RESUMO
BACKGROUND: It has long been known that thyroid disease can lead to changes in energy metabolism, thermoregulation, and anxiety behavior. While these actions have been partially attributed to thyroid hormone receptor α1 (TRα1) action in brain, the precise neuroanatomical substrates have remained elusive. METHODS: We used PET-CT scans to identify brain regions affected by thyroid hormone. Then we inhibited TRα1 signaling specifically in the most affected region, the zona incerta, a still mysterious region previously implicated in thermogenesis and anxiety. To this end we used an adeno-associated virus (AAV) expressing a dominant-negative TRα1R384C in wild-type mice and phenotyped the animals. Finally, we used tyrosine hydroxylase-Cre mice to test specifically the contribution of zona incerta dopaminergic neurons. RESULTS: Our data showed that AAV-mediated inhibition of TRα1 signaling in the zona incerta lead to increased energy expenditure at thermoneutrality, while body temperature regulation remained unaffected. Moreover, circulating glucocorticoid levels were increased, and mild habituation problem was observed in the open field test. No effects were observed when TRα1 signaling was selectively inhibited in dopaminergic neurons. CONCLUSIONS: Our findings suggest that altered thyroid hormone signaling in the zona incerta is not involved in body temperature regulation, but can affect basal metabolism and modulates stress responses.
RESUMO
The Rab-GTPase-activating protein (RabGAP) TBC1D4 (AS160) represents a key component in the regulation of glucose transport into skeletal muscle and white adipose tissue (WAT) and is therefore crucial during the development of insulin resistance and type 2 diabetes. Increased daily activity has been shown to be associated with improved postprandial hyperglycemia in allele carriers of a loss-of-function variant in the human TBC1D4 gene. Using conventional Tbc1d4-deficient mice (D4KO) fed a high-fat diet, we show that moderate endurance exercise training leads to substantially improved glucose and insulin tolerance and enhanced expression levels of markers for mitochondrial activity and browning in WAT from D4KO animals. Importantly, in vivo and ex vivo analyses of glucose uptake revealed increased glucose clearance in interscapular brown adipose tissue and WAT from trained D4KO mice. Thus, chronic exercise is able to overcome the genetically induced insulin resistance caused by Tbc1d4 depletion. Gene variants in TBC1D4 may be relevant in future precision medicine as determinants of exercise response.
Assuntos
Tecido Adiposo Branco , Proteínas Ativadoras de GTPase , Resistência à Insulina , Camundongos Knockout , Condicionamento Físico Animal , Resistência à Insulina/genética , Resistência à Insulina/fisiologia , Proteínas Ativadoras de GTPase/genética , Proteínas Ativadoras de GTPase/metabolismo , Animais , Camundongos , Condicionamento Físico Animal/fisiologia , Tecido Adiposo Branco/metabolismo , Dieta Hiperlipídica , Masculino , Tecido Adiposo Marrom/metabolismo , Músculo Esquelético/metabolismo , Glucose/metabolismo , Camundongos Endogâmicos C57BLRESUMO
Agouti-related peptide (AgRP)-expressing and proopiomelanocortin (POMC)-expressing neurons reciprocally regulate food intake. Here, we combine non-interacting recombinases to simultaneously express functionally opposing chemogenetic receptors in AgRP and POMC neurons for comparing metabolic responses in male and female mice with simultaneous activation of AgRP and inhibition of POMC neurons with isolated activation of AgRP neurons or isolated inhibition of POMC neurons. We show that food intake is regulated by the additive effect of AgRP neuron activation and POMC neuron inhibition, while systemic insulin sensitivity and gluconeogenesis are differentially modulated by isolated-versus-simultaneous regulation of AgRP and POMC neurons. We identify a neurocircuit engaging Npy1R-expressing neurons in the paraventricular nucleus of the hypothalamus, where activated AgRP neurons and inhibited POMC neurons cooperate to promote food consumption and activate Th+ neurons in the nucleus tractus solitarii. Collectively, these results unveil how food intake is precisely regulated by the simultaneous bidirectional interplay between AgRP and POMC neurocircuits.
Assuntos
Neurônios , Pró-Opiomelanocortina , Camundongos , Masculino , Feminino , Animais , Pró-Opiomelanocortina/metabolismo , Proteína Relacionada com Agouti/metabolismo , Neurônios/metabolismo , Hipotálamo/metabolismoRESUMO
BACKGROUND: Transcranial direct current stimulation (tDCS) promotes recovery after stroke in humans. The underlying mechanisms, however, remain to be elucidated. Animal models suggest tDCS effects on neuroinflammation, stem cell proliferation, neurogenesis, and neural plasticity. OBJECTIVE: In a longitudinal study, we employed tDCS in the subacute and chronic phase after experimental focal cerebral ischemia in mice to explore the relationship between functional recovery and cellular processes. METHODS: Mice received photothrombosis in the right motor cortex, verified by Magnetic Resonance Imaging. A composite neuroscore quantified subsequent functional deficits. Mice received tDCS daily: either 5 sessions from day 5 to 9, or 10 sessions with days 12 to 16 in addition. TDCS with anodal or cathodal polarity was compared to sham stimulation. Further imaging to assess proliferation and neuroinflammation was performed by immunohistochemistry at different time points and Positron Emission Tomography at the end of the observation time of 3 weeks. RESULTS: Cathodal tDCS at 198 kC/m2 (220 A/m2) between days 5 and 9 accelerated functional recovery, increased neurogenesis, decreased microglial activation, and mitigated CD16/32-expression associated with M1-phenotype. Anodal tDCS exerted similar effects on neurogenesis and microglial polarization but not on recovery of function or microglial activation. TDCS on days 12 to 16 after stroke did not induce any further effects, suggesting that the therapeutic time window was closed by then. CONCLUSION: Overall, data suggest that non-invasive neuromodulation by tDCS impacts neurogenesis and microglial activation as critical cellular processes influencing functional recovery during the early phase of regeneration from focal cerebral ischemia.
Assuntos
Isquemia Encefálica , Acidente Vascular Cerebral , Estimulação Transcraniana por Corrente Contínua , Humanos , Animais , Camundongos , Estimulação Transcraniana por Corrente Contínua/métodos , Recuperação de Função Fisiológica , Estudos Longitudinais , Isquemia Encefálica/diagnóstico por imagem , Isquemia Encefálica/terapia , Isquemia Encefálica/complicações , Acidente Vascular Cerebral/complicações , Acidente Vascular Cerebral/diagnóstico por imagem , Acidente Vascular Cerebral/terapia , Infarto Cerebral/complicaçõesRESUMO
Brains are among the most energetically costly tissues in the mammalian body.1 This is predominantly caused by expensive neurons with high glucose demands.2 Across mammals, the neuronal energy budget appears to be fixed, possibly posing an evolutionary constraint on brain growth.3-6 Compared to similarly sized mammals, birds have higher numbers of neurons, and this advantage conceivably contributes to their cognitive prowess.7 We set out to determine the neuronal energy budget of birds to elucidate how they can metabolically support such high numbers of neurons. We estimated glucose metabolism using positron emission tomography (PET) and 2-[18F]fluoro-2-deoxyglucose ([18F]FDG) as the radiotracer in awake and anesthetized pigeons. Combined with kinetic modeling, this is the gold standard to quantify cerebral metabolic rate of glucose consumption (CMRglc).8 We found that neural tissue in the pigeon consumes 27.29 ± 1.57 µmol glucose per 100 g per min in an awake state, which translates into a surprisingly low neuronal energy budget of 1.86 × 10-9 ± 0.2 × 10-9 µmol glucose per neuron per minute. This is approximately 3 times lower than the rate in the average mammalian neuron.3 The remarkably low neuronal energy budget explains how pigeons, and possibly other avian species, can support such high numbers of neurons without associated metabolic costs or compromising neuronal signaling. The advantage in neuronal processing of information at a higher efficiency possibly emerged during the distinct evolution of the avian brain.
Assuntos
Fluordesoxiglucose F18 , Glucose , Animais , Aves/metabolismo , Encéfalo/metabolismo , Glucose/metabolismo , Mamíferos , Neurônios/metabolismoRESUMO
Insulin acts on neurons and glial cells to regulate systemic glucose metabolism and feeding. However, the mechanisms of insulin access in discrete brain regions are incompletely defined. Here we show that insulin receptors in tanycytes, but not in brain endothelial cells, are required to regulate insulin access to the hypothalamic arcuate nucleus. Mice lacking insulin receptors in tanycytes (IR∆Tan mice) exhibit systemic insulin resistance, while displaying normal food intake and energy expenditure. Tanycytic insulin receptors are also necessary for the orexigenic effects of ghrelin, but not for the anorexic effects of leptin. IR∆Tan mice exhibit increased agouti-related peptide (AgRP) neuronal activity, while displaying blunted AgRP neuronal adaptations to feeding-related stimuli. Lastly, a highly palatable food decreases tanycytic and arcuate nucleus insulin signalling to levels comparable to those seen in IR∆Tan mice. These changes are rooted in modifications of cellular stress responses and of mitochondrial protein quality control in tanycytes. Conclusively, we reveal a critical role of tanycyte insulin receptors in gating feeding-state-dependent regulation of AgRP neurons and systemic insulin sensitivity, and show that insulin resistance in tanycytes contributes to the pleiotropic manifestations of obesity-associated insulin resistance.
Assuntos
Proteína Relacionada com Agouti/metabolismo , Células Ependimogliais/metabolismo , Hipotálamo/metabolismo , Insulina/metabolismo , Neurônios/metabolismo , Transdução de Sinais , Proteína Relacionada com Agouti/química , Animais , Biomarcadores , Barreira Hematoencefálica/metabolismo , Cálcio , Metabolismo Energético , Imunofluorescência , Grelina/metabolismo , Glucose/metabolismo , Resistência à Insulina , Camundongos , Camundongos Knockout , Mitocôndrias/metabolismo , Modelos Biológicos , Fragmentos de Peptídeos/metabolismo , Receptor de Insulina/metabolismoRESUMO
Sensory neurons relay gut-derived signals to the brain, yet the molecular and functional organization of distinct populations remains unclear. Here, we employed intersectional genetic manipulations to probe the feeding and glucoregulatory function of distinct sensory neurons. We reconstruct the gut innervation patterns of numerous molecularly defined vagal and spinal afferents and identify their downstream brain targets. Bidirectional chemogenetic manipulations, coupled with behavioral and circuit mapping analysis, demonstrated that gut-innervating, glucagon-like peptide 1 receptor (GLP1R)-expressing vagal afferents relay anorexigenic signals to parabrachial nucleus neurons that control meal termination. Moreover, GLP1R vagal afferent activation improves glucose tolerance, and their inhibition elevates blood glucose levels independent of food intake. In contrast, gut-innervating, GPR65-expressing vagal afferent stimulation increases hepatic glucose production and activates parabrachial neurons that control normoglycemia, but they are dispensable for feeding regulation. Thus, distinct gut-innervating sensory neurons differentially control feeding and glucoregulatory neurocircuits and may provide specific targets for metabolic control.
Assuntos
Regulação do Apetite , Eixo Encéfalo-Intestino/fisiologia , Glucose/metabolismo , Células Receptoras Sensoriais/fisiologia , Vias Aferentes/metabolismo , Animais , Apetite/fisiologia , Regulação do Apetite/genética , Comunicação Celular/genética , Metabolismo Energético/genética , Metabolismo Energético/fisiologia , Receptor do Peptídeo Semelhante ao Glucagon 1/genética , Receptor do Peptídeo Semelhante ao Glucagon 1/metabolismo , Proteínas de Homeodomínio/genética , Proteínas de Homeodomínio/metabolismo , Masculino , Camundongos Transgênicos , Gânglio Nodoso/metabolismo , Gânglio Nodoso/fisiologia , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Nervo Vago/metabolismo , Nervo Vago/fisiologia , Proteína Wnt1/genética , Proteína Wnt1/metabolismoRESUMO
BACKGROUND: Treatment of patients with solid tumors and KRAS mutations remains disappointing. One option is the combined inhibition of pathways involved in RAF-MEK-ERK and PI3K-AKT-mTOR. METHODS: Patients with relapsed solid tumors were treated with escalating doses of everolimus (E) 2.5-10.0 mg/d in a 14-day run-in phase followed by combination therapy with sorafenib (S) 800 mg/d from day 15. KRAS mutational status was assessed retrospectively in the escalation phase. Extension phase included KRAS-mutated non-small-cell lung cancer (NSCLC) only. Pharmacokinetic analyses were accompanied by pharmacodynamics assessment of E by FDG-PET. Efficacy was assessed by CT scans every 6 weeks of combination. RESULTS: Of 31 evaluable patients, 15 had KRAS mutation, 4 patients were negative for KRAS mutation, and the KRAS status remained unknown in 12 patients. Dose-limiting toxicity (DLT) was not reached. The maximum tolerated dose (MTD) was defined as 7.5 mg/d E + 800 mg/d S due to toxicities at previous dose level (10 mg/d E + 800 mg/d S) including leucopenia/thrombopenia III° and pneumonia III° occurring after the DLT interval. The metabolic response rate in FDG-PET was 17% on day 5 and 20% on day 14. No patient reached partial response in CT scan. Median progression free survival (PFS) and overall survival (OS) were 3.25 and 5.85 months, respectively. CONCLUSIONS: Treatment of patients with relapsed solid tumors with 7.5 mg/d E and 800 mg/d S is safe and feasible. Early metabolic response in FDG-PET was not confirmed in CT scan several weeks later. The combination of S and E is obviously not sufficient to induce durable responses in patients with KRAS-mutant solid tumors.
Assuntos
Protocolos de Quimioterapia Combinada Antineoplásica/uso terapêutico , Carcinoma Pulmonar de Células não Pequenas/tratamento farmacológico , Everolimo/uso terapêutico , Fluordesoxiglucose F18/metabolismo , Neoplasias Pulmonares/tratamento farmacológico , Tomografia por Emissão de Pósitrons/métodos , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Sorafenibe/uso terapêutico , Adulto , Idoso , Protocolos de Quimioterapia Combinada Antineoplásica/farmacologia , Everolimo/farmacologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Sorafenibe/farmacologiaRESUMO
Astrocytes represent central regulators of brain glucose metabolism and neuronal function. They have recently been shown to adapt their function in response to alterations in nutritional state through responding to the energy state-sensing hormones leptin and insulin. Here, we demonstrate that glucagon-like peptide (GLP)-1 inhibits glucose uptake and promotes ß-oxidation in cultured astrocytes. Conversely, postnatal GLP-1 receptor (GLP-1R) deletion in glial fibrillary acidic protein (GFAP)-expressing astrocytes impairs astrocyte mitochondrial integrity and activates an integrated stress response with enhanced fibroblast growth factor (FGF)21 production and increased brain glucose uptake. Accordingly, central neutralization of FGF21 or astrocyte-specific FGF21 inactivation abrogates the improvements in glucose tolerance and learning in mice lacking GLP-1R expression in astrocytes. Collectively, these experiments reveal a role for astrocyte GLP-1R signaling in maintaining mitochondrial integrity, and lack of GLP-1R signaling mounts an adaptive stress response resulting in an improvement of systemic glucose homeostasis and memory formation.
Assuntos
Astrócitos/metabolismo , Ácidos Graxos/metabolismo , Receptor do Peptídeo Semelhante ao Glucagon 1/metabolismo , Mitocôndrias/metabolismo , Animais , Feminino , Receptor do Peptídeo Semelhante ao Glucagon 1/deficiência , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Oxirredução , Transdução de SinaisRESUMO
Calorie-rich diets induce hyperphagia and promote obesity, although the underlying mechanisms remain poorly defined. We find that short-term high-fat-diet (HFD) feeding of mice activates prepronociceptin (PNOC)-expressing neurons in the arcuate nucleus of the hypothalamus (ARC). PNOCARC neurons represent a previously unrecognized GABAergic population of ARC neurons distinct from well-defined feeding regulatory AgRP or POMC neurons. PNOCARC neurons arborize densely in the ARC and provide inhibitory synaptic input to nearby anorexigenic POMC neurons. Optogenetic activation of PNOCARC neurons in the ARC and their projections to the bed nucleus of the stria terminalis promotes feeding. Selective ablation of these cells promotes the activation of POMC neurons upon HFD exposure, reduces feeding, and protects from obesity, but it does not affect food intake or body weight under normal chow consumption. We characterize PNOCARC neurons as a novel ARC neuron population activated upon palatable food consumption to promote hyperphagia.
Assuntos
Núcleo Arqueado do Hipotálamo/fisiologia , Dieta Hiperlipídica , Comportamento Alimentar/fisiologia , Neurônios GABAérgicos/fisiologia , Hiperfagia , Obesidade , Aumento de Peso/fisiologia , Animais , Núcleo Arqueado do Hipotálamo/citologia , Núcleo Arqueado do Hipotálamo/metabolismo , Neurônios GABAérgicos/metabolismo , Camundongos , Inibição Neural/fisiologia , Neurônios/metabolismo , Neurônios/fisiologia , Optogenética , Pró-Opiomelanocortina/metabolismo , Precursores de Proteínas/metabolismo , Receptores Opioides/metabolismo , Núcleos Septais/fisiologiaRESUMO
Regulation of body temperature critically depends on thyroid hormone (TH). Recent studies revealed that TH induces browning of white adipose tissue, possibly contributing to the observed hyperthermia in hyperthyroid patients and potentially providing metabolic benefits. Here, we show that browning by TH requires TH-receptor ß and occurs independently of the sympathetic nervous system. The beige fat, however, lacks sufficient adrenergic stimulation and is not metabolically activated despite high levels of uncoupling protein 1 (UCP1). Studies at different environmental temperatures reveal that TH instead causes hyperthermia by actions in skeletal muscle combined with a central body temperature set-point elevation. Consequently, the metabolic and thermogenic effects of systemic hyperthyroidism were maintained in UCP1 knockout mice, demonstrating that neither beige nor brown fat contributes to the TH-induced hyperthermia and elevated glucose consumption, and underlining that the mere presence of UCP1 is insufficient to draw conclusions on the therapeutic potential of browning agents.
Assuntos
Tecido Adiposo Bege/metabolismo , Tecido Adiposo Marrom/metabolismo , Tecido Adiposo Branco/metabolismo , Glucose/metabolismo , Termogênese , Hormônios Tireóideos/metabolismo , Tecido Adiposo Bege/fisiologia , Tecido Adiposo Marrom/fisiologia , Tecido Adiposo Branco/fisiologia , Animais , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Músculo Esquelético/metabolismo , Receptores Adrenérgicos beta 3/metabolismo , Proteína Desacopladora 1/genética , Proteína Desacopladora 1/metabolismoRESUMO
To date, the spatiotemporal release of specific neurotransmitters at physiological levels in the human brain cannot be detected. Here, we present a method that relates minute-by-minute fluctuations of the positron emission tomography (PET) radioligand [11C]raclopride directly to subsecond dopamine release events. We show theoretically that synaptic dopamine release induces low frequency temporal variations of extrasynaptic extracellular dopamine levels, at time scales of one minute, that can evoke detectable temporal variations in the [11C]raclopride signal. Hence, dopaminergic activity can be monitored via temporal fluctuations in the [11C]raclopride PET signal. We validate this theory using fast-scan cyclic voltammetry and [11C]raclopride PET in mice during chemogenetic activation of dopaminergic neurons. We then apply the method to data from human subjects given a palatable milkshake and discover immediate and-for the first time-delayed food-induced dopamine release. This method enables time-dependent regional monitoring of stimulus-evoked dopamine release at physiological levels.
Assuntos
Dopamina/metabolismo , Neurônios/metabolismo , Racloprida/metabolismo , Animais , Encéfalo/metabolismo , Encéfalo/cirurgia , Ingestão de Alimentos , Estimulação Elétrica , Eletrodos , Feminino , Humanos , Masculino , Camundongos , Modelos Biológicos , Tomografia por Emissão de Pósitrons/métodos , Ensaio Radioligante , Lobo Temporal/metabolismo , Lobo Temporal/cirurgia , Fatores de TempoRESUMO
Pleasant taste and nutritional value guide food selection behavior. Here, orosensory features of food may be secondary to its nutritional value in underlying reinforcement, but it is unclear how the brain encodes the reward value of food. Orosensory and peripheral physiological signals may act together on dopaminergic circuits to drive food intake. We combined fMRI and a novel [11C]raclopride PET method to assess systems-level activation and dopamine release in response to palatable food intake in humans. We identified immediate orosensory and delayed post-ingestive dopamine release. Both responses recruit segregated brain regions: specialized integrative pathways and higher cognitive centers. Furthermore, we identified brain areas where dopamine release reflected the subjective desire to eat. Immediate dopamine release in these wanting-related regions was inversely correlated with, and presumably inhibited, post-ingestive release in the dorsal striatum. Our results highlight the role of brain and periphery in interacting to reinforce food intake in humans.
Assuntos
Encéfalo/metabolismo , Dopamina/metabolismo , Ingestão de Alimentos/fisiologia , Preferências Alimentares/fisiologia , Paladar/fisiologia , Adulto , Idoso , Voluntários Saudáveis , Humanos , Imageamento por Ressonância Magnética/métodos , Masculino , Pessoa de Meia-IdadeRESUMO
High-fat diet (HFD) feeding induces rapid reprogramming of systemic metabolism. Here, we demonstrate that HFD feeding of mice downregulates glucose transporter (GLUT)-1 expression in blood-brain barrier (BBB) vascular endothelial cells (BECs) and reduces brain glucose uptake. Upon prolonged HFD feeding, GLUT1 expression is restored, which is paralleled by increased expression of vascular endothelial growth factor (VEGF) in macrophages at the BBB. In turn, inducible reduction of GLUT1 expression specifically in BECs reduces brain glucose uptake and increases VEGF serum concentrations in lean mice. Conversely, myeloid-cell-specific deletion of VEGF in VEGF(Δmyel) mice impairs BBB-GLUT1 expression, brain glucose uptake, and memory formation in obese, but not in lean mice. Moreover, obese VEGF(Δmyel) mice exhibit exaggerated progression of cognitive decline and neuroinflammation on an Alzheimer's disease background. These experiments reveal that transient, HFD-elicited reduction of brain glucose uptake initiates a compensatory increase of VEGF production and assign obesity-associated macrophage activation a homeostatic role to restore cerebral glucose metabolism, preserve cognitive function, and limit neurodegeneration in obesity.
Assuntos
Encéfalo/metabolismo , Dieta Hiperlipídica , Glucose/metabolismo , Obesidade/fisiopatologia , Fator A de Crescimento do Endotélio Vascular/metabolismo , Animais , Barreira Hematoencefálica/metabolismo , Cognição , Células Endoteliais/metabolismo , Ácidos Graxos/metabolismo , Transportador de Glucose Tipo 1/genética , Transportador de Glucose Tipo 1/metabolismo , Camundongos , Células Mieloides/metabolismoRESUMO
Activation of Agouti-related peptide (AgRP) neurons potently promotes feeding, and chronically altering their activity also affects peripheral glucose homeostasis. We demonstrate that acute activation of AgRP neurons causes insulin resistance through impairment of insulin-stimulated glucose uptake into brown adipose tissue (BAT). AgRP neuron activation acutely reprograms gene expression in BAT toward a myogenic signature, including increased expression of myostatin. Interference with myostatin activity improves insulin sensitivity that was impaired by AgRP neurons activation. Optogenetic circuitry mapping reveals that feeding and insulin sensitivity are controlled by both distinct and overlapping projections. Stimulation of AgRP â LHA projections impairs insulin sensitivity and promotes feeding while activation of AgRP â anterior bed nucleus of the stria terminalis (aBNST)vl projections, distinct from AgRP â aBNSTdm projections controlling feeding, mediate the effect of AgRP neuron activation on BAT-myostatin expression and insulin sensitivity. Collectively, our results suggest that AgRP neurons in mice induce not only eating, but also insulin resistance by stimulating expression of muscle-related genes in BAT, revealing a mechanism by which these neurons rapidly coordinate hunger states with glucose homeostasis.
Assuntos
Tecido Adiposo Marrom/metabolismo , Regulação do Apetite , Glucose/metabolismo , Resistência à Insulina , Neurônios/metabolismo , Proteína Relacionada com Agouti/metabolismo , Animais , Comportamento Alimentar , Camundongos , Miostatina/genética , Optogenética , TranscriptomaRESUMO
Inflammatory cells such as microglia need energy to exert their functions and to maintain their cellular integrity and membrane potential. Subsequent to cerebral ischemia, inflammatory cells infiltrate tissue with limited blood flow where neurons and astrocytes died due to insufficient supply with oxygen and glucose. Using dual tracer positron emission tomography (PET), we found that concomitant with the presence of inflammatory cells, transport and consumption of glucose increased up to normal levels but returned to pathological levels as soon as inflammatory cells disappeared. Thus, inflammatory cells established sufficient glucose supply to satisfy their energy demands even in regions with insufficient supply for neurons and astrocytes to survive. Our data suggest that neurons and astrocytes died from oxygen deficiency and inflammatory cells metabolized glucose non-oxidatively in regions with residual availability. As a consequence, glucose metabolism of inflammatory cells can mask metabolic deficits in neurodegenerative diseases. We further found that the PET tracer did not bind to inflammatory cells in severely hypoperfused regions and thus only a part of the inflammation was detected. We conclude that glucose consumption of inflammatory cells should be taken into account when analyzing disease-related alterations of local cerebral metabolism.
Assuntos
Isquemia Encefálica/metabolismo , Encéfalo/metabolismo , Metabolismo Energético/fisiologia , Glucose/metabolismo , Inflamação/metabolismo , Animais , Encéfalo/patologia , Processamento de Imagem Assistida por Computador , Inflamação/patologia , Imageamento por Ressonância Magnética , Masculino , Tomografia por Emissão de Pósitrons , Ratos , Ratos WistarRESUMO
We analyzed the metabolic response to cortical spreading depression that drastically increases local energy demand to restore ion homeostasis. During single and multiple cortical spreading depressions in the rat cortex, we simultaneously monitored extracellular levels of glucose and lactate using rapid sampling microdialysis and glucose influx using 18 F-fluorodeoxyglucose positron emission tomography while tracking cortical spreading depression using laser speckle imaging. Combining the acquired data with steady-state requirements we developed a mass-conserving compartment model including neurons and glia that was consistent with the observed data. In summary, our findings are: (1) Early breakdown of glial glycogen provides a major source of energy during increased energy demand and leaves 80% of blood-borne glucose to neurons. (2) Lactate is used solely by neurons and only if extracellular lactate levels are >80% above normal. (3) Although the ratio of oxygen and glucose consumption transiently reaches levels <3, the major part (>90%) of the overall energy supply is from oxidative metabolism. (4) During cortical spreading depression, brain release of lactate exceeds its consumption suggesting that lactate is only a circumstantial energy substrate. Our findings provide a general scenario for the metabolic response to increased cerebral energy demand.
Assuntos
Córtex Cerebral/metabolismo , Depressão Alastrante da Atividade Elétrica Cortical/fisiologia , Metabolismo Energético , Glucose/metabolismo , Ácido Láctico/metabolismo , Animais , Córtex Cerebral/diagnóstico por imagem , Córtex Cerebral/fisiopatologia , Masculino , Microdiálise , Modelos Neurológicos , Neuroimagem , Tomografia por Emissão de Pósitrons , Ratos WistarRESUMO
BACKGROUND: Stroke patients suffering from occlusion of the anterior cerebral artery (ACAo) develop cognitive and executive deficits. Experimental models to investigate such functional impairments and recovery are rare and not satisfyingly validated. NEW METHOD: We stereotactically injected the vasoconstrictor endothelin-1 (ET-1) close to the ACA of rats and assessed magnitude and course of CBF reduction using [(14)C]iodoantipyrine autoradiography and [(15)O]H2O-PET. [(18)F]FDG-PET and T2-weighted MRI determined regional metabolic and structural alterations. To test cognitive and executive functions, we analyzed decision-making in a food-carrying task, spatial working memory in a spontaneous alternation task and anxiety in an elevated plus maze test before and 1 month after ACAo. RESULTS: CBF decreased immediately after ET-1 injection, started to recover 1-2h and returned to control 4h thereafter. Metabolic and structural lesions developed permanently in the ACA territory. Hypometabolism occurring bilaterally in the piriform region may reflect diaschisis. Behavioral testing after ACAo revealed context-dependent changes in decision making, exploratory activity and walking speed, as well as decreased anxiety and spatial working memory. COMPARISON WITH EXISTING METHOD(S): Aside from modeling a known entity of stroke patients, ACAo in rats allows to longitudinally study deterioration of cognitive and executive function without major interference by disturbed primary motor function. It complements therefore stroke research since common models using middle cerebral artery occlusion (MCAo) all affect motor function severely. CONCLUSION: The established ACAo model in rats effectively reflects deficits characteristic for ACA stroke in humans. It is furthermore highly suitable for longitudinal assessment of cognitive and executive functions.