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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 147 (1975), S. 259-271 
    ISSN: 1432-0568
    Keywords: Neuroglia ; Myelin sheath ; Central nervous system diseases
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The number of neuroglial cells in selected fiber tracts of 90-day-old quaking and normal mice was determined by a combination of light and electron microscopy. Oligodendrocytes of quaking mice are normal in number in the anterior commissure and corticospinal tract (in the cervical spinal cord) but are increased two- to fourfold in the optic nerve and the fasciculi cuneatus and gracilis (in the cervical spinal cord). The nuclei and perikarya are normal in size or smaller than normal. Those tracts with the greatest hyperplasia of oligodendrocytes also have the greatest conten of myelin, suggesting that cell number influences content of myelin. However, the volume of myelin per oligodendrocyte also varies, between 2 and 11% of normal, in the different tracts of the mutant. The hyperplasia of oligodendrocytes in quaking mice may arise as compensation for their decreased production of myelin and reflect a normal plasticity in the processes of myelination. If so, the mutant may be a useful system for study of the regulation of myelogenesis.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of neurocytology 9 (1980), S. 537-570 
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This paper describes the fine structure of granule cells and granule-associated interneurons (termed Golgi cells) in the cochlear nuclei of cat, rat and mouse. Granule cells and Golgi cells are present in defined regions of ventral and dorsal cochlear nuclei collectively termed ‘cochlear granule cell domain’. The granule cells are small neurons with two or three short dendrites that give rise to a few branches with terminal expansions. These participate in glomerular synaptic arrays similar to those of the cerebellar cortex. In the glomeruli the dendrites form short type 1 synapses with a large, centrally-located mossy bouton containing round synaptic vesicles and type 2 synapses with peripherally located, smaller boutons containing pleomorphic vesicles. The granule cell axon is thin and beaded and, on its way to the molecular layer of the DCN, takes a straight course, which in the ventral nucleus is parallel to the pial surface. Neurons of the second category resemble cerebellar Golgi cells and occur everywhere interspersed among the granule cells. They are usually larger than the granule cells and give rise to dendrites which may branch close to and curve around the cell body. The dendrites contain numerous mitochondria and are laden with thin appendages, giving them a hairy appearance. Both the cell body and the stem dendrites participate in glomerular synaptic arrays. Golgi cell glomeruli are distinguishable from the granule cell glomeruli by unique features of the dendritic profiles and by longer, type 1 synaptic junctions with the central mossy bouton. The Golgi cell axon forms a beaded plexus close to the parent cell body. The synaptic vesicle population of the mossy boutons suggests that they are a heterogeneous group and may have multiple origins. Apparently, each of the various classes participates in both granule and Golgi cell glomeruli. The smaller peripheral boutons with pleomorphic vesicles in the two types of glomeruli may represent Golgi cell axons which make synaptic contacts with both granule and Golgi cells. The Golgi cell dendrites, on the other hand, are also contacted by small boutonsen passant with round synaptic vesicles, which may represent granule cell axons. A tentative scheme of the circuitry in the cochlear granule cell domain is presented. The similarity with the cerebellar granule cell layer is striking.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of neurocytology 6 (1977), S. 647-668 
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The mode of distribution of Schwann cell cytoplasm in the various regions of the peripheral myelin sheath is reviewed using freeze-fractured and thin sectioned nerves from bullfrogs, chickens and cats, perfused with an aldehyde mixture or fixedin situ with potassium permanganate. It is shown that the peripheral myelin sheath consists of two domains: one ‘semi-compact’ at the outer and the inner turns, and one ‘compact,’ extending from the second to the next-to-last turns. In the semi-compact domain nomajor dense line is formed, although the cytoplasmic layer may be as thin as 50 Å. As is well known, amajor dense line is formed instead in the compact domain. The whole sheath is bordered by a ‘marginal cytoplasmic belt.’ This communicates with a cytoplasmic reticulum present in the semi-compact domains and with a reticulum (formed by longitudinal and circumferential incisures) in the compact domain. Many cytoplasmic channels in the semi-compact domain end blindly, as do many of the longitudinal and the circumferential incisures. It is speculated that these cytoplasmic networks are in a dynamic state, and that the changes within the semi-compact domain may be faster than those in the compact region. Numerous uncoated vesicles, 600–1100 Å in diameter, open onto the plasmalemma in the perinuclear region, along the outer mesaxon, and in the larger cytoplasmic trabeculae on the outer surface of the sheath. These plasmalemmal vesicles (caveolae) do not occur on the thinner cytoplasmic channels, on the inner surface of the sheath or on the incisures. Horseradish peroxidase studies indicate that the plasmalemmal vesicles become filled with the enzyme but do not migrate into the cytoplasm within a 4 h period. The movement of cytoplasm within the myelin sheath and the significance of the vesicles are discussed. The matter is important, since there are indications fromin vitro studies of cultured nervous tissue and of teased fibres, that movements take place in the myelin sheath. These are presumably related to cytoplasmic translocations capable of producing ‘outpocketings and invaginations’ of the sheath's contour and may also involve the Schmidt—Lanterman incisures (Murray and Hermann, 1965; Singer and Bryant, 1969; Gitlin and Singer, 1974). Althoughin vivo observation of intact nerves for several hours did not reveal conspicuous movements (Williams and Hall, 1970, 1971), it is an attractive hypothesis that cytoplasmic movements are involved both in the formation and maintenance of the myelin sheath and in pathologic alterations (Robertson, 1958; Webster, 1965, 1971).
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1573-6830
    Keywords: in situ hybridization ; mouse hepatitis virus ; remyelination ; oligodendrocytes ; myelin basic protein
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. In order to characterize some of the molecular events leading to repair of myelin in the adult central nervous system (CNS), we examined the expression of transcripts for myelin basic protein (MBP) during remyelination in the mouse. C57B1/6 mice develop a demyelinating disease when glial cells are selectively infected by the A59 strain of mouse coronavrius. The virus is spontaneously cleared from the mice by 4 weeks postinfection (WPI), a time when remyelination is starting. 2. At 3 WPI total MBP transcripts are decreased by 75% in demyelinating lesions compared to control white matter. Using RNase protection assays andin situ hybridization with probes for particular MBP exons, we detected an increase in MBP transcripts containing exon 2 information, coincident with the earliest histological signs of remyelination. 3. The expression of MBP transcripts containing exon 2 information was first seen clustered in the perinuclear cytoplasm of oligodendrocytes scattered within the lesions. This is reminiscent of the increased levels and perinuclear clustering of MBP transcripts containing exon 2 seen during early developmental myelination. The peak abundance of exon 2-containing transcripts in the lesions was 13-fold that seen in control white matter. At later stages of remyelination, additional forms of MBP transcripts (without exon 2) increased and their distribution was more diffuse. 4. Thus, during remyelination, preforms of MBP transcripts, which are normally present at low levels in the adult CNS, are abundantly expressed and regulated in a manner similar to that observed in developmental myelination.
    Type of Medium: Electronic Resource
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