Blood-brain barrier transport of nutrients

Lactate-Protected Hypoglycemia (LPH)

Here, we provide an overview of the concept of a lactate-protected hypoglycemia (“LPH”), originally proposed as lowering glucose while simultaneously increasing lactate concentration as a method by which tumors might be targeted. Central to this hypothesis is that lactate can act as a critical salvage fuel for the central nervous system, allowing for wide perturbations in whole body and central nervous system glucose concentrations. Further, many tumors exhibit “the Warburg” effect, consuming glucose and producing and exporting lactate despite adequate oxygenation. While some recent data have provided evidence for a “reverse-Warburg,” where some tumors may preferentially consume lactate, many of these experimental methods rely on a significant elevation in lactate in the tumor microenvironment. To date it remains unclear how various tumors behave in vivo, and how they might respond to perturbations in lactate and glucose concentrations or transport inhibition. By exploiting and targeting lactate transport and metabolism in tumors (with a combination of changes in lactate and glucose concentrations, transport inhibitors, etc.), we can begin developing novel methods for targeting otherwise difficult to treat pathologies in the brain and spinal cord. Here we discuss evidence both experimental and observational, and provide direction for next steps in developing therapies based on these concepts.

L-histidine and L-carnosine exert anti-brain aging effects in D-galactose-induced aged neuronal cells

BACKGROUND/OBJECTIVES

Brain aging is a major risk factor for severe neurodegenerative diseases. Conversely, L-histidine and L-carnosine are known to exhibit neuroprotective effects. The aim of this study was to examine the potential for L-histidine, L-carnosine, and their combination to mediate anti-brain aging effects in neuronal cells subjected to D-galactose-induced aging.

MATERIALS/METHODS

The neuroprotective potential of L-histidine, L-carnosine, and their combination was examined in a retinoic acid-induced neuronal differentiated SH-SY5Y cell line exposed to D-galactose (200 mM) for 48 h. Neuronal cell proliferation, differentiation, and expression of anti-oxidant enzymes and apoptosis markers were subsequently evaluated.

RESULTS

Treatment with L-histidine (1 mM), L-carnosine (10 mM), or both for 48 h efficiently improved the proliferation, neurogenesis, and senescence of D-galactose-treated SH-SY5Y cells. In addition, protein expression levels of both neuronal markers (β tubulin-III and neurofilament heavy protein) and anti-oxidant enzymes, glutathione peroxidase-1 and superoxide dismutase-1 were up-regulated. Conversely, protein expression levels of amyloid β (1-42) and cleaved caspase-3 were down-regulated. Levels of mRNA for the pro-inflammatory cytokines, interleukin (IL)-8, IL-1β, and tumor necrosis factor-α were also down-regulated.

CONCLUSIONS

To the best of our knowledge, we provide the first evidence that L-histidine, L-carnosine, and their combination mediate anti-aging effects in a neuronal cell line subjected to D-galactose-induced aging. These results suggest the potential benefits of L-histidine and L-carnosine as anti-brain aging agents and they support further research of these amino acid molecules.

Cerebrospinal fluid lactate in dogs with inflammatory central nervous system disorders

Background

Cerebrospinal fluid (CSF) lactate is frequently used as a biomarker in humans with inflammatory central nervous system (CNS) disorders including bacterial meningitis and autoimmune disorders such as multiple sclerosis.

Hypothesis

Cerebrospinal fluid lactate concentrations are increased in a subset of dogs with inflammatory CNS disorders.

Animals

One hundred two client‐owned dogs diagnosed with inflammatory CNS disease.

Methods

Case series. Cases were identified both prospectively at the time of diagnosis and retrospectively by review of a CSF biorepository. Cerebrospinal fluid lactate was analyzed with a commercially available, handheld lactate monitor. Subcategories of inflammatory disease were created for comparison (eg, steroid‐responsive meningitis arteritis, meningoencephalitis of unknown etiology).

Results

Cerebrospinal fluid lactate concentrations were above reference range in 47% of dogs (median, 2.5 mmol/L; range, 1.0‐11.7 mmol/L). There was no significant difference in lactate concentrations between disease subcategories (P = .48). Significant but weak correlations were noted between CSF lactate concentration and nucleated cell count (r = .33, P < .001), absolute large mononuclear cell count (r = .44, P < .001), absolute small mononuclear cell count (r = .39, P < .001), absolute neutrophil cell count (r = .24, P = .01), and protein (r = .44, P < .001). No correlation was found between CSF lactate concentration and CSF red blood cell count (P = .58). There was no significant association of CSF lactate concentration with survival (P = .27).

Conclusions and Clinical Importance

Cerebrospinal fluid lactate concentrations could serve as a rapid biomarker of inflammatory CNS disease in dogs.

Preliminary fMRI findings concerning the influence of 5-HTP on food selection

OBJECTIVE

This functional magnetic resonance imaging study was designed to observe how physiological brain states can alter food preferences. A primary goal was to observe food-sensitive regions and moreover examine whether 5-HTP intake would activate areas which have been associated with appetite suppression, anorexia, satiety, and weight loss.

METHODS AND PROCEDURE

Fourteen healthy male and female participants took part in the study, of which half of them received the supplement 5-HTP and the rest vitamin C (control) on an empty stomach. During the scanning session, they passively observed food (high calories, proteins, carbohydrates) and nonfood movie stimuli.

RESULTS

Within the 5-HTP group, a comparison of food and nonfood stimuli showed significant responses that included the limbic system, the basal ganglia, and the prefrontal, temporal, and parietal cortices. For the vitamin C group, activity was mainly located in temporal and occipital regions. Compared to the vitamin C group, the 5-HTP group in response to food showed increased activation on the VMPFC, the DLPFC, limbic, and temporal regions. For the 5-HTP group, activity in response to food high in protein content compared to food high in calories and carbohydrates was located in the limbic system and the right caudomedial OFC, whereas for the vitamin C group, activity was mainly located at the inferior parietal lobes, the anterior cingulate gyri, and the left ventrolateral OFC. Greater responses to carbohydrates and high calorie stimuli in the vitamin C group were located at the right temporal gyrus, the occipital gyrus, the right VLPFC, whereas for the 5-HTP group, activity was observed at the left VMPFC, the parahippocampal gyrus bilaterally, the occipital lobe, and middle temporal gyri.

DISCUSSION

In line with the hypotheses, 5-HTP triggered cortical responses associated with healthy body weight as well as cerebral preferences for protein-rich stimuli. The brain's activity is altered by macronutrients rich or deprived in the body. By reading the organisms physiological states and combining them with memory experiences, it constructs behavioral strategies steering an individual toward or in opposition to a particular food.

The effect of histidine on mental fatigue and cognitive performance in subjects with high fatigue and sleep disruption scores

Our previous study reported that a dried bonito broth known in Japan as 'dashi' improved or ameliorated mood states, including fatigue, during the daily lives of human subjects. Histidine is an amino acid that is present in dried bonito broth, and we sought to evaluate whether histidine would affect feelings of fatigue in humans. We investigated the effects of histidine intake on the feeling of fatigue, mood states and mental task performance by performing a placebo-controlled, double-blind crossover trial. Twenty subjects with high fatigue and sleep disruption scores were asked to ingest histidine or a placebo every day for two weeks. The subjects' mood states were evaluated using the Profile of Mood States (POMS) scale and a visual analog scale (VAS) for eight feelings (fatigue, depression, carelessness, drowsiness, clear thinking, motivation, attentiveness and concentration). We also measured subjects' cognitive performance using the CogHealth test battery. The fatigue T-scores on the POMS test decreased significantly following histidine ingestion compared to placebo ingestion (p<0.05). After two weeks of histidine ingestion, the reaction time for the working memory task in the CogHealth test battery was significantly shorten compared to placebo ingestion. The VAS scores for clear thinking and for attentiveness were increased significantly following histidine ingestion compared to placebo ingestion (p<0.05). These results suggest that daily ingestion of histidine may ameliorate feelings of fatigue, increase performance during working memory tasks, and improve the clear thinking and attentiveness.

Unlocking the Energy Dynamics of Executive Functioning: Linking Executive Functioning to Brain Glycogen

Past work suggests that executive functioning relies on glucose as a depletable energy, such that executive functioning uses a relatively large amount of glucose and is impaired when glucose is low. Glucose from the bloodstream is one energy source for the brain, and glucose stored in the brain as glycogen is another. A review of the literature on glycogen suggests that executive functioning uses it in much the same way as glucose, such that executive functioning uses glycogen and is impaired when glycogen is low. Findings on stress, physical persistence, glucose tolerance, diabetes, sleep, heat, and other topics provide general support for this view.

Effects of rapid tryptophan depletion on salivary cortisol in older people recovered from depression, and the healthy elderly

Reduced serotonin (5-HT) function and abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis are thought to play a role in the aetiology of major depression. We sought to examine this issue in the elderly by assessing the effects of lowering brain 5-HT on salivary and plasma cortisol in elderly patients who had recovered from at least one episode of major depression and in a healthy, age matched comparison group. A double-blind, cross-over design involving administration of two nutritionally balanced amino acid mixtures (with or without tryptophan) was used. Salivary cortisol was measured at intervals before and after the drink. There was no effect of acute tryptophan depletion (ATD) on salivary cortisol (ATD by time; F=0.97, df=7,210, p=0.454) but a significant interaction between group and time (F=3.91, df=7,210, p=0.010). Healthy subjects showed a marked increase in cortisol levels 2-3 hours into the procedure regardless of drink composition while recovered depressed subjects did not. In elderly patients who had recovered from depression there was no evidence of greater vulnerability of hypothalamic 5-HT pathways to 5-HT depletion. However, they demonstrated reduced reactivity of the HPA axis compared to healthy subjects.

Add Alzheimer’s disease to the list of autoimmune diseases

A sole pathological event leading to Alzheimer's disease (AD) remains undiscovered in spite of decades of costly research. In fact, it is more probable that the causes of AD are the result of a myriad of intertwining pathologies. However, hope remains that a single awry event could lead to the many pathological events observed in AD brain tissues thereby creating the presentation of simultaneous pathologies. Age-related vascular diseases, which include an impaired blood-brain barrier (BBB), are a common denominator associated with various degrees of dementia, including AD. Recently, a key finding not only demonstrated the anomalous presence of immunoglobulin (Ig) detection in the brain parenchyma of AD tissues but, most importantly, specific neurons that showed degenerative, apoptotic features contained these vascular-derived antibodies. In addition, subsequent studies detected classical complement components, C1q and C5b-9, in these Ig-positive neurons, which also were spatially more associated with reactive microglia over the Ig-negative neurons. Thus, it is possible that the mere presence of anti-neuronal autoantibodies in the serum, whose importance had been previously dismissed, may be without pathological consequence until there is a BBB dysfunction to allow the deleterious effects of these autoantibodies access on their targets. Hence, these observations suggest autoimmunity-induced cell death in AD.

Usefulness of positron emission tomography in diagnosis and treatment follow-up of brain tumors

Clinical and experimental use of positron emission tomography (PET) is expanding and allows quantitative assessment of brain tumor's pathophysiology and biochemistry. PET therefore provides different biochemical and molecular information about primary brain tumors when compared to histological methods or neuroradiological studies. Common clinical indications for PET contain primary brain tumor diagnosis and identification of the metabolically most active brain tumor reactions (differentiation of viable tumor tissue from necrosis), prediction of treatment response by measurement of tumor perfusion, or ischemia. The interesting key question remains not only whether the magnitude of biochemical alterations demonstrated by PET reveals prognostic value with respect to survival, but also whether it identifies early disease and differentiates benign from malignant lesions. Moreover, an early identification of treatment success or failure by PET could significantly influence patient management by providing more objective decision criteria for evaluation of specific therapeutic strategies. Specially, as PET represents a novel technology for molecular imaging assays of metabolism and signal transduction to gene expression, reporter gene assays are used to trace the location and temporal level of expression of therapeutic and endogenous genes. PET probes and drugs are being developed together as molecular probes to image the function of targets without disturbing them and in mass amounts to modify the target's function as a drug. Molecular imaging by PET helps to close the gap between in vitro to in vivo integrative biology of disease.

The role of drug transporters at the blood-brain barrier

The blood-brain barrier (BBB) is a dynamic interface between the blood and the brain. It eliminates (toxic) substances from the endothelial compartment and supplies the brain with nutrients and other (endogenous) compounds. It can be considered as an organ protecting the brain and regulating its homeostasis. Until now, many transport systems have been discovered that play an important role in maintaining BBB integrity and brain homeostasis. In this review, we focus on the role of carrier- and receptor-mediated transport systems (CMT, RMT) at the BBB. These include CMT systems, such as P-glycoprotein, multidrug-resistance proteins 1-7, nucleoside transporters, organic anion transporters, and large amino-acid transporters; RMT systems, such as the transferrin-1 and -2 receptors; and the scavenger receptors SB-AI and SB-BI.

Ultrasound-induced mild hyperthermia as a novel approach to increase drug uptake in brain microvessel endothelial cells

PURPOSE

Drug delivery to the central nervous system (CNS) is limited by the blood-brain barrier (BBB). Thus, a noninvasive and reversible method to enhance BBB permeation of drugs is highly desirable. In the present work, we studied if ultrasound-induced mild hyperthermia (USHT, 0.4 watts (W)/cm2 at 41 degrees C) can enhance drug absorption in BBB endothelial cells, and we elucidated the mechanism of USHT on cellular accumulation.

METHODS

To accomplish these aims, we studied the effects of hyperthermia (41 degrees C), USHT, P-glycoprotein (P-gp) modulator (PSC 833), and combination of USHT and PSC 833 on accumulation of P-gp substrate (R123) and non-P-gp substrates (sucrose, 2-deoxyglucose, and antipyrine) in monolayers of primary bovine brain microvessel endothelial cells (BBMEC).

RESULTS

USHT, through its thermal effect, produces a significant (relative to controls; no USHT) and comparable increase in R123 accumulation with PSC 833. We also demonstrate that USHT increases permeability of hydrophobic (R123 and [14C]-antipyrine) and not hydrophilic molecules ([14C]-sucrose and 2-[3H]-deoxy-D-glucose). The enhanced permeability is reversible and size dependent, as USHT produces a much larger effect on cellular accumulation of [14C]-antitpyrine (molecular weight of 188 D) than that of R123 (molecular weight of 380.8 D). Although USHT increases membrane permeability, it did not affect P-gp activity or the activity of glucose transporters.

CONCLUSIONS

Our results point to the potential use of USHT as a reversible and noninvasive approach to increase BBB permeation of hydrophobic drugs, including P-gp-recognized substrates.

Effects of rapid tryptophan depletion on salivary and plasma cortisol in Alzheimer's disease and the healthy elderly

Serotonergic function is reduced in dementia of Alzheimer type (DAT) and abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis are also common. There is considerable interaction between the two systems. Effects of lowering brain serotonin on salivary and plasma cortisol were assessed in patients with DAT and in control subjects. A double-blind, cross-over design involving administration of two nutritionally balanced amino acid mixtures with or without tryptophan was used. Salivary and plasma cortisol were measured at intervals before and after the drink. DAT patients had higher salivary cortisol than controls. Despite a reduction of approximately 70% in plasma free tryptophan after 4 h in both groups, there was no effect on salivary or plasma cortisol. We conclude that, in subjects with DAT and healthy elderly subjects, acute tryptophan depletion had no effect on cortisol secretion.

Glucose tolerance predicts performance on tests of memory and cognition

The hypothesis that the ability to control blood glucose levels influence memory and other aspects of cognition was considered. Individual differences in the ability to control blood glucose were measured by giving a glucose tolerance test (GTT) to 46 young adult females. A factor analysis of a series of measures of glucose tolerance produced four dimensions. A week later, having eaten their normal breakfast, they took tests of memory, reaction times and vigilance. The speed with which blood glucose increased, having its lowest point in the GTT, was associated with memory measured a week later. While performing the tests those with higher levels of blood glucose on arrival in the laboratory had quicker reaction times when monitoring eight but not four, two or one lamps. The finding was interpreted as demonstrating that higher levels of blood glucose specially influence tasks placing higher demands on the brain.

Effect of bioflavonoids on vincristine transport across blood-brain barrier

Several grapefruit juice bioflavonoids, including quercetin, are reported to stimulate P-glycoprotein-mediated drug efflux from cultured tumor cells. To see whether these bioflavonoids alter the permeation of vincristine across the blood-brain barrier, we conducted experiments with cultured mouse brain capillary endothelial cells (MBEC4 cells) in vitro and ddY mice in vivo. The steady-state uptake of [3H]vincristine by MBEC4 cells was decreased by 10 microM quercetin, but increased by 50 microM quercetin. Similarly, the in vivo brain-to-plasma concentration ratio of [3H]vincristine in ddY mice was decreased by coadministration of 0.1 mg/kg quercetin, but increased by 1.0 mg/kg quercetin. Kaempferol had a similar biphasic effect on the in vitro uptake of [3H]vincristine. Other aglycones tested (chrysin, flavon, hesperetin, naringenin) increased [3H]vincristine uptake in the 10-50 microM range, and glycosides (hesperidin, naringin, rutin) were without effect. We then addressed the mechanism of the concentration-dependent biphasic action of quercetin. Verapamil, a P-glycoprotein inhibitor, inhibited the efflux of [3H]vincristine from MBEC4 cells, while 10 microM quercetin significantly stimulated it. The uptake of [3H]vincristine by MBEC4 cells was increased by inhibitors of protein kinase C, but decreased by phorbol 12-myristate-13-acetate (PMA), as well as by 10 microM quercetin. The phosphorylation level of P-glycoprotein was increased in the presence of 5 microM quercetin or 100 nM PMA, but decreased by the protein kinase C inhibitor H7 (1-(5-isoquinolinesulfonyl)-2-methylpiperazine, 30 microM). We conclude that low concentrations of quercetin indirectly activate the transport of [3H]vincristine by enhancing the phosphorylation (and hence activity) of P-glycoprotein, whereas high concentrations of quercetin inhibit P-glycoprotein. Our results indicate that patients taking drugs which are P-glycoprotein substrates may need to restrict their intake of bioflavonoid-containing foods and beverages, such as grapefruit juice.

Indinavir-based treatment of HIV-1 infected patients: efficacy in the central nervous system

OBJECTIVE

To study the pharmacokinetic properties and clinical efficacy of the HIV-1 protease inhibitor (PI) indinavir in the central nervous system (CNS).

DESIGN

Twenty-five consecutive HIV-1 infected patients on combination therapy that included indinavir, had cerebrospinal fluid (CSF) and plasma samples taken on 32 different occasions, at different times after indinavir administration. CSF and viral load data obtained from these treated patients were compared with those from 36 untreated HIV-1 infected patients of similar immunological and demographic pre-treatment status.

METHODS

Concentrations of indinavir were measured in CSF and plasma by high-pressure liquid chromatography with ultraviolet light detection and the data were used in pharmacokinetic modelling.

RESULTS

The concentration of indinavir in plasma varied with time over a dose interval by about two orders of magnitude, whereas the concentration in CSF was relatively stable. The median concentration of indinavir in CSF was 210 nmol/l, which is above the 95% inhibitory concentration in vitro. Findings from the pharmacokinetic modelling indicate that indinavir is actively transported out of the CSF (P <0.001 compared with a passive transport-only model). In the PI-treated group there was a reduction in viral load to below 50 copies/ml in most subjects and a normalization of the CSF cell content and IgG-index.

CONCLUSIONS

This study has shown that one PI, indinavir, is present in the CSF at therapeutic concentrations, and is likely to contribute to the antiretroviral activities observed within the CNS.

Developmental expression pattern of Stra6, a retinoic acid-responsive gene encoding a new type of membrane protein

Retinoic acid plays important roles in development, growth and differentiation by regulating the expression of target genes. A new retinoic acid-inducible gene, Stra6, has been identified in P19 embryonal carcinoma cells using a subtractive hybridization cDNA cloning technique. Stra6 codes for a very hydrophobic membrane protein of a new type, which does not display similarities with previously characterized integral membrane proteins. Stra6, which exhibits a specific pattern of expression during development and in the adult, is strongly expressed at the level of blood-organ barriers. Interestingly, in testis Sertoli cells, Stra6 has a spermatogenic cycle-dependent expression which is lost in testes of RAR alpha null mutants where Stra6 is expressed in all tubules. We suggest that the Stra6 protein may be a component of an as yet unidentified transport machinery.

Influence of organic acids on aluminium absorption and storage in rat tissues

Six groups of 16 rats each were fed a standard diet for 8 weeks. Aluminium (Al) complexed with organic anions (citrate, lactate, malate, or tartrate) was added to the diet of four of the groups and aluminium hydroxide to the diet of one group (control 'Al +'). Aluminium concentrations in the diets were 1500-2000 mg/kg. The sixth group (control 'Al -') served as control. Plasma, bone (femur), kidneys, cerebral cortex and cerebellum levels of aluminium were determined at 4 and 8 weeks. All the complexing agents increased tissue accumulations, compared with values in the two control groups, especially citrate in bone and kidneys and lactate in cerebral cortex. There were no significant differences (P < 0.05) in aluminium levels in the tissues considered between the 'Al +' and 'Al -' control groups. Our results show the ability of dietary organic acids to increase aluminium absorption and tissue accumulation and indicate that concurrent intake of aluminium and dietary organic acids is not appropriate.

Brain large neutral amino acids and catecholamines in parenterally nourished preterm rabbits

Total parenteral nutrition (TPN) has been adapted as a standard for providing nutrition to ill term and preterm infants. The availability of tyrosine in amino acid preparations utilized for TPN is limited and may potentiate a tyrosine-deficient state. Phenlyalanine hydroxylase activity, responsible for catalyzing tyrosine synthesis, has been suggested to be decreased in fetal and neonatal animals. Parenterally nourished premature rabbits (n = 16) and suckled rabbits (n = 19) were studied in order to compare growth parameters and amino acids in the plasma and brain, as well as whole brain catecholamine concentrations. Influx velocities into the brain of amino acids were also determined in these two groups. The preterm rabbit's average birth weight (42.6 +/- 6.0) was less than that of term rabbits (56.7 +/- 8.7, P < 0.005). Significantly lower concentrations of the catecholamine precursor tyrosine were found in both the plasma and brain of the parenterally nourished animals compared to the suckled animals. Tyrosine is reduced in the brain in TPN-supported animals reflecting both low tyrosine intake and increased plasma concentrations of large neutral amino acids that compete for uptake at the blood-brain barrier. However, no difference was observed between the two groups in their brain catecholamine concentrations. The seven-day parenterally nourished rabbit appears to be tyrosine-deficient but no evident effects on brain catecholamine concentrations were seen. The effects and impact of a tyrosine-deficient state might better be evaluated by regional evaluation of catecholaminergic areas of the brain or over a longer period of parenteral nutrition.

Effects of handling or immobilization on plasma levels of 3,4-dihydroxyphenylalanine, catecholamines, and metabolites in rats

In conscious animals, handling and immobilization increase plasma levels of the catecholamines norepinephrine (NE) and epinephrine (EPI). This study examined plasma concentrations of endogenous compounds related to catecholamine synthesis and metabolism during and after exposure to these stressors in conscious rats. Plasma levels of 3,4-dihydroxyphenylalanine (DOPA), NE, EPI, and dopamine (DA), the deaminated catechol metabolites 3,4-dihydroxyphenylglycol (DHPG), and 3,4-dihydroxyphenylacetic acid (DOPAC), and their O-methylated derivatives methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured using liquid chromatography with electrochemical detection at 1, 3, 5, 20, 60, and 120 min of immobilization. By 1 min of immobilization, plasma NE and EPI levels had already reached peak values, and plasma levels of DOPA, DHPG, DOPAC, and MHPG were increased significantly from baseline, whereas plasma DA and HVA levels were unchanged. During the remainder of the immobilization period, the increased levels of DOPA, NE, and EPI were maintained, whereas levels of the metabolites progressively increased. In animals immobilized briefly (5 min), elevated concentrations of the metabolites persisted after release from the restraint, whereas DOPA and catecholamine levels returned to baseline. Gentle handling for 1 min also significantly increased plasma levels of DOPA, NE, EPI, and the NE metabolites DHPG and MHPG, without increasing levels of DA or HVA. The results show that in conscious rats, immobilization or even gentle handling rapidly increases plasma levels of catecholamines, the catecholamine precursor DOPA, and metabolites of NE and DA, indicating rapid increases in the synthesis, release, reuptake, and metabolism of catecholamines.

Altered glucose metabolism in microvessels from patients with Alzheimer's disease

Microvessels isolated from temporal cortex of patients with Alzheimer's disease showed decreased uptake of glucose when compared with vessels from age-matched or young control subjects. This was due to decreased hexokinase activity in the Alzheimer samples, as determined by ion exchange chromatography. This finding was confirmed independently by determination of the phosphorylation constant for hexokinase, K3, using positron emission tomography. The results suggest that Alzheimer's disease may result from a global defect in brain energy metabolism.

Glucose improves attention and reaction to frustration in children

There have been many suggestions that both dietary sugar and the level of blood glucose may be associated with abnormal behaviour. To examine this question 60 six- and seven-year old children were given a drink that contained either 25 grams of glucose or a placebo towards the end of the school day. They were then subjected to one test that required sustained attention and to a second that was intentionally frustrating. Those given the drink containing glucose were more capable of sustaining attention and showed fewer signs of frustration.