| 1. |
- Covacu, Ruxandra, et al.
(author)
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Nitric oxide exposure diverts neural stem cell fate from neurogenesis towards astrogliogenesis
- 2006
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In: Stem Cells. - : Oxford University Press (OUP). - 1066-5099 .- 1549-4918. ; 178, s. 268-268
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Journal article (other academic/artistic)abstract
- Regeneration of cells in the central nervous system is a process that might be affected during neurological disease and trauma. Because nitric oxide (NO) and its derivatives are powerful mediators in the inflammatory cascade, we have investigated the effects of pathophysiological concentrations of NO on neurogenesis, gliogenesis, and the expression of proneural genes in primary adult neural stem cell cultures. After exposure to NO, neurogenesis was downregulated, and this corresponded to decreased expression of the proneural gene neurogenin-2 and beta-III-tubulin. The decreased ability to generate neurons was also found to be transmitted to the progeny of the cells. NO exposure was instead beneficial for astroglial differentiation, which was confirmed by increased activation of the Janus tyrosine kinase/signal transducer and activator of transcription transduction pathway. Our findings reveal a new role for NO during neuroinflammatory conditions, whereby its proastroglial fate-determining effect on neural stem cells might directly influence the neuroregenerative process.
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| 2. |
- da Silva, A. F., et al.
(author)
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Influence of Si doping on optical properties of wurtzite GaN
- 2001
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:40, s. 8891-8899
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Journal article (peer-reviewed)abstract
- The band gap shift (BGS) of Si-doped wurtzite GaN for impurity concentrations spanning the insulating to the metallic regimes has been investigated at low temperature. The critical impurity concentration for the metal-non-metal transition is estimated from the generalized Drude approach for the resistivity to be about 1.0 x 10(18) cm(-3). The calculations for the BGS were carried out within a framework of the random phase approximation, taking into account the electron-electron, electron-optical phonon, and electron-ion interactions. In the wake of very recent photoluminescence measurements, we have shown and discussed the possible transitions involved in the experimental results.
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| 3. |
- Danilov, Alexandre, et al.
(author)
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Neurogenesis in the adult spinal cord in an experimental model of multiple sclerosis
- 2006
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In: European Journal of Neuroscience. - : Wiley. - 1460-9568 .- 0953-816X. ; 23:2, s. 394-400
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Journal article (peer-reviewed)abstract
- Multiple sclerosis is an inflammatory disease of the central nervous system characterized by inflammation, demyelination, axonal degeneration and accumulation of neurological disability. Previously, we demonstrated that stem cells constitute a possible endogenous source for remyelination. We now addressed the question of whether neurogenesis can occur in neuroinflammatory lesions. We demonstrated that, in experimental autoimmune encephalomyelitis, induced in rats 1,1'-dioctadecyl-6,6'-di(4sulphopentyl)-3,3,3',3'tetramethylindocarbocyani n(DiI)-labelled ependymal cells not only proliferated but descendants migrated to the area of neuroinflammation and differentiated into cells expressing the neuronal markers beta-III-tubulin and NeuN. Furthermore, these cells were immunoreactive for bromodeoxyuridine and PCNA, markers for cells undergoing cell proliferation. Using the whole-cell patch-clamp technique on freshly isolated 1, DiI-labelled cells from spinal cord lesions we demonstrated the ability of these cells to fire overshooting action potentials similar to those of immature neurones. We thus provide the first evidence for the initiation of neurogenesis in neuroinflammatory lesions in the adult spinal cord.
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| 4. |
- Johansson, Clas B
(author)
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Isolation and characterization of adult neural stem cells
- 2002
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Doctoral thesis (other academic/artistic)abstract
- Injury to the central nervous system (CNS) is one of man's most handicapping situations resulting in severe functional impairment and in some cases a vegetative state where life is supported artificially. The brain and spinal cord, constituting the CNS, have been viewed for decades as having limited capacity of regeneration with no neurogenesis in the adult. The failure to regenerate the CNS was postulated to be due to either: (1) weak intrinsic capacity of neurons to re-grow axons to their target, (2) formation of a compact glial scar (3) the presence of axon-growth inhibiting factors or (4) the lack of neurogenesis. Likely it is a combination of factors, rather than one single factor, that explains the limited regenerative capacity. The focus of this study has been to analyze the mechanisms behind scar formation in response to injury and to try to identify and characterize neural stem cells in the adult CNS. We first focused our studies on the role of the intermediate filaments (IFs) in scar formation in the CNS, using a well-characterized injury model in transgenic animals devoid of different IFs. Glial scar formation appeared normal after spinal cord or brain lesions in GFAP-/- or vimentin-/- mice but was impaired in GFAP-/-vimentin-/- mice. These mice developed less dense scar tissue, frequently accompanied by bleeding. These results show that GFAP and vimentin are required for proper glial scar formation in the injured CNS. Interestingly, we found that nestin, an intermediate filament protein expressed in neuroepithelial stem cells during nervous system development, is re-expressed in the injured CNS. The expression of nestin in adult animals is restricted to endothelial and ependymal cells. After a spinal cord injury, nestin expression is rapidly increased in ependymal cells and the expression then spreads along the midline towards the lesion site. This dynamic nestin expression pattern in response to injury suggested that a latent population of stem cells lining the central canal contribute to scar formation. Previous work suggested that neural stem cells reside in the subventricular zone (SVZ). However, we found that in the spinal cord injury paradigm, ependymal cells proliferate and their progeny migrate and differentiate to astrocytes. Using an antibody that recognize the extracellular domain of Notch 1, the fluorescent dye (Dil) and cell morphology (ependymal cells are ciliated), ependymal cells were isolated and cultured in vitro and clonally derived cultures differentiated into the three major cell types of the CNS. Longterm BrdU experiments and lineage analysis revealed that forebrain ependymal cells divide slowly and give rise to rapidly dividing SVZ cells. Infection of forebrain ependymal cells with adeno- or retrovirus expressing the reporter gene lacZ, or labeling with Dil, showed that progeny of infected ependymal cells migrate to the olfactory bulb and differentiate to interneurons. In order to investigate if the adult human brain harbors neural stem cells we obtained hippocampus and lateral ventricle wall tissue from adult patients. We found that both regions harbor cells that are self-renewing and multipotent in vitro, i.e. bona tide neural stem cells. It was previously thought that the differentiation potential of a stem cell is restricted to the cell types present in the tissue in which it resides. We challenged this view by first co-culturing neural stem cells with embryonic stem (ES) cells. ES cells have the potential to differentiate to all cells in the embryo, and hence we argued that they may be able to instruct the neural stem cells to generate non-neural cells. Neural stem cells from ROSA26 mice were isolated and co-cultured with wild type ES cells. Some of the cells derived from the neural stem cells expressed the muscle specific markers desmin and myosin heavy chain. We next injected neural stem cells into early chick embryos. The injected cells followed the developmental cues in the different germ layers and we found that neural stem cells can differentiate to heart muscle, kidney, liver, epithelial cells and neural tissue. Injection of neural stern cells into mouse blastocysts further supported the notion that neural stem cells can contribute to embryo formation and differentiate to a variety of different cell types. In conclusion, this thesis demonstrates that IFs are necessary for proper scar formation in response to CNS injury. The spinal cord ependymal cells contribute to scar formation and along with ependymal cells in the brain they have been isolated and characterized as neural stem cells. Moreover, these neural stem cells are not restricted to a neural fate but can differentiate to cells of all three germ layers given the proper permissive environment.
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| 5. |
- Johansson, Malin B., et al.
(author)
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Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations
- 2013
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 25:20, s. 205502-
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Journal article (peer-reviewed)abstract
- The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P-tot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P-tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E-g approximate to 3.1 eV, which increase with increasing P-tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic delta-WO3, and monoclinic gamma- and epsilon-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The delta-WO3 and gamma-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that E-g in epsilon-WO3 is higher than in the delta-WO3 and gamma-WO3 phases, which provides an explanation for the P-tot dependence of the optical data.
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| 6. |
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| 7. |
- Persson, Clas, et al.
(author)
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Effective electron and hole masses in intrinsic and heavily n-type doped GaN and AlN
- 2001
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In: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 13:40, s. 8915-8922
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Journal article (peer-reviewed)abstract
- We have investigated the electronic structure near the band edges in intrinsic and heavily n-type doped GaN and AlN. Both the wurtzite and the zincblende polytypes have been considered. The electronic structures of the intrinsic materials were obtained from a full-potential linearized augmented plane wave calculation. We show the importance of performing a fully relativistic calculation. For instance, the hole mass in cubic AIN is a very large and negative quantity if spin-orbit coupling is excluded, whereas the fully relativistic calculation gives a relatively small and positive value. The electron-phonon coupling was taken into account according to the Frohlich Hamiltonian for large polarons, resulting in effective polaron masses. The effects on the effective electron masses due to doping were investigated by using a Green's function formalism within the random phase approximation and with a local-field correction according to Hubbard.
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| 8. |
- Persson, Clas, et al.
(author)
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Optical and reduced band gap in n- and p-type GaN and AlN
- 2002
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 92:6, s. 3207-3216
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Journal article (peer-reviewed)abstract
- We present a full band calculation of the doping-induced energy shifts of the conduction-band minimum and the valence-band maximum for n- and p-type GaN and AlN. Both wurtzite and zinc-blende structures have been considered. The resulting optical and reduced band-gap energies are presented as functions of the ionized impurity concentration in the heavily doped regime. The computational method is based on a zero-temperature Green's function formalism within the random phase approximation and with the local-field correction of Hubbard. The calculation goes beyond the spherical approximation of the energy bands by using energy dispersions and overlap integrals from a first-principle, full-potential band-structure calculation. Inclusion of the spin-orbit interaction is crucial for describing the uppermost valence bands properly, and we show that the nonparabolicity of the valence bands influences the energy shifts strongly, especially the shift of the optical band gap. With the full band structure, we can explain the results of photoluminescence measurements by Yoshikawa [J. Appl. Phys. 86, 4400 (1999)].
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| 9. |
- Wigren, Julia, et al.
(author)
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At-home sampling to meet geographical challenges for serological assessment of SARS-CoV-2 exposure in a rural region of northern Sweden, March to May 2021 : a retrospective cohort study
- 2023
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In: Eurosurveillance. - : European Centre for Disease Control and Prevention (ECDC). - 1025-496X .- 1560-7917. ; 28:13
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Journal article (peer-reviewed)abstract
- Background: The current SARS-CoV-2 pandemic has highlighted a need for easy and safe blood sampling in combination with accurate serological methodology. Venipuncture for testing is usually performed by trained staff at healthcare centres. Long travel distances to healthcare centres in rural regions may introduce a bias of testing towards relatively large communities with closer access. Rural regions are therefore often not represented in population-based data.Aim: The aim of this retrospective cohort study was to develop and implement a strategy for at-home testing in a rural region of Sweden during spring 2021, and to evaluate its role to provide equal health care for its inhabitants.Methods: We developed a sensitive method to measure antibodies to the S-protein of SARS-CoV-2 and optimised this assay for clinical use together with a strategy of at-home capillary blood sampling.Results: We demonstrated that our ELISA gave comparable results after analysis of capillary blood or serum from SARS-CoV-2-experienced individuals. We demonstrated stability of the assay under conditions that reflected temperature and humidity during winter or summer. By assessment of capillary blood samples from 4,122 individuals, we could show both feasibility of the strategy and that implementation shifted the geographical spread of testing in favour of rural areas.Conclusion: Implementation of at-home sampling enabled citizens living in remote rural areas access to centralised and sensitive laboratory antibody tests. The strategy for testing used here could therefore enable disease control authorities to get rapid access to information concerning immunity to infectious diseases, even across vast geographical distance.
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