Therefore, the oxygen concentrations in the brain are an important parameter that influences the function of nerve cells and glial cells. However, how much oxygen is consumed in the brain and how this is related to neuronal activity was so far largely unknown.
The scientists report on their results in the journal BMC Biology. In an already established animal model -- tadpoles of the clawed frog Xenopus laevis -- the scientists used electrochemical sensors to determine the concentration of oxygen in the brain and in one of the brain ventricles. They were able to specifically control the amount of oxygen available to the brain as well as inhibit nerve cell activity with the help of pharmacological substances.
Using the example of nerve cells that control eye movements, the scientists succeeded in directly recording the relationship between oxygen consumption and nerve cell activity. The complete oxygen was therefore immediately used by the cells to synthesize energy-rich substances. The electrophysiology experiments confirmed that oxygen sensing nanoparticles did not measurably alter the electrophysiological properties of the neurons.
I-Clamp trace of neurons in the oxygen sensing nanoparticle treated slice a and the control slice b. Oxygen nanosensors based on phosphorescence quenching can provide information about the brain with improved micron-level spatial and sub-seconds temporal resolution. In this work, the boron nanoparticles were used to study brain activity. Specifically, primary neuronal cell cultures were labeled by blue nanoparticles from BF 2 dbmPLA to confirm intracellular uptake. Electrophysiology experiments revealed that the application of nanoparticles did not have a significant effect on the electrophysiological properties of neurons.
In ex vivo brain slices, it was found that the neuronal cell bodies consume less oxygen than dendrites and synapses where mitochondria are more concentrated for synaptic activities. These data suggested the capability of boron nanoparticles serving as powerful and non-invasive sensing agents in the brain.
Future work will involve oxygen imaging in the living animal and in combination with seizures induced via a cobalt model to study how oxygen levels are related to seizures. All methods were carried out in accordance with relevant guidelines and regulations.
All chemicals were obtained from Sigma Aldrich St. The boron dye-polymer was prepared according to a previously reported method Coupling constants are given in hertz. UV—vis spectra were recorded on a Hewlett—Packard A diode-array spectrophotometer. Steady-state fluorescence spectra for the nanoparticle suspensions were recorded on a Horiba Fluorolog-3 Model FL spectrofluorometer double-grating excitation and double-grating emission monochromator after excitation.
Fluorescence spectra were obtained under ambient conditions i. Nanoparticles were fabricated as previously reported Nanoparticle stability was performed as previously described Mineral oil was added on the top of each well via syringe to form a thin layer to prevent evaporation.
For optical stability of O 2 NPs, the total emission was measured before and after incubation. The hippocampi were transferred to 0. The cells were rinsed with a warm surgical medium by centrifuging for 7 min at rpm and discarding the supernatant. Hippocampi were triturated until no fragments of tissue remained.
Cell density was determined by trypan blue exclusion. After 24 h, the surgical medium was changed to a serum-free neuronal regular medium containing DMEM and neurobasal 2. The medium was replaced with fresh regular medium every two days. Primary neurons were 14 days in vitro DIV at the time of imaging for best observation of synapses. Acutely isolated brain slices were prepared as previously described Slices were labeled by incubating in the oxygenated NP glucose solution for 2 h.
Slices were washed and kept in oxygenated sucrose-ACSF prior to imaging. For imaging cultured neurons, the excitation wavelengths used to visualize blue NPs and MitoTracker Red FM were nm and nm, respectively. Emission filters ranged from to nm for blue, and nm to nm for red.
For imaging live slices, the brain slices were anchored in a closed bath chamber and perfused with oxygenated sucrose-ACSF. A nm laser was used as the excitation source, and emission ranged from to nm to capture fluorescence and nm to nm to capture phosphorescence. Electrophysiological properties of DGC neurons were recorded using a whole-cell patch-clamp technique as described previously Animals were aged around four weeks at the time of the study.
The slices were perfused with oxygenated ACSF. Current-clamp recordings were performed for the measurement of cell membrane properties, and for filling biocytin into the cell. Electrode capacitance was electronically compensated. The currents were analyzed as described before using the MiniAnalysis software. The datasets generated and analyzed in this work are available from the corresponding author upon reasonable request. Weiss, H. Appreciating oxygen. Semenza, G. Life with oxygen.
Science 80— , 62—64 Rich, P. Mink, J. Ratio of central nervous system to body metabolism in vertebrates: its constancy and functional basis. Article Google Scholar. Harris, J. Synaptic energy use and supply. Neuron 75 , — Devine, M. Mitochondria at the neuronal presynapse in health and disease. Neoptolemos, J. Whole-body hypothermia for neonates with hypoxic-ischemic encephalopathy seetha.
Tang, Y. Blood genomic responses differ after stroke, seizures, hypoglycemia, and hypoxia: blood genomic fingerprints of disease. Prass, K. Hypoxia-induced stroke tolerance in the mouse is mediated by erythropoietin. Stroke 34 , — Glass, H. Clinical neonatal seizures are independently associated with outcome in infants at risk for hypoxic-ischemic brain injury. Wirrell, E. Prolonged seizures exacerbate perinatal hypoxic-ischemic brain damage.
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Life Sci. Zhang, X. It has been observed that blood flow in the brains of people with the disorder is impaired when compared to healthy brains.
The difficulty in delivering the oxygen necessary for neuronal activity may help explain the cognitive difficulties that are one of the hallmarks of the disease. The University of Rochester Medical Center is home to approximately 3, individuals who conduct research on everything from cancer to heart disease to Parkinson's, pandemic influenza, and autism. Spread across many centers, institutes, and labs, our scientists have developed therapies that have improved human health locally, in the region, and across the globe.
To learn more visit www. Skip to main content. Ub, ubiquitin; OH, hydroxyl group. ROS are highly reactive free radical molecules that can cause cellular damage through oxidation of lipids, proteins and DNA.
Within the brain, a high neuronal oxidative rate heightens the potential for ROS production and neurons are especially vulnerable to oxidative damage due to low levels of antioxidant enzymes such as glutathione GSH; Dringen et al. Neuronal diversion of glucose catabolism from glycolysis to the PPP through Pfkfb3 degradation therefore not only supports oxidative metabolism of lactate but also enhances neuronal antioxidant capacity through production of the reducing agent, NADH.
In a rat microarray study, seizures induced by injection of Kainate, a potent glutamate-receptor agonist that causes overstimulation of neurons, resulted in a 2. These data support a significant role for hypoxia in neuronal activity, potentially though neurovascular uncoupling and enhanced neuronal oxidative metabolism depleting neuronal oxygen levels.
Neurodegenerative disorders encompass a range of conditions characterized by progressive neuronal damage and degeneration as well as neuronal cell death.
Although neurodegenerative disorders vary in the neuronal populations and cognitive or motor functions affected, metabolic dysfunction is a unifying pathology underlying many of these disorders. In AD patients, regional hypometabolism in the brain is a predictor for progressive cognitive decline and reduced cerebral metabolism is associated with carriers of the AD risk allele of the APOE-4 gene Small et al.
This indicates that early metabolic dysfunction is a key process in AD progression and a potential target for therapeutic intervention. Also preceding extracellular plaque formation in the AD brain significantly increased ROS production and oxidative stress. Substantially increased ROS activity and oxidative damage is consistently detected in AD patients by various measures Hensley et al. Increased oxidative stress occurs early in disease progression being observed in patients with mild AD as well as in cases of mild cognitive impairment, at high-risk of developing AD Baldeiras et al.
Related to oxidative stress, and also implicated in AD pathology, is dysregulated homeostasis of redox transition metal ions including zinc, copper and iron Schrag et al. Both elevation and deficiency of zinc is associated with AD and evidence suggests that altered compartmentalization of zinc rather than altered zinc levels may be the cause of zinc pathology in AD Suh et al. This is supported by dysregulation of numerous zinc transporters in AD patient brains Lovell et al. Zinc has important roles in normal neuronal function and is co-released along with glutamate at the synapse Vogt et al.
A major role of zinc is its significant antioxidant capacity, such that zinc deficiency is linked to neuronal oxidative stress Aimo et al.
The redox active iron, although vital for cellular function, is also a pro-oxidant and promotes generation of highly reactive hydroxyl radicals from hydrogen peroxide. Another common feature of AD that contributes to AD pathology is vascular dysfunction. In animal models, hypoperfusion also leads to symptoms similar to AD and exacerbates existing AD pathology Walsh et al.
Vascular dysfunction contributes to the pathology of AD due to lower capillary density, meaning narrowed blood vessels and decreased CBF Hamel et al. Disrupted metabolic pathways in neurodegenerative diseases. Aside from rare cases of genetic mutations in familial AD, the major risk factor for developing AD is aging.
PD is thought to be caused by both genetic and environmental factors and primarily impacts patient motor function. HD is an inherited neurodegenerative disorder caused by expanded CAG repeats in the Huntingtin HTT gene causing progressive neuronal degeneration and cell death throughout the brain, affecting mood, cognition and motor skills.
Also, common to all three disorders is increased activity of transglutaminase TG; Johnson et al. TG catalyzes polyamination post-translational modifications of proteins, is known to be increased by ROS and also attenuates HIF-1 signaling Campisi et al. Altered metal ion homeostasis may have a role in PD pathology as well with disrupted levels of both zinc and copper observed in PD patients Brewer et al.
In HD, increased oxidative damage to mitochondrial DNA is observed as well as higher frequencies of deletions in the mitochondrial genome and deficits in ETC function with decreased expression of complex II in the striatum and decreased activity of complex IV in striatal and cortical regions Horton et al.
Vascular deficits and disrupted blood flow is a major pathology of HD as well with altered blood vessel density and size found in cortical gray matter, putamen and striatal brain regions.
In HD patients, inclusions of mHTT are also detected in the basal membrane and epithelium of cortical blood vessels and in mouse models of the disease pericytic coverage of cortical and striatal blood vessels is decreased Drouin-Ouellet et al. A number of the metabolic pathologies observed in neurodegenerative disorders are associated with normal aging and may explain the age-related manifestation of neurodegenerative disease phenotypes.
While no longer thought to be directly causative of aging, free radicals and oxidative stress accumulate in the aging brain as in neurodegeneration Smith et al. Mitochondrial function is also linked to aging due to the association of mitochondrial DNA mtDNA haplotypes with longevity and the generation of mtDNA mutator mice that have a premature aging phenotype Trifunovic et al.
It has also been shown there is an increased rate of damaging mutations in mtDNA of post-mitotic aging cells as opposed to aging mitotic cells Greaves et al. While it has been suggested that the somatic rate of mtDNA mutation is unlikely to have a pathological affect due to redundancy in cell mitochondrial numbers, in post-mitotic neurons mtDNA mutation rates are significantly higher than average and, within the cortex, MC with large mtDNA deletions possess a replicative advantage during mitochondrial expansion Song et al.
Aside from AD and PD, deficiency of zinc is also associated with aging, being decreased in the general elderly population Pepersack et al. Diminished CBF occurs in normal aging as well with cortical perfusion found to decrease with age in healthy adults Chen et al.
An age-dependent reduction in perictyes also occurs in mice and is associated with microvascular changes and neurodegeneration Bell et al. Substantial evidence therefore exists supporting disrupted neuronal oxygen supply and oxidative metabolism as a major pathological component of age-related neurodegeneration. Although it has been well established that metabolic regulation is critical to neuronal function and that metabolic dysfunction is a major pathology in diseases affecting behavior and cognition, there is little known regarding how regulators of metabolism may be involved in neuronal plasticity.
A number of studies, however, support a direct role for metabolic regulation and metabolically linked genes in influencing learning and memory. One of the best examples of this is exposure of hypoxia as a modulator of cognitive performance. In rodent models, exposure to hypobaric hypoxia in adult rats for periods of 7—21 days causes decline in spatial learning similar to aging and is associated with aging-related lipofuscin deposition and ultrastructural changes in MC.
Increasing duration of hypobaric hypoxic exposure also positively correlates with increasing expression of aging markers Biswal et al. Brief hypoxic exposure s in rats also causes synaptic arrest of pyramidal CA1 hippocampal neurons and deficits in spatial memory that are both reversed by blockade of receptors for Adenosine, an inhibitory neurotransmitter Sun et al.
Differing effects of hypoxia in brain plasticity are likely related to differing exposures as well as measurement of different outputs. Interestingly, mild hypoxia preconditioning confers protection of cognitive abilities during subsequent exposure to severe hypoxia implicating a role for HIFs and transcriptional changes induced by mild hypoxia Rybnikova et al.
Similar learning deficits and age-related changes are also observed in a D-galactose induced model of aging where oxidative injury was the major stimulus for aging Li et al.
Altered expression of lactate metabolic enzymes and transporters is also related to stress induced improvements in cognitive function. Psychological stress, while harmful under chronic conditions, has evolved to enhance cognitive function and improve reactions to stressful situations through hypothalamic activation of adrenergic receptors and hypothalamic-pituitary-adrenal axis glucocorticoid production Dong et al. Altered expression of ETC oxidative phosphorylation genes is also associated with altered behavior in the honeybee.
In a study exploring molecular profiles in aggressive honeybee behavior, oxidative phosphorylation was most significantly enriched in association with increased aggression.
This was found to be true for aged bees that display increased aggressive behavior as well as following environmentally enhanced aggression by alarm pheromone exposure and genetic-related aggression occurring in the Africanized honeybee population Alaux et al. Consistent with this, inhibition of oxidative phosphorylation by treatment with drugs targeting the TCA cycle increased aggression of honeybees measured using an intruder assay Li-Byarlay et al. In the same study, cell-type-specific knockdown of ETC complex genes using GAL4 drivers in Drosophila found that neuron-specific, but not glia-specific knockdown of the complex I gene NDlike, significantly increased aggressive lunging behavior in flies Li-Byarlay et al.
Also involved in learning and memory are non-coding miRNA genes which are regulated during neuronal activity by various mechanisms and able to regulate translation of various downstream target genes. A number of miRNAs have been associated with plasticity including the hypoxia-regulated, HIF-1 target, miR that is known to be involved in metabolic regulation.
Upregulation of miR correlated with downregulation of a number of metabolically linked protein-coding genes including Gapdh2, Glucose dehydrogenase, Laccase2 and Aldose reductase-like. Inhibition of miR by treatment of honeybees with miR antogmiR also resulted in reduced memory retention in the olfactory conditioning assay indicating a functional role in learning and memory Cristino et al.
Considering the sensitivity of neurons and neural structures to hypoxia, Cristino et al. A follow-up study found that in a human-derived neuronal cell-line, miR targeted neurodegeneration-associated genes as well as other plasticity-related genes within the human transcriptome.
Another hypoxia-regulated miRNA, miRc, is also associated with modulating cognitive function in rats. In a model of chronic cerebral hypoperfusion miRc was continuously inhibited, correlating with upregulation of its plasticity-related target gene, TRIM2. Hypoperfusion in this model was associated with deficits in spatial learning that were ameliorated by hippocampal overexpression of miRc Fang et al.
These studies all provide support to the hypothesis that metabolically regulated genes are directly involved in the regulation of neuronal plasticity. While neurovascular coupling mechanisms appear to maintain steady-state oxygen levels in the brain, it is becoming evident that neurovascular uncoupling may in fact have a physiological role in regulating plasticity via oxygen depletion and induction of downstream hypoxia response pathways.
Disruptions to hypoxia and oxidative metabolism have also been extensively attributed to neurodegeneration pathology albeit, there is a lack of understanding, as to how these disruptions are triggered and how they may be therapeutically targeted to halt disease progression and improve cognitive and motor functions. Altered behavior, including learning and memory, associated with dysregulation of metabolic genes highlights the importance of understanding the role of oxygen metabolism in neuronal plasticity.
Further elucidation of how the hypoxia response pathway and other metabolic genes are involved in neuronal function will be critical in determining the molecular links between cognitive function and oxidative metabolism. This in turn will help elucidate how disrupted metabolism can lead to cognitive deficits and neurodegenerative disease. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
National Center for Biotechnology Information , U. Journal List Front Mol Neurosci v. Front Mol Neurosci. Published online Jun Michelle E. Author information Article notes Copyright and License information Disclaimer.
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