Insulin therapy normalizes GLUT1 glucose transporter mRNA but not immunoreactive transporter protein in streptozocin-diabetic rats

Glucocorticoid receptor activation reduces food intake independent of hyperglycemia in zebrafish

Chronic cortisol exposure suppresses food intake in fish, but the central mechanism(s) involved in appetite regulation are unclear. Stress and the associated increase in cortisol levels increase hepatic gluconeogenesis, leading to hyperglycemia. As hyperglycemia causes a reduction in food intake, we tested the hypothesis that cortisol-induced hyperglycemia suppresses feeding in zebrafish (Danio rerio). We first established that stress-independent hyperglycemia suppressed food intake, and this corresponded with a reduction in the phosphorylation of the nutrient sensor, AMP-activated protein kinase (AMPK) in the brain. Chronic cortisol exposure also led to hyperglycemia and reduced food intake, but the mechanisms were distinct. In cortisol-exposed fish, there were no changes in brain glucose uptake or AMPK phosphorylation. Also, the phosphorylation of Akt and mTOR was reduced along with an increase in redd1, suggesting an enhanced capacity for proteolysis. Loss of the glucocorticoid receptor did not rescue cortisol-mediated feeding suppression but did increase glucose uptake and abolished the changes seen in mTOR phosphorylation and redd1 transcript abundance. Taken together, our results indicate that GR activation enhances brain proteolysis, and the associated amino acids levels, and not hyperglycemia, maybe a key mediator of the feeding suppression in response to chronic cortisol stimulation in zebrafish.

Alzheimer amyloid-β- peptide disrupts membrane localization of glucose transporter 1 in astrocytes: implications for glucose levels in brain and blood

Alzheimer’s disease (AD) is associated with disturbances in blood glucose regulation, and type-2 diabetes elevates the risk for dementia. A role for amyloid-β peptide (Aβ) in linking these age-related conditions has been proposed, tested primarily in transgenic mouse lines that overexpress mutated amyloid precursor protein (APP). Because APP has its own impacts on glucose regulation, we examined the BRI-Aβ42 line (“Aβ₄₂-tg”), which produces extracellular Aβ_1–42 in the CNS without elevation of APP. We also looked for interactions with diet-induced obesity (DIO) resulting from a high-fat, high-sucrose (“western”) diet. Aβ₄₂-tg mice were impaired in both spatial memory and glucose tolerance. Although DIO induced insulin resistance, Aβ_1–42 accumulation did not, and the impacts of DIO and Aβ on glucose tolerance were merely additive. Aβ₄₂-tg mice exhibited no significant differences from wild-type in insulin production, body weight, lipidemia, appetite, physical activity, respiratory quotient, an-/orexigenic factors, or inflammatory factors. These negative findings suggested that the phenotype in these mice arose from perturbation of glucose excursion in an insulin-independent tissue. To wit, cerebral cortex of Aβ₄₂-tg mice had reduced glucose utilization, similar to human patients with AD. This was associated with insufficient trafficking of glucose transporter 1 to the plasma membrane in parenchymal brain cells, a finding also documented in human AD tissue. Together, the lower cerebral metabolic rate of glucose and diminished function of parenchymal glucose transporter 1 indicate that aberrant regulation of blood glucose in AD likely reflects a central phenomenon, resulting from the effects of Aβ on cerebral parenchyma, rather than a generalized disruption of hypothalamic or peripheral endocrinology. The involvement of a specific glucose transporter in this deficit provides a new target for the design of AD therapies.

Glucose transporters in brain in health and disease

Energy demand of neurons in brain that is covered by glucose supply from the blood is ensured by glucose transporters in capillaries and brain cells. In brain, the facilitative diffusion glucose transporters GLUT1-6 and GLUT8, and the Na⁺-d-glucose cotransporters SGLT1 are expressed. The glucose transporters mediate uptake of d-glucose across the blood-brain barrier and delivery of d-glucose to astrocytes and neurons. They are critically involved in regulatory adaptations to varying energy demands in response to differing neuronal activities and glucose supply. In this review, a comprehensive overview about verified and proposed roles of cerebral glucose transporters during health and diseases is presented. Our current knowledge is mainly based on experiments performed in rodents. First, the functional properties of human glucose transporters expressed in brain and their cerebral locations are described. Thereafter, proposed physiological functions of GLUT1, GLUT2, GLUT3, GLUT4, and SGLT1 for energy supply to neurons, glucose sensing, central regulation of glucohomeostasis, and feeding behavior are compiled, and their roles in learning and memory formation are discussed. In addition, diseases are described in which functional changes of cerebral glucose transporters are relevant. These are GLUT1 deficiency syndrome (GLUT1-SD), diabetes mellitus, Alzheimer’s disease (AD), stroke, and traumatic brain injury (TBI). GLUT1-SD is caused by defect mutations in GLUT1. Diabetes and AD are associated with changed expression of glucose transporters in brain, and transporter-related energy deficiency of neurons may contribute to pathogenesis of AD. Stroke and TBI are associated with changes of glucose transporter expression that influence clinical outcome.

Complex mechanisms linking neurocognitive dysfunction to insulin resistance and other metabolic dysfunction

Scientific evidence has established several links between metabolic and neurocognitive dysfunction, and epidemiologic evidence has revealed an increased risk of Alzheimer’s disease and vascular dementia in patients with diabetes. In July 2015, the National Institute of Diabetes, Digestive, and Kidney Diseases gathered experts from multiple clinical and scientific disciplines, in a workshop entitled “The Intersection of Metabolic and Neurocognitive Dysfunction”, to clarify the state-of-the-science on the mechanisms linking metabolic dysfunction, and insulin resistance and diabetes in particular, to neurocognitive impairment and dementia. This perspective is intended to serve as a summary of the opinions expressed at this meeting, which focused on identifying gaps and opportunities to advance research in this emerging area with important public health relevance.

Daily profile of glut1 and glut4 expression in tissues inside and outside the blood-brain barrier in control and streptozotocin-treated rats

Glucose is molecule usually studied in relation to metabolism. Except for this traditional view, it is known that under certain conditions glucose can serve as a signal molecule for the circadian system. The circadian system is entrained by relevant synchronizing cues that can be tissue-dependent. Central oscillator is synchronized mainly by light-dark cycle, while peripheral oscillators can be entrained by food intake. Glucose transport in the organism is controlled by insulin dependent and independent mechanism. Therefore, we employed streptozotocin-induced diabetes to elucidate the influence of metabolic changes on glucose transporter (glut1, glut4) 24-h expression profile in peripheral oscillators in tissues, inside (frontal cortex, cerebellum) and outside (heart) the blood-brain barrier. Diabetes was induced by streptozotocin injection. Seventeen days later, sampling was performed during a 24-h cycle. Gene expression was measured using real-time PCR. We observed down-regulation of glut1 and glut4 expression in the heart of diabetic rats. The expression of glut1 and glut4 in brain areas was not down-regulated, however, we observed trend to phase advance in glut1 expression in the cerebellum. These results may indicate higher glucose levels in diabetic brain, which might influence regulation of clock gene expression in different manner in brain compared to periphery.

The role of glucose transporters in brain disease: diabetes and Alzheimer’s Disease

The occurrence of altered brain glucose metabolism has long been suggested in both diabetes and Alzheimer’s diseases. However, the preceding mechanism to altered glucose metabolism has not been well understood. Glucose enters the brain via glucose transporters primarily present at the blood-brain barrier. Any changes in glucose transporter function and expression dramatically affects brain glucose homeostasis and function. In the brains of both diabetic and Alzheimer’s disease patients, changes in glucose transporter function and expression have been observed, but a possible link between the altered glucose transporter function and disease progress is missing. Future recognition of the role of new glucose transporter isoforms in the brain may provide a better understanding of brain glucose metabolism in normal and disease states. Elucidation of clinical pathological mechanisms related to glucose transport and metabolism may provide common links to the etiology of these two diseases. Considering these facts, in this review we provide a current understanding of the vital roles of a variety of glucose transporters in the normal, diabetic and Alzheimer’s disease brain.

Simultaneous measurement of glucose blood-brain transport constants and metabolic rate in rat brain using in-vivo 1H MRS

Cerebral glucose consumption and glucose transport across the blood-brain barrier are crucial to brain function since glucose is the major energy fuel for supporting intense electrophysiological activity associated with neuronal firing and signaling. Therefore, the development of noninvasive methods to measure the cerebral metabolic rate of glucose (CMR(glc)) and glucose transport constants (K(T): half-saturation constant; T(max): maximum transport rate) are of importance for understanding glucose transport mechanism and neuroenergetics under various physiological and pathological conditions. In this study, a novel approach able to simultaneously measure CMR(glc), K(T), and T(max) via monitoring the dynamic glucose concentration changes in the brain tissue using in-vivo (1)H magnetic resonance spectroscopy (MRS) and in plasma after a brief glucose infusion was proposed and tested using an animal model. The values of CMR(glc), T(max), and K(T) were determined to be 0.44 ± 0.17 μmol/g per minute, 1.35 ± 0.47 μmol/g per minute, and 13.4 ± 6.8 mmol/L in the rat brain anesthetized with 2% isoflurane. The Monte-Carlo simulations suggest that the measurements of CMR(glc) and T(max) are more reliable than that of K(T). The overall results indicate that the new approach is robust and reliable for in-vivo measurements of both brain glucose metabolic rate and transport constants, and has potential for human application.

Brain glucose concentrations in poorly controlled diabetes mellitus as measured by high-field magnetic resonance spectroscopy

Hyperglycemia and diabetes alter the function and metabolism of many tissues. The effect on the brain remains poorly defined, but some animal data suggest that chronic hyperglycemia reduces rates of brain glucose transport and/or metabolism. To address this question in human beings, we measured glucose in the occipital cortex of patients with poorly controlled diabetes and healthy volunteers at the same levels of plasma glucose using proton magnetic resonance spectroscopy. Fourteen patients with poorly controlled diabetes (hemoglobin A 1c = 9.8% +/- 1.7%, mean +/- SD) and 14 healthy volunteers similar with respect to age, sex, and body mass index were studied at a plasma glucose of 300 mg/dL. Brain glucose concentrations of patients with poorly controlled diabetes were lower but not statistically different from those of control subjects (4.7 +/- 0.9 vs 5.3 +/- 1.1 micromol/g wet wt; P = .1). Our sample size gave 80% power to detect a difference as small as 1.1 micromol/g wet wt. We conclude that chronic hyperglycemia in diabetes does not alter brain glucose concentrations in human subjects.

Glucose transport to the brain: a systems model

Glucose transport to the brain involves sophisticated interactions of solutes, transporters, enzymes, and cell signaling processes, within an intricate spatial architecture. The dynamics of the transport are influenced by the adaptive nature of the blood-brain barrier (BBB), the semi-impermeable membranes of brain capillaries. As both the gate and the gatekeeper between blood-borne nutrients and brain tissue, the BBB helps govern brain homeostasis. Glucose in the blood must cross the BBB's luminal and abluminal membranes to reach neural tissue. A robust representation of the glucose transport mechanism can highlight a target for brain therapeutic intervention, help characterize mechanisms behind several disease phenotypes, or suggest a new delivery route for drugs. The challenge for researchers is understanding the relationships between influential physiological variables in vivo, and using that knowledge to predict how alterations or interventions affect glucose transport. This paper reviews factors influencing glucose transport and approaches to representing blood-to-brain glucose transport including in vitro, in vivo, and kinetic models. Applications for different models are highlighted, while their limitations in answering arising questions about the human in vivo BBB lead to a discussion of an alternate approach. A developing complex systems simulation is introduced, initiating a single platform to represent the dynamics of glucose transport across the adapting human blood-brain barrier.

Glucose transporter expression in the central nervous system: relationship to synaptic function

The family of facilitative glucose transporter (GLUT) proteins is responsible for the entry of glucose into cells throughout the periphery and the brain. The expression, regulation and activity of GLUTs play an essential role in neuronal homeostasis, since glucose represents the primary energy source for the brain. Brain GLUTs exhibit both cell type and region specific localizations suggesting that the transport of glucose across the blood-brain barrier is tightly regulated and compartmentalized. As seen in the periphery, insulin-sensitive GLUTs are expressed in the brain and therefore may participate in the central actions of insulin. The aim of this review will be to discuss the localization of GLUTs expressed in the central nervous system (CNS), with a special emphasis upon the recently identified GLUT isoforms. In addition, we will discuss the regulation, activity and insulin-stimulated trafficking of GLUTs in the CNS, especially in relation to the centrally mediated actions of insulin and glucose.

Progressive cortical atrophy after forebrain ischemia in diabetic rats

The morphological changes in the brain of diabetic rats were examined up to 8 weeks after transient forebrain ischemia produced by transient occlusion of both carotid arteries. Using histochemistry, we also examined the extent and rate of development of atrophic changes in the brain, appearance of astrocytes, activated microglia, and glucose transporter 1 (GLUT1) in streptozotocin-treated rat brains after forebrain ischemia. Atrophic changes appeared in the hippocampus in both non-diabetic-- and diabetic--ischemic groups 4 weeks after ischemia. In diabetic--ischemic rats, the atrophic changes were more severe and progressed more rapidly in the hippocampus, and were also observed in the frontal, temporal and parietal cortices, but not in any cortical areas of the non-diabetic--ischemic rats and non-ischemic--diabetic rats. We observed reduced density of GLUT1 in all cortical regions and hippocampus in ischemic-diabetic rats at 4--8 weeks, when the number of activated microglias and astroglias increased in all cortical regions. Although severe atrophic changes were observed in the gray matter, no serious injury was noted in the white matter in the diabetic-ischemic group. Our results indicate that brain ischemia in the presence of diabetes causes more severe late-onset damage culminating in brain atrophy, compared with non-diabetics.

Neurological changes induced by stress in streptozotocin diabetic rats

Previous studies from our laboratory demonstrated that chronic stress produces molecular, morphological, and ultrastructural changes in the rat hippocampus that are accompanied by cognitive deficits. Glucocorticoid impairment of glucose utilization is proposed as a causative factor involved in stress-induced changes. Current studies have examined the neurological changes induced by stress in rats with a preexisting strain upon their homeostatic load--namely, in streptozotocin (stz)-diabetic rats. Administration of stz (70 mg/kg, i.v.) produced diabetic symptoms such as weight loss, polyuria, polydipsia, hyperglycemia, and neuroendocrine dysfunction. Morphological analysis of hippocampal neurons revealed that diabetes alone produced dendritic atrophy of CA3 pyramidal neurons, an effect potentiated by 7 days of restraint stress. Analysis of genes critical to neuronal homeostasis revealed that glucose transporter 3 (GLUT3) mRNA and protein levels were specifically increased in the hippocampus of diabetic rats, while stress had no effect upon GLUT3 expression. Insulin-like growth factor (IGF) receptor expression was also increased in the hippocampus of diabetic rats subjected to stress. In spite of the activation of these adaptive mechanisms, diabetic rats subjected to stress also had signs of neuronal damage and oxidative damage. Collectively, these results suggest that the hippocampus of diabetic rats is extremely susceptible to additional stressful events, which in turn can lead to irreversible hippocampal damage.

Blood-brain barrier glucose transporter: effects of hypo- and hyperglycemia revisited

The transport of glucose across the blood-brain barrier (BBB) is mediated by the high molecular mass (55-kDa) isoform of the GLUT1 glucose transporter protein. In this study we have utilized the tritiated, impermeant photolabel 2-N-[4-(1 -azi-2,2,2-trifluoroethyl)[2-3H]propyl]-1,3-bis(D-mannose-4-ylo xy)-2-propylamine to develop a technique to specifically measure the concentration of GLUT1 glucose transporters on the luminal surface of the endothelial cells of the BBB. We have combined this methodology with measurements of BBB glucose transport and immunoblot analysis of isolated brain microvessels for labeled luminal GLUT1 and total GLUT1 to reevaluate the effects of chronic hypoglycemia and diabetic hyperglycemia on transendothelial glucose transport in the rat. Hypoglycemia was induced with continuous-release insulin pellets (6 U/day) for a 12- to 14-day duration; diabetes was induced by streptozotocin (65 mg/kg i.p.) for a 14- to 21-day duration. Hypoglycemia resulted in 25-45% increases in regional BBB permeability-surface area (PA) values for D-[14C]glucose uptake, when measured at identical glucose concentration using the in situ brain perfusion technique. Similarly, there was a 23+/-4% increase in total GLUT1/mg of microvessel protein and a 52+/-13% increase in luminal GLUT1 in hypoglycemic animals, suggesting that both increased GLUT1 synthesis and a redistribution to favor luminal transporters account for the enhanced uptake. A corresponding (twofold) increase in cortical GLUT1 mRNA was observed by in situ hybridization. In contrast, no significant changes were observed in regional brain glucose uptake PA, total microvessel 55-kDa GLUT1, or luminal GLUT1 concentrations in hyperglycemic rats. There was, however, a 30-40% increase in total cortical GLUT1 mRNA expression, with a 96% increase in the microvessels. Neither condition altered the levels of GLUT3 mRNA or protein expression. These results show that hypoglycemia, but not hyperglycemia, alters glucose transport activity at the BBB and that these changes in transport activity result from both an overall increase in total BBB GLUT1 and an increased transporter concentration at the luminal surface.

Shortening of poly (A) tail of glucose transporter--one mRNA in experimental diabetes mellitus

To determine the molecular mechanisms of diabetes-related changes in the expression of GLUT-1 in cerebral tissue, streptozotocin-induced diabetic rats and vehicle injected controls were studied after 4 weeks of diabetes. The GLUT-1 mass in cerebral microvessels was reduced in diabetic rats by approximately 38% (P < 0.01). The GLUT-1 concentration in insulin-treated diabetic group was not significantly different from controls. The GLUT-1 mRNA content of cerebral tissue in diabetic rats (0.064 +/- 0.007) was significantly reduced compared to control rats (0.122 +/- 0.011) or insulin-treated diabetic rats (0.122 +/- 0.015) P < 0.01. The in vitro translation of GLUT-1 mRNA of diabetic rats (0.793 +/- 0.047 arbitrary units) was also significantly lower than that in control rats (1.403 +/- 0.153) P < 0.01 or insulin-treated diabetic rats. (1.124 +/- 0.083) P < 0.01. These changes occurred in asssociation with a reduction in poly (A) tail length of GLUT-1 mRNA which decreased from a control value of 200-350 nt to only 50-100 nt in diabetic rats. Shortening of poly (A) tail of mRNAs is a novel mechanism of diabetes-related changes in the expression of specific genes which are regulated at a translational level.

Central nervous system complications of diabetes mellitus--a perspective from the blood-brain barrier

A host of diabetes-related changes in the central nervous system (CNS) has been recognized. The underlying causes of these changes are multiple. An important contributor to the changes in the CNS is the blood-brain barrier (BBB). Diabetes is associated with changes in both the barrier and transport functions of the cerebral microvessels. Structural changes in cerebral microvessels may account for some of the observed changes. Additional mechanisms include alterations in hemodynamic variables such as arteriovenous shunting, changes in biophysical properties and biochemical compositions of the endothelial cells including changes in lipid fluidity and composition, and alterations of neurotransmitter activity in the cerebral microvessels, notably altered beta adrenergic neurotransmission. These observations indicate that the CNS is not immune against the microangiopathic complications commonly found in various tissues of diabetic animals.

The estrogen connection: the etiological relationship between diabetes, cancer, rheumatoid arthritis and psychiatric disorders

For some considerable time, there has been a growing awareness that defective essential fatty acid metabolism plays a causal role in the pathogenesis of both schizophrenia and non-insulin-dependent diabetes mellitus (NIDDM) but the influence of defective essential fatty acid metabolism in the pathogenesis of rheumatoid arthritis and cancer is less well appreciated. An EFA deficiency, or defective EFA metabolism, negatively influences prostaglandin synthesis and glucose regulation and transport. Moreover, defective EFA metabolism negatively influences estrogen availability which contributes to the observed gender bias some of these illnesses manifest. While fluctuations of estrogen are known to contribute to the pathogenesis of these conditions, so also do fluctuations of IGF-II and there is some suggestion that IGF-II and insulin may well be inversely regulated. In addition, insulin-dependent diabetes mellitus (IDDM), rheumatoid arthritis, and schizophrenia are thought to be autoimmune disorders, while cancer is associated with immune system failure. Consequently, this paper aims to examine the pathophysiological similarities and differences between mental illness, diabetes, rheumatoid arthritis and cancer in respect of which the causal relationship that obtains between essential fatty acids, estrogen, IGF-II, glucose regulation and autoimmunity will be addressed.

Down-regulation of blood-brain glucose transport in the hyperglycemic nonobese diabetic mouse

The intracarotid injection method has been utilized to examine blood-brain barrier (BBB) glucose transport in hyperglycemic (4-6 days) mice. In anesthetized mice, Brain Uptake Indices were measured over a range of glucose concentrations from 0.010-50 mmol/l; glucose uptake was found to be saturable and kinetically characterized. The maximal velocity (Vmax) for glucose transport was 989 +/- 214 nmol.min-1.g-1. and the half-saturation constant estimated to be 5.80 +/- 1.38 mmol/l. The unsaturated Permeability Surface area product (PS) is = 171 + 8 microliters.min.-1.g-1. A rabbit polyclonal antiserum to a synthetic peptide encoding the 13 C-terminal amino acids of the human erythrocyte glucose transporter immunocytochemically confirmed the presence of the GLUT1 isoform in non-obese diabetic (NOD) mouse brain capillary endothelia. These studies indicate that a down-regulation of BBB glucose transport occurs in these spontaneously hyperglycemic mice; both BBB glucose permeability (as indicated by PS product) and transporter maximal velocity are reduced (in comparison to normoglycemic CD-1 mice), but the half-saturation constant remains unchanged.

Glucose transporter gene expression: regulation of transcription and mRNA stability

The facilitated diffusion of D-glucose across the plasma membrane is carried out by a set of stereospecific transport proteins known as the glucose transporters. These integral membrane proteins are members of a gene family where tissue-specific expression of one or more members will determine in part the net rate of glucose entry into the cell. The regulation of glucose transporter gene expression is a critical feature of cellular homeostasis, as defects in specific transporter expression can lead to profound alterations in cellular physiology. In this review, we provide a brief descriptive background on the family of glucose transporters and examine in depth the regulation of the two transporters expressed in adipose tissue, GLUTI, a basal growth-related transporter and GLUT4, the insulin-responsive glucose transporter.

Schizophrenia, suicide and the serotonin story

In this paper, the relationship between schizophrenia, suicide and serotonin will be examined. Throughout, it will be argued that the fundamental problem does not lie with the neurotransmitter per se, but rather with uncontrolled fluctuations of brain glycaemic levels acting in conjunction with insulin resistance. It will be shown that the area of dopaminergic and serotonergic activity in the brain is intimately tied to the relative distribution of the central glucose transporters and, hence, to glucose metabolism and insulin activity. It will be argued that mania and positive schizophrenia represent a continuum of liability associated with hyperglycaemia, hyperdopaminergia, and hyperserotonergia. In contrast, depression and negative schizophrenia represent another continuum of liability involving hypoglycaemia, hypodopaminergia, and hyposerotonergia. This serves as a useful distinction in drawing together a large number of seemingly unrelated, diverse facts concerning both schizophrenia and suicide and, in particular, the possible relationship that obtains between cholesterol-lowering drugs, low serotonin and suicide. Essentially, this paper reaffirms a previously stated contention that mental illness, in its many guises, is a general manifestation of a diabetic brain state which has been termed 'cerebral diabetes'.

Palmitoylation of the glucose transporter in blood-brain barrier capillaries

Palmitoylation of GLUT1 was investigated in brain capillaries. The glucose transporter was shown to be palmitoylated using [3H]palmitate labeling and immunoprecipitation. The labeling was sensitive to methanolic KOH or hydroxylamine hydrolysis, indicating the presence of an ester or thioester bond. The released fatty acid was analyzed by reverse-phase HPLC and was identified as [3H]palmitate. Specificity of the immunoprecipitation was assessed by competitive inhibition of anti-GLUT1 binding with a synthetic C-terminal peptide against which the antibody was raised. In vivo studies were performed using capillaries isolated from control rats, streptozotocin-induced diabetic rats and diet-induced hyperglycemic rats. Glycemia was increased 2- and 5-fold in the hyperglycemic and diabetic groups, respectively. GLUT1 expression was evaluated in the three groups by Western blot analysis. A 36% decrease in GLUT1 expression was observed in the diabetic group, while there was no significant variation in GLUT1 expression in the hyperglycemic group. Palmitoylation of GLUT1 was increased in both diet-induced hyperglycemic and diabetic groups. These results suggest that palmitoylation may be involved in the regulation of glucose transport activity in hyperglycemia.

Blood-brain glucose transfer in the mouse

The intracarotid injection method has been utilized to examine blood-brain barrier (BBB) glucose transport in normal mice, and after a 2-day fast. In anesthetized mice, cerebral blood flow (CBF) rates were reduced from 0.86 ml.min-1 x gm-1 in control to 0.80 ml.min-1 x gm-1 in fasted animals (p > 0.05). Brain Uptake Indices were significantly (p < 0.05) higher in fasted (plasma glucose = 4.7 mM) than control (plasma glucose = 6.5 mM) mice, while plasma glucose was significantly lower. The maximal velocity (Vmax) for glucose transport was 1562 +/- 303 nmoles.min-1 x g-1, and the half-saturation constant (Km =) 6.67 +/- 1.46 mM in normally fed mice. In fasted mice the Vmax was 2053 +/- 393 nmoles.min-1 x g-1 (p > 0.05), and the half-saturation constant (Km =) 7.40 +/- 1.60 mM (not significant, P > 0.05). A rabbit polyclonal antiserum to a synthetic peptide encoding the 13 C-terminal amino acids of the human erythrocyte glucose transporter (GLUT-1) immunocytochemically confirmed that the mouse brain capillary endothelial glucose transporter is a GLUT-1 transporter, and immunoreactivity was similar in brain endothelia from fed and fasted animals. In conclusion, after a 2-day fast in the mouse, we saw significant reductions in forebrain weight (7%), and plasma glucose levels (27%). Increased brain glucose extraction (25%, p < 0.05), and a 22% increase in the unsaturated permeability-surface area product (p < 0.05) was also observed.