasized the astroglial participation in this mechanism. Growing evidence suggest that astrocytes form a complex network and have to be considered as spatially coordinated and regulated metabolic units. In this review we aim to provide an updated view of the molecular and respective cellular pathways involved in hypothalamic glucose sensing, and their relevance in physiological and pathological states.

Ancestral lymphoid cells reside in adipose tissues, and their numbers are highly altered in obesity. Leptin, production of which is correlated to fat mass, is strongly involved in the relationships between adipose tissues and immune system. We investigated in epididymal (EPI) and inguinal (ING) fat pads to determine whether 1) lymphocyte phenotypes were correlated to the tissue weight and 2) leptin was involved in such relationships. Immunohistological analyses revealed a tight relationship between the T and NK lymphocytes of the stromal vascular fraction and adipocytes. We identified a significant negative and positive correlation between EPI weight and the percentage of NK and total T cells respectively by cytofluorometric analyses. The NK and ancestral gammadelta T cell contents were directly dependent of leptin since they increased significantly in high-fat (HF) diet mice but not in leptin-deficient (ob/ob) mice as compared to control. By contrast, the alphabeta T cell content seemed independent of leptin because their percentages increased significantly with the EPI weight whatever the type of mice (control, HF, ob/ob). The present study suggests that adipose tissues present, according to their localization, different immunological mechanisms that might be involved in the regulation of adipose cells functions and proliferations.

Using pharmacological tools, a role for opioid receptors in the regulation of food intake has been documented. However, the involvement of specific receptor subtypes remains questionable, and little information is available regarding a role for opioid receptors in energy metabolism. Using adult male mice lacking the μ-opioid receptor (MOR) gene (MOR−/−), we show that the MOR is not essential for the maintenance of normal levels of ad libitum food intake but does modulate the efficiency of energy storage during high-fat diets through the regulation of energy partitioning. When fed a regular diet, MOR−/− mice displayed only subtle alterations in energy homeostasis, suggesting a relative overuse of fat as a fuel source in the fed state. When fed a high-fat diet, MOR−/− mice were resistant to obesity and impaired glucose tolerance, despite having similar energy intake to wild-type mice. This resistance to obesity was associated with a strong induction of the expression of key mitochondrial enzymes involved in fatty acid oxidation within skeletal muscle. This metabolic role of the MOR, which is consistent with the properties of a “thrifty gene,” suggests that the MOR pathway is a potential target for pharmacological intervention in the treatment of obesity associated with the intake of fatty diets.

Although it is well accepted that treatment with nucleoside reverse transcriptase inhibitors (NRTIs) modifies fat metabolism and fat distribution in humans, the mechanisms underlying these modifications are not yet known. The present investigation examines the effects of chronic oral administration of 3'-azido-3'-deoxythymidine (AZT) on the mitochondrial metabolism and the redox status management of rat white adipose tissues originating from two anatomical sites, as well as of the rat liver. Results showed that AZT treatment induced differential effects on the mitochondrial functions depending on the anatomical localisation. Indeed, in inguinal adipose tissue, a significant decrease in the cytochrome c oxidase activity and in the mitochondrial DNA (mtDNA) content was observed, whereas the activity of citrate synthase, a mitochondrial protein exclusively encoded by the nucleus, was not affected. In contrast, no significant change in these parameters could be detected for epididymal tissue and for liver. In parallel, no oxidative stress could be detected after treatment, for both white adipose tissues and for liver, even though treated liver exhibited several modifications in redox management. Taken together, these data demonstrate differential mitochondrial effects of AZT on subcutaneous versus visceral white adipose tissue. Moreover, the decrease in mitochondrial oxidative capacity of inguinal adipocyte consecutive to AZT treatment is not primarily due to an oxidative stress per se, but rather to a depletion of the mtDNA content per cell.

Fibrates and thiazolidinediones are commonly used for the treatment of dyslipidemia and type 2 diabetes, respectively. The aim of this study was to investigate the effects on body weight as well as on glucose and lipid homeostasis of ligands for PPARalpha and PPARgamma, Fenofibrate and Rosiglitazone, alone or in association.Ob/ob mice were divided into four groups: control, and mice daily injected (intraperitoneally), either with 10 mg/kg Rosiglitazone, 100 mg/kg Fenofibrate or both molecules. Body weight and food intake were monitored daily. After 13 days of treatment, mice were killed, and blood samples were collected for posterior metabolite quantification. The liver and adipose tissues were dissected and weighed.Body weight was significantly reduced or increased by Fenofibrate and Rosiglitazone, respectively. The effect of Rosiglitazone was prevented by coadministration of Fenofibrate. This was accompanied by a normalization of the daily food efficiency. Compared to those treated with Rosiglitazone, animals treated with Fenofibrate alone or in combination presented a decreased white adipose tissue mass. Fenofibrate or Rosiglitazone alone significantly reduced the levels of plasma lipid parameters. Surprisingly, Fenofibrate also decreased blood glucose levels in ob/ob mice, despite having no effect on insulin levels. By contrast, both glucose and insulin levels were decreased by Rosiglitazone treatment. Coadministration of both drugs improved all parameters as with Rosiglitazone. Fenofibrate restored almost normal hepatocyte morphology and significantly reduced the triglyceride content of the liver. This was accompanied by an increase in fatty acid oxidation in the liver in all groups receiving Fenofibrate.These biological effects suggest that combined therapy with a PPARalpha and a PPARgamma ligand is more effective in ameliorating, specifically, lipid homeostasis than in activating any of this receptor separately. Furthermore, Fenofibrate prevents one of the most undesirable effects of Rosiglitazone, namely increased adiposity and body weight gain.

Reciprocal inhibition between ankle flexors and extensors has been the subject of numerous studies in Man. They have demonstrated that this reciprocal inhibition is in all likelihood caused by a disynaptic pathway at least partly fed by Ia afferents. It is thus generally agreed that this reciprocally organized inhibition between ankle flexors and extensors in Man is similar to the reciprocal Ia inhibition described in the cat. This conclusion has, however, been challenged, when Jankowska and McCrea described in the cat a non-reciprocal group I inhibition involving interneurones co-excited by Ia and Ib afferents and mediating inhibition to both antagonistic and non-antagonistic motoneurones. The only way to distinguish between reciprocal Ia inhibition and non-reciprocal group I inhibition is to test if the inhibition is blocked by recurrent inhibition, since only Ia interneurones are inhibited by recurrent inhibition. In the present study, reciprocal inhibition from soleus to tibialis anterior was thus investigated following activation of soleus-coupled Renshaw cells in normal human subjects. It was found that reciprocal inhibition induced in tibialis anterior motoneurones by the activation of soleus group I afferents is deeply depressed by activation of soleus-coupled Renshaw cells. This finding provides the missing data to identify disynaptic inhibition between antagonistic ankle muscles as a reciprocal Ia inhibition.

Melatonin is a neurohormone synthesized in the pineal gland during the dark period in all species, including humans. The diversity and differences in melatonin receptor distribution in the brain and extracerebral organs suggest multiple functional roles for melatonin. Administration of melatonin agonists reduces neophobia and treatment with a melatonin antagonist during the dark period reverses the anxiolytic-like effect of endogenous melatonin. Chronic treatment with agonists prevents various perturbations induced by chronic mild stress. Melatonin in vivo directly constricts cerebral arterioles in rats and decreases the lower limit of cerebral blood flow autoregulation, suggesting that melatonin may diminish the risk of hypoperfusion-induced cerebral ischemia. At the extracerebral level, melatonin regulates intestinal motility in rats. The intestinal postprandial motor response is shorter in the dark phase than in the light phase and this reduction is reversed in animals pretreated with a melatonin antagonist. Moreover, melatonin reduces the duration of cholecystokinin excitomotor effect. Endogenous melatonin may modulate intestinal motility to coordinate intestinal functions such as digestion and transit and control the metabolism of the animal. An adipocyte melatonin binding site may also participate in this control. Melatonin is involved in a wide range of physiological functions. The question remains as to whether evolution, adaptation and diurnal life have modified the physiological role of melatonin in humans. Moreover, the functional role of each of the receptor subtypes has to be characterized to design selective ligands to treat specific diseases.

Preadipocytes are present throughout adult life in adipose tissues and can proliferate and differentiate into mature adipocytes according to the energy balance. An increasing number of reports demonstrate that cells from adipose lineages (preadipocytes and adipocytes) and macrophages share numerous functional or antigenic properties. No large scale comparison reflecting the phenotype complexity has been performed between these different cell types until now. We used profiling analysis to define the common features shared by preadipocyte, adipocyte, and macrophage populations. Our analysis showed that the preadipocyte profile is surprisingly closer to the macrophage than to the adipocyte profile. From these data, we hypothesized that in a macrophage environment preadipocytes could effectively be converted into macrophages. We injected labeled stroma-vascular cells isolated from mouse white adipose tissue or 3T3-L1 preadipocyte cell line into the peritoneal cavity of nude mice and investigated changes in their phenotype. Preadipocytes rapidly and massively acquired high phagocytic activity and index. 60-70% of preadipocytes also expressed five macrophage-specific antigens: F4/80, Mac-1, CD80, CD86, and CD45. These values were similar to those observed for peritoneal macrophages. In vitro experiments showed that cell-to-cell contact between preadipocytes and peritoneal macrophages partially induced this preadipocyte phenotype conversion. Overall, these results suggest that preadipocyte and macrophage phenotypes are very similar and that preadipocytes have the potential to be very efficiently and rapidly converted into macrophages. This work emphasizes the great cellular plasticity of adipose precursors and reinforces the link between adipose tissue and innate immunity processes.

The hypothalamus participates in the regulation of carbohydrate metabolism involving a feedback loop between the brain and the periphery in which glucose-sensitive hypothalamic areas appear to be involved. We have previously shown that a glucose injection (9 mg/kg) in the carotid artery toward the brain, in an amount that did not modify glycaemia, caused a rapid and transient increase in plasma insulin concentrations. To determine whether central insulin could influence this response, we investigated the change in central glucose-induced insulin secretion in intracerebroventricular (i.c.v) insulin-injected rats and in hyperinsulinaemic obese Zucker rats. Central glucose-induced insulin secretion was increased by 50% in i.c.v. insulin-injected rats compared to control rats. When a similar test was performed at a lower dose of glucose (3 mg/kg), a significant insulin secretion was observed only in rats submitted to a prior central insulin injection. These data indicate an increase in the brain response to glucose after insulin treatment. Using an identical lower glucose dose, we also demonstrated an enhanced brain glucose sensitivity in hyperinsulinaemic and insulin-resistant obese Zucker rats. Together, these results indicate that acute i.c.v. insulin or pathological hyperinsulinaemic state (i.e. obese Zucker rat) modulates the nervous control of insulin secretion by increasing the brain response to glucose.

We investigated here whether non-esterified fatty acids (NEFA) influence insulin secretion and action through a direct effect on central nervous system sites involved in the control of glucose homeostasis. Normal Wistar rats received a 48-h intracerebroventricular infusion of either a 10% triglyceride (Intralipid, IL)/heparin emulsion (IL/h) or saline/heparin solution (control). At 48 h, insulin secretion as measured by an intravenous glucose tolerance test, was more elevated in IL/h than in control rats. Pancreatic noradrenaline turnover was decreased by 57% in IL/h rats, suggesting low pancreatic sympathetic output that could account partly for the elevated insulin secretion. The time course of glycaemia was similar in both groups, suggesting insulin resistance. Euglycaemic-hyperinsulinaemic clamps were imposed to assess peripheral and hepatic insulin sensitivity. At each insulin concentration glucose utilization was increased to a similar extent in both groups, whereas hepatic glucose production decreased much less in IL/h than in control rats. Hepatic insulin insensitivity could be related partly to activation of the hypothalamic-pituitary-adrenocortical axis, since plasma corticosterone concentration was significantly increased in IL/h rats compared with controls. Our data indicate that lipids may alter both insulin secretion and hepatic sensitivity to insulin through their effect on central nervous system.

We previously showed that a 48-h intravenous lipid infusion in rats induces pancreatic β-cell hypersensitivity to catecholamines. Our aim was to study the lipid-related changes that may account for such hypersensitivity in pancreatic islets. We show here that a 48-h increase in plasma FFA alters the binding characteristics of β-cell α2 adrenoceptors in rats. Lipid infusion decreases pancreatic norepinephrine (NE) turnover rate by 28%, reflecting a reduction of pancreatic NE stores. Following lipid infusion, the density of α2 adrenoceptor binding sites is significantly lower and receptor affinity higher, both in islet homogenates (by three- and fivefold, respectively) and isolated whole β-cells (by two- and sixfold, respectively). These changes correlate with the elevated insulin response to glucose found in lipid-infused rats. We also found a modification of islet phospholipid content, particularly in phosphoethanolamine species containing infused FA such as palmitate, oleate, stearate, and linoleate. This may account for the modifications in receptor affinity. These results suggest that hyperlipidemia-associated pathologies such as diabetes and obesity not only may result from alterations of metabolic pathways but also may be a consequence of early modifications in nervous firing rates and signal transduction pathways.

Introduction et but de l’etude La perception sensorielle gustative et les preferences alimentaires pourraient etre modifiees chez les sujets obeses, encourageant alors une prise alimentaire plus calorique (sucree et grasse). Nous avons emis l’hypothese qu’une difference de traitement cortical de l’information sensorielle gustative entre les sujets sains et les sujets obeses pourrait etre impliquee dans la modification des choix alimentaires. Ces differences de traitement cortical de l’information sensorielle gustative, traduites par des modifications des potentiels evoques gustatifs, pourraient etre liees aux variations hormonales de ghreline et leptine, ainsi qu’a celles de l’insuline et de la dopamine. Lors d’une etude preliminaire, notre equipe a observe un allongement de la latence des potentiels evoques gustatifs, technique d’exploration non invasive et reproductible de la voie sensorielle gustative, chez des sujets jeunes sains, apres un repas standardise. Les objectifs de l’etude etaient de comparer, chez des sujets obeses et normoponderaux, les potentiels evoques gustatifs enregistres avant et apres un repas standardise, puis d’etudier les correlations entre les mesures electro-physiologiques et les taux sanguins de ghreline, leptine, insuline et dopamine plasmatiques. Materiel et methodes Tous les sujets ont participe a deux sessions d’evaluation sensorielle au Centre des sciences du gout, selon un ordre randomise. Lors de chaque session espacee de 2–3 jours, les sujets avaient une seance d’enregistrement de potentiels evoques gustatifs (par electrodes de scalp) en fin de matinee et une deuxieme en debut d’apres-midi, les deux seances etant precedees d’une prise de sang pour dosages de leptine, ghreline, insuline et dopamine plasmatiques. Lors d’une seance, le sujet beneficiait d’un repas standardise equilibre (sans sucre rapide), alors que dans l’autre, le sujet etait laisse a jeun. Tous les patients ont beneficie d’une evaluation sensorielle et nutritionnelle complete. Resultats Six sujets obeses (âges de 52,7 ± 6,5 ans ; IMC moyen : 37,18 ± 5,43 kg/m 2 ) et quatre sujets de poids normal (âges de 46,0 ± 11,0 ; IMC moyen : 22,43 ± 2,64 kg/m 2 ) ont ete inclus. Les resultats preliminaires ne mettent pas en evidence de difference significative en termes de latences et d’amplitudes des potentiels evoques gustatifs entre sujets obeses et temoins. Chez les sujets obeses, le taux de ghreline est correle positivement a la latence initiale P1 des potentiels evoques gustatifs (coefficient de correlation a 0,70) en regard de l’aire gustative primaire. Conclusion Ces resultats preliminaires ne permettent pas d’observer des differences en termes de potentiels evoques gustatifs entre sujets obeses et temoins. L’augmentation du nombre de sujets dans chaque groupe est en cours, afin de pouvoir caracteriser les eventuels troubles de la sensorialite gustative chez les sujets obeses.

Aims/hypothesis: Due to their ability to regulate various signalling pathways (cytokines, hormones, growth factors), the suppressor of cytokine signalling (SOCS) proteins are thought to be promising therapeutic targets for metabolic and inflammatory disorders. Hence, their role in vivo has to be precisely determined. Methods: We generated transgenic mice constitutively producing SOCS-3 in skeletal muscle to define whether the sole abundance of SOCS-3 is sufficient to induce metabolic disorders and whether SOCS-3 is implicated in physiological roles distinct from metabolism. Results: We demonstrate here that chronic expression of SOCS-3 in skeletal muscle leads to overweight in mice and worsening of high-fat diet-induced systemic insulin resistance. Counter-intuitively, insulin sensitivity in muscle of transgenic mice appears to be unaltered. However, following constitutive SOCS-3 production, several genes had deregulated expression, among them other members of the SOCS family. This could maintain the insulin signal into skeletal muscle. Interestingly, we found that SOCS-3 interacts with calcineurin, which has been implicated in muscle contractility. In Socs-3 transgenic muscle, this leads to delocalisation of calcineurin to the fibre periphery. Relevant to this finding, Socs-3 transgenic animals had dilatation of the sarcoplasmic reticulum associated with swollen mitochondria and decreased voluntary activity. Conclusions/interpretation: Our results show that constitutive SOCS-3 production in skeletal muscle is not in itself sufficient to induce the establishment of metabolic disorders such as diabetes. In contrast, we reveal a novel role of SOCS-3, which appears to be important for muscle integrity and locomotor activity. Refereed/Peer-reviewed

Overfeeding causes rapid synaptic remodeling in hypothalamus feeding circuits. Polysialylation of cell surface molecules is a key step in this neuronal rewiring and allows normalization of food intake. Here we examined the role of hypothalamic polysialylation in the long-term maintenance of body weight, and deciphered the molecular sequence underlying its nutritional regulation. We found that upon high fat diet (HFD), reduced hypothalamic polysialylation exacerbated the diet-induced obese phenotype in mice. Upon HFD, the histone acetyltransferase MOF was rapidly recruited on the St8sia4 polysialyltransferase-encoding gene. Mof silencing in the mediobasal hypothalamus of adult mice prevented activation of the St8sia4 gene transcription, reduced polysialylation, altered the acute homeostatic feeding response to HFD and increased the body weight gain. These findings indicate that impaired hypothalamic polysialylation contribute to the development of obesity, and establish a role for MOF in the brain control of energy balance.

International audience; The reversible phosphorylation of the a subunit of eukaryotic initiation factor 2 (eIF2 alpha) is a highly conserved signal implicated in the cellular adaptation to numerous stresses such as the one caused by amino acid limitation. In response to dietary amino acid deficiency, the brain-specific activation of the eIF2 alpha kinase GCN2 leads to food intake inhibition. We report here that GCN2 is rapidly activated in the mediobasal hypothalamus (MBH) after consumption of a leucine-deficient diet. Furthermore, knockdown of GCN2 in this particular area shows that MBH GCN2 activity controls the onset of the aversive response. Importantly, pharmacological experiments demonstrate that the sole phosphorylation of eIF2 alpha in the MBH is sufficient to regulate food intake. eIF2 alpha signaling being at the crossroad of stress pathways activated in several pathological states, our study indicates that hypothalamic eIF2 alpha phosphorylation could play a critical role in the onset of anorexia associated with certain diseases.

The insulin sensitive glucose transporter Glut4 is expressed in neurons of the brain among which those of hypothalamic nuclei. It has been proposed that this transporter might be involved in the hypothalamic glucose-insulin sensing mechanism and thus in the nervous regulation of metabolism. In order to get further insights into its putative role, Glut4 expression was analyzed by quantitative competitive reverse transcription-polymerase chain reaction, in hypothalamic nuclei of hyperglycemic-hyperinsulinemic (HG-HI) rats, a model characterized by alteration of the autonomic nervous system activity. Glut4 mRNA content was decreased in the lateral hypothalamic area (33%) and arcuate nucleus (27%) but significantly only in the former. It was unchanged in other structures. These results are in favor of an alteration of Glut4 expression by short-term hyperglycemia and hyperinsulinemia that, in turn, could affect autonomic nervous system activity.

Photoperiod variations are known to participate in the regulation of energy balance in different rodent species via melatonin, a neurosecretory product synthesized by the pineal gland during the night. A direct effect of melatonin on adipose tissue has been suggested since binding sites for the indole have been described on brown adipocytes. The aim of this study was to investigate a genetic effect of melatonin on isolated Siberian hamster brown adipocytes using differential display RT-PCR (DDRT-PCR). Brown adipose cells were isolated from brown adipose tissue and treated for 3 hr with 0.1 and 10 μM melatonin. Total RNA was extracted and DDRT-PCR experiments were performed. A differential band, which disappeared after melatonin treatment, was detected. After confirmation and cloning, the corresponding cDNA fragment B18 was sequenced. B18 had 85 and 81% similarity with a portion of rat and mouse cytochrome b mRNA, respectively, suggesting that B18 corresponds to hamster cytochrome b. This hypothesis was confirmed by the close parallel between the changes in mRNA content, detected by B18, and by cytochrome b mRNA content, detected by a rat probe. Cytochrome b mRNA is encoded by the mitochondrial genome, suggesting a similar effect of melatonin on the whole mitochondrial transcripts. Indeed, 3 hr of treatment with melatonin (10 nM and 0.1 μM) decreased by 44% mitochondrial transcript contents. This work constitutes the first evidence of a direct biological effect of melatonin on Siberian hamster brown adipocytes.

International audience; Learned association between odor, taste and further post-ingestive consequence is known as flavor nutrient conditioned preference. Amygdala is supposed to be one of the areas involved in these associations. In the present study, one flavor was associated with a 16% glucose (CS+) whereas another flavor was paired with less reinforcing 4% glucose (CS-). We showed that CS+ presentation after conditioning increased Fos expression in the basolateral nucleus of amygdala (BLA). Furthermore, we performed electrophysiological recordings in the BLA in free moving rats. After preference acquisition, rats were exposed to either the CS+ or the CS-. The proportion of neurons showing a decreased activity during the CS- presentation was significantly higher in conditioned rats compared to controls. Among this neuronal population recorded in conditioned rats, we noticed a significant proportion of neurons that also showed a decreased activity during the CS+ presentation. Our data indicate an involvement of BLA during retrieval of learned flavors. It also suggests that both flavors might have acquired a biological value through conditioning.

OBJECTIVE AND DESIGN: As well as its involvement in control of adipose mass and body energy balance, several reports suggest a link between leptin and hemopoiesis. To test its putative role in human hemopoiesis, we developed a homologous system, ie recombinant human leptin treatment of purified CD34+ progenitors from adult human bone marrow. RESULTS: Leptin (50–100 ng/ml) significantly stimulated the appearance of granulocyte-macrophage colonies in the presence or absence of erythropoietin. The concentration of leptin required for this effect was rather high but within the range of plasma leptin levels observed in obesity. Two results further support the hypothesis that leptin may be involved in the leukocytosis associated with obesity: (i) leptin concentrations in bone marrow and plasma of subjects studied were highly correlated; (ii) leptin and leukocyte count were correlated only in obese subjects. Paracrine effects of locally released leptin from bone marrow adipocytes could also be involved in the regulation of hemopoiesis, a hypothesis supported by marrow immunocytochemistry revealing the close association of CD34+ cells with adipocytes and by previous demonstration that leptin is secreted at a high level by these cells. CONCLUSION: These results indicate that leptin acts on human multilineage CD34+ cells and that high plasma leptin levels associated with obesity could participate in the differentiation of granulocytes from hemopoietic progenitors.

Presynaptic inhibition of Ia terminals and postactivation depression at the Ia fibre-motor neuron (MN) synapses were compared in the upper and lower limbs of both sides in subjects from different populations: 49 spastic patients with hemiplegia [mainly with a lesion in the middle cerebral artery (MCA) area], two tetraplegics and 35 healthy subjects. Presynaptic inhibition was assessed using D1 inhibition of the soleus and the flexor carpi radialis (FCR) H reflexes elicited by electrical stimuli applied to the nerve supplying antagonistic muscles, and postactivation depression was explored by varying the time interval between two consecutive H reflexes. In normal subjects no right-left asymmetry was found in the amount of presynaptic Ia inhibition, homosynaptic depression or the H(max)/M(max) ratio. In the hemiplegic side of patients with MCA area lesions, the H(max)/M(max) ratio was significantly increased in the soleus but not in the FCR. Presynaptic inhibition of Ia terminals, which was significantly reduced at the cervical level on the hemiplegic side (and also, but to a lesser extent, on the unaffected side), was unchanged at the lumbar level. Homosynaptic depression was similarly reduced at the cervical and lumbar levels on the hemiplegic side but not modified on the unaffected side. It is argued that the decrease in presynaptic inhibition of Ia terminals is more a correlate of spasticity than a mechanism underlying it. The decrease in postactivation depression, which very probably contributes to the exaggeration of the stretch reflex characterizing spasticity, might be a consequence of the changes in the pattern of activation of Ia afferents and MNs following the motor impairment.

Despite a large number of studies, the role of melatonin on glucose metabolism is still controversial. The aim of the present work was to further characterize the effect of melatonin on insulin action during: i) intravenous insulin tolerance test performed at different times of the day using melatonin, a melatonin agonist (S-20304), a melatonin antagonist (S-20928) or in pinealectomized rats. ii) euglycemic-hyperinsulinemic clamp performed in melatonin agonist-treated as well as in pinealectomized rats. The fall in glycemia after the insulin injection was not significantly affected by melatonin and melatonin agonist (S-20304) at ZT6, nor by the melatonin antagonist (S-20928) at ZT13 nor in pinealectomized animals at ZT6 in comparison to their respective control. Acute treatment with S-20304 or chronic suppression of melatonin by pinealectomy did not significantly alter basal plasma glucose and insulin levels or hepatic glucose production and whole body or individual tissue glucose utilization. These data do not give support to a crucial role of melatonin on insulin action in normal rats.

Introduction L’hypothalamus medio-basal (MBH) renferme des neurones gluco-excites impliques dans le controle de l’homeostasie glucidique. Neanmoins, les mecanismes mis en jeu dans la reponse au glucose de ces neurones sont inconnus mis a part des donnees preliminaires montrant l’implication d’especes actives de l’oxygene (EAOs). Certains canaux de la famille des « transient receptor potential-canonical ° » (TRPC), qui presentent une conductance ionique observee dans les neurones gluco-excites, sont directement modules par les EAOs. Nous avons emis l’hypothese qu’une voie de signalisation EAOs-TRPC-dependante est impliquee dans la reponse au glucose des neurones gluco-excites hypothalamiques. Materiels et methodes In vitro : l’activite de cellules dissociees de MBH de rats ou souris est enregistree par imagerie calcique en reponse a l’augmentation de la concentration en glucose de 2,5 a 10 mm, en presence d’inhibiteurs de canaux TRPC. In vivo: la secretion d’insuline induite par l’injection intra-carotidienne d’un bolus de glucose, la tolerance au glucose et a l’insuline sont etudiees en reponse a l’administration d’inhibiteurs TRPC dans le MBH chez le rat et chez des souris deficientes pour le canal TRPC3. Resultats L’intensite des reponses calciques au glucose des neurones gluco-excites diminue significativement en presence des inhibiteurs TRPC non selectifs ou TRPC3-selectifs. Ces donnees suggerent que ce canal est implique dans la reponse au glucose des neurones gluco-excites du MBH. In vivo, l’administration d’un inhibiteur TRPC3-selectif dans le MBH inhibe la secretion d’insuline induite par l’injection intracarotidienne de glucose. Les souris deficientes pour le canal TRPC3 presentent egalement un defaut de secretion d’insuline en reponse a cette injection, parallelement a une intolerance au glucose, une hyperglycemie a jeun et un surpoids. Conclusion Nos donnees mettent en evidence une nouvelle voie de signalisation EAOs-TRPC3 jouant un role clef dans la reponse au glucose des neurones gluco-excites de MBH et le controle de l’homeostasie glucidique. Declaration d’interet Les auteurs declarent ne pas avoir d’interet direct ou indirect (financier ou en nature) avec un organisme prive, industriel ou commercial en relation avec le sujet presente.

Recent data suggest that some imidazoline derivatives can lower plasma glucose in experimental animal models of diabetes. We studied the activity of an imidazoline S-22068, in rat model of non-insulin-dependent diabetes mellitus (NIDDM) produced with a low dose of streptozotocin (35 mg kg(-1), i.v.) in the adult. The respective increase over basal value in glucose (deltaG) and insulin (deltaI), and the rate of glucose disappearance (K), were measured during a 30 min intravenous glucose tolerance test. After an intraperitoneal injection of S-22068 (24 mg kg(-1)), deltaG (mM min(-1)) was decreased (91.67+/-5.83 vs 120.5+/-3.65; P

Adipocytes participate in the microenvironment of the bone marrow (BM), but their exact role remains to be determined. It has recently been shown that leptin, a hormone secreted from extramedullary adipocytes, could be involved in hematopoiesis. Therefore we have developed a primary culture system of human BM adipocytes to characterize their differentiation and determine whether leptin is also secreted from these adipocytes. BM cells were cultured with fetal calf and horse sera. In the presence of dexamethasone, cells with vesicles containing lipids appeared within 15 days. They expressed glycerol phosphate dehydrogenase activity and a lipolytic activity in response to isoproterenol, but expressed neither the adrenergic beta3 receptor nor the mitochondrial uncoupling protein UCP1. The addition of insulin alone to the culture media did not promote adipocyte differentiation. Leptin was expressed and secreted at high levels during adipocyte differentiation. Acute exposure of differentiated adipocytes to insulin had little effect on leptin expression whereas forskolin strongly inhibited it. These results show that although human BM adipocytes differ from extramedullary adipose tissues in their sensitivity to different effectors, they are a secondary source of leptin production. They suggest that BM adipocytes could contribute to hematopoiesis via the secretion of leptin in the vicinity of hematopoietic stem cells.