O P Ottersen

University of Oslo, Kristiania (historical), Oslo, Norway

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Publications (381)1785.36 Total impact

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    ABSTRACT: Astrocytic endfeet are specialized cell compartments whose important homeostatic roles depend on their enrichment of water and ion channels anchored by the dystrophin associated protein complex (DAPC). This protein complex is known to disassemble in patients with mesial temporal lobe epilepsy and in the latent phase of experimental epilepsies. The mechanistic underpinning of this disassembly is an obvious target of future therapies, but remains unresolved. Here we show in a kainate model of temporal lobe epilepsy that astrocytic endfeet display an enhanced stimulation-evoked Ca(2+) signal that outlast the Ca(2+) signal in the cell bodies. While the amplitude of this Ca(2+) signal is reduced following group I/II metabotropic receptor (mGluR) blockade, the duration is sustained. Based on previous studies it has been hypothesized that the molecular disassembly in astrocytic endfeet is caused by dystrophin cleavage mediated by Ca(2+) dependent proteases. Using a newly developed genetically encoded Ca(2+) sensor, the present study bolsters this hypothesis by demonstrating long-lasting, enhanced stimulation-evoked Ca(2+) signals in astrocytic endfeet.
    Frontiers in Cellular Neuroscience 01/2015; 9:49. DOI:10.3389/fncel.2015.00049 · 4.18 Impact Factor
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    ABSTRACT: Brain ependymal cells, which form an epithelial layer covering the cerebral ventricles, have been shown to play a role in the regulation of cerebrospinal and interstitial fluids. The machinery underlying this, however, remains largely unknown. Here, we report the specific localization of an inwardly rectifying K(+) channel, Kir4.1, on the ependymal cell membrane suggesting involvement of the channel in this function. Immunohistochemical study with confocal microscopy identified Kir4.1 labeling on the lateral but not apical membrane of ependymal cells. Ultrastructural analysis revealed that Kir4.1-immunogold particles were specifically localized and clustered on adjacent membranes at puncta adherens type junctions, whereas an aquaporin water channel, AQP4, that was also detected on the lateral membrane only occurred at components other than adherens junctions. Therefore, in ependymal cells, Kir4.1 and AQP4 are partitioned into distinct membrane compartments that might respectively transport either K(+) or water. Kir4.1 was also expressed in a specialized form of ependymal cell, namely the tanycyte, being abundant in tanycyte processes wrapping neuropils and blood vessels. These specific localizations suggest that Kir4.1 mediates intercellular K(+) exchange between ependymal cells and also K(+)-buffering transport via tanycytes that can interconnect neurons and vessels/ventricles. We propose that ependymal cells and tanycytes differentially operate Kir4.1 and AQP4 actively to control the property of fluids at local areas in the brain.
    Cell and Tissue Research 11/2014; 359(2). DOI:10.1007/s00441-014-2030-6 · 3.33 Impact Factor
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    ABSTRACT: Astrocytes are highly polarised cells with processes that ensheath microvessels, cover the brain surface, and abut synapses. The endfoot membrane domains facing microvessels and pia are enriched with aquaporin-4 water channels (AQP4) and other members of the dystrophin associated protein complex (DAPC). Several lines of evidence show that loss of astrocyte polarization, defined by the loss of proteins that are normally enriched in astrocyte endfeet, is a common denominator of several neurological diseases such as mesial temporal lobe epilepsy, Alzheimer's disease, and stroke. Little is known about the mechanisms responsible for inducing astrocyte polarization in vivo. Here we introduce the term endfoot-basal lamina junctional complex (EBJC) to denote the proteins that consolidate and characterize the gliovascular interface. The present study was initiated in order to resolve the developmental profile of the EBJC in mouse brain. We show that the EBJC is established after the first week postnatally. Through a combination of methodological approaches, including light microscopic and high resolution immunogold cytochemistry, quantitative RT-PCR, and Western blotting, we demonstrate that the different members of this complex exhibit distinct ontogenic profiles--with the extracellular matrix (ECM) proteins laminin and agrin appearing earlier than the other members of the complex. Specifically, while laminin and agrin expression peak at P7, quantitative immunoblot analyses indicate that AQP4, α-syntrophin, and the inwardly rectifying K(+) channel Kir4.1 expression increases towards adulthood. Our findings are consistent with ECM having an instructive role in establishing astrocyte polarization in postnatal development and emphasize the need to explore the involvement of ECM in neurological disease.
    Brain Structure and Function 04/2014; DOI:10.1007/s00429-014-0775-z · 4.57 Impact Factor
  • The Lancet 04/2014; 383(9926):1380-1. DOI:10.1016/S0140-6736(14)60676-0 · 39.21 Impact Factor
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    ABSTRACT: The coupling between the water channel aquaporin-4 (AQP4) and K(+) transport has attracted much interest. In this study, we assessed the effect of Aqp4 deletion on activity-induced [K(+)]o changes in acute slices from hippocampus and corpus callosum of adult mice. We show that Aqp4 deletion has a layer-specific effect on [K(+)]o that precisely mirrors the known effect on extracellular volume dynamics. In CA1, the peak [K(+)]o in stratum radiatum during 20 Hz stimulation of Schaffer collateral/commissural fibers was significantly higher in Aqp4 (-/-) mice than in wild types, whereas no differences were observed throughout the [K(+)]o recovery phase. In stratum pyramidale and corpus callosum, neither peak [K(+)]o nor post-stimulus [K(+)]o recovery was affected by Aqp4 deletion. Our data suggest that AQP4 modulates [K(+)]o during synaptic stimulation through its effect on extracellular space volume.
    Brain Structure and Function 04/2014; DOI:10.1007/s00429-014-0767-z · 4.57 Impact Factor
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    The Lancet 02/2014; 383(9917). DOI:10.1016/S0140-6736(13)62407-1 · 39.21 Impact Factor
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    ABSTRACT: The focal swellings of dendrites (dendritic beading) are an early morphological hallmark of neuronal injury and dendrotoxicity. They are associated with a variety of pathological conditions including brain ischemia and cause an acute disruption of synaptic transmission and neuronal network function, which contributes to subsequent neuronal death. Here we show that increased synaptic activity prior to excitotoxic injury protects, in a transcription-dependent manner, against dendritic beading. Expression of Activating transcription factor 3 (ATF3), a nuclear calcium-regulated gene and member of the core gene program for acquired neuroprotection, can protect against dendritic beading. Conversely, knock-down of ATF3 exacerbates dendritic beading. Assessment of neuronal network functions using multi-electrode array recordings revealed that hippocampal neurons expressing ATF3 were able to regain their ability of functional synaptic transmission and to participate in coherent neuronal network activity within 48 h after exposure to toxic concentrations of NMDA. Thus, in addition to attenuating cell death, synaptic activity and expression of ATF3 render hippocampal neurons more resistant to acute dendrotoxicity and loss of synapses. Dendroprotection can enhance recovery of neuronal network functions after excitotoxic insults.
    Journal of Biological Chemistry 02/2014; 289(14). DOI:10.1074/jbc.M113.502914 · 4.60 Impact Factor
  • Erlend A Nagelhus, Ole P Ottersen
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    ABSTRACT: Aquaporin-4 (AQP4) is one of the most abundant molecules in the brain and is particularly prevalent in astrocytic membranes at the blood-brain and brain-liquor interfaces. While AQP4 has been implicated in a number of pathophysiological processes, its role in brain physiology has remained elusive. Only recently has evidence accumulated to suggest that AQP4 is involved in such diverse functions as regulation of extracellular space volume, potassium buffering, cerebrospinal fluid circulation, interstitial fluid resorption, waste clearance, neuroinflammation, osmosensation, cell migration, and Ca(2+) signaling. AQP4 is also required for normal function of the retina, inner ear, and olfactory system. A review will be provided of the physiological roles of AQP4 in brain and of the growing list of data that emphasize the polarized nature of astrocytes.
    Physiological Reviews 10/2013; 93(4):1543-62. DOI:10.1152/physrev.00011.2013 · 29.04 Impact Factor
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    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.
    PLoS ONE 07/2013; 8(7):e68044. DOI:10.1371/journal.pone.0068044 · 3.53 Impact Factor
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    ABSTRACT: It has been suggested that loss of the astrocytic water channel aquaporin-4 (AQP4) from perivascular endfeet in sclerotic hippocampi contributes to increased seizure propensity in human mesial temporal lobe epilepsy (MTLE). Whether this loss occurs prior to or as a consequence of epilepsy development remains to be resolved. In the present study, we investigated whether the expression and distribution of AQP4 was altered prior to (i.e., in the latent phase) or after the onset of chronic epileptic seizures (i.e., in the chronic phase) in the kainate (KA) model of MTLE. Immunogold electron microscopic analysis revealed that AQP4 density in adluminal endfoot membranes was reduced in KA treated rats already in the latent phase, while the AQP4 density in the abluminal endfoot membrane was stable or slightly increased. The decrease in adluminal AQP4 immunogold labeling was accompanied by a reduction in the density of AQP4's anchoring protein alpha-syntrophin. The latent and chronic phases were associated with an upregulation of the M1 isoform of AQP4, as judged by semi-quantitative Western blot analysis. Taken together, the findings in this model suggest that a mislocalization of AQP4 - reflecting a loss of astrocyte polarization - is an integral part of the epileptogenic process.
    Epilepsy research 07/2013; 105(1-2). DOI:10.1016/j.eplepsyres.2013.01.006 · 2.19 Impact Factor
  • Mahmood Amiry-Moghaddam, Ole Petter Ottersen
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    ABSTRACT: The complexity of the central nervous system calls for immunocytochemical procedures that allow target proteins to be localized with high precision and with opportunities for quantitation. Immunogold procedures stand out as particularly powerful in this regard. Although these procedures have found wide application in the neuroscience community, they present limitations and pitfalls that must be taken into account. At the same time, these procedures offer potentials that remain to be fully realized.
    Nature Neuroscience 06/2013; 16(7):798-804. DOI:10.1038/nn.3418 · 14.98 Impact Factor
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    ABSTRACT: Aquaporin 4 (AQP4) is the predominant water channel in the brain, expressed mainly in astrocytes and involved in water transport in physiologic and pathologic conditions. Besides the classical isoforms M1 (a) and M23 (c), additional ones may be present at the plasma membrane, such as the recently described AQP4b, d, e, and f. Water permeability regulation by AQP4 isoforms may involve several processes, such as channel conformational changes, the extent and arrangement of channels at the plasma membrane, and the dynamics of channel trafficking to/from the plasma membrane. To test whether vesicular trafficking affects the abundance of AQP4 channel at the plasma membrane, we studied the subcellular localization of AQP4 in correlation with vesicle mobility of AQP4e, one of the newly discovered AQP4 isoforms. In cultured rat astrocytes, recombinant AQP4e acquired plasma membrane localization, which resembled that of the antibody labeled endogenous AQP4 localization. Under conditions mimicking reactivation of astrocytes (increase in cytosolic cAMP) and brain edema, an increase in the AQP4 plasma membrane localization was observed. The cytoskeleton remained unaffected with the exception of rearranged actin filaments in the model of reactive astrocytes and vimentin meshwork depolymerization in hypoosmotic conditions. AQP4e vesicle mobility correlated with changes in the plasma membrane localization of AQP4 in all stimulated conditions. Hypoosmotic stimulation triggered a transient reduction in AQP4e vesicle mobility mirrored by the transient changes in AQP4 plasma membrane localization. We suggest that regulation of AQP4 surface expression in pathologic conditions is associated with the mobility of AQP4-carrying vesicles.
    Glia 06/2013; 61(6). DOI:10.1002/glia.22485 · 5.47 Impact Factor
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    ABSTRACT: Using in vivo two-photon imaging, we show that mice deficient in aquaporin-4 (AQP4) display increased fluorescence of nicotinamide adenine dinucleotide (NADH) when subjected to cortical spreading depression. The increased NADH signal, a proxy of tissue hypoxia, was restricted to microwatershed areas remote from the vasculature. Aqp4 deletion had no effects on the hyperemia response, but slowed [K(+)]o recovery. These observations suggest that K(+) uptake is suppressed in Aqp4(-/-) mice as a consequence of decreased oxygen delivery to tissue located furthest away from the vascular source of oxygen, although increased oxygen consumption may also contribute to our observations.Journal of Cerebral Blood Flow & Metabolism advance online publication, 24 April 2013; doi:10.1038/jcbfm.2013.63.
    Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism 04/2013; DOI:10.1038/jcbfm.2013.63 · 5.34 Impact Factor
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    ABSTRACT: It has been suggested that loss of the astrocytic water channel aquaporin-4 (AQP4) from perivascular endfeet in sclerotic hippocampi contributes to increased seizure propensity in human mesial temporal lobe epilepsy (MTLE). Whether this loss occurs prior to or as a consequence of epilepsy development remains to be resolved. In the present study, we investigated whether the expression and distribution of AQP4 was altered prior to (i.e., in the latent phase) or after the onset of chronic epileptic seizures (i.e., in the chronic phase) in the kainate (KA) model of MTLE. Immunogold electron microscopic analysis revealed that AQP4 density in adluminal endfoot membranes was reduced in KA treated rats already in the latent phase, while the AQP4 density in the abluminal endfoot membrane was stable or slightly increased. The decrease in adluminal AQP4 immunogold labeling was accompanied by a reduction in the density of AQP4's anchoring protein alpha-syntrophin. The latent and chronic phases were associated with an upregulation of the M1 isoform of AQP4, as judged by semi-quantitative Western blot analysis. Taken together, the findings in this model suggest that a mislocalization of AQP4 - reflecting a loss of astrocyte polarization - is an integral part of the epileptogenic process.
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    ABSTRACT: Key roles of macroglia are inextricably coupled to specialized membrane domains. The perivascular endfoot membrane has drawn particular attention, as this domain contains a unique complement of aquaporin-4 (AQP4) and other channel proteins that distinguishes it from perisynaptic membranes. Recent studies indicate that the polarization of macroglia is lost in a number of diseases, including temporal lobe epilepsy and Alzheimer's disease. A better understanding is required of the molecular underpinning of astroglial polarization, particularly when it comes to the significance of the dystrophin associated protein complex (DAPC). Here, we employ immunofluorescence and immunogold cytochemistry to analyze the molecular scaffolding in perivascular endfeet in macroglia of retina and three regions of brain (cortex, dentate gyrus, and cerebellum), using AQP4 as a marker. Compared with brain astrocytes, Müller cells (a class of retinal macroglia) exhibit lower densities of the scaffold proteins dystrophin and α-syntrophin (a DAPC protein), but higher levels of AQP4. In agreement, depletion of dystrophin or α-syntrophin-while causing a dramatic loss of AQP4 from endfoot membranes of brain astrocytes-had only modest or insignificant effect, respectively, on the AQP4 pool in endfoot membranes of Müller cells. In addition, while polarization of brain macroglia was less affected by dystrophin depletion than by targeted deletion of α-syntrophin, the reverse was true for retinal macroglia. These data indicate that the molecular scaffolding in perivascular endfeet is more complex than previously assumed and that macroglia are heterogeneous with respect to the mechanisms that dictate their polarization. © 2012 Wiley Periodicals, Inc.
    Glia 12/2012; 60(12):2018-26. DOI:10.1002/glia.22416 · 5.47 Impact Factor
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    ABSTRACT: Aquaporins (AQPs) are channel-forming membrane proteins highly permeable to water. AQP4 is found in mammalian hearts; however, its expression sites, regulation and function are largely unknown. The aim was to investigate cardiac AQP4 expression in humans and mice, its regulation by ischemia and hypoxia, and in particular its role in cardiac ischemic injury using AQP4 knockout (KO) mice. Comparable levels of AQP4 were detected by Western blot and qPCR in biopsies from human donor hearts and wild type C57Bl6 mouse hearts. In mice, AQP4 was expressed on cardiomyocyte plasmalemma (qPCR, Western blot, immunogold), and its mRNA decreased following ischemia/reperfusion (isolated hearts, p = 0.02) and after normobaric hypoxia in vivo (oxygen fraction 10 % for 1 week, p < 0.001). Isolated hearts from AQP4 KO mice undergoing global ischemia and reperfusion had reduced infarct size (p = 0.05) and attenuated left ventricular end-diastolic pressure during reperfusion (p = 0.04). Infarct size was also reduced in AQP4 KO mice 24 h after left coronary artery ligation in vivo (p = 0.036). AQP4 KO hearts had no compensatory change in AQP1 protein expression. AQP4 KO cardiomyocytes were partially resisted to hypoosmotic stress in the presence of hypercontracture. AQP4 is expressed in human and mouse hearts, in the latter confined to the cardiomyocyte plasmalemma. AQP4 mRNA expression is downregulated by hypoxia and ischemia. Deletion of AQP4 is protective in acute myocardial ischemia-reperfusion, and this molecule might be a future target in the treatment of acute myocardial infarction.
    Archiv für Kreislaufforschung 09/2012; 107(5):280. DOI:10.1007/s00395-012-0280-6 · 5.96 Impact Factor
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    ABSTRACT: Recent experimental data in mice have shown that the inwardly rectifying K channel Kir4.1 mediates K spatial buffering in the hippocampus. Here we used immunohistochemistry to examine the distribution of Kir4.1 in hippocampi from patients with medication-refractory temporal lobe epilepsy. The selectivity of the antibody was confirmed in mice with a glial conditional deletion of the gene encoding Kir4.1. These mice showed a complete loss of labeled cells, indicating that Kir4.1 is restricted to glia. In human cases, Kir4.1 immunoreactivity observed in cells morphologically consistent with astrocytes was significantly reduced in 12 patients with hippocampal sclerosis versus 11 patients without sclerosis and 4 normal autopsy controls. Loss of astrocytic Kir4.1 immunoreactivity was most pronounced around vessels and was restricted to gliotic areas. Loss of Kir4.1 expression was associated with loss of dystrophin and α-syntrophin, but not with loss of β-dystroglycan, suggesting partial disruption of the dystrophin-associated protein complex. The changes identified in patients with hippocampal sclerosis likely interfere with K homeostasis and may contribute to the epileptogenicity of the sclerotic hippocampus.
    Journal of Neuropathology and Experimental Neurology 08/2012; 71(9):814-25. DOI:10.1097/NEN.0b013e318267b5af · 4.37 Impact Factor
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    ABSTRACT: Aquaporin-4 (AQP4) is known to have two main isoforms M1 and M23 in the brain. Immunoblot analyses have provided evidence of additional AQP4 immunopositive bands, suggesting that the repertoire of AQP4 isoforms is broader than previously assumed. As isoforms beyond M1 and M23 are not observed in recombinant systems, investigation of novel isoforms requires the use of a native source. Here we report purification of AQP4 to three silver-stained proteins on SDS-PAGE. This was achieved by organelle separation, alkaline stripping of cellular membranes, detergent solubilization and multiple chromatographic steps. The three proteins that co-purified were identified as AQP4 by mass spectrometry. These results represent the first purification of AQP4 from a native source and demonstrate by mass spectrometry the presence of a third AQP4 isoform of 36kDa in the rat brain. Immunoblots revealed that the same isoform is present in the mouse, pig, and human brain.
    Journal of neuroscience methods 08/2012; 211(1):31-9. DOI:10.1016/j.jneumeth.2012.07.021 · 1.96 Impact Factor
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    Devin K Binder, Erlend A Nagelhus, Ole Petter Ottersen
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    ABSTRACT: Recent studies have implicated glial cells in modulation of synaptic transmission, so it is plausible that glial cells may have a functional role in the hyperexcitability characteristic of epilepsy. Indeed, alterations in distinct astrocyte membrane channels, receptors, and transporters have all been associated with the epileptic state. This review focuses on the potential roles of the glial water channel aquaporin-4 (AQP4) in modulation of brain excitability and in epilepsy. We will review studies of mice lacking AQP4 (Aqp4(-/-) mice) or α-syntrophin (an AQP4 anchoring protein) and discuss the available human studies demonstrating alterations of AQP4 in human epilepsy tissue specimens. We will conclude with new studies of AQP4 regulation and discuss the potential role of AQP4 in the development of epilepsy (epileptogenesis). While many questions remain unanswered, the available data indicate that AQP4 and its molecular partners may represent important new therapeutic targets.
    Glia 08/2012; 60(8):1203-14. DOI:10.1002/glia.22317 · 5.47 Impact Factor
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    ABSTRACT: Glutamate has been implicated in signal transmission between inner hair cells and afferent fibers of the organ of Corti. The inner hair cells are enriched in glutamate and the postsynaptic membranes express AMPA glutamate receptors. However, it is not known whether inner hair cells contain a mechanism for glutamate replenishment. Such a mechanism must be in place to sustain glutamate neurotransmission. Here we provide RT-PCR and immunofluorescence data indicating that system A transporter 1 (SLC38A1), which is associated with neuronal glutamine transport and synthesis of the neurotransmitters GABA and glutamate in CNS, is expressed in inner hair cells. It was previously shown that inner hair cells contain glutaminase that converts glutamine to glutamate. Thus, our finding that inner hair cells express a glutamine transporter and the key glutamine metabolizing enzyme glutaminase, provides a mechanism for glutamate replenishment and bolsters the idea that glutamate serves as a transmitter in the peripheral synapse of the auditory system.
    Hearing research 07/2012; 292(1-2):59-63. DOI:10.1016/j.heares.2012.07.005 · 2.85 Impact Factor

Publication Stats

24k Citations
1,785.36 Total Impact Points

Institutions

  • 1970–2015
    • University of Oslo
      • • Department of Anatomy
      • • Centre for Molecular Biology and Neuroscience
      • • Institute of Basic Medical Sciences
      Kristiania (historical), Oslo, Norway
  • 2012
    • Oslo University Hospital
      • Department of Neurology
      Oslo, Oslo, Norway
  • 2005
    • Center for Autism and Related Disorders
      Burbank, California, United States
  • 2004
    • Yale University
      • Department of Neurosurgery
      New Haven, CT, United States
  • 2003
    • Humboldt-Universität zu Berlin
      • Institute of Finance
      Berlín, Berlin, Germany
  • 2002
    • Shinshu University
      • Department of Otorhinolaryngology
      Shonai, Nagano, Japan
  • 1998
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 1997
    • Aarhus University
      • Institute of Anatomy
      Aars, Region North Jutland, Denmark
  • 1992–1996
    • Karolinska Institutet
      • Institutionen för neurovetenskap
      Solna, Stockholm, Sweden
    • Linköping University
      • Faculty of Health Sciences
      Linköping, OEstergoetland, Sweden
  • 1990
    • Uppsala University
      Uppsala, Uppsala, Sweden
  • 1986–1988
    • University of Bristol
      Bristol, England, United Kingdom