1
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Buxton RB. Thermodynamic limitations on brain oxygen metabolism: physiological implications. J Physiol 2024; 602:683-712. [PMID: 38349000 DOI: 10.1113/jp284358] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 01/03/2024] [Indexed: 02/20/2024] Open
Abstract
Recent thermodynamic modelling indicates that maintaining the brain tissue ratio of O2 to CO2 (abbreviated tissue O2 /CO2 ) is critical for preserving the entropy increase available from oxidative metabolism of glucose, with a fall of that available entropy leading to a reduction of the phosphorylation potential and impairment of brain energy metabolism. This provides a novel perspective for understanding physiological responses under different conditions in terms of preserving tissue O2 /CO2 . To enable estimation of tissue O2 /CO2 in the human brain, a detailed mathematical model of O2 and CO2 transport was developed, and applied to reported physiological responses to different challenges, asking: how well is tissue O2 /CO2 preserved? Reported experimental results for increased neural activity, hypercapnia and hypoxia due to high altitude are consistent with preserving tissue O2 /CO2 . The results highlight two physiological mechanisms that control tissue O2 /CO2 : cerebral blood flow, which modulates tissue O2 ; and ventilation rate, which modulates tissue CO2 . The hypoxia modelling focused on humans at high altitude, including acclimatized lowlanders and Tibetan and Andean adapted populations, with a primary finding that decreasing CO2 by increasing ventilation rate is more effective for preserving tissue O2 /CO2 than increasing blood haemoglobin content to maintain O2 delivery to tissue. This work focused on the function served by particular physiological responses, and the underlying mechanisms require further investigation. The modelling provides a new framework and perspective for understanding how blood flow and other physiological factors support energy metabolism in the brain under a wide range of conditions. KEY POINTS: Thermodynamic modelling indicates that preserving the O2 /CO2 ratio in brain tissue is critical for preserving the entropy change available from oxidative metabolism of glucose and the phosphorylation potential underlying energy metabolism. A detailed model of O2 and CO2 transport was developed to allow estimation of the tissue O2 /CO2 ratio in the human brain in different physiological states. Reported experimental results during hypoxia, hypercapnia and increased oxygen metabolic rate in response to increased neural activity are consistent with maintaining brain tissue O2 /CO2 ratio. The hypoxia modelling of high-altitude acclimatization and adaptation in humans demonstrates the critical role of reducing CO2 with increased ventilation for preserving tissue O2 /CO2 . Preservation of tissue O2 /CO2 provides a novel perspective for understanding the function of observed physiological responses under different conditions in terms of preserving brain energy metabolism, although the mechanisms underlying these functions are not well understood.
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Affiliation(s)
- Richard B Buxton
- Center for Functional Magnetic Resonance Imaging, Department of Radiology, University of California, San Diego, California, USA
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2
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Chen JJ, Uthayakumar B, Hyder F. Mapping oxidative metabolism in the human brain with calibrated fMRI in health and disease. J Cereb Blood Flow Metab 2022; 42:1139-1162. [PMID: 35296177 PMCID: PMC9207484 DOI: 10.1177/0271678x221077338] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Conventional functional MRI (fMRI) with blood-oxygenation level dependent (BOLD) contrast is an important tool for mapping human brain activity non-invasively. Recent interest in quantitative fMRI has renewed the importance of oxidative neuroenergetics as reflected by cerebral metabolic rate of oxygen consumption (CMRO2) to support brain function. Dynamic CMRO2 mapping by calibrated fMRI require multi-modal measurements of BOLD signal along with cerebral blood flow (CBF) and/or volume (CBV). In human subjects this "calibration" is typically performed using a gas mixture containing small amounts of carbon dioxide and/or oxygen-enriched medical air, which are thought to produce changes in CBF (and CBV) and BOLD signal with minimal or no CMRO2 changes. However non-human studies have demonstrated that the "calibration" can also be achieved without gases, revealing good agreement between CMRO2 changes and underlying neuronal activity (e.g., multi-unit activity and local field potential). Given the simpler set-up of gas-free calibrated fMRI, there is evidence of recent clinical applications for this less intrusive direction. This up-to-date review emphasizes technological advances for such translational gas-free calibrated fMRI experiments, also covering historical progression of the calibrated fMRI field that is impacting neurological and neurodegenerative investigations of the human brain.
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Affiliation(s)
- J Jean Chen
- Medical Biophysics, University of Toronto, Toronto, Canada.,Rotman Research Institute, Baycrest, Toronto, Canada
| | - Biranavan Uthayakumar
- Medical Biophysics, University of Toronto, Toronto, Canada.,Sunnybrook Research Institute, Toronto, Canada
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, USA.,Department of Radiology, Yale University, New Haven, Connecticut, USA.,Quantitative Neuroscience with Magnetic Resonance (QNMR) Research Program, Yale University, New Haven, Connecticut, USA.,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA
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3
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Sanganahalli BG, Thompson GJ, Parent M, Verhagen JV, Blumenfeld H, Herman P, Hyder F. Thalamic activations in rat brain by fMRI during tactile (forepaw, whisker) and non-tactile (visual, olfactory) sensory stimulations. PLoS One 2022; 17:e0267916. [PMID: 35522646 PMCID: PMC9075615 DOI: 10.1371/journal.pone.0267916] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Accepted: 04/18/2022] [Indexed: 11/18/2022] Open
Abstract
The thalamus is a crucial subcortical hub that impacts cortical activity. Tracing experiments in animals and post-mortem humans suggest rich morphological specificity of the thalamus. Very few studies reported rodent thalamic activations by functional MRI (fMRI) as compared to cortical activations for different sensory stimuli. Here, we show different portions of the rat thalamus in response to tactile (forepaw, whisker) and non-tactile (visual, olfactory) sensory stimuli with high field fMRI (11.7T) using a custom-build quadrature surface coil to capture high sensitivity signals from superficial and deep brain regions simultaneously. Results demonstrate reproducible thalamic activations during both tactile and non-tactile stimuli. Forepaw and whisker stimuli activated broader regions within the thalamus: ventral posterior lateral (VPL), ventral posterior medial (VPM), lateral posterior mediorostral (LPMR) and posterior medial (POm) thalamic nuclei. Visual stimuli activated dorsal lateral geniculate nucleus (DLG) of the thalamus but also parts of the superior/inferior colliculus, whereas olfactory stimuli activated specifically the mediodorsal nucleus of the thalamus (MDT). BOLD activations in LGN and MDT were much stronger than in VPL, VPM, LPMR and POm. These fMRI-based thalamic activations suggest that forepaw and whisker (i.e., tactile) stimuli engage VPL, VPM, LPMR and POm whereas visual and olfactory (i.e., non-tactile) stimuli, respectively, recruit DLG and MDT exclusively.
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Affiliation(s)
- Basavaraju G. Sanganahalli
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, United States of America,Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut, United States of America,* E-mail: (BGS); (FH)
| | - Garth J. Thompson
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, United States of America,Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut, United States of America,iHuman Institute, ShanghaiTech University, Shanghai, China
| | - Maxime Parent
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, United States of America,Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut, United States of America
| | - Justus V. Verhagen
- The John B. Pierce Laboratory, New Haven, Connecticut, United States of America,Department of Neuroscience, Yale University, New Haven, Connecticut, United States of America
| | - Hal Blumenfeld
- Department of Neuroscience, Yale University, New Haven, Connecticut, United States of America,Department of Neurology, Yale University, New Haven, Connecticut, United States of America,Department of Neurosurgery, Yale University, New Haven, Connecticut, United States of America
| | - Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, United States of America,Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut, United States of America
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, United States of America,Department of Radiology and Biomedical Imaging, Yale University, New Haven, Connecticut, United States of America,Department of Biomedical Engineering, Yale University, New Haven, Connecticut, United States of America,* E-mail: (BGS); (FH)
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4
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Xu M, Bo B, Pei M, Chen Y, Shu CY, Qin Q, Hirschler L, Warnking JM, Barbier EL, Wei Z, Lu H, Herman P, Hyder F, Liu ZJ, Liang Z, Thompson GJ. High-resolution relaxometry-based calibrated fMRI in murine brain: Metabolic differences between awake and anesthetized states. J Cereb Blood Flow Metab 2022; 42:811-825. [PMID: 34910894 PMCID: PMC9014688 DOI: 10.1177/0271678x211062279] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Functional magnetic resonance imaging (fMRI) techniques using the blood-oxygen level-dependent (BOLD) signal have shown great potential as clinical biomarkers of disease. Thus, using these techniques in preclinical rodent models is an urgent need. Calibrated fMRI is a promising technique that can provide high-resolution mapping of cerebral oxygen metabolism (CMRO2). However, calibrated fMRI is difficult to use in rodent models for several reasons: rodents are anesthetized, stimulation-induced changes are small, and gas challenges induce noisy CMRO2 predictions. We used, in mice, a relaxometry-based calibrated fMRI method which uses cerebral blood flow (CBF) and the BOLD-sensitive magnetic relaxation component, R2', the same parameter derived in the deoxyhemoglobin-dilution model of calibrated fMRI. This method does not use any gas challenges, which we tested on mice in both awake and anesthetized states. As anesthesia induces a whole-brain change, our protocol allowed us to overcome the former limitations of rodent studies using calibrated fMRI. We revealed 1.5-2 times higher CMRO2, dependent upon brain region, in the awake state versus the anesthetized state. Our results agree with alternative measurements of whole-brain CMRO2 in the same mice and previous human anesthesia studies. The use of calibrated fMRI in rodents has much potential for preclinical fMRI.
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Affiliation(s)
- Mengyang Xu
- iHuman Institute, ShanghaiTech University, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China.,Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Binshi Bo
- CAS Center for Excellence in Brain Sciences and Intelligence Technology, Institute of Neuroscience, Chinese Academy of Sciences, Shanghai, China
| | - Mengchao Pei
- CAS Center for Excellence in Brain Sciences and Intelligence Technology, Institute of Neuroscience, Chinese Academy of Sciences, Shanghai, China
| | - Yuyan Chen
- CAS Center for Excellence in Brain Sciences and Intelligence Technology, Institute of Neuroscience, Chinese Academy of Sciences, Shanghai, China
| | - Christina Y Shu
- Biomedical Engineering, Yale University, New Haven, CT, USA.,Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA
| | - Qikai Qin
- iHuman Institute, ShanghaiTech University, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China.,Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai, China
| | - Lydiane Hirschler
- Grenoble Institut des Neurosciences, Inserm, Univ. Grenoble Alpes, Grenoble, France.,C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Jan M Warnking
- Grenoble Institut des Neurosciences, Inserm, Univ. Grenoble Alpes, Grenoble, France
| | - Emmanuel L Barbier
- Grenoble Institut des Neurosciences, Inserm, Univ. Grenoble Alpes, Grenoble, France
| | - Zhiliang Wei
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, MD, USA
| | - Hanzhang Lu
- Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA.,F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Research Institute, Baltimore, MD, USA
| | - Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA.,Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA.,Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Fahmeed Hyder
- Biomedical Engineering, Yale University, New Haven, CT, USA.,Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA.,Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA.,Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Zhi-Jie Liu
- iHuman Institute, ShanghaiTech University, Shanghai, China.,School of Life Science and Technology, ShanghaiTech University, Shanghai, China.,Center for Excellence in Molecular Cell Science, Shanghai Institute of Biochemistry and Cell Biology, Chinese Academy of Sciences, Shanghai, China
| | - Zhifeng Liang
- CAS Center for Excellence in Brain Sciences and Intelligence Technology, Institute of Neuroscience, Chinese Academy of Sciences, Shanghai, China
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5
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Louadi Z, Elkjaer ML, Klug M, Lio CT, Fenn A, Illes Z, Bongiovanni D, Baumbach J, Kacprowski T, List M, Tsoy O. Functional enrichment of alternative splicing events with NEASE reveals insights into tissue identity and diseases. Genome Biol 2021; 22:327. [PMID: 34857024 PMCID: PMC8638120 DOI: 10.1186/s13059-021-02538-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2021] [Accepted: 11/10/2021] [Indexed: 01/27/2023] Open
Abstract
Alternative splicing (AS) is an important aspect of gene regulation. Nevertheless, its role in molecular processes and pathobiology is far from understood. A roadblock is that tools for the functional analysis of AS-set events are lacking. To mitigate this, we developed NEASE, a tool integrating pathways with structural annotations of protein-protein interactions to functionally characterize AS events. We show in four application cases how NEASE can identify pathways contributing to tissue identity and cell type development, and how it highlights splicing-related biomarkers. With a unique view on AS, NEASE generates unique and meaningful biological insights complementary to classical pathways analysis.
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Affiliation(s)
- Zakaria Louadi
- Chair of Experimental Bioinformatics, TUM School of Life Sciences, Technical University of Munich, 85354, Freising, Germany
- Institute for Computational Systems Biology, University of Hamburg, Notkestrasse 9, 22607, Hamburg, Germany
| | - Maria L Elkjaer
- Department of Neurology, Odense University Hospital, Odense, Denmark
- Institute of Clinical Research, University of Southern Denmark, Odense, Denmark
- Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Melissa Klug
- Chair of Experimental Bioinformatics, TUM School of Life Sciences, Technical University of Munich, 85354, Freising, Germany
- Department of Internal Medicine I, School of Medicine, University hospital rechts der Isar, Technical University of Munich, Munich, Germany
- German Center for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Munich, Germany
| | - Chit Tong Lio
- Chair of Experimental Bioinformatics, TUM School of Life Sciences, Technical University of Munich, 85354, Freising, Germany
- Institute for Computational Systems Biology, University of Hamburg, Notkestrasse 9, 22607, Hamburg, Germany
| | - Amit Fenn
- Chair of Experimental Bioinformatics, TUM School of Life Sciences, Technical University of Munich, 85354, Freising, Germany
- Institute for Computational Systems Biology, University of Hamburg, Notkestrasse 9, 22607, Hamburg, Germany
| | - Zsolt Illes
- Department of Neurology, Odense University Hospital, Odense, Denmark
- Institute of Clinical Research, University of Southern Denmark, Odense, Denmark
- Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Dario Bongiovanni
- Department of Internal Medicine I, School of Medicine, University hospital rechts der Isar, Technical University of Munich, Munich, Germany
- German Center for Cardiovascular Research (DZHK), Partner Site Munich Heart Alliance, Munich, Germany
- Department of Cardiovascular Medicine, Humanitas Clinical and Research Center IRCCS and Humanitas University, Rozzano, Milan, Italy
| | - Jan Baumbach
- Institute for Computational Systems Biology, University of Hamburg, Notkestrasse 9, 22607, Hamburg, Germany
- Institute of Mathematics and Computer Science, University of Southern Denmark, Campusvej 55, 5000, Odense, Denmark
| | - Tim Kacprowski
- Division Data Science in Biomedicine, Peter L. Reichertz Institute for Medical Informatics of Technische Universität Braunschweig and Hannover Medical School, Braunschweig, Germany
- Braunschweig Integrated Centre of Systems Biology (BRICS), TU Braunschweig, Braunschweig, Germany
| | - Markus List
- Chair of Experimental Bioinformatics, TUM School of Life Sciences, Technical University of Munich, 85354, Freising, Germany.
| | - Olga Tsoy
- Institute for Computational Systems Biology, University of Hamburg, Notkestrasse 9, 22607, Hamburg, Germany.
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6
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Sanganahalli BG, Chitturi J, Herman P, Elkabes S, Heary R, Hyder F, Kannurpatti S. Supraspinal sensorimotor and pain-related reorganization after a hemicontusion rat cervical spinal cord injury. J Neurotrauma 2021; 38:3393-3405. [PMID: 34714150 DOI: 10.1089/neu.2021.0190] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Since the presence of pain impedes motor recovery in individuals with spinal cord injury (SCI), it is necessary to understand their supraspinal substrates in translational animal models. Using functional magnetic resonance imaging (fMRI) in a rat model of hemicontusion cervical SCI, supraspinal changes were mapped and correlated with sensorimotor behavioral outcomes. Female adult rats underwent sham or SCI using a 2.5 mm impactor and 150 kDyne force. SCI permanently impaired motor activity in only the ipsilesional forelimb along with thermal hyperalgesia at 5 and 6 wks. Spinal MRI at 8 wks after SCI showed ipsilateral T1 and T2 lesions with no discernable lesions across shams. fMRI mapping during electrical forepaw stimulation indicated SCI-induced sensorimotor reorganization with an expansion of the contralesional forelimb representation. Resting state fMRI based functional connectivity density (FCD), a marker of regional neuronal hubs increased or decreased across brain regions involved in nociception. FCD increases after SCI were in the primary and secondary somatosensory cortices (S1 and S2), anterior cingulate cortex (ACC), insula and the prefrontal cortex (PFC) and decreases were across the hippocampus, thalamus, hypothalamus and amygdala in SCI. Resting state functional connectivity (RSFC) assessments from the FCD altered regions of interest indicated cortico-cortical RSFC increases and cortico-insular, cortico-thalamic and cortico-hypothalamic RSFC decreases after SCI. Hippocampus, amygdala and thalamus showed decreased RSFC with most cortical regions and between themselves except the hippocampus-amygdala network, which showed increased RSFC after SCI. While select nociceptive region's intrinsic activity associated strongly with evoked pain behaviors after SCI (eg., PFC, ACC, hippocampus, thalamus, hypothalamus, M1 and S1BF) other nociceptive regions had weaker associations (eg., amygdala, insula, auditory cortex, S1FL, S1HL, S2 and M2), but differed significantly in their intrinsic activities between sham and SCI. The weaker associated nociceptive regions may possibly encode both the evoked and affective components of pain.
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Affiliation(s)
- Basavaraju G Sanganahalli
- Yale University School of Medicine, 12228, Diagnostic Radiology, New Haven, Connecticut, United States;
| | - Jyothsna Chitturi
- Rutgers Biomedical and Health Sciences, 5751, Radiology, Newark, New Jersey, United States;
| | - Peter Herman
- Yale University School of Medicine, 12228, Magnetic Resonance Research Center, Department of Diagnostic Radiology and Biomedical Engineering, Section of Bioimaging Science, New Haven, Connecticut, United States;
| | - Stella Elkabes
- Rutgers Biomedical and Health Sciences, 5751, Neurosurgery, Newark, New Jersey, United States;
| | - Robert Heary
- Hackensack Meridian School of Medicine, 576909, Nutley, New Jersey, United States;
| | | | - Sridhar Kannurpatti
- Rutgers Biomedical and Health Sciences, 5751, Radiology, Newark, New Jersey, United States;
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7
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Zhao Y, Liu P, Turner MP, Abdelkarim D, Lu H, Rypma B. The neural-vascular basis of age-related processing speed decline. Psychophysiology 2021; 58:e13845. [PMID: 34115388 DOI: 10.1111/psyp.13845] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 04/14/2021] [Accepted: 04/19/2021] [Indexed: 12/12/2022]
Abstract
Most studies examining neurocognitive aging are based on the blood-oxygen level-dependent signal obtained during functional magnetic resonance imaging (fMRI). The physiological basis of this signal is neural-vascular coupling, the process by which neurons signal cerebrovasculature to dilate in response to an increase in active neural metabolism due to stimulation. These fMRI studies of aging rely on the hemodynamic equivalence assumption that this process is not disrupted by physiologic deterioration associated with aging. Studies of neural-vascular coupling challenge this assumption and show that neural-vascular coupling is closely related to cognition. In this review, we put forward a theory of processing speed decline in aging and how it is related to age-related neural-vascular coupling changes based on the results of studies elucidating the relationships between cognition, cerebrovascular dynamics, and aging.
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Affiliation(s)
- Yuguang Zhao
- School of Behavioral and Brain Sciences, Center for Brain Health, University of Texas at Dallas, Richardson, TX, USA
| | - Peiying Liu
- School of Medicine, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA
| | - Monroe P Turner
- School of Behavioral and Brain Sciences, Center for Brain Health, University of Texas at Dallas, Richardson, TX, USA
| | - Dema Abdelkarim
- School of Behavioral and Brain Sciences, Center for Brain Health, University of Texas at Dallas, Richardson, TX, USA
| | - Hanzhang Lu
- School of Medicine, Department of Radiology, Johns Hopkins University, Baltimore, MD, USA
| | - Bart Rypma
- School of Behavioral and Brain Sciences, Center for Brain Health, University of Texas at Dallas, Richardson, TX, USA
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8
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Zhang X, Pan WJ, Keilholz S. The Relationship Between Local Field Potentials and the Blood-Oxygenation-Level Dependent MRI Signal Can Be Non-linear. Front Neurosci 2019; 13:1126. [PMID: 31708727 PMCID: PMC6823197 DOI: 10.3389/fnins.2019.01126] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Accepted: 10/04/2019] [Indexed: 01/29/2023] Open
Abstract
Functional magnetic resonance imaging (fMRI) is currently one of the most important neuroimaging methods in neuroscience. The image contrast in fMRI relies on the blood-oxygenation-level dependent (BOLD) signal, which indirectly reflects neural activity through neurovascular coupling. Because the mechanism that links the BOLD signal to neural activities involves multiple complicated processes, where neural activity, regional metabolism, hemodynamics, and the BOLD signal are all inter-connected, understanding the quantitative relationship between the BOLD signal and the underlying neural activities is crucial for interpreting fMRI data. Simultaneous local field potential (LFP) and fMRI recordings provide a method to study neurovascular coupling. There were a few studies that have shown non-linearities in stimulus related responses, but whether there is any non-linearity in LFP—BOLD relationship at rest has not been specifically quantified. In this study, we analyzed the simultaneous LFP and resting state-fMRI data acquired from rodents, and found that the relationship between LFP and BOLD is non-linear under isoflurane (ISO) anesthesia, but linear under dexmedetomidine (DMED) anesthesia. Subsequent analysis suggests that such non-linearity may come from the non-Gaussian distribution of LFP power and switching from LFP power to LFP amplitude can alleviate the problem to a degree. We also confirmed that, despite the non-linearity in the mean LFP—BOLD curve, the Pearson correlation between the two signals is relatively unaffected.
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Affiliation(s)
- Xiaodi Zhang
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States
| | - Wen-Ju Pan
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States
| | - Shella Keilholz
- The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Emory University, Atlanta, GA, United States
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9
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Schneider J, Berndt N, Papageorgiou IE, Maurer J, Bulik S, Both M, Draguhn A, Holzhütter HG, Kann O. Local oxygen homeostasis during various neuronal network activity states in the mouse hippocampus. J Cereb Blood Flow Metab 2019; 39:859-873. [PMID: 29099662 PMCID: PMC6501513 DOI: 10.1177/0271678x17740091] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Accepted: 10/02/2017] [Indexed: 12/14/2022]
Abstract
Cortical information processing comprises various activity states emerging from timed synaptic excitation and inhibition. However, the underlying energy metabolism is widely unknown. We determined the cerebral metabolic rate of oxygen (CMRO2) along a tissue depth of <0.3 mm in the hippocampal CA3 region during various network activities, including gamma oscillations and sharp wave-ripples that occur during wakefulness and sleep. These physiological states associate with sensory perception and memory formation, and critically depend on perisomatic GABA inhibition. Moreover, we modelled vascular oxygen delivery based on quantitative microvasculature analysis. (1) Local CMRO2 was highest during gamma oscillations (3.4 mM/min), medium during sharp wave-ripples, asynchronous activity and isoflurane application (2.0-1.6 mM/min), and lowest during tetrodotoxin application (1.4 mM/min). (2) Energy expenditure of axonal and synaptic signaling accounted for >50% during gamma oscillations. (3) CMRO2 positively correlated with number and synchronisation of activated synapses, and neural multi-unit activity. (4) The median capillary distance was 44 µm. (5) The vascular oxygen partial pressure of 33 mmHg was needed to sustain oxidative phosphorylation during gamma oscillations. We conclude that gamma oscillations featuring high energetics require a hemodynamic response to match oxygen consumption of respiring mitochondria, and that perisomatic inhibition significantly contributes to the brain energy budget.
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Affiliation(s)
- Justus Schneider
- Institute of Physiology and Pathophysiology, and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany
| | - Nikolaus Berndt
- Computational Systems Biochemistry, Institute of Biochemistry, Charité–Universitätsmedizin Berlin, Berlin, Germany
| | - Ismini E Papageorgiou
- Institute of Physiology and Pathophysiology, and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany
| | - Jana Maurer
- Institute of Physiology and Pathophysiology, and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany
| | - Sascha Bulik
- Computational Systems Biochemistry, Institute of Biochemistry, Charité–Universitätsmedizin Berlin, Berlin, Germany
| | - Martin Both
- Institute of Physiology and Pathophysiology, and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany
| | - Andreas Draguhn
- Institute of Physiology and Pathophysiology, and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany
| | - Hermann-Georg Holzhütter
- Computational Systems Biochemistry, Institute of Biochemistry, Charité–Universitätsmedizin Berlin, Berlin, Germany
| | - Oliver Kann
- Institute of Physiology and Pathophysiology, and Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Heidelberg, Germany
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10
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Bauer AQ, Kraft AW, Baxter GA, Wright PW, Reisman MD, Bice AR, Park JJ, Bruchas MR, Snyder AZ, Lee JM, Culver JP. Effective Connectivity Measured Using Optogenetically Evoked Hemodynamic Signals Exhibits Topography Distinct from Resting State Functional Connectivity in the Mouse. Cereb Cortex 2018; 28:370-386. [PMID: 29136125 PMCID: PMC6057523 DOI: 10.1093/cercor/bhx298] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Indexed: 02/07/2023] Open
Abstract
Brain connectomics has expanded from histological assessment of axonal projection connectivity (APC) to encompass resting state functional connectivity (RS-FC). RS-FC analyses are efficient for whole-brain mapping, but attempts to explain aspects of RS-FC (e.g., interhemispheric RS-FC) based on APC have been only partially successful. Neuroimaging with hemoglobin alone lacks specificity for determining how activity in a population of cells contributes to RS-FC. Wide-field mapping of optogenetically defined connectivity could provide insights into the brain's structure-function relationship. We combined optogenetics with optical intrinsic signal imaging to create an efficient, optogenetic effective connectivity (Opto-EC) mapping assay. We examined EC patterns of excitatory neurons in awake, Thy1-ChR2 transgenic mice. These Thy1-based EC (Thy1-EC) patterns were evaluated against RS-FC over the cortex. Compared to RS-FC, Thy1-EC exhibited increased spatial specificity, reduced interhemispheric connectivity in regions with strong RS-FC, and appreciable connection strength asymmetry. Comparing the topography of Thy1-EC and RS-FC patterns to maps of APC revealed that Thy1-EC more closely resembled APC than did RS-FC. The more general method of Opto-EC mapping with hemoglobin can be determined for 100 sites in single animals in under an hour, and is amenable to other neuroimaging modalities. Opto-EC mapping represents a powerful strategy for examining evolving connectivity-related circuit plasticity.
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Affiliation(s)
- Adam Q Bauer
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Andrew W Kraft
- Department of Neurology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Grant A Baxter
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Patrick W Wright
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Matthew D Reisman
- Department of Physics, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Annie R Bice
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Jasmine J Park
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Michael R Bruchas
- Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Anesthesiology, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Neuroscience, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Abraham Z Snyder
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Jin-Moo Lee
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Neurology, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, MO 63110, USA
| | - Joseph P Culver
- Department of Radiology, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Biomedical Engineering, Washington University School of Medicine, Saint Louis, MO 63110, USA.,Department of Physics, Washington University School of Medicine, Saint Louis, MO 63110, USA
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11
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Yu Y, Herman P, Rothman DL, Agarwal D, Hyder F. Evaluating the gray and white matter energy budgets of human brain function. J Cereb Blood Flow Metab 2018; 38:1339-1353. [PMID: 28589753 PMCID: PMC6092772 DOI: 10.1177/0271678x17708691] [Citation(s) in RCA: 105] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The insatiable appetite for energy to support human brain function is mainly supplied by glucose oxidation (CMRglc(ox)). But how much energy is consumed for signaling and nonsignaling processes in gray/white matter is highly debated. We examined this issue by combining metabolic measurements of gray/white matter and a theoretical calculation of bottom-up energy budget using biophysical properties of neuronal/glial cells in conjunction with species-exclusive electrophysiological and morphological data. We calculated a CMRglc(ox)-derived budget and confirmed it with experimental results measured by PET, autoradiography, 13C-MRS, and electrophysiology. Several conserved principles were observed regarding the energy costs for brain's signaling and nonsignaling components in both human and rat. The awake resting cortical signaling processes and mass-dependent nonsignaling processes, respectively, demand ∼70% and ∼30% of CMRglc(ox). Inhibitory neurons and glia need 15-20% of CMRglc(ox), with the rest demanded by excitatory neurons. Nonsignaling demands dominate in white matter, in near opposite contrast to gray matter demands. Comparison between 13C-MRS data and calculations suggests ∼1.2 Hz glutamatergic signaling rate in the awake human cortex, which is ∼4 times lower than signaling in the rat cortex. Top-down validated bottom-up budgets could allow computation of anatomy-based CMRglc(ox) maps and accurate cellular level interpretation of brain metabolic imaging.
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Affiliation(s)
- Yuguo Yu
- 1 School of Life Science and the Collaborative Innovation Center for Brain Science, the Center for Computational Systems Biology, Fudan University, Shanghai, China
| | - Peter Herman
- 2 Department of Radiology and Biomedical Imaging Yale University, New Haven, CT, USA.,3 Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.,4 Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, CT, USA
| | - Douglas L Rothman
- 2 Department of Radiology and Biomedical Imaging Yale University, New Haven, CT, USA.,3 Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.,4 Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, CT, USA.,5 Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Divyansh Agarwal
- 3 Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.,4 Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, CT, USA.,6 Currently at Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Fahmeed Hyder
- 2 Department of Radiology and Biomedical Imaging Yale University, New Haven, CT, USA.,3 Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.,4 Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, CT, USA.,5 Department of Biomedical Engineering, Yale University, New Haven, CT, USA
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12
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Abstract
Metabolism is central to neuroimaging because it can reveal pathways by which neuronal and glial cells use nutrients to fuel their growth and function. We focus on advanced magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) methods used in brain metabolic studies. 17O-MRS and 31P-MRS, respectively, provide rates of oxygen use and ATP synthesis inside mitochondria, whereas 19F-MRS enables measurement of cytosolic glucose metabolism. Calibrated functional MRI (fMRI), an advanced form of fMRI that uses contrast generated by deoxyhemoglobin, provides maps of oxygen use that track neuronal firing across brain regions. 13C-MRS is the only noninvasive method of measuring both glutamatergic neurotransmission and cell-specific energetics with signaling and nonsignaling purposes. Novel MRI contrasts, arising from endogenous diamagnetic agents and exogenous paramagnetic agents, permit pH imaging of glioma. Overall, these magnetic resonance methods for imaging brain metabolism demonstrate translational potential to better understand brain disorders and guide diagnosis and treatment.
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Affiliation(s)
- Fahmeed Hyder
- Department of Biomedical Engineering, Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, and Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut 06520;
| | - Douglas L Rothman
- Department of Biomedical Engineering, Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, and Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut 06520;
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13
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Volumetric Spatial Correlations of Neurovascular Coupling Studied using Single Pulse Opto-fMRI. Sci Rep 2017; 7:41583. [PMID: 28176823 PMCID: PMC5296864 DOI: 10.1038/srep41583] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 12/21/2016] [Indexed: 11/21/2022] Open
Abstract
Neurovascular coupling describes the link between neuronal activity and cerebral blood flow. This relationship has been the subject of intense scrutiny, with most previous work seeking to understand temporal correlations that describe neurovascular coupling. However, to date, the study of spatial correlations has been limited to two-dimensional mapping of neuronal or vascular derived signals emanating from the brain’s surface, using optical imaging techniques. Here, we investigate spatial correlations of neurovascular coupling in three dimensions, by applying a single 10 ms pulse of light to trigger optogenetic activation of cortical neurons transduced to express channelrhodopsin2, with concurrent fMRI. We estimated the spatial extent of increased neuronal activity using a model that takes into the account the scattering and absorption of blue light in brain tissue together with the relative density of channelrhodopsin2 expression across cortical layers. This method allows precise modulation of the volume of activated tissue in the cerebral cortex with concurrent three-dimensional mapping of functional hyperemia. Single pulse opto-fMRI minimizes adaptation, avoids heating artefacts and enables confined recruitment of the neuronal activity. Using this novel method, we present evidence for direct proportionality of volumetric spatial neurovascular coupling in the cerebral cortex.
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14
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Kannurpatti SS. Mitochondrial calcium homeostasis: Implications for neurovascular and neurometabolic coupling. J Cereb Blood Flow Metab 2017; 37:381-395. [PMID: 27879386 PMCID: PMC5381466 DOI: 10.1177/0271678x16680637] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Mitochondrial function is critical to maintain high rates of oxidative metabolism supporting energy demands of both spontaneous and evoked neuronal activity in the brain. Mitochondria not only regulate energy metabolism, but also influence neuronal signaling. Regulation of "energy metabolism" and "neuronal signaling" (i.e. neurometabolic coupling), which are coupled rather than independent can be understood through mitochondria's integrative functions of calcium ion (Ca2+) uptake and cycling. While mitochondrial Ca2+ do not affect hemodynamics directly, neuronal activity changes are mechanistically linked to functional hyperemic responses (i.e. neurovascular coupling). Early in vitro studies lay the foundation of mitochondrial Ca2+ homeostasis and its functional roles within cells. However, recent in vivo approaches indicate mitochondrial Ca2+ homeostasis as maintained by the role of mitochondrial Ca2+ uniporter (mCU) influences system-level brain activity as measured by a variety of techniques. Based on earlier evidence of subcellular cytoplasmic Ca2+ microdomains and cellular bioenergetic states, a mechanistic model of Ca2+ mobilization is presented to understand systems-level neurovascular and neurometabolic coupling. This integrated view from molecular and cellular to the systems level, where mCU plays a major role in mitochondrial and cellular Ca2+ homeostasis, may explain the wide range of activation-induced coupling across neuronal activity, hemodynamic, and metabolic responses.
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15
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Sanganahalli BG, Herman P, Rothman DL, Blumenfeld H, Hyder F. Metabolic demands of neural-hemodynamic associated and disassociated areas in brain. J Cereb Blood Flow Metab 2016; 36:1695-1707. [PMID: 27562867 PMCID: PMC5076793 DOI: 10.1177/0271678x16664531] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Revised: 07/04/2016] [Accepted: 07/19/2016] [Indexed: 12/31/2022]
Abstract
Interpretation of regional blood oxygenation level-dependent (BOLD) responses in functional magnetic resonance imaging (fMRI) is contingent on whether local field potential (LFP) and multi-unit activity (MUA) is either dissociated or associated. To examine whether neural-hemodynamic associated and dissociated areas have different metabolic demands, we recorded sensory-evoked responses of BOLD signal, blood flow (CBF), and blood volume (CBV), which with calibrated fMRI provided oxidative metabolism (CMRO2) from rat's ventral posterolateral thalamic nucleus (VPL) and somatosensory forelimb cortex (S1FL) and compared these neuroimaging signals to neurophysiological recordings. MUA faithfully recorded evoked latency differences between VPL and S1FL because evoked MUA in these regions were similar in magnitude. Since evoked LFP was significantly attenuated in VPL, we extracted the time courses of the weaker thalamic LFP to compare with the stronger cortical LFP using wavelet transform. BOLD and CBV responses were greater in S1FL than in VPL, similar to LFP regional differences. CBF and CMRO2 responses were both comparably larger in S1FL and VPL. Despite different levels of CBF-CMRO2 and LFP-MUA couplings in VPL and S1FL, the CMRO2 was well matched with MUA in both regions. These results suggest that neural-hemodynamic associated and dissociated areas in VPL and S1FL can have similar metabolic demands.
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Affiliation(s)
- Basavaraju G Sanganahalli
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, USA Department of Radiology and Biomedical Imaging, Yale University, New Haven, USA
| | - Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, USA Department of Radiology and Biomedical Imaging, Yale University, New Haven, USA
| | - Douglas L Rothman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, USA Department of Radiology and Biomedical Imaging, Yale University, New Haven, USA Department of Biomedical Engineering, Yale University, New Haven, USA
| | - Hal Blumenfeld
- Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, USA Department of Neurology, Yale University, New Haven, USA Department of Neurobiology, Yale University, New Haven, USA
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, USA Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, USA Department of Radiology and Biomedical Imaging, Yale University, New Haven, USA Department of Biomedical Engineering, Yale University, New Haven, USA
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16
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Shu CY, Sanganahalli BG, Coman D, Herman P, Hyder F. New horizons in neurometabolic and neurovascular coupling from calibrated fMRI. PROGRESS IN BRAIN RESEARCH 2016; 225:99-122. [PMID: 27130413 DOI: 10.1016/bs.pbr.2016.02.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Neurovascular coupling relates changes in neuronal activity to constriction/dilation of microvessels. However neurometabolic coupling, which is less well known, relates alterations in neuronal activity with metabolic demands. The link between the blood oxygenation level dependent (BOLD) signal and neural activity opened doors for functional MRI (fMRI) to be a powerful neuroimaging tool in the neurosciences. But due to the complex makeup of BOLD contrast, researchers began to investigate the relationship between BOLD signal and blood flow and/or volume changes during functional brain activation, which together provided the tools to measure oxygen consumption on the basis of the biophysical model of BOLD. This field is called calibrated fMRI, thereby allowed probing of both neurometabolic and neurovascular couplings for a variety of health conditions in animals and humans. Calibrated fMRI may provide brain disorder biomarkers that could be used for monitoring effective therapies.
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Affiliation(s)
- C Y Shu
- Yale University, New Haven, CT, United States
| | - B G Sanganahalli
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States
| | - D Coman
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States
| | - P Herman
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States
| | - F Hyder
- Yale University, New Haven, CT, United States; Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, United States.
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17
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Sanganahalli BG, Rebello MR, Herman P, Papademetris X, Shepherd GM, Verhagen JV, Hyder F. Comparison of glomerular activity patterns by fMRI and wide-field calcium imaging: Implications for principles underlying odor mapping. Neuroimage 2015; 126:208-18. [PMID: 26631819 DOI: 10.1016/j.neuroimage.2015.11.048] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2015] [Revised: 11/18/2015] [Accepted: 11/20/2015] [Indexed: 10/22/2022] Open
Abstract
Functional imaging signals arise from distinct metabolic and hemodynamic events at the neuropil, but how these processes are influenced by pre- and post-synaptic activities need to be understood for quantitative interpretation of stimulus-evoked mapping data. The olfactory bulb (OB) glomeruli, spherical neuropil regions with well-defined neuronal circuitry, can provide insights into this issue. Optical calcium-sensitive fluorescent dye imaging (OICa(2+)) reflects dynamics of pre-synaptic input to glomeruli, whereas high-resolution functional magnetic resonance imaging (fMRI) using deoxyhemoglobin contrast reveals neuropil function within the glomerular layer where both pre- and post-synaptic activities contribute. We imaged odor-specific activity patterns of the dorsal OB in the same anesthetized rats with fMRI and OICa(2+) and then co-registered the respective maps to compare patterns in the same space. Maps by each modality were very reproducible as trial-to-trial patterns for a given odor, overlapping by ~80%. Maps evoked by ethyl butyrate and methyl valerate for a given modality overlapped by ~80%, suggesting activation of similar dorsal glomerular networks by these odors. Comparison of maps generated by both methods for a given odor showed ~70% overlap, indicating similar odor-specific maps by each method. These results suggest that odor-specific glomerular patterns by high-resolution fMRI primarily tracks pre-synaptic input to the OB. Thus combining OICa(2+) and fMRI lays the framework for studies of OB processing over a range of spatiotemporal scales, where OICa(2+) can feature the fast dynamics of dorsal glomerular clusters and fMRI can map the entire glomerular sheet in the OB.
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Affiliation(s)
- Basavaraju G Sanganahalli
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA.
| | - Michelle R Rebello
- Department of Neurobiology, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT, USA
| | - Peter Herman
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA
| | - Xenophon Papademetris
- Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | | | - Justus V Verhagen
- Department of Neurobiology, Yale University, New Haven, CT, USA; The John B. Pierce Laboratory, New Haven, CT, USA.
| | - Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, CT, USA; Quantitative Neuroscience with Magnetic Resonance (QNMR) Core Center, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging, Yale University, New Haven, CT, USA; Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
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18
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Kannurpatti SS, Sanganahalli BG, Herman P, Hyder F. Role of mitochondrial calcium uptake homeostasis in resting state fMRI brain networks. NMR IN BIOMEDICINE 2015; 28:1579-1588. [PMID: 26439799 PMCID: PMC4621005 DOI: 10.1002/nbm.3421] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2015] [Revised: 08/27/2015] [Accepted: 09/01/2015] [Indexed: 06/05/2023]
Abstract
Mitochondrial Ca(2+) uptake influences both brain energy metabolism and neural signaling. Given that brain mitochondrial organelles are distributed in relation to vascular density, which varies considerably across brain regions, we hypothesized different physiological impacts of mitochondrial Ca(2+) uptake across brain regions. We tested the hypothesis by monitoring brain "intrinsic activity" derived from the resting state functional MRI (fMRI) blood oxygen level dependent (BOLD) fluctuations in different functional networks spanning the somatosensory cortex, caudate putamen, hippocampus and thalamus, in normal and perturbed mitochondrial Ca(2+) uptake states. In anesthetized rats at 11.7 T, mitochondrial Ca(2+) uptake was inhibited or enhanced respectively by treatments with Ru360 or kaempferol. Surprisingly, mitochondrial Ca(2+) uptake inhibition by Ru360 and enhancement by kaempferol led to similar dose-dependent decreases in brain-wide intrinsic activities in both the frequency domain (spectral amplitude) and temporal domain (resting state functional connectivity; RSFC). The fact that there were similar dose-dependent decreases in the frequency and temporal domains of the resting state fMRI-BOLD fluctuations during mitochondrial Ca(2+) uptake inhibition or enhancement indicated that mitochondrial Ca(2+) uptake and its homeostasis may strongly influence the brain's functional organization at rest. Interestingly, the resting state fMRI-derived intrinsic activities in the caudate putamen and thalamic regions saturated much faster with increasing dosage of either drug treatment than the drug-induced trends observed in cortical and hippocampal regions. Regional differences in how the spectral amplitude and RSFC changed with treatment indicate distinct mitochondrion-mediated spontaneous neuronal activity coupling within the various RSFC networks determined by resting state fMRI.
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Affiliation(s)
| | - Basavaraju G. Sanganahalli
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT 06520-808
- Magnetic Resonance Research Center (MRRC), Yale University School of Medicine, New Haven, CT 06520-808
- Core Center for Quantitative Neuroscience with Magnetic Resonance (QNMR), Yale University School of Medicine, New Haven, CT 06520-808
| | - Peter Herman
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT 06520-808
- Magnetic Resonance Research Center (MRRC), Yale University School of Medicine, New Haven, CT 06520-808
- Core Center for Quantitative Neuroscience with Magnetic Resonance (QNMR), Yale University School of Medicine, New Haven, CT 06520-808
| | - Fahmeed Hyder
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT 06520-808
- Department of Biomedical Engineering, Yale University School of Medicine, New Haven, CT 06520-808
- Magnetic Resonance Research Center (MRRC), Yale University School of Medicine, New Haven, CT 06520-808
- Core Center for Quantitative Neuroscience with Magnetic Resonance (QNMR), Yale University School of Medicine, New Haven, CT 06520-808
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19
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Shu CY, Herman P, Coman D, Sanganahalli BG, Wang H, Juchem C, Rothman DL, de Graaf RA, Hyder F. Brain region and activity-dependent properties of M for calibrated fMRI. Neuroimage 2015; 125:848-856. [PMID: 26529646 DOI: 10.1016/j.neuroimage.2015.10.083] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Revised: 10/28/2015] [Accepted: 10/30/2015] [Indexed: 11/28/2022] Open
Abstract
Calibrated fMRI extracts changes in oxidative energy demanded by neural activity based on hemodynamic and metabolic dependencies of the blood oxygenation level-dependent (BOLD) response. This procedure requires the parameter M, which is determined from the dynamic range of the BOLD signal between deoxyhemoglobin (paramagnetic) and oxyhemoglobin (diamagnetic). Since it is unclear if the range of M-values in human calibrated fMRI is due to regional/state differences, we conducted a 9.4T study to measure M-values across brain regions in deep (α-chloralose) and light (medetomidine) anesthetized rats, as verified by electrophysiology. Because BOLD signal is captured differentially by gradient-echo (R2*) and spin-echo (R2) relaxation rates, we measured M-values by the product of the fMRI echo time and R2' (i.e., the reversible magnetic susceptibility component), which is given by the absolute difference between R2* and R2. While R2' mapping was shown to be dependent on the k-space sampling method used, at nominal spatial resolutions achieved at high magnetic field of 9.4T the M-values were quite homogenous across cortical gray matter. However cortical M-values varied in relation to neural activity between brain states. The findings from this study could improve precision of future calibrated fMRI studies by focusing on the global uniformity of M-values in gray matter across different resting activity levels.
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Affiliation(s)
- Christina Y Shu
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA.
| | - Peter Herman
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Daniel Coman
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Basavaraju G Sanganahalli
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Helen Wang
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Christoph Juchem
- Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA; Department of Neurology, Yale University, New Haven, CT, USA
| | - Douglas L Rothman
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Robin A de Graaf
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA
| | - Fahmeed Hyder
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Department of Radiology and Biomedical Imaging and Magnetic Resonance Research Center, Yale University, New Haven, CT, USA.
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20
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Iordanova B, Vazquez AL, Poplawsky AJ, Fukuda M, Kim SG. Neural and hemodynamic responses to optogenetic and sensory stimulation in the rat somatosensory cortex. J Cereb Blood Flow Metab 2015; 35:922-32. [PMID: 25669905 PMCID: PMC4640245 DOI: 10.1038/jcbfm.2015.10] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2014] [Revised: 12/17/2014] [Accepted: 01/04/2015] [Indexed: 11/10/2022]
Abstract
Introducing optogenetics into neurovascular research can provide novel insights into the cell-specific control of the hemodynamic response. To generalize findings from molecular approaches, it is crucial to determine whether light-activated circuits have the same effect on the vasculature as sensory-activated ones. For that purpose, rats expressing channelrhodopsin (ChR2) specific to excitatory glutamatergic neurons were used to measure neural activity, blood flow, hemoglobin-based optical intrinsic signal, and blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) during optogenetic and sensory stimulation. The magnitude of the evoked hemodynamic responses was monotonically correlated with optogenetic stimulus strength. The BOLD hemodynamic response function was consistent for optogenetic and sensory stimuli. The relationship between electrical activities and hemodynamic responses was comparable for optogenetic and sensory stimuli, and better explained by the local field potential (LFP) than the firing rate. The LFP was well correlated with cerebral blood flow, moderately with cerebral blood volume, and less with deoxyhemoglobin (dHb) level. The presynaptic firing rate had little impact on evoking vascular response. Contribution of the postsynaptic LFP to the blood flow response induced by optogenetic stimulus was further confirmed by the application of glutamate receptor antagonists. Overall, neurovascular coupling during optogenetic control of glutamatergic neurons largely conforms to that of a sensory stimulus.
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Affiliation(s)
- Bistra Iordanova
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Alberto L Vazquez
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | | | - Mitsuhiro Fukuda
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Seong-Gi Kim
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Center for Neuroscience Imaging Research, Institute for Basic Science, Suwon, Korea
- Departments of Biomedical Engineering and Biological Sciences, Sungkyunkwan University, Suwon, Korea
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21
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Sonnay S, Just N, Duarte JMN, Gruetter R. Imaging of prolonged BOLD response in the somatosensory cortex of the rat. NMR IN BIOMEDICINE 2015; 28:414-421. [PMID: 25702944 DOI: 10.1002/nbm.3263] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 11/21/2014] [Accepted: 01/05/2015] [Indexed: 06/04/2023]
Abstract
Blood oxygenation level-dependent (BOLD) functional MRI is a widely employed methodology in experimental and clinical neuroscience, although its nature is not fully understood. To gain insights into BOLD mechanisms and take advantage of the new functional methods, it is of interest to investigate prolonged paradigms of activation suitable for long experimental protocols and to observe any long-term modifications induced by these functional challenges. While different types of sustained stimulation paradigm have been explored in human studies, the BOLD response is typically limited to a few minutes in animal models, due to fatigue, anesthesia effects and physiological instability. In the present study, the rat forepaw was electrically stimulated for 2 h, which resulted in a prolonged and localized cortical BOLD response over that period. The stimulation paradigm, including an inter-stimulus interval (ISI) of 10 s, that is 25% of the total time, was applied at constant or variable frequency over 2 h. The steady-state level of the BOLD response was reached after 15-20 min of stimulation and was maintained until the end of the stimulation. On average, no substantial loss in activated volume was observed at the end of the stimulation, but less variability in the fraction of remaining activated volume and higher steady-state BOLD amplitude were observed when stimulation frequency was varied between 2 and 3 Hz every 5 min. We conclude that the combination of ISI and variable stimulus frequency reproducibly results in robust, prolonged and localized BOLD activation.
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Affiliation(s)
- Sarah Sonnay
- Laboratory for Functional and Metabolic Imaging, École Polytechnique Fédérale Lausanne, Switzerland
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Shulman RG, Hyder F, Rothman DL. Insights from neuroenergetics into the interpretation of functional neuroimaging: an alternative empirical model for studying the brain's support of behavior. J Cereb Blood Flow Metab 2014; 34:1721-35. [PMID: 25160670 PMCID: PMC4269754 DOI: 10.1038/jcbfm.2014.145] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/12/2014] [Revised: 06/12/2014] [Accepted: 07/21/2014] [Indexed: 02/05/2023]
Abstract
Functional neuroimaging measures quantitative changes in neurophysiological parameters coupled to neuronal activity during observable behavior. These results have usually been interpreted by assuming that mental causation of behavior arises from the simultaneous actions of distinct psychological mechanisms or modules. However, reproducible localization of these modules in the brain using functional magnetic resonance imaging (MRI) and positron emission tomography (PET) imaging has been elusive other than for sensory systems. In this paper, we show that neuroenergetic studies using PET, calibrated functional magnetic resonance imaging (fMRI), (13)C magnetic resonance spectroscopy, and electrical recordings do not support the standard approach, which identifies the location of mental modules from changes in brain activity. Of importance in reaching this conclusion is that changes in neuronal activities underlying the fMRI signal are many times smaller than the high ubiquitous, baseline neuronal activity, or energy in resting, awake humans. Furthermore, the incremental signal depends on the baseline activity contradicting theoretical assumptions about linearity and insertion of mental modules. To avoid these problems, while making use of these valuable results, we propose that neuroimaging should be used to identify observable brain activities that are necessary for a person's observable behavior rather than being used to seek hypothesized mental processes.
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Affiliation(s)
- Robert G Shulman
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
| | - Fahmeed Hyder
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
- Departments of Diagnostic Radiology, Yale University, New Haven, Connecticut, USA
- Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut, USA
| | - Douglas L Rothman
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
- Departments of Diagnostic Radiology, Yale University, New Haven, Connecticut, USA
- Biomedical Engineering, Yale University, New Haven, Connecticut, USA
- Quantitative Neuroscience with Magnetic Resonance Core Center, Yale University, New Haven, Connecticut, USA
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Purinergic Modulation of Spinal Neuroglial Maladaptive Plasticity Following Peripheral Nerve Injury. Mol Neurobiol 2014; 52:1440-1457. [PMID: 25352445 DOI: 10.1007/s12035-014-8943-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Accepted: 10/16/2014] [Indexed: 12/22/2022]
Abstract
Modulation of spinal reactive gliosis following peripheral nerve injury (PNI) is a promising strategy to restore synaptic homeostasis. Oxidized ATP (OxATP), a nonselective antagonist of purinergic P2X receptors, was found to recover a neuropathic behavior following PNI. We investigated the role of intraperitoneal (i.p.) OxATP treatment in restoring the expression of neuronal and glial markers in the mouse spinal cord after sciatic spared nerve injury (SNI). Using in vivo two-photon microscopy, we imaged Ca(2+) transients in neurons and astrocytes of the dorsal horn of spinal cord at rest and upon right hind paw electrical stimulation in sham, SNI, and OxATP-treated mice. Neuropathic behavior was investigated by von Frey and thermal plantar test. Glial [glial fibrillary acidic protein (GFAP), ionized calcium-binding adaptor molecule 1 (Iba1)] and GABAergic [vesicular GABA transporter (vGAT) and glutamic acid decarboxylase 65/76 (GAD65/67)] markers and glial [glutamate transporter (GLT1) and GLAST] and neuronal amino acid [EAAC1, vesicular glutamate transporter 1 (vGLUT1)] transporters have been evaluated. In SNI mice, we found (i) increased glial response, (ii) decreased glial amino acid transporters, and (iii) increased levels of neuronal amino acid transporters, and (iv) in vivo analysis of spinal neurons and astrocytes showed a persistent increase of Ca(2+) levels. OxATP administration reduced glial activation, modulated the expression of glial and neuronal glutamate/GABA transporters, restored neuronal and astrocytic Ca(2+) levels, and prevented neuropathic behavior. In vitro studies validated that OxATP (i) reduced levels of reactive oxygen species (ROS), (ii) reduced astrocytic proliferation, (iii) increase vGLUT expression. All together, these data support the correlation between reactive gliosis and perturbation of the spinal synaptic homeostasis and the role played by the purinergic system in modulating spinal plasticity following PNI.
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Quantitative basis for neuroimaging of cortical laminae with calibrated functional MRI. Proc Natl Acad Sci U S A 2013; 110:15115-20. [PMID: 23980158 DOI: 10.1073/pnas.1307154110] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Layer-specific neurophysiologic, hemodynamic, and metabolic measurements are needed to interpret high-resolution functional magnetic resonance imaging (fMRI) data in the cerebral cortex. We examined how neurovascular and neurometabolic couplings vary vertically in the rat's somatosensory cortex. During sensory stimulation we measured dynamic layer-specific responses of local field potential (LFP) and multiunit activity (MUA) as well as blood oxygenation level-dependent (BOLD) signal and cerebral blood volume (CBV) and blood flow (CBF), which in turn were used to calculate changes in oxidative metabolism (CMR(O2)) with calibrated fMRI. Both BOLD signal and CBV decreased from superficial to deep laminae, but these responses were not well correlated with either layer-specific LFP or MUA. However, CBF changes were quite stable across laminae, similar to LFP. However, changes in CMR(O2) and MUA varied across cortex in a correlated manner and both were reduced in superficial lamina. These results lay the framework for quantitative neuroimaging across cortical laminae with calibrated fMRI methods.
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Mitochondrial calcium uptake capacity modulates neocortical excitability. J Cereb Blood Flow Metab 2013; 33:1115-26. [PMID: 23591650 PMCID: PMC3705442 DOI: 10.1038/jcbfm.2013.61] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/01/2013] [Revised: 03/14/2013] [Accepted: 03/15/2013] [Indexed: 12/25/2022]
Abstract
Local calcium (Ca(2+)) changes regulate central nervous system metabolism and communication integrated by subcellular processes including mitochondrial Ca(2+) uptake. Mitochondria take up Ca(2+) through the calcium uniporter (mCU) aided by cytoplasmic microdomains of high Ca(2+). Known only in vitro, the in vivo impact of mCU activity may reveal Ca(2+)-mediated roles of mitochondria in brain signaling and metabolism. From in vitro studies of mitochondrial Ca(2+) sequestration and cycling in various cell types of the central nervous system, we evaluated ranges of spontaneous and activity-induced Ca(2+) distributions in multiple subcellular compartments in vivo. We hypothesized that inhibiting (or enhancing) mCU activity would attenuate (or augment) cortical neuronal activity as well as activity-induced hemodynamic responses in an overall cytoplasmic and mitochondrial Ca(2+)-dependent manner. Spontaneous and sensory-evoked cortical activities were measured by extracellular electrophysiology complemented with dynamic mapping of blood oxygen level dependence and cerebral blood flow. Calcium uniporter activity was inhibited and enhanced pharmacologically, and its impact on the multimodal measures were analyzed in an integrated manner. Ru360, an mCU inhibitor, reduced all stimulus-evoked responses, whereas Kaempferol, an mCU enhancer, augmented all evoked responses. Collectively, the results confirm aforementioned hypotheses and support the Ca(2+) uptake-mediated integrative role of in vivo mitochondria on neocortical activity.
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Vazquez AL, Fukuda M, Crowley JC, Kim SG. Neural and hemodynamic responses elicited by forelimb- and photo-stimulation in channelrhodopsin-2 mice: insights into the hemodynamic point spread function. Cereb Cortex 2013; 24:2908-19. [PMID: 23761666 DOI: 10.1093/cercor/bht147] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Hemodynamic responses are commonly used to map brain activity; however, their spatial limits have remained unclear because of the lack of a well-defined and malleable spatial stimulus. To examine the properties of neural activity and hemodynamic responses, multiunit activity, local field potential, cerebral blood volume (CBV)-sensitive optical imaging, and laser Doppler flowmetry were measured from the somatosensory cortex of transgenic mice expressing Channelrhodopsin-2 in cortex Layer 5 pyramidal neurons. The magnitude and extent of neural and hemodynamic responses were modulated using different photo-stimulation parameters and compared with those induced by somatosensory stimulation. Photo-stimulation-evoked spiking activity across cortical layers was similar to forelimb stimulation, although their activity originated in different layers. Hemodynamic responses induced by forelimb- and photo-stimulation were similar in magnitude and shape, although the former were slightly larger in amplitude and wider in extent. Altogether, the neurovascular relationship differed between these 2 stimulation pathways, but photo-stimulation-evoked changes in neural and hemodynamic activities were linearly correlated. Hemodynamic point spread functions were estimated from the photo-stimulation data and its full-width at half-maximum ranged between 103 and 175 µm. Therefore, submillimeter functional structures separated by a few hundred micrometers may be resolved using hemodynamic methods, such as optical imaging and functional magnetic resonance imaging.
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Affiliation(s)
- Alberto L Vazquez
- Neuroimaging Laboratory, Department of Radiology, Department of Bioengineering
| | | | - Justin C Crowley
- Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, PA, USA
| | - Seong-Gi Kim
- Neuroimaging Laboratory, Department of Radiology, Department of Bioengineering, Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA and
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Moradi F, Buxton RB. Adaptation of cerebral oxygen metabolism and blood flow and modulation of neurovascular coupling with prolonged stimulation in human visual cortex. Neuroimage 2013; 82:182-9. [PMID: 23732885 DOI: 10.1016/j.neuroimage.2013.05.110] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2013] [Revised: 05/11/2013] [Accepted: 05/27/2013] [Indexed: 11/27/2022] Open
Abstract
Prolonged visual stimulation results in neurophysiologic and hemodynamic adaptation. However, the hemodynamic adaptation appears to be small compared to neural adaptation. It is not clear how the cerebral metabolic rate of oxygen (CMRO2) is affected by adaptation. We measured cerebral blood flow (CBF) and CMRO2 change in responses to peripheral stimulation either continuously, or intermittently (on/off cycles). A linear system's response to the continuous input should be equal to the sum of the original response to the intermittent input and a version of that response shifted by half a cycle. The CMRO2 response showed a large non-linearity consistent with adaptation, the CBF response adapted to a lesser degree, and the blood oxygenation level dependent (BOLD) response was nearly linear. The metabolic response was coupled with a larger flow in the continuous condition than in the intermittent condition. Our results suggest that contrast adaptation improves energy economy of visual processing. However BOLD modulations may not accurately represent the underlying metabolic nonlinearity due to modulation of the coupling of blood flow and oxygen metabolism changes.
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Affiliation(s)
- Farshad Moradi
- Department of Radiology, University of California, San Diego, CA 92103-8756, USA.
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Sanganahalli BG, Herman P, Behar KL, Blumenfeld H, Rothman DL, Hyder F. Functional MRI and neural responses in a rat model of Alzheimer's disease. Neuroimage 2013; 79:404-11. [PMID: 23648961 DOI: 10.1016/j.neuroimage.2013.04.099] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2013] [Revised: 04/17/2013] [Accepted: 04/20/2013] [Indexed: 12/28/2022] Open
Abstract
Based on the hypothesis that brain plaques and tangles can affect cortical function in Alzheimer's disease (AD), we investigated functional responses in an AD rat model (called the Samaritan Alzheimer's rat achieved by ventricular infusion of amyloid peptide) and age-matched healthy control. High-field functional magnetic resonance imaging (fMRI) and extracellular neural activity measurements were applied to characterize sensory-evoked responses. Electrical stimulation of the forepaw led to BOLD and neural responses in the contralateral somatosensory cortex and thalamus. In AD brain we noted much smaller BOLD activation patterns in the somatosensory cortex (i.e., about 50% less activated voxels compared to normal brain). While magnitudes of BOLD and neural responses in the cerebral cortex were markedly attenuated in AD rats compared to normal rats (by about 50%), the dynamic coupling between the BOLD and neural responses in the cerebral cortex, as assessed by transfer function analysis, remained unaltered between the groups. However thalamic BOLD and neural responses were unaltered in AD brain compared to controls. Thus cortical responses in the AD model were indeed diminished compared to controls, but the thalamic responses in the AD and control rats were quite similar. Therefore these results suggest that Alzheimer's disease may affect cortical function more than subcortical function, which may have implications for interpreting altered human brain functional responses in fMRI studies of Alzheimer's disease.
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Sanganahalli BG, Herman P, Hyder F, Kannurpatti SS. Mitochondrial functional state impacts spontaneous neocortical activity and resting state FMRI. PLoS One 2013; 8:e63317. [PMID: 23650561 PMCID: PMC3641133 DOI: 10.1371/journal.pone.0063317] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 04/01/2013] [Indexed: 11/19/2022] Open
Abstract
Mitochondrial Ca2+ uptake, central to neural metabolism and function, is diminished in aging whereas enhanced after acute/sub-acute traumatic brain injury. To develop relevant translational models for these neuropathologies, we determined the impact of perturbed mitochondrial Ca2+ uptake capacities on intrinsic brain activity using clinically relevant markers. From a multi-compartment estimate of probable baseline Ca2+ ranges in the brain, we hypothesized that reduced or enhanced mitochondrial Ca2+ uptake capacity would decrease or increase spontaneous neuronal activity respectively. As resting state fMRI-BOLD fluctuations and stimulus-evoked BOLD responses have similar physiological origins [1] and stimulus-evoked neuronal and hemodynamic responses are modulated by mitochondrial Ca2+ uptake capacity [2], [3] respectively, we tested our hypothesis by measuring hemodynamic fluctuations and spontaneous neuronal activities during normal and altered mitochondrial functional states. Mitochondrial Ca2+ uptake capacity was perturbed by pharmacologically inhibiting or enhancing the mitochondrial Ca2+ uniporter (mCU) activity. Neuronal electrical activity and cerebral blood flow (CBF) fluctuations were measured simultaneously and integrated with fMRI-BOLD fluctuations at 11.7T. mCU inhibition reduced spontaneous neuronal activity and the resting state functional connectivity (RSFC), whereas mCU enhancement increased spontaneous neuronal activity but reduced RSFC. We conclude that increased or decreased mitochondrial Ca2+ uptake capacities lead to diminished resting state modes of brain functional connectivity.
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Affiliation(s)
- Basavaraju G. Sanganahalli
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Department of Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Peter Herman
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Department of Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Fahmeed Hyder
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Department of Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Department of Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Sridhar S. Kannurpatti
- Department of Radiology, UMDNJ-New Jersey Medical School, Newark, New Jersey, United States of America
- * E-mail:
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Herzog RI, Jiang L, Herman P, Zhao C, Sanganahalli BG, Mason GF, Hyder F, Rothman DL, Sherwin RS, Behar KL. Lactate preserves neuronal metabolism and function following antecedent recurrent hypoglycemia. J Clin Invest 2013; 123:1988-98. [PMID: 23543056 DOI: 10.1172/jci65105] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Accepted: 01/31/2013] [Indexed: 12/30/2022] Open
Abstract
Hypoglycemia occurs frequently during intensive insulin therapy in patients with both type 1 and type 2 diabetes and remains the single most important obstacle in achieving tight glycemic control. Using a rodent model of hypoglycemia, we demonstrated that exposure to antecedent recurrent hypoglycemia leads to adaptations of brain metabolism so that modest increments in circulating lactate allow the brain to function normally under acute hypoglycemic conditions. We characterized 3 major factors underlying this effect. First, we measured enhanced transport of lactate both into as well as out of the brain that resulted in only a small increase of its contribution to total brain oxidative capacity, suggesting that it was not the major fuel. Second, we observed a doubling of the glucose contribution to brain metabolism under hypoglycemic conditions that restored metabolic activity to levels otherwise only observed at euglycemia. Third, we determined that elevated lactate is critical for maintaining glucose metabolism under hypoglycemia, which preserves neuronal function. These unexpected findings suggest that while lactate uptake was enhanced, it is insufficient to support metabolism as an alternate substrate to replace glucose. Lactate is, however, able to modulate metabolic and neuronal activity, serving as a "metabolic regulator" instead.
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Affiliation(s)
- Raimund I Herzog
- Department of Internal Medicine, Section of Endocrinology, Yale School of Medicine, New Haven, Connecticut 06520-8040, USA.
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Hyder F, Herman P, Sanganahalli BG, Coman D, Blumenfeld H, Rothman DL. Role of ongoing, intrinsic activity of neuronal populations for quantitative neuroimaging of functional magnetic resonance imaging-based networks. Brain Connect 2013; 1:185-93. [PMID: 22433047 DOI: 10.1089/brain.2011.0032] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
A primary objective in neuroscience is to determine how neuronal populations process information within networks. In humans and animal models, functional magnetic resonance imaging (fMRI) is gaining increasing popularity for network mapping. Although neuroimaging with fMRI-conducted with or without tasks-is actively discovering new brain networks, current fMRI data analysis schemes disregard the importance of the total neuronal activity in a region. In task fMRI experiments, the baseline is differenced away to disclose areas of small evoked changes in the blood oxygenation level-dependent (BOLD) signal. In resting-state fMRI experiments, the spotlight is on regions revealed by correlations of tiny fluctuations in the baseline (or spontaneous) BOLD signal. Interpretation of fMRI-based networks is obscured further, because the BOLD signal indirectly reflects neuronal activity, and difference/correlation maps are thresholded. Since the small changes of BOLD signal typically observed in cognitive fMRI experiments represent a minimal fraction of the total energy/activity in a given area, the relevance of fMRI-based networks is uncertain, because the majority of neuronal energy/activity is ignored. Thus, another alternative for quantitative neuroimaging of fMRI-based networks is a perspective in which the activity of a neuronal population is accounted for by the demanded oxidative energy (CMR(O2)). In this article, we argue that network mapping can be improved by including neuronal energy/activity of both the information about baseline and small differences/fluctuations of BOLD signal. Thus, total energy/activity information can be obtained through use of calibrated fMRI to quantify differences of ΔCMR(O2) and through resting-state positron emission tomography/magnetic resonance spectroscopy measurements for average CMR(O2).
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Affiliation(s)
- Fahmeed Hyder
- Magnetic Resonance Research Center (MRRC), Yale University, New Haven, Connecticut, USA.
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Cortical energy demands of signaling and nonsignaling components in brain are conserved across mammalian species and activity levels. Proc Natl Acad Sci U S A 2013; 110:3549-54. [PMID: 23319606 DOI: 10.1073/pnas.1214912110] [Citation(s) in RCA: 184] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The continuous need for ion gradient restoration across the cell membrane, a prerequisite for synaptic transmission and conduction, is believed to be a major factor for brain's high oxidative demand. However, do energy requirements of signaling and nonsignaling components of cortical neurons and astrocytes vary with activity levels and across species? We derived oxidative ATP demand associated with signaling (P(s)) and nonsignaling (P(ns)) components in the cerebral cortex using species-specific physiologic and anatomic data. In rat, we calculated glucose oxidation rates from layer-specific neuronal activity measured across different states, spanning from isoelectricity to awake and sensory stimulation. We then compared these calculated glucose oxidation rates with measured glucose metabolic data for the same states as reported by 2-deoxy-glucose autoradiography. Fixed values for P(s) and P(ns) were able to predict the entire range of states in the rat. We then calculated glucose oxidation rates from human EEG data acquired under various conditions using fixed P(s) and P(ns) values derived for the rat. These calculated metabolic data in human cerebral cortex compared well with glucose metabolism measured by PET. Independent of species, linear relationship was established between neuronal activity and neuronal oxidative demand beyond isoelectricity. Cortical signaling requirements dominated energy demand in the awake state, whereas nonsignaling requirements were ∼20% of awake value. These predictions are supported by (13)C magnetic resonance spectroscopy results. We conclude that mitochondrial energy support for signaling and nonsignaling components in cerebral cortex are conserved across activity levels in mammalian species.
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van Raaij ME, Lindvere L, Dorr A, He J, Sahota B, Foster FS, Stefanovic B. Quantification of blood flow and volume in arterioles and venules of the rat cerebral cortex using functional micro-ultrasound. Neuroimage 2012; 63:1030-7. [DOI: 10.1016/j.neuroimage.2012.07.054] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2012] [Revised: 07/19/2012] [Accepted: 07/23/2012] [Indexed: 10/28/2022] Open
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Calcium imaging of living astrocytes in the mouse spinal cord following sensory stimulation. Neural Plast 2012; 2012:425818. [PMID: 23091738 PMCID: PMC3468146 DOI: 10.1155/2012/425818] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2012] [Accepted: 09/02/2012] [Indexed: 12/24/2022] Open
Abstract
Astrocytic Ca2+ dynamics have been extensively studied in ex vivo models; however, the recent development of two-photon microscopy and astrocyte-specific labeling has allowed the study of Ca2+ signaling in living central nervous system. Ca2+ waves in astrocytes have been described in cultured cells and slice preparations, but evidence for astrocytic activation during sensory activity is lacking. There are currently few methods to image living spinal cord: breathing and heart-beating artifacts have impeded the widespread application of this technique. We here imaged the living spinal cord by two-photon microscopy in C57BL6/J mice. Through pressurized injection, we specifically loaded spinal astrocytes using the red fluorescent dye sulforhodamine 101 (SR101) and imaged astrocytic Ca2+ levels with Oregon-Green BAPTA-1 (OGB). Then, we studied astrocytic Ca2+ levels at rest and after right electrical hind paw stimulation. Sensory stimulation significantly increased astrocytic Ca2+ levels within the superficial dorsal horn of the spinal cord compared to rest. In conclusion, in vivo morphofunctional imaging of living astrocytes in spinal cord revealed that astrocytes actively participate to sensory stimulation.
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Quantitative fMRI and oxidative neuroenergetics. Neuroimage 2012; 62:985-94. [PMID: 22542993 DOI: 10.1016/j.neuroimage.2012.04.027] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Revised: 04/09/2012] [Accepted: 04/10/2012] [Indexed: 11/22/2022] Open
Abstract
The discovery of functional magnetic resonance imaging (fMRI) has greatly impacted neuroscience. The blood oxygenation level-dependent (BOLD) signal, using deoxyhemoglobin as an endogenous paramagnetic contrast agent, exposes regions of interest in task-based and resting-state paradigms. However the BOLD contrast is at best a partial measure of neuronal activity, because the functional maps obtained by differencing or correlations ignore the total neuronal activity in the baseline state. Here we describe how studies of brain energy metabolism at Yale, especially with (13)C magnetic resonance spectroscopy and related techniques, contributed to development of quantitative functional brain imaging with fMRI by providing a reliable measurement of baseline energy. This narrative takes us on a journey, from molecules to mind, with illuminating insights about neuronal-glial activities in relation to energy demand of synaptic activity. These results, along with key contributions from laboratories worldwide, comprise the energetic basis for quantitative interpretation of fMRI data.
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Kannurpatti SS, Rypma B, Biswal BB. Prediction of Task-Related BOLD fMRI with Amplitude Signatures of Resting-State fMRI. Front Syst Neurosci 2012; 6:7. [PMID: 22408609 PMCID: PMC3294272 DOI: 10.3389/fnsys.2012.00007] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 02/04/2012] [Indexed: 11/13/2022] Open
Abstract
Blood oxygen contrast-functional magnetic resonance imaging (fMRI) signals are a convolution of neural and vascular components. Several studies indicate that task-related (T-fMRI) or resting-state (R-fMRI) responses linearly relate to hypercapnic task responses. Based on the linearity of R-fMRI and T-fMRI with hypercapnia demonstrated by different groups using different study designs, we hypothesized that R-fMRI and T-fMRI signals are governed by a common physiological mechanism and that resting-state fluctuation of amplitude (RSFA) should be linearly related to T-fMRI responses. We tested this prediction in a group of healthy younger humans where R-fMRI, T-fMRI, and hypercapnic (breath hold, BH) task measures were obtained form the same scan session during resting state and during performance of motor and BH tasks. Within individual subjects, significant linear correlations were observed between motor and BH task responses across voxels. When averaged over the whole brain, the subject-wise correlation between the motor and BH tasks showed a similar linear relationship within the group. Likewise, a significant linear correlation was observed between motor-task activity and RSFA across voxels and subjects. The linear rest-task (R-T) relationship between motor activity and RSFA suggested that R-fMRI and T-fMRI responses are governed by similar physiological mechanisms. A practical use of the R-T relationship is its potential to estimate T-fMRI responses in special populations unable to perform tasks during fMRI scanning. Using the R-T relationship determined from the first group of 12 healthy subjects, we predicted the T-fMRI responses in a second group of 7 healthy subjects. RSFA in both the lower and higher frequency ranges robustly predicted the magnitude of T-fMRI responses at the subject and voxel levels. We propose that T-fMRI responses are reliably predictable to the voxel level in situations where only R-fMRI measures are possible, and may be useful for assessing neural activity in task non-compliant clinical populations.
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Affiliation(s)
- Sridhar S Kannurpatti
- Department of Radiology, New Jersey Medical School, University of Medicine and Dentistry of New Jersey Newark, NJ, USA
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Lacar B, Herman P, Hartman NW, Hyder F, Bordey A. S phase entry of neural progenitor cells correlates with increased blood flow in the young subventricular zone. PLoS One 2012; 7:e31960. [PMID: 22359646 PMCID: PMC3281100 DOI: 10.1371/journal.pone.0031960] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2011] [Accepted: 01/16/2012] [Indexed: 01/09/2023] Open
Abstract
The postnatal subventricular zone (SVZ) contains proliferating neural progenitor cells in close proximity to blood vessels. Insults and drug treatments acutely stimulate cell proliferation in the SVZ, which was assessed by labeling cells entering S phase. Although G1-to-S progression is metabolically demanding on a minute-to-hour time scale, it remains unknown whether increased SVZ cell proliferation is accompanied by a local hemodynamic response. This neurovascular coupling provides energy substrates to active neuronal assemblies. Transcardial dye perfusion revealed the presence of capillaries throughout the SVZ that constrict upon applications of the thromboxane A2 receptor agonist U-46119 in acute brain slice preparations. We then monitored in vivo blood flow using laser Doppler flowmetry via a microprobe located either in the SVZ or a mature network. U-46119 injections into the lateral ventricle decreased blood flow in the SVZ and the striatum, which are near the ventricle. A 1-hour ventricular injection of epidermal and basic fibroblast growth factor (EGF and bFGF) significantly increased the percentage of Sox2 transcription factor-positive cells in S phase 1.5 hours post-injection. This increase was accompanied by a sustained rise in blood flow in the SVZ but not in the striatum. Direct growth factor injections into the cortex did not alter local blood flow, ruling out direct effects on capillaries. These findings suggest that an acute increase in the number of G1-to-S cycling SVZ cells is accompanied by neurometabolic-vascular coupling, which may provide energy and nutrient for cell cycle progression.
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Affiliation(s)
- Benjamin Lacar
- Department of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Peter Herman
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Nathaniel W. Hartman
- Department of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Fahmeed Hyder
- Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Department of Biomedical Engineering, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, United States of America
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut, United States of America
| | - Angelique Bordey
- Department of Neurosurgery and Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, United States of America
- * E-mail:
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Bailey CJ, Sanganahalli BG, Herman P, Blumenfeld H, Gjedde A, Hyder F. Analysis of time and space invariance of BOLD responses in the rat visual system. ACTA ACUST UNITED AC 2012; 23:210-22. [PMID: 22298731 DOI: 10.1093/cercor/bhs008] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Neuroimaging studies of functional magnetic resonance imaging (fMRI) and electrophysiology provide the linkage between neural activity and the blood oxygenation level-dependent (BOLD) response. Here, BOLD responses to light flashes were imaged at 11.7T and compared with neural recordings from superior colliculus (SC) and primary visual cortex (V1) in rat brain--regions with different basal blood flow and energy demand. Our goal was to assess neurovascular coupling in V1 and SC as reflected by temporal/spatial variances of impulse response functions (IRFs) and assess, if any, implications for general linear modeling (GLM) of BOLD responses. Light flashes induced high magnitude neural/BOLD responses reproducibly from both regions. However, neural/BOLD responses from SC and V1 were markedly different. SC signals followed the boxcar shape of the stimulation paradigm at all flash rates, whereas V1 signals were characterized by onset/offset transients that exhibited different flash rate dependencies. We find that IRF(SC) is generally time-invariant across wider flash rate range compared with IRF(V1), whereas IRF(SC) and IRF(V1) are both space invariant. These results illustrate the importance of measured neural signals for interpretation of fMRI by showing that GLM of BOLD responses may lead to misinterpretation of neural activity in some cases.
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Lamanna JC. Angioplasticity and cerebrovascular remodeling. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 737:13-7. [PMID: 22259075 DOI: 10.1007/978-1-4614-1566-4_2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Joseph C Lamanna
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, USA.
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40
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Mishra AM, Ellens DJ, Schridde U, Motelow JE, Purcaro MJ, DeSalvo MN, Enev M, Sanganahalli BG, Hyder F, Blumenfeld H. Where fMRI and electrophysiology agree to disagree: corticothalamic and striatal activity patterns in the WAG/Rij rat. J Neurosci 2011; 31:15053-64. [PMID: 22016539 PMCID: PMC3432284 DOI: 10.1523/jneurosci.0101-11.2011] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Revised: 07/27/2011] [Accepted: 08/14/2011] [Indexed: 11/21/2022] Open
Abstract
The relationship between neuronal activity and hemodynamic changes plays a central role in functional neuroimaging. Under normal conditions and in neurological disorders such as epilepsy, it is commonly assumed that increased functional magnetic resonance imaging (fMRI) signals reflect increased neuronal activity and that fMRI decreases represent neuronal activity decreases. Recent work suggests that these assumptions usually hold true in the cerebral cortex. However, less is known about the basis of fMRI signals from subcortical structures such as the thalamus and basal ganglia. We used WAG/Rij rats (Wistar albino Glaxo rats of Rijswijk), an established animal model of human absence epilepsy, to perform fMRI studies with blood oxygen level-dependent and cerebral blood volume (CBV) contrasts at 9.4 tesla, as well as laser Doppler cerebral blood flow (CBF), local field potential (LFP), and multiunit activity (MUA) recordings. We found that, during spike-wave discharges, the somatosensory cortex and thalamus showed increased fMRI, CBV, CBF, LFP, and MUA signals. However, the caudate-putamen showed fMRI, CBV, and CBF decreases despite increases in LFP and MUA signals. Similarly, during normal whisker stimulation, the cortex and thalamus showed increases in CBF and MUA, whereas the caudate-putamen showed decreased CBF with increased MUA. These findings suggest that neuroimaging-related signals and electrophysiology tend to agree in the cortex and thalamus but disagree in the caudate-putamen. These opposite changes in vascular and electrical activity indicate that caution should be applied when interpreting fMRI signals in both health and disease from the caudate-putamen, as well as possibly from other subcortical structures.
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Affiliation(s)
- Asht Mangal Mishra
- Departments of Neurology
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut 06520
| | | | | | | | | | | | | | - Basavaraju G. Sanganahalli
- Diagnostic Radiology
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Fahmeed Hyder
- Diagnostic Radiology
- Biomedical Engineering, and
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Hal Blumenfeld
- Departments of Neurology
- Neurobiology
- Neurosurgery
- Core Center for Quantitative Neuroscience with Magnetic Resonance, Yale University School of Medicine, New Haven, Connecticut 06520
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41
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Herman P, Sanganahalli BG, Hyder F, Eke A. Fractal analysis of spontaneous fluctuations of the BOLD signal in rat brain. Neuroimage 2011; 58:1060-9. [PMID: 21777682 DOI: 10.1016/j.neuroimage.2011.06.082] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2011] [Revised: 06/14/2011] [Accepted: 06/26/2011] [Indexed: 12/01/2022] Open
Abstract
Analysis of task-evoked fMRI data ignores low frequency fluctuations (LFF) of the resting-state the BOLD signal, yet LFF of the spontaneous BOLD signal is crucial for analysis of resting-state connectivity maps. We characterized the LFF of resting-state BOLD signal at 11.7T in α-chloralose and domitor anesthetized rat brain and modeled the spontaneous signal as a scale-free (i.e., fractal) distribution of amplitude power (|A|²) across a frequency range (f) compatible with an |A(f)|² ∝ 1/f(β) model where β is the scaling exponent (or spectral index). We compared β values from somatosensory forelimb area (S1FL), cingulate cortex (CG), and caudate putamen (CPu). With α-chloralose, S1FL and CG β values dropped from ~0.7 at in vivo to ~0.1 at post mortem (p<0.0002), whereas CPu β values dropped from ~0.3 at in vivo to ~0.1 at post mortem (p<0.002). With domitor, cortical (S1FL, CG) β values were slightly higher than with α-chloralose, while subcortical (CPu) β values were similar with α-chloralose. Although cortical and subcortical β values with both anesthetics were significantly different in vivo (p<0.002), at post mortem β values in these regions were not significantly different and approached zero (i.e., range of -0.1 to 0.2). Since a water phantom devoid of susceptibility gradients had a β value of zero (i.e., random), we conclude that deoxyhemoglobin present in voxels post-sacrifice still impacts tissue water diffusion. These results suggest that in the anesthetized rat brain the LFF of BOLD signal at 11.7T follow a general 1/f(β) model of fractality where β is a variable responding to physiology. We describe typical experimental pitfalls which may elude detection of fractality in the resting-state BOLD signal.
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Affiliation(s)
- Peter Herman
- Magnetic Resonance Research Center, Yale University, New Haven, Connecticut, USA
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42
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van Raaij ME, Lindvere L, Dorr A, He J, Sahota B, Foster FS, Stefanovic B. Functional micro-ultrasound imaging of rodent cerebral hemodynamics. Neuroimage 2011; 58:100-8. [PMID: 21704715 DOI: 10.1016/j.neuroimage.2011.05.088] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Revised: 04/11/2011] [Accepted: 05/23/2011] [Indexed: 11/16/2022] Open
Abstract
Healthy cerebral microcirculation is crucial to neuronal functioning. We present a new method to investigate microvascular hemodynamics in living rodent brain through a focal cranial window based on high-frequency ultrasound imaging. The method has a temporal resolution of 40ms, and a 100μm in-plane and 600μm through-plane spatial resolution. We use a commercially available high-frequency ultrasound imaging system to quantify changes in the relative cerebral blood volume (CBV) by measuring the scattered signal intensity from an ultrasound contrast agent circulating in the vasculature. Generalized linear model analysis is then used to produce effect size and significance maps of changes in cerebral blood volume upon electrical stimulation of the forepaw. We observe larger CBV increases in the forelimb representation of the primary somatosensory cortex than in the deep gray matter with stimuli as short as 2s (5.1 ± 1.3% vs. 3.3 ± 0.6%). We also investigate the temporal evolution of the blood volume changes in cortical and subcortical gray matter, pial vessels and subcortical major vessels, and show shorter response onset times in the parenchymal regions than in the neighboring large vessels (1.6 ± 1.0s vs. 2.6 ± 1.3s in the cortex for a 10 second stimulus protocol). This method, which we termed functional micro-ultrasound imaging or fMUS, is a novel, highly accessible, and cost-effective way of imaging rodent brain microvascular topology and hemodynamics in vivo at 100micron resolution over a 1-by-1cm field of view with 10s-100s frames per second that opens up a new set of questions regarding brain function in preclinical models of health and disease.
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Affiliation(s)
- Martijn E van Raaij
- Sunnybrook Research Institute, Sunnybrook Health Sciences Centre, Toronto, ON, Canada.
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43
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Goense J, Whittingstall K, Logothetis NK. Neural and BOLD responses across the brain. WILEY INTERDISCIPLINARY REVIEWS. COGNITIVE SCIENCE 2011; 3:75-86. [PMID: 26302473 DOI: 10.1002/wcs.153] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Functional Magnetic Resonance Imaging (fMRI) has quickly grown into one of the most important tools for studying brain function, especially in humans. Despite its prevalence, we still do not have a clear picture of what exactly the blood oxygenation level dependent (BOLD) signal represents or how it compares to the signals obtained with other methods (e.g., electrophysiology). We particularly refer to single neuron recordings and electroencephalography when we mention 'electrophysiological methods', given that these methods have been used for more than 50 years, and have formed the basis of much of our current understanding of brain function. Brain function involves the coordinated activity of many different areas and many different cell types that can participate in an enormous variety of processes (neural firing, inhibitory and excitatory synaptic activity, neuromodulation, oscillatory activity, etc.). Of these cells and processes, only a subset is sampled with electrophysiological techniques, and their contribution to the recorded signals is not exactly known. Functional imaging signals are driven by the metabolic needs of the active cells, and are most likely also biased toward certain cell types and certain neural processes, although we know even less about which processes actually drive the hemodynamic response. This article discusses the current status on the interpretation of the BOLD signal and how it relates to neural activity measured with electrophysiological techniques. WIREs Cogn Sci 2012, 3:75-86. doi: 10.1002/wcs.153 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Jozien Goense
- Department of Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Kevin Whittingstall
- Department of Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Nikos K Logothetis
- Department of Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Tübingen, Germany.,Imaging Science and Biomedical Engineering, University of Manchester, Manchester, United Kingdom
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44
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Evidence for the importance of measuring total brain activity in neuroimaging. Proc Natl Acad Sci U S A 2011; 108:5475-6. [PMID: 21441108 DOI: 10.1073/pnas.1102026108] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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45
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Hirano Y, Stefanovic B, Silva AC. Spatiotemporal evolution of the functional magnetic resonance imaging response to ultrashort stimuli. J Neurosci 2011; 31:1440-7. [PMID: 21273428 PMCID: PMC3078723 DOI: 10.1523/jneurosci.3986-10.2011] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2010] [Revised: 10/15/2010] [Accepted: 11/22/2010] [Indexed: 11/21/2022] Open
Abstract
The specificity of the hemodynamic response function (HRF) is determined spatially by the vascular architecture and temporally by the evolution of hemodynamic changes. The stimulus duration has additional influence on the spatiotemporal evolution of the HRF, as brief stimuli elicit responses that engage only the local vasculature, whereas long stimuli lead to the involvement of remote vascular supply and drainage. Here, we used functional magnetic resonance imaging to investigate the spatiotemporal evolution of the blood oxygenation level-dependent (BOLD), cerebral blood flow (CBF), and cerebral blood volume (CBV) HRF to ultrashort forelimb stimulation in an anesthetized rodent model. The HRFs to a single 333-μs-long stimulus were robustly detected and consisted of a rapid response in both CBF and CBV, with an onset time (OT) of 350 ms and a full width at half-maximum of 1 s. In contrast, longer stimuli elicited a dispersive transit of oxygenated blood across the cortical microvasculature that significantly prolonged the evolution of the CBV HRF, but not the CBF. The CBF and CBV OTs suggest that vasoactive messengers are synthesized, released, and effective within 350 ms. However, the difference between the BOLD and CBV OT (∼100 ms) was significantly smaller than the arteriolar-venular transit time (∼500 ms), indicating an arterial contribution to the BOLD HRF. Finally, the rapid rate of growth of the active region with stimulus elongation suggests that functional hyperemia is an integrative process that involves the entire functional cortical depth. These findings offer a new view into the spatiotemporal dynamics of functional hemodynamic regulation in the brain.
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Affiliation(s)
- Yoshiyuki Hirano
- Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1065
| | - Bojana Stefanovic
- Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1065
| | - Afonso C. Silva
- Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-1065
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46
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Hyder F, Sanganahalli BG, Herman P, Coman D, Maandag NJG, Behar KL, Blumenfeld H, Rothman DL. Neurovascular and Neurometabolic Couplings in Dynamic Calibrated fMRI: Transient Oxidative Neuroenergetics for Block-Design and Event-Related Paradigms. FRONTIERS IN NEUROENERGETICS 2010; 2. [PMID: 20838476 PMCID: PMC2936934 DOI: 10.3389/fnene.2010.00018] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Accepted: 07/02/2010] [Indexed: 11/13/2022]
Abstract
Functional magnetic resonance imaging (fMRI) with blood-oxygenation level dependent (BOLD) contrast is an important tool for mapping brain activity. Interest in quantitative fMRI has renewed awareness in importance of oxidative neuroenergetics, as reflected by cerebral metabolic rate of oxygen consumption(CMRO2), for supporting brain function. Relationships between BOLD signal and the underlying neurophysiological parameters have been elucidated to allow determination of dynamic changes inCMRO2 by "calibrated fMRI," which require multi-modal measurements of BOLD signal along with cerebral blood flow (CBF) and volume (CBV). But how doCMRO2 changes, steady-state or transient, derived from calibrated fMRI compare with neural activity recordings of local field potential (LFP) and/or multi-unit activity (MUA)? Here we discuss recent findings primarily from animal studies which allow high magnetic fields studies for superior BOLD sensitivity as well as multi-modal CBV and CBF measurements in conjunction with LFP and MUA recordings from activated sites. A key observation is that while relationships between neural activity and sensory stimulus features range from linear to non-linear, associations between hyperemic components (BOLD, CBF, CBV) and neural activity (LFP, MUA) are almost always linear. More importantly, the results demonstrate good agreement between the changes inCMRO2 and independent measures of LFP or MUA. The tight neurovascular and neurometabolic couplings, observed from steady-state conditions to events separated by <200 ms, suggest rapid oxygen equilibration between blood and tissue pools and thus calibrated fMRI at high magnetic fields can provide high spatiotemporal mapping ofCMRO2 changes.
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Affiliation(s)
- Fahmeed Hyder
- Magnetic Resonance Research Center, School of Medicine, Yale University New Haven, CT, USA
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47
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Hyder F, Rothman DL. Neuronal correlate of BOLD signal fluctuations at rest: err on the side of the baseline. Proc Natl Acad Sci U S A 2010; 107:10773-4. [PMID: 20534504 PMCID: PMC2890714 DOI: 10.1073/pnas.1005135107] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Fahmeed Hyder
- Magnetic Resonance Research Center, Yale University, New Haven, CT 06520
| | - Douglas L. Rothman
- Magnetic Resonance Research Center, Yale University, New Haven, CT 06520
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48
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No increase of the blood oxygenation level-dependent functional magnetic resonance imaging signal with higher field strength: implications for brain activation studies. J Neurosci 2010; 30:5234-41. [PMID: 20392946 DOI: 10.1523/jneurosci.0844-10.2010] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Experimental data up to 7.0 T show that the blood oxygenation level-dependent (BOLD) signal of functional magnetic resonance imaging (fMRI) increases with higher magnetic field strength. Although several studies at 11.7 T report higher BOLD signal compared with studies at 7.0 T, no direct comparison at these two field strengths has been performed under the exact same conditions. It therefore remains unclear whether the expected increase of BOLD effect with field strength will still continue to hold for fields >7.0 T. To examine this issue, we compared the BOLD activation signal at 7.0 and 11.7 T with the two common sequences, spin-echo (SE) and gradient-echo (GE) echo planar imaging (EPI). We chose the physiologically well controlled rat model of electrical forepaw stimulation under medetomidine sedation. While a linear to superlinear increase in activation with field strengths up to 7.0 T was reported in the literature, we observed no significant activation difference between 7.0 and 11.7 T with either SE or GE. Discussing the results in light of the four-component model of the BOLD signal, we showed that at high field only two extravascular contributions remain relevant, while both intravascular components vanish. Constancy of the BOLD effect is discussed due to motional narrowing, i.e., susceptibility gradients become so strong that phase variance of diffusing spins decreases and therefore the BOLD signal also decreases. This finding will be of high significance for the planning of future human and animal fMRI studies at high fields and their quantitative analysis.
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49
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Kelly ME, Blau CW, Griffin KM, Gobbo OL, Jones JFX, Kerskens CM. Quantitative functional magnetic resonance imaging of brain activity using bolus-tracking arterial spin labeling. J Cereb Blood Flow Metab 2010; 30:913-22. [PMID: 20068581 PMCID: PMC2949184 DOI: 10.1038/jcbfm.2009.284] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) is the most widely used method for mapping neural activity in the brain. The interpretation of altered BOLD signals is problematic when cerebral blood flow (CBF) or cerebral blood volume change because of aging and/or neurodegenerative diseases. In this study, a recently developed quantitative arterial spin labeling (ASL) approach, bolus-tracking ASL (btASL), was applied to an fMRI experiment in the rat brain. The mean transit time (MTT), capillary transit time (CTT), relative cerebral blood volume of labeled water (rCBV(lw)), relative cerebral blood flow (rCBF), and perfusion coefficient in the forelimb region of the somatosensory cortex were quantified during neuronal activation and in the resting state. The average MTT and CTT were 1.939+/-0.175 and 1.606+/-0.106 secs, respectively, in the resting state. Both times decreased significantly to 1.616+/-0.207 and 1.305+/-0.201 secs, respectively, during activation. The rCBV(lw), rCBF, and perfusion coefficient increased on average by a factor of 1.123+/-0.006, 1.353+/-0.078, and 1.479+/-0.148, respectively, during activation. In contrast to BOLD techniques, btASL yields physiologically relevant indices of the functional hyperemia that accompanies neuronal activation.
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Affiliation(s)
- Michael E Kelly
- Trinity College Institute of Neuroscience, Trinity College Dublin, Dublin, Ireland
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50
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Comprehensive correlation between neuronal activity and spin-echo blood oxygenation level-dependent signals in the rat somatosensory cortex evoked by short electrical stimulations at various frequencies and currents. Brain Res 2010; 1317:116-23. [DOI: 10.1016/j.brainres.2009.12.084] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Revised: 12/28/2009] [Accepted: 12/29/2009] [Indexed: 11/21/2022]
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