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Sun N, Cui WQ, Min XM, Zhang GM, Liu JZ, Wu HY. A new perspective on hippocampal synaptic plasticity and post-stroke depression. Eur J Neurosci 2023; 58:2961-2984. [PMID: 37518943 DOI: 10.1111/ejn.16093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 07/01/2023] [Accepted: 07/03/2023] [Indexed: 08/01/2023]
Abstract
Post-stroke depression, a common complication after stroke, severely affects the recovery and quality of life of patients with stroke. Owing to its complex mechanisms, post-stroke depression treatment remains highly challenging. Hippocampal synaptic plasticity is one of the key factors leading to post-stroke depression; however, the precise molecular mechanisms remain unclear. Numerous studies have found that neurotrophic factors, protein kinases and neurotransmitters influence depressive behaviour by modulating hippocampal synaptic plasticity. This review further elaborates on the role of hippocampal synaptic plasticity in post-stroke depression by summarizing recent research and analysing possible molecular mechanisms. Evidence for the correlation between hippocampal mechanisms and post-stroke depression helps to better understand the pathological process of post-stroke depression and improve its treatment.
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Affiliation(s)
- Ning Sun
- First College of Clinical Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China
| | - Wen-Qiang Cui
- Department of Neurology, Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan, China
| | - Xiao-Man Min
- College of Chinese Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China
| | - Guang-Ming Zhang
- College of Chinese Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China
| | - Jia-Zheng Liu
- College of Chinese Medicine, Shandong University of Traditional Chinese Medicine, Jinan, China
| | - Hong-Yun Wu
- Department of Neurology, Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan, China
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Region- and Activity-Dependent Regulation of Extracellular Glutamate. J Neurosci 2018; 38:5351-5366. [PMID: 29760178 DOI: 10.1523/jneurosci.3213-17.2018] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 04/19/2018] [Accepted: 05/03/2018] [Indexed: 11/21/2022] Open
Abstract
Transporter-mediated glutamate uptake plays an essential role in shaping synaptic neurotransmission. The rapid removal of synaptically released glutamate ensures the high temporal dynamics characteristic of fast excitatory chemical neurotransmission and prevents the overexcitation of extrasynaptic NMDA receptors that have been implicated in synaptic plasticity impairments and cell death. Despite clear regional differences in plasticity and excitotoxic thresholds, few studies have compared extracellular glutamate dynamics across different brain regions and in response to a range of neural activity including plasticity-inducing stimuli. Here, we used the rapid extracellular fluorescent glutamate sensor iGluSnFR (intensity-based glutamate-sensing fluorescent reporter) and high-speed imaging (205 frames per second) to quantify relative differences in glutamate clearance rates over a wide range of presynaptic activity in situ in the hippocampus, cortex, and striatum of male C57/BL6NCrl mice. We found that the hippocampus was significantly more efficient than the cortex and striatum at clearing synaptically released glutamate and that this efficiency could be attributed, at least in part, to faster glutamate diffusion away from the release site. In addition, we found that pharmacological inhibition of GLT-1, the brain's most abundant glutamate transporter, slowed clearance rates to only a fraction (∼20-25%) of the effect induced by nonselective transporter blockade, regardless of the brain region and the duration of presynaptic activity. In all, our data reveal clear regional differences in glutamate dynamics after neural activity and suggest that non-GLT-1 transporters can make a large contribution to the rate of glutamate clearance in the hippocampus, cortex, and striatum.SIGNIFICANCE STATEMENT Glutamate is the brain's most abundant neurotransmitter, and although essential for rapid cell-cell communication, too much glutamate can negatively impact cellular health. Extracellular glutamate levels are tightly regulated by membrane-bound transporters that rapidly remove the glutamate that is released during neural activity, thereby shaping both the spatial and temporal dynamics of excitatory neurotransmission. Using high-speed imaging of an optical sensor of extracellular glutamate, we show that glutamate dynamics vary widely from one brain region to the next and are highly dependent on the duration of synaptic activity. Our data demonstrate the heterogeneous nature of glutamate regulation in the brain and suggest that such regional differences can dramatically affect both the localization and duration of postsynaptic receptor activation during synaptic neurotransmission.
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Liu S, Lam MA, Sial A, Hemley SJ, Bilston LE, Stoodley MA. Fluid outflow in the rat spinal cord: the role of perivascular and paravascular pathways. Fluids Barriers CNS 2018; 15:13. [PMID: 29704892 PMCID: PMC5924677 DOI: 10.1186/s12987-018-0098-1] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2018] [Accepted: 04/16/2018] [Indexed: 01/12/2023] Open
Abstract
BACKGROUND Cerebrospinal fluid (CSF) is thought to flow into the brain via perivascular spaces around arteries, where it mixes with interstitial fluid. The precise details concerning fluid outflow remain controversial. Although fluid dynamics have been studied in the brain, little is known about spinal cord fluid inflow and outflow. Understanding the normal fluid physiology of the spinal cord may give insight into the pathogenesis of spinal cord oedema and CSF disorders such as syringomyelia. We therefore aimed to determine the fluid outflow pathways in the rat spinal cord. METHODS A fluorescent tracer, Alexa-Fluor®-647 Ovalbumin, was injected into the extracellular space of either the cervicothoracic lateral white matter or the grey matter in twenty-two Sprague-Dawley rats over 250 s. The rats were sacrificed at 20 or 60 min post injection. Spinal cord segments were sectioned and labelled with vascular antibodies for immunohistochemistry. RESULTS Fluorescent tracer was distributed over two to three spinal levels adjacent to the injection site. In grey matter injections, tracer spread radially into the white matter. In white matter injections, tracer was confined to and redistributed along the longitudinal axonal fibres. Tracer was conducted towards the pial and ependymal surfaces along vascular structures. There was accumulation of tracer around the adventitia of the intramedullary arteries, veins and capillaries, as well as the extramedullary vessels. A distinct layer of tracer was deposited in the internal basement membrane of the tunica media of arteries. In half the grey matter injections, tracer was detected in the central canal. CONCLUSIONS These results suggest that in the spinal cord interstitial fluid movement is modulated by tissue diffusivity of grey and white matter. The central canal, and the compartments around or within blood vessels appear to be dominant pathways for fluid drainage in these experiments. There may be regional variations in fluid outflow capacity due to vascular and other anatomical differences between the grey and white matter.
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Affiliation(s)
- Shinuo Liu
- Department of Clinical Medicine, Faculty of Medicine and Health Sciences, Macquarie University, Suite 407, Clinic Building, 2 Technology Place, Sydney, NSW, 2109, Australia.
| | - Magdalena A Lam
- Department of Clinical Medicine, Faculty of Medicine and Health Sciences, Macquarie University, Suite 407, Clinic Building, 2 Technology Place, Sydney, NSW, 2109, Australia
| | - Alisha Sial
- Department of Clinical Medicine, Faculty of Medicine and Health Sciences, Macquarie University, Suite 407, Clinic Building, 2 Technology Place, Sydney, NSW, 2109, Australia
| | - Sarah J Hemley
- Department of Clinical Medicine, Faculty of Medicine and Health Sciences, Macquarie University, Suite 407, Clinic Building, 2 Technology Place, Sydney, NSW, 2109, Australia
| | - Lynne E Bilston
- Neuroscience Research Australia, Prince of Wales Clinical School, University of New South Wales, Margarete Ainsworth Building, Barker Street, Randwick, Sydney, NSW, 2031, Australia
| | - Marcus A Stoodley
- Department of Clinical Medicine, Faculty of Medicine and Health Sciences, Macquarie University, Suite 407, Clinic Building, 2 Technology Place, Sydney, NSW, 2109, Australia
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Abe Y, Van Nguyen K, Tsurugizawa T, Ciobanu L, Le Bihan D. Modulation of water diffusion by activation-induced neural cell swelling in Aplysia Californica. Sci Rep 2017; 7:6178. [PMID: 28733682 PMCID: PMC5522485 DOI: 10.1038/s41598-017-05586-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 05/31/2017] [Indexed: 01/26/2023] Open
Abstract
Diffusion functional magnetic resonance imaging (DfMRI) has been proposed as a method for functional neuroimaging studies, as an alternative to blood oxygenation level dependent (BOLD)-fMRI. DfMRI is thought to more directly reflect neural activation, but its exact mechanism remains unclear. It has been hypothesized that the water apparent diffusion coefficient (ADC) decrease observed upon neural activation results from swelling of neurons or neuron parts. To elucidate the origin of the DfMRI response at cellular level we performed diffusion MR microscopy at 17.2 T in Aplysia californica buccal ganglia and compared the water ADCs at cellular and ganglia levels before and after neuronal activation induced by perfusion with a solution containing dopamine. Neural cell swelling, evidenced from optical microscopy imaging, resulted in an intracellular ADC increase and an ADC decrease at ganglia level. Furthermore, the intracellular ADC increase was found to have a significant positive correlation with the increase in cell size. Our results strongly support the hypothesis that the ADC decrease observed with DfMRI upon neuronal activation at tissue level reflects activation-induced neural cell swelling.
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Affiliation(s)
- Yoshifumi Abe
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France
| | - Khieu Van Nguyen
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France.,University Paris-Saclay, 15 rue Georges Clemenceau, 91400, Orsay, France
| | - Tomokazu Tsurugizawa
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France
| | - Luisa Ciobanu
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France
| | - Denis Le Bihan
- NeuroSpin, Bât 145, Joliot Institute, CEA-Paris-Saclay Center, Point Courrier 156, 91191, Gif-sur-Yvette, France.
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Characterization of Mechanically Matched Hydrogel Coatings to Improve the Biocompatibility of Neural Implants. Sci Rep 2017; 7:1952. [PMID: 28512291 PMCID: PMC5434064 DOI: 10.1038/s41598-017-02107-2] [Citation(s) in RCA: 96] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2016] [Accepted: 04/07/2017] [Indexed: 01/01/2023] Open
Abstract
Glial scar is a significant barrier to neural implant function. Micromotion between the implant and tissue is suspected to be a key driver of glial scar formation around neural implants. This study explores the ability of soft hydrogel coatings to modulate glial scar formation by reducing local strain. PEG hydrogels with controllable thickness and elastic moduli were formed on the surface of neural probes. These coatings significantly reduced the local strain resulting from micromotion around the implants. Coated implants were found to significantly reduce scarring in vivo, compared to hard implants of identical diameter. Increasing implant diameter was found to significantly increase scarring for glass implants, as well as increase local BBB permeability, increase macrophage activation, and decrease the local neural density. These results highlight the tradeoff in mechanical benefit with the size effects from increasing the overall diameter following the addition of a hydrogel coating. This study emphasizes the importance of both mechanical and geometric factors of neural implants on chronic timescales.
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Richter F, Eitner A, Leuchtweis J, Bauer R, Lehmenkühler A, Schaible HG. Effects of interleukin-1ß on cortical spreading depolarization and cerebral vasculature. J Cereb Blood Flow Metab 2017; 37:1791-1802. [PMID: 27037093 PMCID: PMC5435277 DOI: 10.1177/0271678x16641127] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/02/2015] [Revised: 01/26/2016] [Accepted: 02/22/2016] [Indexed: 11/16/2022]
Abstract
During brain damage and ischemia, the cytokine interleukin-1ß is rapidly upregulated due to activation of inflammasomes. We studied whether interleukin-1ß influences cortical spreading depolarization, and whether lipopolysaccharide, often used for microglial stimulation, influences cortical spreading depolarizations. In anaesthetized rats, cortical spreading depolarizations were elicited by microinjection of KCl. Interleukin-1ß, the IL-1 receptor 1 antagonist, the GABAA receptor blocker bicuculline, and lipopolysaccharide were administered either alone or combined (interleukin-1ß + IL-1 receptor 1 antagonist; interleukin-1ß + bicuculline; lipopolysaccharide + IL-1 receptor 1 antagonist) into a local cortical treatment area. Using microelectrodes, cortical spreading depolarizations were recorded in a non-treatment and in the treatment area. Plasma extravasation in cortical grey matter was assessed with Evans blue. Local application of interleukin-1ß reduced cortical spreading depolarization amplitudes in the treatment area, but not at a high dose. This reduction was prevented by IL-1 receptor 1 antagonist and by bicuculline. However, interleukin-1ß induced pronounced plasma extravasation independently on cortical spreading depolarizations. Application of lipopolysaccharide reduced cortical spreading depolarization amplitudes but prolonged their duration; EEG activity was still present. These effects were also blocked by IL-1 receptor 1 antagonist. Interleukin-1ß evokes changes of neuronal activity and of vascular functions. Thus, although the reduction of cortical spreading depolarization amplitudes at lower doses of interleukin-1ß may reduce deleterious effects of cortical spreading depolarizations, the sum of interleukin-1ß effects on excitability and on the vasculature rather promote brain damaging mechanisms.
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Affiliation(s)
- Frank Richter
- Institute of Physiology I/Neurophysiology, Jena University Hospital – Friedrich Schiller University Jena, Jena, Germany
| | - Annett Eitner
- Institute of Physiology I/Neurophysiology, Jena University Hospital – Friedrich Schiller University Jena, Jena, Germany
| | - Johannes Leuchtweis
- Institute of Physiology I/Neurophysiology, Jena University Hospital – Friedrich Schiller University Jena, Jena, Germany
| | - Reinhard Bauer
- Institute of Molecular Cell Biology, Jena University Hospital – Friedrich Schiller University Jena, Jena, Germany
| | | | - Hans-Georg Schaible
- Institute of Physiology I/Neurophysiology, Jena University Hospital – Friedrich Schiller University Jena, Jena, Germany
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Abe Y, Tsurugizawa T, Le Bihan D. Water diffusion closely reveals neural activity status in rat brain loci affected by anesthesia. PLoS Biol 2017; 15:e2001494. [PMID: 28406906 PMCID: PMC5390968 DOI: 10.1371/journal.pbio.2001494] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Accepted: 03/16/2017] [Indexed: 11/18/2022] Open
Abstract
Diffusion functional MRI (DfMRI) reveals neuronal activation even when neurovascular coupling is abolished, contrary to blood oxygenation level—dependent (BOLD) functional MRI (fMRI). Here, we show that the water apparent diffusion coefficient (ADC) derived from DfMRI increased in specific rat brain regions under anesthetic conditions, reflecting the decreased neuronal activity observed with local field potentials (LFPs), especially in regions involved in wakefulness. In contrast, BOLD signals showed nonspecific changes, reflecting systemic effects of the anesthesia on overall brain hemodynamics status. Electrical stimulation of the central medial thalamus nucleus (CM) exhibiting this anesthesia-induced ADC increase led the animals to transiently wake up. Infusion in the CM of furosemide, a specific neuronal swelling blocker, led the ADC to increase further locally, although LFP activity remained unchanged, and increased the current threshold awakening the animals under CM electrical stimulation. Oppositely, induction of cell swelling in the CM through infusion of a hypotonic solution (−80 milliosmole [mOsm] artificial cerebrospinal fluid [aCSF]) led to a local ADC decrease and a lower current threshold to wake up the animals. Strikingly, the local ADC changes produced by blocking or enhancing cell swelling in the CM were also mirrored remotely in areas functionally connected to the CM, such as the cingulate and somatosensory cortex. Together, those results strongly suggest that neuronal swelling is a significant mechanism underlying DfMRI. It has been reported that neuronal activation results in a decrease of water diffusion in activated neural tissue. This new approach, known as diffusion functional MRI (DfMRI), has high potential for functional imaging of the brain, as the currently widespread blood oxygenation level—dependent (BOLD)-functional MRI (fMRI) method, which is based on neurovascular coupling, remains an indirect marker of neuronal activation. Here, we show that the water apparent diffusion coefficient (ADC) derived from DfMRI increased in specific rat brain regions under anesthetic conditions, reflecting the decreased neuronal activity, especially in regions involved in wakefulness. Electrical stimulation of the central medial (CM) thalamic nucleus exhibiting this anesthesia-induced ADC increase led the animals to transiently wake up. Infusion of the CM with furosemide—a specific blocker of neuronal swelling—led the ADC to increase further locally and increased the current threshold for waking the animals. Conversely, induction of cell swelling in the CM through infusion of a hypotonic solution led to a local ADC decrease and a lower current threshold to wake the animals. Strikingly, the local ADC changes produced by blocking or enhancing cell swelling in the CM were also mirrored remotely in areas functionally connected to the CM, such as the cingulate and somatosensory cortex. Those results strongly suggest that neuronal swelling is a significant mechanism underlying DfMRI.
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Affiliation(s)
- Yoshifumi Abe
- NeuroSpin, Joliot Institute, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France
| | - Tomokazu Tsurugizawa
- NeuroSpin, Joliot Institute, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France
| | - Denis Le Bihan
- NeuroSpin, Joliot Institute, Commissariat à l'énergie atomique et aux énergies alternatives, Gif-sur-Yvette, France
- * E-mail:
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Abstract
Quantitative magnetic resonance imaging can be combined with advanced biophysical models to measure microstructural features of white matter. Non-invasive microstructural imaging has the potential to revolutionize neuroscience, and acquiring these measures in clinically feasible times would greatly improve patient monitoring and clinical studies of drug efficacy. However, a good understanding of microstructural imaging techniques is essential to set realistic expectations and to prevent over-interpretation of results. This review explains the methodology behind microstructural modeling and imaging, and gives an overview of the breakthroughs and challenges associated with it.
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Vorisek I, Syka M, Vargova L. Brain Diffusivity and Structural Changes in the R6/2 Mouse Model of Huntington Disease. J Neurosci Res 2016; 95:1474-1484. [DOI: 10.1002/jnr.23965] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2016] [Revised: 09/08/2016] [Accepted: 09/21/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Ivan Vorisek
- Department of Neuroscience; Institute of Experimental Medicine AS CR, v.v.i.; Prague Czech Republic
| | - Michael Syka
- Department of Neuroscience; Institute of Experimental Medicine AS CR, v.v.i.; Prague Czech Republic
- International Clinical Research Center, St. Anne's University Hospital; Brno Czech Republic
| | - Lydia Vargova
- Department of Neuroscience; Institute of Experimental Medicine AS CR, v.v.i.; Prague Czech Republic
- Department of Neuroscience; Charles University, 2nd Faculty of Medicine; Prague Czech Republic
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Kimelberg HK. ■ Review : Cell Volume in the CNS: Regulation and Implications for Nervous System Function and Pathology. Neuroscientist 2016. [DOI: 10.1177/107385840000600110] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Swelling of cells in the nervous system is frequently associated with pathological states such as cerebral ischemia. The major cell type that swells in gray matter appears to be the astrocyte, although swelling of neuronal dendrites also occurs. Such swelling probably affects function by reducing the volume of the extracellular space. In addition the properties of the swollen cells themselves are altered, such as the swelling-induced release of excitatory amino acids, which are likely to be deleterious. Recent work has shown that these effects, linked to astrocytic swelling, may be involved in pathological states such as cerebral ischemia and trauma. Increased understanding of such swelling in the CNS will thus be of great importance in understanding mechanisms of brain damage and may provide specific sites for therapeutic intervention. NEUROSCIENTIST 6:14-25, 2000
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Richter F, Koulen P, Kaja S. N-Palmitoylethanolamine Prevents the Run-down of Amplitudes in Cortical Spreading Depression Possibly Implicating Proinflammatory Cytokine Release. Sci Rep 2016; 6:23481. [PMID: 27004851 PMCID: PMC4804239 DOI: 10.1038/srep23481] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 03/08/2016] [Indexed: 02/07/2023] Open
Abstract
Cortical spreading depression (CSD), a wave of neuronal depolarization in the cerebral cortex following traumatic brain injury or cerebral ischemia, significantly aggravates brain damage. Here, we tested whether N-palmitoylethanolamine (PEA), a substance that effectively reduces lesion volumes and neurological deficits after ischemic stroke, influences CSD. CSD was elicited chemically in adult rats and occurrence, amplitude, duration and propagation velocity of CSD was determined prior to and for 6 hours after intraperitoneal injection of PEA. The chosen systemic administration of PEA stabilized the amplitude of CSD for at least four hours and prevented the run-down of amplitudes that is typically observed and was also seen in untreated controls. The propagation velocity of the CSD waves was unaltered indicating stable neuronal excitability. The stabilization of CSD amplitudes by PEA indicates that inhibition or prevention of CSD does not underlie PEA's profound neuroprotective effect. Rather, PEA likely inhibits proinflammatory cytokine release thereby preventing the run-down of CSD amplitudes. This contribution of PEA to the maintenance of neuronal excitability in healthy tissue during CSD potentially adds to neuroprotection outside a damaged area, while other mechanisms control PEA-mediated neuroprotection in damaged tissue resulting from traumatic brain injury or cerebral ischemia.
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Affiliation(s)
- Frank Richter
- Institute of Physiology I/Neurophysiology, Jena University Hospital-Friedrich Schiller University Jena, Jena, Germany
| | - Peter Koulen
- Vision Research Center, Department of Ophthalmology, University of Missouri – Kansas City, School of Medicine, 2411 Holmes St., Kansas City, MO 64108, USA
- Department of Basic Medical Science, University of Missouri – Kansas City, School of Medicine, 2411 Holmes St., Kansas City, MO 64108, USA
| | - Simon Kaja
- Vision Research Center, Department of Ophthalmology, University of Missouri – Kansas City, School of Medicine, 2411 Holmes St., Kansas City, MO 64108, USA
- Departments of Ophthalmology and Molecular Pharmacology and Therapeutics, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave., Maywood, IL 60153, USA
- Edward Hines Jr. VA Hospital, Research Service, 5000 S Fifth Ave., Hines, IL 60141, USA
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Vargová L, Syková E. Astrocytes and extracellular matrix in extrasynaptic volume transmission. Philos Trans R Soc Lond B Biol Sci 2015; 369:20130608. [PMID: 25225101 DOI: 10.1098/rstb.2013.0608] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Volume transmission is a form of intercellular communication that does not require synapses; it is based on the diffusion of neuroactive substances across the brain extracellular space (ECS) and their binding to extrasynaptic high-affinity receptors on neurons or glia. Extracellular diffusion is restricted by the limited volume of the ECS, which is described by the ECS volume fraction α, and the presence of diffusion barriers, reflected by tortuosity λ, that are created, for example, by fine astrocytic processes or extracellular matrix (ECM) molecules. Organized astrocytic processes, ECM scaffolds or myelin sheets channel the extracellular diffusion so that it is facilitated in a certain direction, i.e. anisotropic. The diffusion properties of the ECS are profoundly influenced by various processes such as the swelling and morphological rebuilding of astrocytes during either transient or persisting physiological or pathological states, or the remodelling of the ECM in tumorous or epileptogenic tissue, during Alzheimer's disease, after enzymatic treatment or in transgenic animals. The changing diffusion properties of the ECM influence neuron-glia interaction, learning abilities, the extent of neuronal damage and even cell migration. From a clinical point of view, diffusion parameter changes occurring during pathological states could be important for diagnosis, drug delivery and treatment.
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Affiliation(s)
- Lýdia Vargová
- Department of Neuroscience, 2nd Faculty of Medicine, Charles University, Prague, Czech Republic Department of Neuroscience, Institute of Experimental Medicine AS CR, Prague, Czech Republic
| | - Eva Syková
- Department of Neuroscience, 2nd Faculty of Medicine, Charles University, Prague, Czech Republic Department of Neuroscience, Institute of Experimental Medicine AS CR, Prague, Czech Republic
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Sherpa AD, van de Nes P, Xiao F, Weedon J, Hrabetova S. Gliotoxin-induced swelling of astrocytes hinders diffusion in brain extracellular space via formation of dead-space microdomains. Glia 2014; 62:1053-65. [PMID: 24687699 DOI: 10.1002/glia.22661] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Revised: 03/04/2014] [Accepted: 03/04/2014] [Indexed: 11/07/2022]
Abstract
One of the hallmarks of numerous life-threatening and debilitating brain diseases is cellular swelling that negatively impacts extracellular space (ECS) structure. The ECS structure is determined by two macroscopic parameters, namely tortuosity (λ) and volume fraction (α). Tortuosity represents hindrance imposed on the diffusing molecules by the tissue in comparison with an obstacle-free medium. Volume fraction is the proportion of tissue volume occupied by the ECS. From a clinical perspective, it is essential to recognize which factors determine the ECS parameters and how these factors change in brain diseases. Previous studies demonstrated that dead-space (DS) microdomains increased λ during ischemia and hypotonic stress, as these pocket-like structures transiently trapped diffusing molecules. We hypothesize that astrocytes play a key role in the formation of DS microdomains because their thin processes have concave shapes that may elongate as astrocytes swell in these pathologies. Here we selectively swelled astrocytes in the somatosensory neocortex of rat brain slices with a gliotoxin DL-α-Aminoadipic Acid (DL-AA), and we quantified the ECS parameters using Integrative Optical Imaging (IOI) and Real-Time Iontophoretic (RTI) diffusion methods. We found that α decreased and λ increased during DL-AA application. During recovery, α was restored whereas λ remained elevated. Increase in λ during astrocytic swelling and recovery is consistent with the formation of DS microdomains. Our data attribute to the astrocytes an important role in determining the ECS parameters, and indicate that extracellular diffusion can be improved not only by reducing the swelling but also by disrupting the DS microdomains.
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Affiliation(s)
- Ang Doma Sherpa
- Department of Cell Biology, State University of New York Downstate Medical Center, Brooklyn, New York; Neural and Behavioral Science Graduate Program, State University of New York Downstate Medical Center, Brooklyn, New York
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Dmytrenko L, Cicanic M, Anderova M, Vorisek I, Ottersen OP, Sykova E, Vargova L. The impact of alpha-syntrophin deletion on the changes in tissue structure and extracellular diffusion associated with cell swelling under physiological and pathological conditions. PLoS One 2013; 8:e68044. [PMID: 23861848 PMCID: PMC3702576 DOI: 10.1371/journal.pone.0068044] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Accepted: 05/23/2013] [Indexed: 01/08/2023] Open
Abstract
Aquaporin-4 (AQP4) is the primary cellular water channel in the brain and is abundantly expressed by astrocytes along the blood-brain barrier and brain-cerebrospinal fluid interfaces. Water transport via AQP4 contributes to the activity-dependent volume changes of the extracellular space (ECS), which affect extracellular solute concentrations and neuronal excitability. AQP4 is anchored by α-syntrophin (α-syn), the deletion of which leads to reduced AQP4 levels in perivascular and subpial membranes. We used the real-time iontophoretic method and/or diffusion-weighted magnetic resonance imaging to clarify the impact of α-syn deletion on astrocyte morphology and changes in extracellular diffusion associated with cell swelling in vitro and in vivo. In mice lacking α-syn, we found higher resting values of the apparent diffusion coefficient of water (ADCW) and the extracellular volume fraction (α). No significant differences in tortuosity (λ) or non-specific uptake (k'), were found between α-syn-negative (α-syn -/-) and α-syn-positive (α-syn +/+) mice. The deletion of α-syn resulted in a significantly smaller relative decrease in α observed during elevated K(+) (10 mM) and severe hypotonic stress (-100 mOsmol/l), but not during mild hypotonic stress (-50 mOsmol/l). After the induction of terminal ischemia/anoxia, the final values of ADCW as well as of the ECS volume fraction α indicate milder cell swelling in α-syn -/- in comparison with α-syn +/+ mice. Shortly after terminal ischemia/anoxia induction, the onset of a steep rise in the extracellular potassium concentration and an increase in λ was faster in α-syn -/- mice, but the final values did not differ between α-syn -/- and α-syn +/+ mice. This study reveals that water transport through AQP4 channels enhances and accelerates astrocyte swelling. The substantially altered ECS diffusion parameters will likely affect the movement of neuroactive substances and/or trophic factors, which in turn may modulate the extent of tissue damage and/or drug distribution.
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Affiliation(s)
- Lesia Dmytrenko
- Institute of Experimental Medicine AS CR, v.v.i., Prague, Czech Republic
| | - Michal Cicanic
- Institute of Experimental Medicine AS CR, v.v.i., Prague, Czech Republic
- Charles University, 2nd Faculty of Medicine, Prague, Czech Republic
| | - Miroslava Anderova
- Institute of Experimental Medicine AS CR, v.v.i., Prague, Czech Republic
- Charles University, 2nd Faculty of Medicine, Prague, Czech Republic
| | - Ivan Vorisek
- Institute of Experimental Medicine AS CR, v.v.i., Prague, Czech Republic
- Charles University, 2nd Faculty of Medicine, Prague, Czech Republic
| | - Ole Petter Ottersen
- Center for Molecular Biology and Neuroscience and Department of Anatomy, University of Oslo, Oslo, Norway
| | - Eva Sykova
- Institute of Experimental Medicine AS CR, v.v.i., Prague, Czech Republic
- Charles University, 2nd Faculty of Medicine, Prague, Czech Republic
| | - Lydia Vargova
- Institute of Experimental Medicine AS CR, v.v.i., Prague, Czech Republic
- Charles University, 2nd Faculty of Medicine, Prague, Czech Republic
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15
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Florence CM, Baillie LD, Mulligan SJ. Dynamic volume changes in astrocytes are an intrinsic phenomenon mediated by bicarbonate ion flux. PLoS One 2012; 7:e51124. [PMID: 23226475 PMCID: PMC3511399 DOI: 10.1371/journal.pone.0051124] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Accepted: 10/30/2012] [Indexed: 11/18/2022] Open
Abstract
Astrocytes, the major type of non-neuronal cells in the brain, play an important functional role in extracellular potassium ([K(+)](o)) and pH homeostasis. Pathological brain states that result in [K(+)](o) and pH dysregulation have been shown to cause astrocyte swelling. However, whether astrocyte volume changes occur under physiological conditions is not known. In this study we used two-photon imaging to visualize real-time astrocyte volume changes in the stratum radiatum of the hippocampus CA1 region. Astrocytes were observed to swell by 19.0±0.9% in response to a small physiological increase in the concentration of [K(+)](o) (3 mM). Astrocyte swelling was mediated by the influx of bicarbonate (HCO(3-)) ions as swelling was significantly decreased when the influx of HCO(3-) was reduced. We found: 1) in HCO(3-) free extracellular solution astrocytes swelled by 5.4±0.7%, 2) when the activity of the sodium-bicarbonate cotransporter (NBC) was blocked the astrocytes swelled by 8.3±0.7%, and 3) in the presence of an extracellular carbonic anhydrase (CA) inhibitor astrocytes swelled by 11.4±0.6%. Because a significant HCO(3-) efflux is known to occur through the γ-amino-butyric acid (GABA) channel, we performed a series of experiments to determine if astrocytes were capable of HCO(3-) mediated volume shrinkage with GABA channel activation. Astrocytes were found to shrink -7.7±0.5% of control in response to the GABA(A) channel agonist muscimol. Astrocyte shrinkage from GABA(A) channel activation was significantly decreased to -5.0±0.6% of control in the presence of the membrane-permeant CA inhibitor acetazolamide (ACTZ). These dynamic astrocyte volume changes may represent a previously unappreciated yet fundamental mechanism by which astrocytes regulate physiological brain functioning.
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Affiliation(s)
- Clare M. Florence
- Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Landon D. Baillie
- Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Sean J. Mulligan
- Department of Physiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
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16
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Saxena T, Gilbert J, Stelzner D, Hasenwinkel J. Mechanical characterization of the injured spinal cord after lateral spinal hemisection injury in the rat. J Neurotrauma 2012; 29:1747-57. [PMID: 22435754 DOI: 10.1089/neu.2011.1818] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The glial scar formed at the site of traumatic spinal cord injury (SCI) has been classically hypothesized to be a potent physical and biochemical barrier to nerve regeneration. One longstanding hypothesis is that the scar acts as a physical barrier due to its increased stiffness in comparison to uninjured spinal cord tissue. However, the information regarding the mechanical properties of the glial scar in the current literature is mostly anecdotal and not well quantified. We monitored the mechanical relaxation behavior of injured rat spinal cord tissue at the site of mid-thoracic spinal hemisection 2 weeks and 8 weeks post-injury using a microindentation test method. Elastic moduli were calculated and a modified standard linear model (mSLM) was fit to the data to estimate the relaxation time constant and viscosity. The SLM was modified to account for a spectrum of relaxation times, a phenomenon common to biological tissues, by incorporating a stretched exponential term. Injured tissue exhibited significantly lower stiffness and elastic modulus in comparison to uninjured control tissue, and the results from the model parameters indicated that the relaxation time constant and viscosity of injured tissue were significantly higher than controls. This study presents direct micromechanical measurements of injured spinal cord tissue post-injury. The results of this study show that the injured spinal tissue displays complex viscoelastic behavior, likely indicating changes in tissue permeability and diffusivity.
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Affiliation(s)
- Tarun Saxena
- Department of Biomedical and Chemical Engineering, Syracuse University, Syracuse, New York 13244, USA
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17
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Zamecnik J, Homola A, Cicanic M, Kuncova K, Marusic P, Krsek P, Sykova E, Vargova L. The extracellular matrix and diffusion barriers in focal cortical dysplasias. Eur J Neurosci 2012; 36:2017-24. [PMID: 22536791 DOI: 10.1111/j.1460-9568.2012.08107.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Focal cortical dysplasias (FCDs) of the brain are recognized as a frequent cause of intractable epilepsy. To contribute to the current understanding of the mechanisms of epileptogenesis in FCD, our study provides evidence that not only cellular alterations and synaptic transmission, but also changed diffusion properties of the extracellular space (ECS), induced by modified extracellular matrix (ECM) composition and astrogliosis, might be involved in the generation or spread of seizures in FCD. The composition of the ECM in FCD and non-malformed cortex (in 163 samples from 62 patients) was analyzed immunohistochemically and correlated with the corresponding ECS diffusion parameter values determined with the real-time iontophoretic method in freshly resected cortex (i.e. the ECS volume fraction and the geometrical factor tortuosity, describing the hindrances to diffusion in the ECS). The ECS in FCD was shown to differ from that in non-malformed cortex, mainly by the increased accumulation of certain ECM molecules (tenascin R, tenascin C, and versican) or by their reduced expression (brevican), and by the presence of an increased number of astrocytic processes. The consequent increase of ECS diffusion barriers observed in both FCD type I and II (and, at the same time, the enlargement of the ECS volume in FCD type II) may alter the diffusion of neuroactive substances through the ECS, which mediates one of the important modes of intercellular communication in the brain - extrasynaptic volume transmission. Thus, the changed ECM composition and altered ECS diffusion properties might represent additional factors contributing to epileptogenicity in FCD.
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Affiliation(s)
- Josef Zamecnik
- Department of Pathology and Molecular Medicine, 2nd Faculty of Medicine, Charles University in Prague and University Hospital Motol, V Uvalu 84, 150 06 Prague, Czech Republic.
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18
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Astrogliosis: a target for intervention in intracerebral hemorrhage? Transl Stroke Res 2012; 3:80-7. [PMID: 24323864 DOI: 10.1007/s12975-012-0165-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2012] [Revised: 03/23/2012] [Accepted: 03/27/2012] [Indexed: 01/18/2023]
Abstract
Intracerebral hemorrhage (ICH) is a debilitating neurological injury, accounting for 10-15 % of all strokes. Despite neurosurgical intervention and supportive care, the 30-day mortality rate remains ~50 %, with ICH survivors frequently displaying neurological impairments and requiring long-term assisted care. Unfortunately, the lack of medical interventions to improve clinical outcomes has led to the notion that ICH is the least treatable form of stroke. Hence, additional studies are warranted to better understand the pathophysiology of ICH. Astrogliosis is an underlying astrocytic response to a wide range of brain injuries and postulated to have both beneficial and detrimental effects. However, the molecular mechanisms and functional roles of astrogliosis remain least characterized following ICH. Herein, we review the functional roles of astrogliosis in brain injuries and raise the prospects of therapeutically targeting astrogliosis after ICH.
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19
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Prasad A, Sanchez JC. Quantifying long-term microelectrode array functionality using chronic in vivo impedance testing. J Neural Eng 2012; 9:026028. [PMID: 22442134 DOI: 10.1088/1741-2560/9/2/026028] [Citation(s) in RCA: 98] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Long-term acquisition of high-quality neural recordings is a cornerstone of neuroprosthetic system design. Mitigating the experimental variability of chronically implanted arrays has been a formidable task because the sensor recording sites can be influenced by biotic and abiotic responses. Several studies have implicated changes in electrical interface impedance as a preliminary marker to infer electrode viability. Microelectrode impedance plays an important role in the monitoring of low amplitude and high-resolution extracellular neural signals. In this work, we seek to quantify long-term microelectrode array functionality and derive an impedance-based predictor for electrode functionality that correlates the recording site electrical properties with the functional neuronal recordings in vivo. High temporal resolution metrics of this type would allow one to assess, predict, and improve electrode performance in the future. In a large cohort of animals, we performed daily impedance measurements and neural signal recordings over long periods (up to 21 weeks) of time in rats using tungsten microwire arrays implanted into the somatosensory cortex. This study revealed that there was a time-varying trend in the modulation of impedance that was related to electrode performance. Single units were best detected from electrodes at time points when the electrode entered into the 40-150 KΩ impedance range. This impedance trend was modeled across the full cohort of animals to predict future electrode performance. The model was tested on data from all animals and was able to provide predictions of electrode performance chronically. Insight from this study can be combined with knowledge of electrode materials and histological analysis to provide a more comprehensive predictive model of electrode failure in the future.
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Affiliation(s)
- Abhishek Prasad
- Department of Biomedical Engineering, University of Miami, Miami, FL, USA.
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20
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Glial K+ Clearance and Cell Swelling: Key Roles for Cotransporters and Pumps. Neurochem Res 2012; 37:2299-309. [DOI: 10.1007/s11064-012-0731-3] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Revised: 01/13/2012] [Accepted: 02/11/2012] [Indexed: 10/28/2022]
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21
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Abstract
Astrocytes are possibly the most numerous cells of the vertebrate central nervous system, yet a detailed characterization of their functions is still missing. One potential reason for the obscurity of astrocytic function is that they represent a diverse population of cells that all share some critical characteristics. In the CNS, astrocytes have been proposed to perform many functions. For example, they are supportive cells that provide guidance to newly formed migrating neurons and axons. They regulate the functions of endothelial cells at the blood brain barrier, provide nutrients, and maintain homeostasis including ionic balance within the CNS. More recently, dissecting the central role of astrocytes in mediating injury responses in the CNS, particularly the spinal cord, has become an area of considerable importance. The ability to culture-enriched populations of astrocytes has facilitated a detailed dissection of their potential roles in the developing and adult, normal, and injured brain and spinal cord. Most importantly, in vitro models have defined molecular signals that may mediate or regulate astrocyte functions and the capacity to modulate these signals may provide new opportunities for therapeutic intervention after spinal cord injury and other neural insults.
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Affiliation(s)
- Amber E Kerstetter
- Department of Neurosurgery, Center for Translational Neurosciences, Case Western Reserve University, Cleveland, OH, USA
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22
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Abstract
Astrocytes dynamically interact with neurons to regulate synaptic transmission. Although the gap junction proteins connexin 30 (Cx30) and connexin 43 (Cx43) mediate the extensive network organization of astrocytes, their role in synaptic physiology is unknown. Here we show, by inactivating Cx30 and Cx43 genes, that astroglial networks tone down hippocampal synaptic transmission in CA1 pyramidal neurons. Gap junctional networking facilitates extracellular glutamate and potassium removal during synaptic activity through modulation of astroglial clearance rate and extracellular space volume. This regulation limits neuronal excitability, release probability, and insertion of postsynaptic AMPA receptors, silencing synapses. By controlling synaptic strength, connexins play an important role in synaptic plasticity. Altogether, these results establish connexins as critical proteins for extracellular homeostasis, important for the formation of functional synapses.
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23
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Cai L, Du T, Song D, Li B, Hertz L, Peng L. Astrocyte ERK phosphorylation precedes K+-induced swelling but follows hypotonicity-induced swelling. Neuropathology 2010; 31:250-64. [DOI: 10.1111/j.1440-1789.2010.01172.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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24
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Vauquelin G, Charlton SJ. Long-lasting target binding and rebinding as mechanisms to prolong in vivo drug action. Br J Pharmacol 2010; 161:488-508. [PMID: 20880390 PMCID: PMC2990149 DOI: 10.1111/j.1476-5381.2010.00936.x] [Citation(s) in RCA: 212] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2010] [Revised: 05/17/2010] [Accepted: 06/10/2010] [Indexed: 11/28/2022] Open
Abstract
An increasing number of examples in the literature suggest that the in vivo duration of drug action not only depends on macroscopic pharmacokinetic properties like plasma half-life and the time needed to equilibrate between the plasma and the effect compartments, but is also influenced by long-lasting target binding and rebinding. The present review combines information from different research areas and simulations to explore the nature of these mechanisms and the conditions in which they are most prevalent. Simulations reveal that these latter phenomena become especially influential when there is no longer sufficient free drug around to maintain high levels of receptor occupancy. There is not always a direct link between slow dissociation and long-lasting in vivo target protection, as the rate of free drug elimination from the effect compartment is also a key influencing factor. Local phenomena that hinder the diffusion of free drug molecules away from their target may allow them to consecutively bind to the same target and/or targets nearby (denoted as 'rebinding') even when their concentration in the bulk phase has already dropped to insignificant levels. The micro-anatomic properties of many effect compartments are likely to intensify this phenomenon. By mimicking the complexity of tissues, intact cells offer the opportunity to investigate both mechanisms under the same, physiologically relevant conditions.
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Affiliation(s)
- Georges Vauquelin
- Department of Molecular and Biochemical Pharmacology, Vrije Universiteit Brussel, Brussels, Belgium.
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25
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Nesic O, Guest JD, Zivadinovic D, Narayana PA, Herrera JJ, Grill RJ, Mokkapati VUL, Gelman BB, Lee J. Aquaporins in spinal cord injury: the janus face of aquaporin 4. Neuroscience 2010; 168:1019-35. [PMID: 20109536 PMCID: PMC2885549 DOI: 10.1016/j.neuroscience.2010.01.037] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Revised: 01/16/2010] [Accepted: 01/19/2010] [Indexed: 02/07/2023]
Abstract
Although malfunction of spinal cord water channels (aquaporins, AQP) likely contributes to severe disturbances in ion/water homeostasis after spinal cord injury (SCI), their roles are still poorly understood. Here we report and discuss the potential significance of changes in the AQP4 expression in human SCI that generates glial fibrillary acidic protein (GFAP)-labeled astrocytes devoid of AQP4, and GFAP-labeled astroglia that overexpress AQP4. We used a rat model of contusion SCI to study observed changes in human SCI. AQP4-negative astrocytes are likely generated during the process of SCI-induced replacement of lost astrocytes, but their origin and role in SCI remains to be investigated. We found that AQP4-overexpression is likely triggered by hypoxia. Our transcriptional profiling of injured rat cords suggests that elevated AQP4-mediated water influx accompanies increased uptake of chloride and potassium ions which represents a protective astrocytic reaction to hypoxia. However, unbalanced water intake also results in astrocytic swelling that can contribute to motor impairment, but likely only in milder injuries. In severe rat SCI, a low abundance of AQP4-overexpressing astrocytes was found during the motor recovery phase. Our results suggest that severe rat contusion SCI is a better model to analyze AQP4 functions after SCI. We found that AQP4 increases in the chronic post-injury phase are associated with the development of pain-like behavior in SCI rats, while possible mechanisms underlying pain development may involve astrocytic swelling-induced glutamate release. In contrast, the formation and size of fluid-filled cavities occurring later after SCI does not appear to be affected by the extent of increased AQP4 levels. Therefore, the effect of therapeutic interventions targeting AQP4 will depend not only on the time interval after SCI or animal models, but also on the balance between protective role of increased AQP4 in hypoxia and deleterious effects of ongoing astrocytic swelling.
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Affiliation(s)
- O Nesic
- Department of Biochemistry and Molecular Biology, University of Texas Medical Branch, Galveston, TX, USA.
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26
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Fitting S, Zou S, Chen W, Vo P, Hauser KF, Knapp PE. Regional heterogeneity and diversity in cytokine and chemokine production by astroglia: differential responses to HIV-1 Tat, gp120, and morphine revealed by multiplex analysis. J Proteome Res 2010; 9:1795-804. [PMID: 20121167 DOI: 10.1021/pr900926n] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
HIV-infected individuals who abuse opiates show a faster progression to AIDS and higher incidence of encephalitis. The HIV-1 proteins Tat and gp120 have been shown to cause neurodegenerative changes either in vitro or when injected or expressed in the CNS, and we have shown that opiate drugs can exacerbate neurotoxic effects in the striatum through direct actions on pharmacologically discrete subpopulations of mu-opioid receptor-expressing astroglia. Opiate coexposure also significantly enhances release of specific inflammatory mediators by astroglia from the striatum, and we theorize that astroglial reactivity may underlie aspects of HIV neuropathology. To determine whether astroglia from different regions of the central nervous system have distinct, intrinsic responses to HIV-1 proteins and opiates, we used multiplex suspension array analyses to define and compare the inflammatory signature of cytokines released by murine astrocytes grown from cerebral cortex, cerebellum, and spinal cord. Results demonstrate significant regional differences in baseline secretion patterns, and in responses to viral proteins. Of importance for the disease process, astrocytes from all regions have very limited inflammatory response to gp120 protein, as compared to Tat protein, either in the presence or absence of morphine. Overall, the chemokine/cytokine release is higher from spinal cord and cortical astroglia than from cerebellar astroglia, paralleling the relatively low incidence of HIV-related neuropathology in the cerebellum.
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Affiliation(s)
- Sylvia Fitting
- Department of Anatomy and Neurobiology, Department of Pharmacology and Toxicology, and Institute for Drug and Alcohol Studies, Virginia Commonwealth University, Richmond, Virginia 23298-0709, USA
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27
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Beyond oncology--application of HPMA copolymers in non-cancerous diseases. Adv Drug Deliv Rev 2010; 62:258-71. [PMID: 19909776 DOI: 10.1016/j.addr.2009.10.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Revised: 10/27/2009] [Accepted: 10/29/2009] [Indexed: 11/22/2022]
Abstract
Macromolecular drug conjugates have been developed to improve the efficacy and safety profile of various therapeutic agents for many years. Among them, N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-drug conjugates are the most extensively studied delivery platforms for the effective treatment of cancer. In recent years, the applications of HPMA copolymers for the treatment of a broader range of non-cancerous diseases have also been explored. This review highlights the recent developments in the rational design, synthesis, and evaluation of novel HPMA copolymer-drug conjugates for non-cancerous diseases, such as musculoskeletal diseases, infectious diseases and spinal cord injury. The translation potential of these applications is also briefly discussed.
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28
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McConnell GC, Butera RJ, Bellamkonda RV. Bioimpedance modeling to monitor astrocytic response to chronically implanted electrodes. J Neural Eng 2009; 6:055005. [DOI: 10.1088/1741-2560/6/5/055005] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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29
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Schliess F, Görg B, Häussinger D. RNA oxidation and zinc in hepatic encephalopathy and hyperammonemia. Metab Brain Dis 2009; 24:119-34. [PMID: 19148713 DOI: 10.1007/s11011-008-9125-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Accepted: 10/28/2008] [Indexed: 01/31/2023]
Abstract
Hepatic encephalopathy is a neuropsychiatric manifestation of acute and chronic liver failure. Ammonia plays a key role in the pathogenesis of hepatic encephalopathy by inducing astrocyte swelling and/or sensitizing astrocytes to swelling by a heterogeneous panel of precipitating factors and conditions. Whereas astrocyte swelling in acute liver failure contributes to a clinically overt brain edema, a low grade glial edema without clinically overt brain edema is observed in hepatic encephalopathy in liver cirrhosis. Astrocyte swelling produces reactive oxygen and nitrogen oxide species (ROS/RNOS), which again increase astrocyte swelling, thereby creating a self-amplifying signaling loop. Astroglial swelling and ROS/RNOS increase protein tyrosine nitration and may account for neurotoxic effects of ammonia and other precipitants of hepatic encephalopathy. Recently, RNA oxidation and an increase of free intracellular zinc ([Zn(2+)](i)) were identified as further consequences of astrocyte swelling and ROS/RNOS production. An elevation of [Zn(2+)](i) mediates mRNA expression of metallothionein and the peripheral benzodiazepine receptor (PBR) induced by hypoosmotic astrocyte swelling. Further, Zn(2+) mediates RNA oxidation in ammonia-treated astrocytes. In the brain of hyperammonemic rats oxidized RNA localizes in part to perivascular astrocyte processes and to postsynaptic dendritic spines. RNA oxidation may impair postsynaptic protein synthesis, which is critically involved in learning and memory consolidation. RNA oxidation offers a novel explanation for multiple disturbances of neurotransmitter systems and gene expression and the cognitive deficits observed in hepatic encephalopathy.
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Affiliation(s)
- Freimut Schliess
- Heinrich-Heine-Universität Düsseldorf, Klinik für Gastroenterologie, Hepatologie, und Infektiologie, Moorenstrasse 5, D-40225 Düsseldorf, Germany
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30
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Wang YF, Hatton GI. Astrocytic plasticity and patterned oxytocin neuronal activity: dynamic interactions. J Neurosci 2009; 29:1743-54. [PMID: 19211881 PMCID: PMC3849422 DOI: 10.1523/jneurosci.4669-08.2009] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2008] [Revised: 11/21/2008] [Accepted: 12/19/2008] [Indexed: 11/21/2022] Open
Abstract
Astroglial-neuronal interactions are important in brain functions. However, roles of glial fibrillary acidic protein (GFAP) in this interaction remain unclear in acute physiological processes. We explored this issue using the supraoptic nucleus (SON) in lactating rats. At first, we identified the essential role of astrocytes in the milk-ejection reflex (MER) by disabling astrocytic functions via intracerebroventricular application of l-aminoadipic acid (l-AAA). l-AAA blocked the MER and reduced GFAP levels in the SON. In brain slices, l-AAA suppressed oxytocin (OT) neuronal activity and EPSCs. Suckling reduced GFAP in immunocytochemical images and in Western blots, reductions that were partially reversed after the MER. OT, the dominant hormone mediating the MER, reduced GFAP expression in brain slices. Tetanus toxin suppressed EPSCs but did not influence OT-reduced GFAP. Protease inhibitors did not influence OT-reduced GFAP images but blocked the degradation of GFAP molecules. In the presence of OT, transient 12 mm K(+) exposure, simulating effects of synchronized bursts before the MER, reversed OT-reduced GFAP expression. Consistently, suckling first reduced and then increased the expression of aquaporin 4, astrocytic water channels coupled to K(+) channels. Moreover, GFAP molecules were associated with astrocytic proteins, including aquaporin 4, actin, and glutamine synthetase and serine racemase. GFAP-aquaporin 4 association decreased during initial suckling and increased after the MER, whereas opposite changes occurred between GFAP and actin. MER also decreased the association between GFAP and glutamine synthetase. These results indicate that suckling elicits dynamic glial neuronal interactions in the SON; GFAP plasticity dynamically reflects OT neuronal activity.
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Affiliation(s)
- Yu-Feng Wang
- Department of Cell Biology and Neuroscience, University of California, Riverside, California 92521, USA.
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31
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Abstract
Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding, or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix, and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is approximately 20% and the tortuosity is approximately 1.6 (i.e., free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge, and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases, and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties is valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain.
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Affiliation(s)
- Eva Syková
- Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic
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32
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Bamber NI, Li H, Lu X, Oudega M, Aebischer P, Xu XM. Neurotrophins BDNF and NT-3 promote axonal re-entry into the distal host spinal cord through Schwann cell-seeded mini-channels. Eur J Neurosci 2008. [DOI: 10.1111/j.1460-9568.2001.01387.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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33
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Brain metabolism and diffusion in the rat cerebral cortex during pilocarpine-induced status epilepticus. Exp Neurol 2008; 209:145-54. [DOI: 10.1016/j.expneurol.2007.09.008] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2007] [Revised: 08/13/2007] [Accepted: 09/11/2007] [Indexed: 11/19/2022]
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34
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Ellingson BM, Ulmer JL, Schmit BD. Morphology and morphometry of human chronic spinal cord injury using diffusion tensor imaging and fuzzy logic. Ann Biomed Eng 2007; 36:224-36. [PMID: 18066663 DOI: 10.1007/s10439-007-9415-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2007] [Accepted: 11/27/2007] [Indexed: 11/28/2022]
Abstract
Diffusion tensor imaging (DTI) was performed on regions rostral to the injury site in four human subjects with chronic spinal cord injury (SCI) and equivalent regions in four neurologically intact subjects. Apparent diffusion coefficients were measured and compared between subjects. A fuzzy logic tissue classification algorithm was used to segment gray and white matter regions for morphometric analysis, including comparisons of cross-sectional areas of gray and white matter along with frontal and sagittal diameters. Results indicated a general decrease in both longitudinal and transverse diffusivity in the upper cervical segments of subjects with chronic SCI. Further, a decrease in the cross-sectional area of the entire spinal cord was observed in subjects with SCI, consistent with severe atrophy of the spinal cord. These observations have implications in tracking the progression of SCI from the acute to the chronic stages. We conclude that DTI with fuzzy logic tissue classification has potential for monitoring morphological changes in the spinal cord in people with SCI.
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Affiliation(s)
- Benjamin M Ellingson
- Department of Biomedical Engineering, Marquette University, P.O. Box 1881, Milwaukee, WI 53201-1881, USA
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Chvátal A, Anderová M, Kirchhoff F. Three-dimensional confocal morphometry - a new approach for studying dynamic changes in cell morphology in brain slices. J Anat 2007; 210:671-83. [PMID: 17488344 PMCID: PMC2375758 DOI: 10.1111/j.1469-7580.2007.00724.x] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Pathological states in the central nervous system lead to dramatic changes in the activity of neuroactive substances in the extracellular space, to changes in ionic homeostasis and often to cell swelling. To quantify changes in cell morphology over a certain period of time, we employed a new technique, three-dimensional confocal morphometry. In our experiments, performed on enhanced green fluorescent protein/glial fibrillary acidic protein astrocytes in brain slices in situ and thus preserving the extracellular microenvironment, confocal morphometry revealed that the application of hypotonic solution evoked two types of volume change. In one population of astrocytes, hypotonic stress evoked small cell volume changes followed by a regulatory volume decrease, while in the second population volume changes were significantly larger without subsequent volume regulation. Three-dimensional cell reconstruction revealed that even though the total astrocyte volume increased during hypotonic stress, the morphological changes in various cell compartments and processes were more complex than have been previously shown, including swelling, shrinking and structural rearrangement. Our data show that astrocytes in brain slices in situ during hypotonic stress display complex behaviour. One population of astrocytes is highly capable of cell volume regulation, while the second population is characterized by prominent cell swelling, accompanied by plastic changes in morphology. It is possible to speculate that these two astrocyte populations play different roles during physiological and pathological states.
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Affiliation(s)
- Alexandr Chvátal
- Department of Cellular Neurophysiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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Chvátal A, Anderová M, Hock M, Prajerová I, Neprasová H, Chvátal V, Kirchhoff F, Syková E. Three-dimensional confocal morphometry reveals structural changes in astrocyte morphology in situ. J Neurosci Res 2007; 85:260-71. [PMID: 17086549 DOI: 10.1002/jnr.21113] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Neuronal activity and many pathological states in the CNS are accompanied by transient astrocytic swelling, which affects excitability, extrasynaptic transmission, and neuron-glia interactions. By using three-dimensional confocal morphometry (3DCM), we quantified the morphometric parameters of astrocytes in intact tissue. In experiments performed in brain cortex slices from transgenic GFAP/EGFP mice, we applied 3DCM to study the dynamic changes in astrocyte morphology during hypotonic stress. Our morphometric analysis showed that the effect of a 10-min application of hypotonic solution (200 mmol/kg) on the swelling of different cell compartments was dependent on the extent of the swelling of the total astrocyte volume. If the swelling of the whole cell, i.e., soma and processes, was less than approximately 10%, there were no differences between the swelling of the soma and the processes. However, if the swelling of the total cell volume was greater than 10%, the swelling of the processes was greater than the swelling of the soma. Analyzing the effect of hypotonic solution on the morphology of these astrocytes revealed that the total cell volume increased; however, certain cell compartments were distinguished in which the volume increased, whereas in other compartments cell volume decreased or apparently did not change, and the structure of some compartments was altered. Our data show that astrocytes in brain slices undergoing hypotonic stress display cell volume regulation as well as transient changes in morphology.
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Affiliation(s)
- Alexandr Chvátal
- Department of Neurobiology, Institute of Experimental Medicine, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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Kornelsen J, Stroman PW. Detection of the neuronal activity occurring caudal to the site of spinal cord injury that is elicited during lower limb movement tasks. Spinal Cord 2007; 45:485-90. [PMID: 17245349 DOI: 10.1038/sj.sc.3102019] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
STUDY DESIGN Functional magnetic resonance imaging (fMRI) of the spinal cord (spinal fMRI) was used to detect neuronal activity elicited by passive and active lower limb movement tasks, in regions caudal to the injury site in volunteers with spinal cord injury. OBJECTIVES The objectives of this project are: (1) to assess the use of spinal fMRI as a tool for detecting neuronal function in the spinal cord below an injury, and (2) to characterize the neuronal response to active and passive movement tasks. SETTING Institute for Biodiagnostics, National Research Council of Canada, Winnipeg, Manitoba, Canada. METHODS fMRI of the spinal cord was carried out in 12 volunteers with cervical or thoracic spinal cord injuries. Spinal fMRI was carried out in a 1.5 T clinical MR system using established methods. Active and passive lower limb movement tasks were performed, and sagittal images spanning the entire lumbar spinal cord were obtained. RESULTS Activity was detected in all volunteers regardless of the extent of injury. During both active and passive participation, activity was seen caudal to the injury site, although the number of active voxels detected with passive movement was less than with the active movement task. Average percent signal change was 13.6% during active participation and 15.0% during passive participation. CONCLUSIONS Spinal fMRI is able to detect a neuronal response during both active and passive lower limb movement tasks in the spinal cord caudal to the injury site.
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Affiliation(s)
- J Kornelsen
- Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada
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Kim YT, Bridge MJ, Tresco PA. The influence of the foreign body response evoked by fibroblast transplantation on soluble factor diffusion in surrounding brain tissue. J Control Release 2007; 118:340-7. [PMID: 17320236 DOI: 10.1016/j.jconrel.2007.01.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2006] [Revised: 01/04/2007] [Accepted: 01/08/2007] [Indexed: 01/29/2023]
Abstract
The transplantation of genetically engineered fibroblasts has been shown to be an effective approach for achieving continuous and site-specific delivery of therapeutic molecules to various regions of the central nervous system. However, to our knowledge no one has asked whether soluble factors released from the transplanted fibroblasts influence the delivery of therapeutic molecules from the engrafted cells. To address this issue, we used a newly developed cell encapsulation device to study the functional consequence of the foreign body response on soluble factor delivery from fibroblasts transplanted into adult brain tissue. We found that transplanted fibroblasts increased the level of inflammation and glial cell encapsulation at the transplantation site, and reduced the diffusion of a 70 kDa dextran probe through the reactive tissue. The response, however, did not prevent the diffusion of the 70 kDa dextran test probe indicating that the approach appears suitable for the delivery of neurotrophins and other therapeutic molecules with a molecular weight less than 70 kDa. The results suggest that less reactive cell types may be better suited for sustained delivery of therapeutic molecules into brain tissue.
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Affiliation(s)
- Young-Tae Kim
- The Keck Center for Tissue Engineering, Department of Bioengineering, College of Engineering, University of Utah, Salt Lake City, UT 84112, United States
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Schliess F, Görg B, Häussinger D. Pathogenetic interplay between osmotic and oxidative stress: the hepatic encephalopathy paradigm. Biol Chem 2006; 387:1363-70. [PMID: 17081108 DOI: 10.1515/bc.2006.171] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hepatic encephalopathy (HE) defines a primary gliopathy associated with acute and chronic liver disease. Astrocyte swelling triggered by ammonia in synergism with different precipitating factors, including hyponatremia, tumor necrosis factor (TNF)-alpha, glutamate and ligands of the peripheral benzodiazepine receptor (PBR), is an early pathogenetic event in HE. On the other hand, reactive nitrogen and oxygen species (RNOS) including nitric oxide are considered to play a major role in HE. There is growing evidence that osmotic and oxidative stresses are closely interrelated. Astrocyte swelling produces RNOS and vice versa. Based on recent investigations, this review proposes a working model that integrates the pathogenetic action of osmotic and oxidative stresses in HE. Under participation of the N-methyl-D-aspartate (NMDA) receptor, Ca(2+), the PBR and organic osmolyte depletion, astrocyte swelling and RNOS production may constitute an autoamplificatory signaling loop that integrates at least some of the signals released by HE-precipitating factors.
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Affiliation(s)
- Freimut Schliess
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich Heine University, D-40225 Düsseldorf, Germany.
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40
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Neprasova H, Anderova M, Petrik D, Vargova L, Kubinova S, Chvatal A, Sykova E. High extracellular K(+) evokes changes in voltage-dependent K(+) and Na (+) currents and volume regulation in astrocytes. Pflugers Arch 2006; 453:839-49. [PMID: 17031668 DOI: 10.1007/s00424-006-0151-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2006] [Revised: 06/27/2006] [Accepted: 08/08/2006] [Indexed: 10/24/2022]
Abstract
[K(+)](e) increase accompanies many pathological states in the CNS and evokes changes in astrocyte morphology and glial fibrillary acidic protein expression, leading to astrogliosis. Changes in the electrophysiological properties and volume regulation of astrocytes during the early stages of astrocytic activation were studied using the patch-clamp technique in spinal cords from 10-day-old rats after incubation in 50 mM K(+). In complex astrocytes, incubation in high K(+) caused depolarization, an input resistance increase, a decrease in membrane capacitance, and an increase in the current densities (CDs) of voltage-dependent K(+) and Na(+) currents. In passive astrocytes, the reversal potential shifted to more positive values and CDs decreased. No changes were observed in astrocyte precursors. Under hypotonic stress, astrocytes in spinal cords pre-exposed to high K(+) revealed a decreased K(+) accumulation around the cell membrane after a depolarizing prepulse, suggesting altered volume regulation. 3D confocal morphometry and the direct visualization of astrocytes in enhanced green fluorescent protein/glial fibrillary acidic protein mice showed a smaller degree of cell swelling in spinal cords pre-exposed to high K(+) compared to controls. We conclude that exposure to high K(+), an early event leading to astrogliosis, caused not only morphological changes in astrocytes but also changes in their membrane properties and cell volume regulation.
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Affiliation(s)
- Helena Neprasova
- Department of Neurobiology, Institute of Experimental Medicine, The Academy of Sciences of the Czech Republic, Prague, Czech Republic
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41
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Merrill DR, Tresco PA. Impedance characterization of microarray recording electrodes in vitro. IEEE Trans Biomed Eng 2005; 52:1960-5. [PMID: 16285400 DOI: 10.1109/tbme.2005.856245] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The mechanisms underlying performance degradation of chronically implanted silicon microelectrode arrays in the central nervous system (CNS) remain unclear. Humoral and cellular components of the brain foreign body response were evaluated to determine whether their presence on the electrode surface results in increased electrical impedance. Iridium oxide microelectrode recording arrays were electrically characterized in saline, culture media with 10% fetal bovine serum, and coated with various CNS cell types isolated from rat brain. Electrochemical impedance spectroscopy and cyclic voltammetry were performed using a three-electrode system. Potential cycling caused an immediate decrease in electrical impedance, which increased with time toward precycling values, with the effect of cycling remaining significant for several days. The addition of serum caused a significant increase in impedance of up to 28% relative to the saline control. Microelectrodes coated with various cell types known to participate in the foreign body response caused a 20%-80% increase in impedance immediately after contact that remained constant or gradually increased for several weeks. Our findings suggest that the attachment of molecular and cellular species following microelectrode implantation into brain tissue likely contribute to increases in impedance, but do not appear sufficient to hinder recording performance.
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Affiliation(s)
- Daniel R Merrill
- Department of Bioengineering, University of Utah, Salt Lake City 84112-9458, USA
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42
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Papadopoulos MC, Kim JK, Verkman AS. Extracellular space diffusion in central nervous system: anisotropic diffusion measured by elliptical surface photobleaching. Biophys J 2005; 89:3660-8. [PMID: 16143636 PMCID: PMC1366858 DOI: 10.1529/biophysj.105.068114] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Diffusion in the extracellular space (ECS) is crucial for normal central nervous system physiology. The determinants of ECS diffusion include viscous interactions with extracellular matrix/plasma membranes ("viscosity") and ECS geometry ("tortuosity"). To resolve viscosity versus tortuosity effects, we measured direction-dependent (anisotropic) diffusion in ECS in mouse spinal cord by photobleaching using an elliptical spot produced by a cylindrical lens in the excitation path. Anisotropic diffusion slowed fluorescence recovery when the long axis of the ellipse was parallel versus perpendicular to the direction of faster diffusion. A mathematical model was constructed to deduce diffusion coefficients (D(x), D(y)) from fluorescence recovery measured for parallel and perpendicular orientations of the long axis of the ellipse. Elliptical spot photobleaching was validated by photobleaching aqueous-phase fluorophores on a diffraction grating, where diffusion is one-dimensional. Measurement of the diffusion of 70 kDa FITC-dextran in spinal cord in living mice indicated that viscosity slows diffusion by approximately 1.8-fold compared with its diffusion in solution. ECS geometry hinders diffusion across (but not along) axonal fibers in spinal cord further by approximately fivefold. In cerebral cortex, however, approximately 50% of the hindrance to ECS diffusion comes from viscosity and approximately 50% from tortuosity. We suggest that the extracellular matrix might have evolved to facilitate rather than hinder diffusion even for large molecules.
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Affiliation(s)
- Marios C Papadopoulos
- Departments of Medicine and Physiology, Cardiovascular Research Institute, 1246 Health Sciences East Tower, University of California-San Francisco, San Francisco, CA 94143, USA
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43
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Uckermann O, Vargová L, Ulbricht E, Klaus C, Weick M, Rillich K, Wiedemann P, Reichenbach A, Syková E, Bringmann A. Glutamate-evoked alterations of glial and neuronal cell morphology in the guinea pig retina. J Neurosci 2005; 24:10149-58. [PMID: 15537885 PMCID: PMC6730174 DOI: 10.1523/jneurosci.3203-04.2004] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Neuronal activity is accompanied by transmembranous ion fluxes that cause cell volume changes. In whole mounts of the guinea pig retina, application of glutamate resulted in fast swelling of neuronal cell bodies in the ganglion cell layer (GCL) and the inner nuclear layer (INL) (by approximately 40%) and a concomitant decrease of the thickness of glial cell processes in the inner plexiform layer (IPL) (by approximately 40%) that was accompanied by an elongation of the glial cells, by a thickening of the whole retinal tissue, and by a shrinkage of the extracellular space (by approximately 18%). The half-maximal effect of glutamate was observed at approximately 250 mum, after approximately 4 min. The swelling was caused predominantly by AMPA-kainate receptor-mediated influx of Na+ into retinal neurons. Similar but transient morphological alterations were induced by high K+ and dopamine, which caused release of endogenous glutamate and subsequent activation of AMPA-kainate receptors. Apparently, retinal glutamatergic transmission is accompanied by neuronal cell swelling that causes compensatory morphological alterations of glial cells. The effect of dopamine was elicitable only during light adaptation but not in the dark, and glutamate and high K+ induced strong ereffects in the dark than in the light. This suggests that not only the endogenous release of dopamine but also the responsiveness of glutamatergic neurons to dopamine is regulated by light-dark adaptation. Similar morphological alterations (neuronal swelling and decreased glial process thickness) were observed in whole mounts isolated immediately after experimental retinal ischemia, suggesting an involvement of AMPA-kainate receptor activation in putative neurotoxic cell swelling in the postischemic retina.
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Affiliation(s)
- Ortrud Uckermann
- Paul-Flechsig-Institute of Brain Research, University of Leipzig, D-04109 Leipzig, Germany
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44
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Gaillard S, Nasarre C, Gonthier B, Bagnard D. Mécanismes cellulaires et moléculaires de la croissance axonale. Rev Neurol (Paris) 2005; 161:153-72. [PMID: 15798515 DOI: 10.1016/s0035-3787(05)85019-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
INTRODUCTION During embryonic and post-natal development, numerous axonal connections are formed establishing a functional nervous system. Knowledge of the underlying molecular and cellular mechanisms controlling this phenomenon is improving. STATE OF THE ART In this review, we present the general principles of axon guidance together with the major families of guidance signals. This includes the tyrosine kinase receptors Eph and their ligands Ephrins, the netrins, the semaphorins, the slits and other major components of the extracellular matrix. These types of guidance signals share common functional properties leading to actin cytoskeleton remodelling. The direct or indirect interactions between the receptors of these guidance cues and actin modulators is the final step of the signalling cascade constituting the fundamental mechanism defining the orientation and extension of the axonal growth cone. These factors are involved in the formation of many, if not all, axonal projections for which they act as repulsive (inhibitory) or attractive (promoting) signals. PERSPECTIVES the knowledge of these mechanisms is particularly interesting since the inhibition of axonal outgrowth is considered to be one of the major obstacles to nerve regeneration in the central nervous system. Indeed, most of the guidance signals expressed during brain development are up-regulated in lesion sites where they contribute to the lack of nerve re-growth. Here, we present the nature of the mechanical barrier, the so called glial scar, and we describe the major inhibitory molecules preventing axonal extension. CONCLUSION the comprehension of the molecular mechanisms involved in axon growth and guidance represents a major advance towards the definition of novel therapeutic strategies improving nerve regeneration. The path to the clinical application of these molecular factors remains long. Nevertheless, the next decade will undoubtedly provide challenging data that will modify the current therapeutic approaches.
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Affiliation(s)
- S Gaillard
- INSERM U575, Physiopathologie du Système Nerveux, Groupe de Physiologie Moléculaire de la Régénération Nerveuse, 67084 Strasbourg
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45
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Stroman PW, Kornelsen J, Lawrence J. An improved method for spinal functional MRI with large volume coverage of the spinal cord. J Magn Reson Imaging 2005; 21:520-6. [DOI: 10.1002/jmri.20315] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
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46
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Hauser KF, Aldrich JV, Anderson KJ, Bakalkin G, Christie MJ, Hall ED, Knapp PE, Scheff SW, Singh IN, Vissel B, Woods AS, Yakovleva T, Shippenberg TS. Pathobiology of dynorphins in trauma and disease. FRONTIERS IN BIOSCIENCE : A JOURNAL AND VIRTUAL LIBRARY 2005; 10:216-35. [PMID: 15574363 PMCID: PMC4304872 DOI: 10.2741/1522] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Dynorphins, endogenous opioid neuropeptides derived from the prodynorphin gene, are involved in a variety of normative physiologic functions including antinociception and neuroendocrine signaling, and may be protective to neurons and oligodendroglia via their opioid receptor-mediated effects. However, under experimental or pathophysiological conditions in which dynorphin levels are substantially elevated, these peptides are excitotoxic largely through actions at glutamate receptors. Because the excitotoxic actions of dynorphins require supraphysiological concentrations or prolonged tissue exposure, there has likely been little evolutionary pressure to ameliorate the maladaptive, non-opioid receptor mediated consequences of dynorphins. Thus, dynorphins can have protective and/or proapoptotic actions in neurons and glia, and the net effect may depend upon the distribution of receptors in a particular region and the amount of dynorphin released. Increased prodynorphin gene expression is observed in several disease states and disruptions in dynorphin processing can accompany pathophysiological situations. Aberrant processing may contribute to the net negative effects of dysregulated dynorphin production by tilting the balance towards dynorphin derivatives that are toxic to neurons and/or oligodendroglia. Evidence outlined in this review suggests that a variety of CNS pathologies alter dynorphin biogenesis. Such alterations are likely maladaptive and contribute to secondary injury and the pathogenesis of disease.
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Affiliation(s)
- Kurt F Hauser
- Department of Anatomy and Neurobiology, University of Kentucky College of Medicine, Lexington, Kentucky 40536-0298, USA.
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Johnson EA, Svetlov SI, Pike BR, Tolentino PJ, Shaw G, Wang KKW, Hayes RL, Pineda JA. Cell-specific upregulation of survivin after experimental traumatic brain injury in rats. J Neurotrauma 2004; 21:1183-95. [PMID: 15453988 DOI: 10.1089/neu.2004.21.1183] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In this study, we examined the expression and cellular localization of survivin and proliferating cell nuclear antigen (PCNA) after controlled cortical impact traumatic brain injury (TBI) in rats. There was a remarkable and sustained induction of survivin mRNA and protein in the ipsilateral cortex and hippocampus of rats after TBI, peaking at five days post injury. In contrast, both survivin mRNA and protein were virtually undetectable in craniotomy control animals. Concomitantly, expression of PCNA was also significantly enhanced in the ipsilateral cortex and hippocampus of these rats with similar temporal and spatial patterns. Immunohistochemistry revealed that survivin and PCNA were co-expressed in the same cells and had a focal distribution within the injured brain. Further analysis revealed a frequent co-localization of survivin and GFAP, an astrocytic marker, in both the ipsilateral cortex and hippocampus, while a much smaller subset of cells showed co-localization of survivin and NeuN, a mature neuronal marker. Neuronal localization of survivin was observed predominantly in the ipsilateral cortex and contralateral hippocampus after TBI. PCNA protein expression was detected in both astrocytes and neurons of the ipsilateral cortex and hippocampus after TBI. Collectively these data demonstrate that the anti-apoptotic protein survivin, previously characterized in cancer cells, is abundantly expressed in brain tissues of adult rats subjected to TBI. We found survivin expression in both astrocytes and a sub-set of neurons. In addition, the expression of survivin was co-incident with PCNA, a cell cycle protein. This suggests that survivin may be involved in regulation of neural cell proliferative responses after traumatic brain injury.
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Affiliation(s)
- Erik A Johnson
- Center for Traumatic Brain Injury Studies, E.F and W.L. McKnight Brain Institute of the University of Florida, 100 S. Newell Drive, Gainesville, FL 32610, USA
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Schliess F, Foster N, Görg B, Reinehr R, Häussinger D. Hypoosmotic swelling increases protein tyrosine nitration in cultured rat astrocytes. Glia 2004; 47:21-9. [PMID: 15139009 DOI: 10.1002/glia.20019] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Astrocyte swelling is observed in different types of brain injury. We studied a potential contribution of swelling to protein tyrosine nitration (PTN) by using cultured rat astrocytes exposed to hypoosmotic (205 mosmol/L) medium. Hypoosmolarity (2 h) increases total PTN by about 2-fold in 2 h. The hypoosmotic PTN is significantly inhibited by the NMDA receptor antagonist MK-801, the nitric oxide synthase (NOS) inhibitor L-NMMA, the extracellular Ca2+ chelator EGTA and the calmodulin antagonist W13, suggesting the involvement of NMDA receptor activation, influx of extracellular Ca2+ and Ca2+/calmodulin-dependent NO synthesis. Further, superoxide dismutase plus catalase and uric acid strongly inhibit hypoosmotic PTN, suggesting the involvement of the toxic metabolite peroxynitrite (ONOO-) as a nitrating agent. Hypoosmotic astrocyte swelling rapidly stimulates generation of reactive oxygen intermediates; this process is prevented by MK-801 and EGTA. In addition, MK-801 inhibits the hypoosmotic elevation of [Ca2+]i. The findings support the view that astrocyte swelling as induced, for example, by toxins relevant for hepatic encephalopathy is sufficient to produce oxidative stress and PTN and thus contributes to altered astroglial and neuronal function.
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Affiliation(s)
- Freimut Schliess
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany.
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Hrabetová S, Nicholson C. Contribution of dead-space microdomains to tortuosity of brain extracellular space. Neurochem Int 2004; 45:467-77. [PMID: 15186912 DOI: 10.1016/j.neuint.2003.11.011] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/10/2003] [Indexed: 10/26/2022]
Abstract
The extracellular space (ECS) of the brain is a major channel for intercellular communication, nutrient and metabolite trafficking, and drug delivery. The dominant transport mechanism is diffusion, which is governed by two structural parameters, tortuosity and volume fraction. Tortuosity (lambda) represents the hindrance imposed on the diffusing molecules by the tissue in comparison with an obstacle-free medium, while volume fraction (alpha) is the proportion of tissue volume occupied by the ECS. Diffusion of small ECS markers can be exploited to measure lambda and alpha. In healthy brain tissue, lambda is about 1.6 but increases to 1.9-2.0 in pathologies that involve cellular swelling. Previously it was thought that lambda could be explained by the circumnavigation of diffusing molecules around cells. Numerical models of assemblies of convex cells, however, give an upper limit of about 1.23 for lambda. Therefore, additional factors must be responsible for lambda in brain. In principle, two mechanisms could account for the measured value: a more complex ECS geometry or an extracellular macromolecular matrix. Here we review recent work in ischemic tissue suggesting concave geometrical formations, dead-space microdomains, as a major determinant of extracellular tortuosity. A theoretical model of lambda based on diffusion dwell times supports this hypothesis and predicts that, in ischemia, dead spaces occupy approximately 60% of ECS volume fraction leaving only approximately 40% for well-connected channels. It is further proposed that dead spaces are present in healthy brain tissue where they constitute about 40% of alpha. The presence of dead-space microdomains in the ECS implies microscopic heterogeneity of extracellular channels with fundamental implications for molecular transport in brain.
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Affiliation(s)
- Sabina Hrabetová
- Department of Physiology and Neuroscience, New York University School of Medicine, 550 First Avenue, New York, NY 10016, USA.
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50
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Woerly S, Doan VD, Sosa N, de Vellis J, Espinosa-Jeffrey A. Prevention of gliotic scar formation by NeuroGel? allows partial endogenous repair of transected cat spinal cord. J Neurosci Res 2004; 75:262-272. [PMID: 14705147 DOI: 10.1002/jnr.10774] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Spinal cords of adult cats were transected and subsequently reconnected with the biocompatible porous poly (N-[2-hydroxypropyl] methacrylamide) hydrogel, NeuroGel. Tissue repair was examined at various time points from 6-21 months post reconstructive surgery. We examined two typical phenomena, astrogliosis and scar formation, in spines reconstructed with the gel and compared them to those from transected non-reconstructed spines. Confocal examination with double immunostaining for glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP) showed that the interface formed between the hydrogel and the spine stumps did prevent scar formation and only a moderate gliosis was observed. The gel implant provided an adequate environment for growth of myelinated fibers and we saw angiogenesis within the gel. Electron microscopy showed that regenerating axons were myelinated by Schwann cells rather than oligodendrocytes. Moreover, the presence of the gel implant lead to a considerable reduction in damage to distal caudal portions of the spine as assessed by the presence of more intact myelinated fibers and a reduction of myelin degradation. Neurologic assessments of hindlimb movement at various times confirmed that spinal cord reconstruction was not only structural but also functional. We conclude that NeuroGel lead to functional recovery by providing a favorable substrate for regeneration of transected spinal cord, reducing glial scar formation and allowing angiogenesis.
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Affiliation(s)
| | | | - Norma Sosa
- Mental Retardation Research Center, Neuropsychiatric Institute, David Geffen School of Medicine at UCLA, Los Angeles, California
| | - Jean de Vellis
- Mental Retardation Research Center, Neuropsychiatric Institute, David Geffen School of Medicine at UCLA, Los Angeles, California
| | - Araceli Espinosa-Jeffrey
- Mental Retardation Research Center, Neuropsychiatric Institute, David Geffen School of Medicine at UCLA, Los Angeles, California
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