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  • 11
    ISSN: 1432-0533
    Keywords: Retrograde Nerve Cell Reaction ; Regeneration ; Degeneration ; Glial Reaction ; Microglia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die Gliareaktion im Facialiskern erwachsener Mäuse wurde nach Quetschung und kompletter Durchtrennung des N. facialis untersucht. Die Läsionen waren von kompletter Nervenzellregeneration bzw. ausgedehnter Nervenzelldesintegration gefolgt. Nach Quetschung kam es zur funktionellen Restitution am 10.–11. Tage ohne Nervenzellausfälle. Nach Nervendurchtrennung trat ein Ausfall von rund zwei Drittel der Nervenzellen zwischen der 3. und 9. Woche auf. Beide Läsionsformen verursachten eine Reaktion von Astrocyten und kleinen perineuralen Gliazellen, die den lichtoptisch nachgewiesenen Mikrogliocyten entsprachen. Die Mikroglia hatte kleine, dichte Kerne, eine diffuse, dichte Cytoplasmamatrix mit langen, engen Zisternen von granulärem oder agranulärem EPR sowie freien Ribosomen, die als Einzelelemente wie auch in Haufen von wechselnder Größe auftraten. Die Natur dieser Zellen wird diskutiert. Nach Nervendurchtrennung dehnten sich die schmalen Fortsäze der Mikrogliazellen entlang der Oberfläche der Nervenzellen und Dendriten aus und führten dadurch zu einer Trennung der Boutons von ihren Kontaktstellen. In späteren Stadien räumten die Mikrogliazellen die Neuronen durch Phagocytose ab. Nach Quetschung erstreckten sich die Mikrogliafortsätze gleichfalls bis zur Oberfläche der Nervenzellen und Dendriten, bedeckten aber nur kurze Abschnitte ihrer Oberfläche. Eindeutige Isolierung von Boutons wurde nach Läsionen mit folgender Regeneration nicht beobachtet. Die funktionalle Bedeutung der Gliareaktion wird diskutiert.
    Notes: Summary The glial reaction was examined in the facial nucleus of adult mice after crush lesions and complete section of the facial nerve. These lesions were followed by complete nerve cell regeneration and extensive nerve cell disintegration, respectively. After crush lesions the function reappeared on the tenth or eleventh day and there was no nerve cell loss. After nerve section about two thirds of the nerve cells disintegrated between the third and the ninth week. Both types of lesion induced reaction of astrocytes and of small perineuronal glial cells, which correspond to the microgliacytes demonstrated in light microscopy. The microglia had small dense nuclei, a diffusely dense cytoplasmic matrix, long narrow cisterns of agranular or granular endoplasmic reticulum, and free ribosomes which occurred both as single elements and in clusters of varying size. The possible nature of these cells is discussed. After nerve section the slender processes from the microglial cells extended along the surface of the nerve cells and dendrites, thus separating the boutons from their contacts. In late stages the microglial cells removed the neurons by phagocytosis. After crush lesions the microglial processes also extended to the surface of the neurons and dendrites but they covered only short segments of the surface. Convincing separation of boutons was not observed after lesions which produced regeneration. The functional significance of the glial reaction is discussed.
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  • 12
    ISSN: 1432-0533
    Keywords: Retrograde Nerve Cell Reaction ; Regeneration ; Degeneration ; Facial Nucleus ; Mouse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Die Nervenzellveränderungen im Facialiskern von Mäusen wurden nach Quetschung und kompletter Durchtrennung des N. facialis untersucht. Die Läsionen waren von kompletter Nervenzellregeneration bzw. ausgedehnter Nervenzelldesintegration gefolgt. Lichtoptische Untersuchungen zeigten Zerstreuung der Nissl-Substanz ab dem 1. Tage nach beiden Läsionsformen; Zunahme der Cytoplasmabasophilie in der 1. Woche. Nach Quetschung begann die Nissl-Substanz nach 1 Woche wieder aufzutreten, und nach 30 Tagen waren die Neuronen wieder regelrecht. Nach Nervendurchtrennung blieb die basophile Substanz zerstreut. Es kam zum langsamen Verschwinden der Basophilie und zum Untergang der meisten Zellen 14–60 Tage nach der Läsion. Die ultrastrukturellen Veränderungen waren in den ersten Tagen nach beiden Läsionen identisch: Die aus parallelen Zisternen des granulären EPR und Haufen freier Ribosomen zwischen Lamellen bestehenden Nissl-Körper wurden durch kurze Segmente granulären EPR und freie Ribosomenhaufen im gesamten Cytoplasma ersetzt. Nach Quetschung fanden sich keine Veränderungen an anderen Zellorganellen. Die Nissl-Körper traten nach 1 Woche wieder auf. Es wird vermutet, daß die Dispersion und Neubildung der Nissl-Substanz nicht durch einen massiven Austausch von Organellen, sondern eher durch einfache Verteilung der Membranen und Ribosomenhaufen sowie eine Neuordnung dieser Strukturen während der Erholungsperiode beding ist. Nach Nervendurchtrennung bleibt das EPR verstreut, ohne daß weitere Veränderungen bis kurz vor der Desintegration auftreten. Später zeigt das Cytoplasma eindeutige Degenerationszeichen. Die Neurone werden schließlich durch Phagocytose durch Mikrogliazellen entfernt.
    Notes: Summary The neuronal changes were studied in the facial nucleus of mice after crush lesions and complete section of the facial nerve. These lesions were followed by complete nerve cell regeneration and extensive nerve cell disintegration, respectively. Light microscopical examination showed dispersion of the Nissl substance from the first day after both types of lesion, and the cytoplasmic basophilia increased during the first week. After crush lesions the Nissl substance began to reappear after one week, and after 30 days the neurons again were normal. After section of the nerve the basophilic substance remained dispersed and there was a slow depletion of the basophilia until the majority of the cells disappeared between 14 and 60 days after the lesion. The ultrastructural changes were identical during the first days after both types of lesion: The Nissl bodies, which consisted of parallel cisterns of granular endoplasmic reticulum and clusters of free ribosomes between the lamellae, were replaced by short segments of granular endoplasmic reticulum and free ribosomal clusters throughout the cytoplasm. After crush lesions no changes were seen in any of the other cell organelles. New Nissl bodies began to reappear after one week. It is suggested that the dispersion and re-formation of the Nissl substance is not caused by a massive exchange of organelles but rather by a simple spreading of the membranes and ribosomal clusters and a re-arrangement of the same structures during recovery. After section of the nerve the endoplasmic reticulum remained dispersed without further changes until shortly before disintegration. The cytoplasm then showed extensive degeneration. The neurons were ultimately removed through phagocytosis by microglial cells.
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  • 13
    Electronic Resource
    Electronic Resource
    Springer
    Acta neuropathologica 57 (1982), S. 85-92 
    ISSN: 1432-0533
    Keywords: Skeletal muscle ; Ageing ; Cachexia ; Malignant neoplasms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of ageing, cachexia and neoplasms on striated muscle were examined in histological sections of an autopsy material. Paraffin sections were examined from four separate muscles of 30 previously healthy subjects who died suddenly, from eight cases with cachexia and from 16 cases with cachexia and neoplasms. In addition, ATP-ase stained cryostat sections were examined from two muscles from most of the cases. All the sections were evaluated with regard to atiophy, myopathic changes and fibre type grouping. Furthermore, the exact size of 100 fibres of each type was determined in the enzyme stained sections. Myopathic changes were found in a few muscles, mainly in the normal cases. They were considered incidental findings without clinical significance. Fibre type grouping could not be evaluated in the anterior tibial muscle because large clusters of the same fibre type occur normally in this muscle. In the biceps brachii only two normal cases and none of the cachectic cases showed fibre type grouping. A moderate small grouped muscle fibre atrophy was found in normal cases with increasing age. The cases with cachexia showed a marked small grouped atrophy which involved both fibre types. There were only small and uncertain differences between cases with cachexia and tumours and those with cachexia alone. Thus, no changes were observed which could be ascribed to tumours alone. The small grouped atrophy in ageing and cachexia resembled that seen in denervation atrophy but the exact mechanism of the changes remains obscure.
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  • 14
    ISSN: 1433-8491
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Zusammenfassung Bei jungen Katzen wurden Läsionen des Kleinhirns gesetzt, und die Tiere wurden nach einigen Tagen nach der modifizierten Guddenschen Methode (Brodal, 1939, 1940) getötet. In thioningefärbten transversalen Serienschnitten durch den Hirnstamm wurden die Vestibulariskerne auf das Vorkommen von retrograden Zellveränderungen untersucht. Typische retrograde Zellveränderungen (vgl. Abb. 1) wurden nach Läsionen gefunden, welche einen oder mehrere der folgenden Kleinhirnabschnitte umfassen: Nodulus, Uvula, Dachkern und Flocculus. Typisch veränderte Zellen kommen nur im spinalen und medialen Kern vor, und zwar besonders in den ventrolateralen Gebieten der caudalen Hälfte des spinalen (absteigenden) Kerns. (Abb. 2). Daneben finden sich einige in mehr dorsalen Abschnitten desselben Kerns sowie in einer kleinen Zellgruppe (hier mit x bezeichnet) lateral vom spinalen Kern und in den ventralen Gebieten des medialen Kerns. Die Fasern zum Flocculus entstammen vornehmlich den mehr rostralen Bezirken des ganzen Ursprungsgebietes (Abb. 4). und verlaufen fast ausschließlich homolateral. Die Verbindungen mit dem Dachkern und dem Wurm scheinen sowohl gekreuzt wie ungekreuzt zu sein. Anhaltspunkte dafür, daß der Deiterssche und Bechterewsche Kern an der sekundären vestibulocerebellaren Projektion teilnehmen, konnten nicht gefunden werden. Übereinstimmend mit unseren Befunden sprechen auch die Ergebnisse anderer Autoren dafür, daß die vestibulären Impulse auf ihrem Weg nach dem Kleinhirn in dem spinalen Kern durch Impulse aus dem Rückenmark und dem Kleinhirn modifiziert werden können.
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  • 15
    Electronic Resource
    Electronic Resource
    Springer
    Acta neurochirurgica 41 (1978), S. 3-5 
    ISSN: 0942-0940
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 16
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 244-245 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate the optical properties of GaN grown over SiO2 on SiC substrates by electron cyclotron resonance assisted molecular beam epitaxy. The photoluminescence spectra and refractive index of GaN were compared for GaN/SiO2/SiC and GaN/SiC. Strong band-edge luminescence was observed at 3.40 eV from the GaN on both SiO2/SiC and on SiC. No defect-related yellow luminescence was observed. The refractive index of GaN at 1.96 eV (632.8 nm) was measured at 2.22 and 2.24 for GaN/SiO2/SiC and GaN/SiC, respectively. © 1998 American Institute of Physics.
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  • 17
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 2098-2100 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room temperature operation of erbium and oxygen coimplanted GaN m-i-n (metal–insulator–n-type) diodes is demonstrated. Erbium related electroluminescence at λ=1.54 μm was detected under reverse bias after a postimplant anneal at 800°C for 45 min in flowing NH3. The integrated light emission intensity showed a linear dependence on applied reverse drive current. © 1996 American Institute of Physics.
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  • 18
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6343-6350 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Efficient Er-related photo-, cathodo-, and electroluminescence at 1539 nm was detected from Er and O co-implanted n-type GaN on sapphire substrates. Several combinations of Er and O implants and postimplant annealing conditions were studied. The Er doses were in the range (0.01–5)×1015 ions/cm2 and O doses (0.1–1)×1016 ions/cm2. GaN films implanted with 2×1015 Er2+/cm2 at 350 keV and co-implanted with 1016 O+/cm2 at 80 keV yielded the strongest photoluminescence intensity at 1539 nm. The annealing condition yielding the strongest Er-related photoluminescence intensity was a single anneal at 800 °C (45 min) or at 900 °C (30 min) in flowing NH3. The optimum O:Er ratio was found to be between 5:1 and 10:1. Co-implanting the GaN:Er films with F was also found to optically activate the Er, with slightly (20%) less photoluminescence intensity at 1539 nm compared to equivalent GaN:Er,O films. The Er-related luminescence lifetime at 1539 nm was found to depend on the excitation mechanism. Luminescence lifetimes as long as 2.95±0.15 ms were measured at 77 K under direct excitation with an InGaAs laser diode at 983 nm. At room temperature the luminescence lifetimes were 2.35±0.12, 2.15±0.11, and 1.74±0.08 ms using below-band-gap excitation, above-band-gap excitation, and impact excitation (reverse biased light emitting diode), respectively. The cross sections for Er in GaN were estimated to be 4.8×10−21 cm2 for direct optical excitation at 983 nm and 4.8×10−16 cm2 for impact excitation. The cross-section values are believed to be within a factor of 2–4. © 1997 American Institute of Physics.
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  • 19
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Presently, GaN-based photodiodes grown on sapphire substrates exhibit broad spectral cutoffs, poor visible rejection, and low quantum efficiencies when illuminated through a p-type contact/window layer. We, therefore, investigate the effect of threading dislocations, Mg doping, and etching on the photoconductivity spectra in GaN. Highly resistive bulk GaN:Mg nearly free of threading dislocations has more than 1000 times better visible rejection ratio compared to highly dislocated and comparably doped p-GaN thin films grown on sapphire substrates. However, the heavy Mg compensation in both the bulk and the epitaxial film causes a broad spectral cutoff. Unintentionally doped semi-insulating GaN with low dislocation density has a similar rejection ratio compared to bulk GaN:Mg, but much sharper spectral cutoff due to the absence of intentional doping. Furthermore, postgrowth processing steps such as etching and polishing significantly increase the surface recombination compared to the as-grown surface. © 1999 American Institute of Physics.
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  • 20
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Intracerebral injections of actinomycin D caused extensive changes in the nucleus and cytoplasm of all neurons in the mouse facial nucleus. In addition to the well known nucleolar segregation, the drug caused aggregation of the various components of the nucleoplasm into multiple large particles. After long term treatment there was also a marked shedding of the membrane-bound ribosomes and a disaggregation of the ribosomal rosettes into free single elements. However, this change took place only in areas of loosely scattered and dispersed rough endoplasmic reticulum; the compact Nissl bodies remained remarkably stable. The findings suggest that compact and dispersed areas of the rough endoplasmic reticulum may be in different functional states. In accordance with previous light microscopic observations, injection of actinomycin D prior to transection of the facial nerve prevented the dispersion of the compact Nissl bodies in the facial neurons. Synthesis of new RNA after axotomy may thus be necessary for the initiation of the retrograde reaction. Injection of actinomycin at the time when the Nissl bodies were dispersed after axotomy caused disaggregation of the ribosomes throughout the neuronal cytoplasm.
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