Plasma Metabolome Analysis Suggests That L-Arginine Supplementation Affects Microbial Activity Resulting in a Decrease in Trimethylamine N-oxide-A Randomized Controlled Trial in Healthy Overweight Adults with Cardiometabolic Risk Factors.

Background: The effects of supplementation with L-arginine (L-arg), the precursor of nitric oxide (NO), on vascular and cardiometabolic health have largely been explored. Whether other mechanisms of the action of L-arg exist remains unknown, as arginine metabolism is complicated. Objective: We aimed to characterize the effect of low dose L-arg supplementation on overall human metabolism both in a fasting state and in response to an allostatic stress. Methods: In a randomized, double-blind, crossover study, 32 healthy overweight adults (mean age 45 y) with cardiometabolic risk (fasting plasma triglycerides >150 mg/dL; waist circumference >94 cm [male] or >80 cm [female]) were treated with 1.5 g sustained-release L-arg 3 times/d (4.5 g/d) or placebo for 4 wk. On the last day of treatment, volunteers consumed a high-fat meal challenge (900 kcal, 80% as fat, 13% as carbohydrate, and 7% as protein). Plasma was collected at fasting, 2, 4, and 6 h after the challenge, and the metabolome was analyzed by high-resolution liquid chromatography-mass spectrometry. Metabolic profiles were analyzed using linear mixed models-principal component analysis. Results: The challenge meal explained most of the changes in the metabolome. The overall effect of L-arg supplementation significantly explained 0.5% of the total variance, irrespective of the response to the challenge meal (P < 0.05). Among the metabolites that explain most of the L-arg effect, we found many amino acids, including branched-chain amino acids, that were decreased by L-arg supplementation. L-arg also decreased trimethylamine N-oxide (TMAO). Other changes suggest that L-arg increased methyl demand. Conclusions: Analysis of the effect of 4 wk of L-arg supplementation on the metabolome reveals important effects on methyl balance and gut microbiota activity, such as a decrease in TMAO. Further studies are needed to investigate those mechanisms and the implications of these changes for long-term health.This trial was registered at clinicaltrials.gov as NCT02354794.

A Mix of Dietary Fibres Changes Interorgan Nutrients Exchanges and Muscle-Adipose Energy Handling in Overfed Mini-Pigs.

This study evaluates the capacity of a bread enriched with fermentable dietary fibres to modulate the metabolism and nutrients handling between tissues, gut and peripheral, in a context of overfeeding. Net fluxes of glucose, lactate, urea, short chain fatty acids (SCFA), and amino acids were recorded in control and overfed female mini-pigs supplemented or not with fibre-enriched bread. SCFA in fecal water and gene expressions, but not protein levels or metabolic fluxes, were measured in muscle, adipose tissue, and intestine. Fibre supplementation increased the potential for fatty acid oxidation and mitochondrial activity in muscle (acox, ucp2, sdha and cpt1-m, p < 0.05) as well as main regulatory transcription factors of metabolic activity such as pparα, pgc-1α and nrf2. All these features were associated with a reduced muscle fibre cross sectional area, resembling to controls (i.e., lean phenotype). SCFA may be direct inducers of these cross-talk alterations, as their feces content (+52%, p = 0.05) was increased in fibre-supplemented mini-pigs. The SCFA effects could be mediated at the gut level by an increased production of incretins (increased gcg mRNA, p < 0.05) and an up-regulation of SCFA receptors (increased gpr41 mRNA, p < 0.01). Hence, consumption of supplemented bread with fermentable fibres can be an appropriate strategy to activate muscle energy catabolism and limit the establishment of an obese phenotype.

A mix of dietary fermentable fibers improves lipids handling by the liver of overfed minipigs.

Obesity induced by overfeeding ultimately can lead to nonalcoholic fatty liver disease, whereas dietary fiber consumption is known to have a beneficial effect. We aimed to determine if a supplementation of a mix of fibers (inulin, resistant starch and pectin) could limit or alleviate overfeeding-induced metabolic perturbations. Twenty female minipigs were fed with a control diet (C) or an enriched fat/sucrose diet supplemented (O + F) or not (O) with fibers. Between 0 and 56 days of overfeeding, insulin (+88%), HOMA (+102%), cholesterol (+45%) and lactate (+63%) were increased, without any beneficial effect of fibers supplementation. However, fibers supplementation limited body weight gain (vs. O, -15% at D56) and the accumulation of hepatic lipids droplets induced by overfeeding. This could be explained by a decreased lipids transport potential (-50% FABP1 mRNA, O + F vs. O) inducing a down-regulation of regulatory elements of lipids metabolism / lipogenesis (-36% SREBP1c mRNA, O + F vs. O) but not to an increased oxidation (O + F not different from O and C for proteins and mRNA measured). Glucose metabolism was also differentially regulated by fibers supplementation, with an increased net hepatic release of glucose in the fasted state (diet × time effect, P<.05 at D56) that can be explained partially by a possible increased glycogen synthesis in the fed state (+82% GYS2 protein, O + F vs. O, P=.09). The direct role of short chain fatty acids on gluconeogenesis stimulation is questioned, with probably a short-term impact (D14) but no effect on a long-term (D56) basis.

Effects of nutritional state, aging and high chronic intake of sucrose on brain protein synthesis in rats: modulation of it by rutin and other micronutrients.

Little is still known about brain protein synthesis. In order to increase our knowledge of it, we aimed to modulate brain protein synthesis rates through aging, variations in nutritional state (fed state vs. fasted state), high sucrose diet and micronutrient supplementation. Four groups of 16 month-old male rats were fed for five months with a diet containing either 13% or 62% sucrose (wheat starch was replaced with sucrose), supplemented or not with rutin (5 g kg-1 diet), vitamin E (4×), A (2×), D (5×), selenium (10×) and zinc (+44%) and compared with an adult control group. We measured cerebellum protein synthesis and hippocampus gene expression of antioxidant enzymes, inflammatory cytokines and transcription factors. We showed that cerebellum protein synthesis was unchanged by the nutritional state, decreased during aging (-8%), and restored to the adult level by micronutrient supplementation. Sucrose diet did not change protein synthesis but reduced the protein content. Micronutrient supplementation had no effect in sucrose fed rats. Hippocampus gene expressions were affected by age (an increase of TNF-α), sucrose treatment (an increase of IL-1ß and IL-6), and micronutrient supplementation (a decrease of heme oxygenase, catalase, glutathione peroxidase, TNF-α, and Nrf2). We noted that cerebellum protein synthesis and hippocampus TNF-α gene expression were modulated by the same factors: they were affected by aging and micronutrient supplementation and unchanged by feeding and by high sucrose diet.

Effect of high chronic intake of sucrose on liver metabolism in aging rats. Modulation by rutin and micronutrients.

High-sugar intake and senescence share common deleterious effects, in particular in liver, but combination of these two factors was little studied. Our aims were to examine the effect of a high-sucrose diet in liver of old rats and also the potential benefices of a polyphenol/micronutrient supplementation. Four groups of 22-month-old male rats fed during 5 months with a diet containing either 13 or 62% sucrose, supplemented or not with rutin, vitamin E, A, D, selenium, and zinc were compared. We measured liver macronutrient composition, glycation/oxidative stress, enzyme activities (lipogenesis, ß-oxidation, fructokinase), gene expression (enzymes and transcription factors), in vivo protein synthesis rates and plasma parameters. Sucrose induced an increase in plasma and liver lipid content, and a stimulation of liver protein synthesis rates. Gene expression was little changed by sucrose, with lower levels for LXR-α and LXR-ß. Polyphenol/micronutrient supplementation tended to limit liver triglyceride infiltration through variations in fatty acid synthase, acyl coA oxidase, and possibly ATP-citrate lyase activities. In conclusion, despite differences in enzymatic regulations, and blunted responses of gene expression, high-sucrose diet was still able to induce a marked increase in liver lipid content in old animals. However, it probably attenuated the positive impact of polyphenol/micronutrients.

Chronic Intake of Sucrose Accelerates Sarcopenia in Older Male Rats through Alterations in Insulin Sensitivity and Muscle Protein Synthesis.

BACKGROUND: Today, high chronic intake of added sugars is frequent, which leads to inflammation, oxidative stress, and insulin resistance. These 3 factors could reduce meal-induced stimulation of muscle protein synthesis and thus aggravate the age-related loss of muscle mass (sarcopenia). OBJECTIVES: Our aims were to determine if added sugars could accelerate sarcopenia and to assess the capacity of antioxidants and anti-inflammatory agents to prevent this. METHODS: For 5 mo, 16-mo-old male rats were starch fed (13% sucrose and 49% wheat starch diet) or sucrose fed (62% sucrose and 0% wheat starch diet) with or without rutin (5 g/kg diet), vitamin E (4 times), vitamin A (2 times), vitamin D (5 times), selenium (10 times), and zinc (+44%) (R) supplementation. We measured the evolution of body composition and inflammation, plasma insulin-like growth factor 1 (IGF-I) concentration and total antioxidant status, insulin sensitivity (oral-glucose-tolerance test), muscle weight, superoxide dismutase activity, glutathione concentration, and in vivo protein synthesis rates. RESULTS: Sucrose-fed rats lost significantly more lean body mass (-8.1% vs. -5.4%, respectively) and retained more fat mass (+0.2% vs. -33%, respectively) than starch-fed rats. Final muscle mass was 11% higher in starch-fed rats than in sucrose-fed rats. Sucrose had little effect on inflammation, oxidative stress, and plasma IGF-I concentration but reduced the insulin sensitivity index (divided by 2). Meal-induced stimulation of muscle protein synthesis was significantly lower in sucrose-fed rats (+7.3%) than in starch-fed rats (+22%). R supplementation slightly but significantly reduced oxidative stress and increased muscle protein concentration (+4%) but did not restore postprandial stimulation of muscle protein synthesis. CONCLUSIONS: High chronic sucrose intake accelerates sarcopenia in older male rats through an alteration of postprandial stimulation of muscle protein synthesis. This effect could be explained by a decrease of insulin sensitivity rather than by changes in plasma IGF-I, inflammation, and/or oxidative stress.

Evidence of a metabolic fatty acid-sensing system in the hypothalamus and Brockmann bodies of rainbow trout: implications in food intake regulation.

Enhanced lipid levels inhibit food intake in fish but no studies have characterized the possible mechanisms involved. We hypothesize that the presence of fatty acid (FA)-sensing mechanisms could be related to the control of food intake. Accordingly, we evaluated in the hypothalamus, hindbrain, and Brockmann bodies (BB) of rainbow trout changes in parameters related to fatty acid metabolism, transport of FA, nuclear receptors, and transcription factors involved in lipid metabolism, and components of the K(ATP) channel after intraperitoneal administration of different doses of oleic acid (long-chain fatty acid, LCFA) or octanoic acid (medium-chain fatty acid, MCFA). The increase in circulating LCFA or MCFA levels elicited an inhibition in food intake and induced in the hypothalamus a response compatible with fatty acid sensing in which fatty acid metabolism, binding to cluster of differentiation 36 (CD36), and mitochondrial activity are apparently involved, which is similar to that suggested in mammals except for the apparent capacity of rainbow trout to detect changes in MCFA levels. Changes in those hypothalamic pathways can be related to the control of food intake, since food intake was inhibited when FA metabolism was perturbed (using fatty acid synthase or acetyl-CoA carboxylase inhibitors) and changes in mRNA levels of specific neuropeptides such as neuropeptide Y and proopiomelancortin were also noticed. This response seems to be exclusive for the hypothalamus, since the other center controlling food intake (hindbrain) was unaffected by treatments. The results obtained in BB suggest that at least two of the components of a putative fatty acid-sensing system (based on fatty acid metabolism and binding to CD36) could be present. Therefore, the present study provides, for the first time in fish, evidence for a specific role for FA (MCFA and LCFA) as metabolic signals in hypothalamus and BB, where the detection of those FA can be associated with the control of food intake and hormone release.

Glucose-induced insulin secretion: nutritional prevention and novel avenues for therapy.

Insulin resistance, the most important pathophysiological feature in various prediabetic and diabetic states is partly related to impaired glucose-stimulated insulin secretion and insulin modulation of pancreatic beta cell with peripheral impaired insulin response. This chapter concentrates on aspects of potential new strategies in the treatment of the disease going from nutritional preventive approaches towards currently utilized drugs for treatment that target the pancreatic beta cells with potentiation of glucose-stimulated insulin secretion.

Cholecystokinin impact on rainbow trout glucose homeostasis: possible involvement of central glucosensors.

Although the role of cholecystokinin (CCK) on fish appetite regulation has been widely studied, its involvement in the regulation of glucose metabolism had been little explored to date. In the present study we have carried out different experimental approaches to study CCK effects in rainbow trout (a so-called 'glucose intolerant' fish species) glucose homeostasis. We have found that for the first time in a vertebrate species, systemic or central CCK administration causes hyperglycemia, which is at least in part related to the presence of an ancestral gut-brain axis in which CCK is involved. By using capsaicin we have found that part of the action of CCK on glucose homeostasis is mediated by vagal and splanchnic afferents. Changes in hepatic metabolism after systemic CCK administration suggest that the effects are not directly taking place on the liver, but probably in other tissues, while after the central CCK administration, the glycogenolytic response observed in liver could be mediated by the activation of the sympathetic system. In hypothalamus and hindbrain changes elicited by CCK-8 treatment are likely related to the glucosensor response to the increased glycemia and/or vagal/splanchnic afferences whereas in hindbrain a possible action through specific CCK-1 receptors cannot be excluded. All these processes result in changes in metabolic parameters related with glucose homeostasis control. Further studies are needed to fully understand the role of this peptide on glucose homeostasis control in fish.

Central leptin treatment modulates brain glucosensing function and peripheral energy metabolism of rainbow trout.

The aim of the present study was to obtain evidence for the possible modulatory effect of leptin on glucosensing capacity in hypothalamus and hindbrain of rainbow trout. In a first experiment, trout were injected ICV with saline alone or containing increased doses of leptin (0.3-30 microg microl(-1)). Leptin induced in general in both hypothalamus and hindbrain dose-dependent changes in parameters related to glucosensing (increased glycogenic and glycolytic potentials together with increased GK activity, and increased mRNA levels of genes involved in glucosensing response) compatible with those occurring under hyperglycemic conditions, a situation that is known to produce anorexia. The anorectic action of leptin in our experimental conditions was observed in a second experiment. The specificity of leptin action was tested in a third experiment in which trout were injected ICV with saline, or leptin alone, or leptin plus agents known to inhibit leptin signaling pathways in mammals. The results obtained suggest that the central action of leptin on glucosensing system can be related to the JAK/STAT and IRS-PI(3)K pathways. Finally, we also provide evidence for a peripheral effect of central leptin treatment (increased liver glycogenolytic potential), which could be associated with increased sympathetic activity.

Hepatic protein kinase B (Akt)-target of rapamycin (TOR)-signalling pathways and intermediary metabolism in rainbow trout (Oncorhynchus mykiss) are not significantly affected by feeding plant-based diets.

The aim of the present study was to analyse the effects of partial or total replacement of fish meal (FM) and fish oil (FO) by a mixture of plant protein (PP) and a mixture of vegetable oils (VO) on the hepatic insulin-nutrient-signalling pathway and intermediary metabolism-related gene expression in rainbow trout (Oncorhynchus mykiss). Triplicate groups of fish were fed four practical diets containing graded levels of replacement of FM and FO by PP and VO for 12 weeks: diet 0/0 (100 % FM, 100 % FO); diet 50/50 (50 % FM and 50 % PP, 50 % FO and 50 % VO); diet 50/100 (50 % FM and 50 % PP, 100 % VO); diet 100/100 (100 % PP, 100 % VO). Samplings were performed on trout starved for 5 d then refed with their allocated diet. In contrast to partial substitution (diet 50/50), total substitution of FM and FO (diet 100/100) led to significantly lower growth compared with diet 0/0. The insulin-nutrient-signalling pathway (protein kinase B (Akt), target of rapamycin (TOR), S6 protein kinase 1 (S6K1) and S6) was characterised in trout liver and found to be activated by refeeding. However, changes in diet compositions did not differentially affect the Akt-TOR-signalling pathway. Moreover, expression of genes encoding fructose-1,6-biphosphatase, mitochondrial phosphoenolpyruvate carboxykinase, glucokinase, pyruvate kinase and carnitine palmitoyl transferase 1 were not affected by refeeding or by dietary changes. Refeeding down- and up-regulated the expression of gluconeogenic glucose-6-phosphatase isoform 1 and lipogenic fatty acid synthase genes, respectively. Expression of both genes was also increased with partial replacement of FM and total replacement of FO (diet 50/100). These findings indicate that plant-based diets barely affect glucose and lipid metabolism in trout.

Altered dietary carbohydrates significantly affect gene expression of the major glucosensing components in Brockmann bodies and hypothalamus of rainbow trout.

Carnivorous fish have a limited capacity to utilize dietary carbohydrates even though glucosensing components exist in the hypothalamus and Brockmann bodies. Therefore, we fed trout for 10 days with two experimental diets containing a high level of carbohydrates (20%) or a carbohydrate-free level (<0.3%) to test the capacity of dietary carbohydrates to regulate gene expression of glucosensing components. Fish were fed and killed 1, 6, and 24 h after the meal to analyze plasma glucose levels, glucosensing-related biochemical parameters, and gene expression of the major components of the glucosensing system in the hypothalamus and Brockmann bodies. Glucose facilitative transporter type 2 and glucokinase gene expression were confirmed by real-time PCR data and two new components of the glucosensing mechanism, Kir6.-like and sulfonylurea receptor-like, were detected for the first time in fish in both tissues. In addition, a clear adaptation to dietary carbohydrates was found in trout Brockmann bodies, based on increased gene expression of major components of the system as well as enhanced glucokinase activities and glycogen levels. In contrast, in the hypothalamus, only glucokinase gene expression and activity showed a response to dietary carbohydrates, supporting the key role of that enzyme in glucosensing mechanism. Finally, a differential postprandial profile was found between tissues regarding the glucosensing potential, since the hypothalamus seems to respond to hyperglycemia earlier than the Brockmann bodies, whose response took place later. Altogether, these data describe for the first time in fish a complete response of major glucosensing components to dietary carbohydrates in trout hypothalamus and Brockmann bodies, supporting an efficient adaptation of both tissues to those dietary components.

Changes in food intake and glucosensing function of hypothalamus and hindbrain in rainbow trout subjected to hyperglycemic or hypoglycemic conditions.

To evaluate the possible role of glucose in the control of food intake (FI) in fish and the involvement of glucosensing system in that role, we have subjected rainbow trout (via intraperitoneal injections) to control, hyperglycemic (500 mg kg(-1) glucose body mass) or hypoglycemic (4 mg kg(-1) bovine insulin) conditions for 10 days. The experimental design was appropriate since hypoglycemia and hyperglycemia were observed the first 5 days after treatment and changes observed in metabolic parameters in liver were similar to those of fish literature. Hyperglycemic conditions elicited small changes in FI accompanied by increased glucose and glycogen levels, glucokinase (GK) activity and glycolytic potential in hypothalamus and hindbrain. In contrast, hypoglycemic conditions elicited a marked increase in FI accompanied by decreased glucose and glycogen levels and GK activity in the same brain regions whereas both regions displayed different responses in glycolytic potential. These results allow us to hypothesize that, despite the relative intolerance to glucose of carnivorous fish, changes in plasma glucose levels in rainbow trout detected by glucosensing areas in brain regions (hypothalamus and hindbrain) are integrated in those or near areas eliciting a response in FI, which was more important under hypoglycemic than under hyperglycemic conditions.

Dietary carbohydrates induce changes in glucosensing capacity and food intake of rainbow trout.

We hypothesize that variations in dietary carbohydrate levels produce changes in glucosensor parameters in previously characterized glucosensing areas (hypothalamus and hindbrain) related with the regulation of food intake of a carnivorous fish species like rainbow trout. Therefore, we fed trout with standard, carbohydrate-free (CF) or high-carbohydrate (HC) diets for 10 days to assess changes in glucosensing system and food intake. Fish fed CF diet displayed hypoglycemia and increased food intake. Fish fed a HC diet displayed hyperglycemia and decreased food intake. Changes in food intake due to dietary carbohydrates were accompanied in hypothalamus and hindbrain of fish fed with HC diet by changes in parameters involved in glucosensing, such as increased glucose, glucose 6-phosphate, and glycogen levels and increased glucokinase (GK), glycogen synthase, and pyruvate kinase activities as well as increased GK and GLUT2 expression. All those results address for the first time in fish, despite the relative intolerance to glucose of carnivorous species, that dietary carbohydrates are important regulators of the glucosensing system in carnivorous fish, suggesting that the information generated by this system can be associated with the changes observed in food intake.

Involvement of lactate in glucose metabolism and glucosensing function in selected tissues of rainbow trout.

The aim of this study was to obtain evidence in rainbow trout for a role of lactate in glucose homeostasis as well as in the function of glucosensing tissues. In a first set of experiments, trout were injected, either (1) intraperitoneally (N=8) with 5 ml kg(-1) of Cortland saline alone (control) or saline containing l-(+)-lactate (22.5 mg kg(-1) or 45 mg kg(-1)), oxamate (22.5 mg kg(-1)) or d-glucose (500 mg kg(-1)), or (2) intracerebroventricularly (N=11) with 1 microl 100 g(-1) body mass of Cortland saline alone (control) or containing d-glucose (400 microg microl(-1)) or l-(+)-lactate (400 microg microl(-1)), with samples being obtained 6 h after treatment. In a second set of experiments, hypothalamus, hindbrain and Brockmann bodies were incubated in vitro for 1 h at 15 degrees C in modified Hanks' medium containing 2, 4 or 8 mmol l(-1) l-(+)-lactate alone (control) or with 50 mmol l(-1) oxamate, 1 mmol l(-1) DIDS, 1 mmol l(-1) dichloroacetate, 10 mmol l(-1) 2-deoxy-d-glucose, 1 mmol l(-1) alpha-cyano-4-hydroxy cinnamate or 10 mmol l(-1) d-glucose. The response of parameters assessed (metabolite levels, enzyme activities and glucokinase expression) in tissues provided evidence for (1) a role for lactate in the regulation of glucose homeostasis through changes not only in brain regions but also in liver energy metabolism, which are further reflected in changes in plasma levels of metabolites; (2) the possible presence in trout brain of an astrocyte-neuron lactate shuttle similar to that found in mammals; and (3) the lack of capacity of lactate to mimic in vitro (but not in vivo) glucose effects in fish glucosensing regions.

In vitro evidences for glucosensing capacity and mechanisms in hypothalamus, hindbrain, and Brockmann bodies of rainbow trout.

We aimed to support in vitro the glucosensing capacity observed in vivo in rainbow trout hypothalamus, hindbrain, and Brockmann bodies (BB) and to obtain preliminary evidence of the mechanisms involved. The response of parameters involved in the glucosensing capacity [hexokinase, hexokinase IV (glucokinase), and pyruvate kinase activities and glucose and glycogen levels] was assessed in these tissues incubated for 1 h with 2, 4, or 8 mM D-glucose alone (control) or with specific agonists/inhibitors of the steps involved in glucosensing capacity in mammals. These agents were a competitor for glucose phosphorylation (15 mM mannose), sulfonylurea receptor-1 effectors (500 microM tolbutamide or diazoxide), glycolytic intermediates (15 mM glycerol, lactate, or pyruvate), and inhibitors of glucose transport (10 microM cytochalasin B), glycolysis [20 mM 2-deoxy-D-glucose (2-DG)], and L-type calcium channel (1 microM nifedipine). Control incubations of the three tissues displayed increased glucose and glycogen levels and glucokinase activities in response to increased medium glucose, thus supporting our previous in vivo studies. Furthermore, critical components of the glucosensing mammalian machinery are apparently functioning in the three tissues. The responses in brain regions to all substances tested (except 2-DG and nifedipine) were similar to those observed in mammals, suggesting a similar glucosensing machinery. In contrast, in BB, only the effects of 2-DG, lactate, pyruvate, diazoxide, and nifedipine were similar to those of mammalian beta-cells, suggesting that some of the components of the piscine glucosensing model are different than those of mammals. Such differences may relate to the importance of amino acids rather than glucose signaling in the trout BB.

Evidence for the presence of a glucosensor in hypothalamus, hindbrain, and Brockmann bodies of rainbow trout.

The aim of this study was to evaluate the existence of a glucosensor in different regions of the brain and in the Brockmann bodies (BB) of the rainbow trout, Oncorhynchus mykiss. Five groups (n = 12) of trout were injected intraperitoneally with saline alone (control) or saline-containing bovine glucagon (100 mug/kg), bovine insulin (4 mg/kg), 2-deoxy-d-glucose (100 mg/kg), or d-glucose (500 mg/kg) to promote hyperglycemia (glucagon, d-glucose, 2-deoxy-d-glucose) or hypoglycemia (insulin). Six hours after injection, samples from four brain regions (hypothalamus, telencephalon, hindbrain, and midbrain) and the entire BB were taken. Our results demonstrate within the BB and both the hypothalamus and hindbrain a metabolic response different to that observed in other tissues (midbrain, telencephalon) but similar to that described in tissues known to be glucosensors in mammals. The metabolic responses of these areas to changes in plasma glycemia were characterized by parallel changes in GLUT-2 expression, hexokinase-IV, or glucokinase activity and expression, glycolytic potential, and levels of glycogen and glucose. These changes are similar to those reported in mammalian pancreatic beta-cells and glucose-excited (GE) neurons, two cell types containing glucosensors. This study provides evidence for the presence of glucosensors responsive to hyper- and hypoglycemia in rainbow trout BB, hypothalamus, and hindbrain.