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At least 19 recordsLinked to original sources

PubMed1979

Studies on cultured rat Schwann cells. II. Comparison with a rat Schwann cell line.

Cultured rat Schwann cells do not exhibit the ring-like changes in cell shape previously reported to be induced in the Schwann cell line RN22 by elevation of intracellular cyclic AMP. They do, however, undergo different shape changes on treatment with cholera toxin or low serum concentration. Furthermore, DNA synthesis in the cell line is inhibited by treatment with cholera toxin and unaffected by bovine pituitary extract, though both of these agents stimulate DNA synthesis in normal Schwann cells. Our results, therefore, do not support the hypothesis that elevation of intracellular cyclic AMP is a positive signal for myelination by the Schwann cell. Moreover, they illustrate the need for caution in drawing conclusions about normal cells of the nervous system from studies on neural cell lines.

Animals↗

PubMed1978

[Granular cell tumor and the phagocytozing form of Schwann cells. Electron microscopic examinations of 3 cases (author's transl)].

In granular cell tumors, the granule-containing tumor cells and their processes form rounded complexes surrounded by a common bounding membrane. In the tumor, these complexes are closely related to the peripheral nerves and are seen in the perineurium and in the endoneurium. In addition, there are mixed complexes composed both of Schwann cells and granular tumor cells: the two types of cells are in close contact with each other and are also surrounded by a common bounding membrane. Furthermore, there one contacts between granular tumor cells and axons. These observations strongly suggest the existence of a relationship between Schwann cells and the cells of granular cell tumors. A comparison between the granular tumor cells and the phagocytic forms of Schwann cells reveals striking similarities: the granular cell tumor complexes are comparable with the Büngner bands of phagocytozing Schwann cells. A relationship between granular cell tumors and the phagocytozing form of Schwann cells is therefore assumed.

Adult↗

PubMed1978

Schwann cell growth factors.

Purified rat Schwann cells were found to proliferate very slowly in normal growth medium containing 10% fetal calf serum (FCS). Crude extracts of bovine pituitary or brain markedly enhanced Schwann cell growth, while similar extracts of nerve roots, liver and kidney did not. Pituitary extracts were more potent than brain extracts, and extracts from both anterior and posterior pituitary were active. The mitogenic activity of pituitary extracts was reduced by treatment with trypsin, and abolished by pronase and by boiling. A variety of known anterior and posterior pituitary hormones, as well as fibroblast, epidermal and nerve growth factors, were not mitogenic. FCS (greater than 1%) was required for Schwann cell proliferation, but even high concentrations of FCS did not substitute for pituitary or brain extracts, and serum from various other species did not support Schwann cell growth. Although various agents that increase cyclic AMP levels (such as cholera toxin) had been shown to be Schwann cell mitogens, extracts of pituitary or brain did not increase cyclic AMP levels. Extracts of various bovine tissues, including pituitary, brain, liver and kidney, acted synergistically with cholera toxin in stimulating Schwann cell proliferation, although the increase in cyclic AMP induced by the mixture was not greater than that seen with cholera toxin alone. We conclude that there are at least two separate pathways for stimulating Schwann cell division, only one of which involves an increase in intracellular cyclic AMP.

Animals↗

PubMed1979

Studies on cultured rat Schwann cells. I. Establishment of purified populations from cultures of peripheral nerve.

We have previously reported that in dissociated cultures of neonatal rat sciatic nerve, all of the cells could be identified by indirect immunofluorescence with two antisera to cell surface antigens. The Schwann cells, but not the fibroblasts, expressed the Ran-1 antigen, while the fibroblasts, but not the Schwann cells, expressed the Thy-1 antigen. We have exploited this difference to derive pure populations of Schwann cells. A combination of [3H]thymidine autoradiography and immunofluorescence marking showed that in Modified Eagle's Medium with 10% foetal calf serum, the Schwann cells divided slowly while the fibroblasts divided rapidly. Accordingly, two day old cultures were exposed to cytosine arabinoside to select against the fibroblasts, followed by growth in medium containing an extract of bovine pituitary which stimulated division of the Schwann cells. After 7 days the confluent cultures, which contained 80-90% Schwann cells, were passaged after treatment in suspension with antiserum to Thy-1 and rabbit complement. After continued growth in medium with pituitary extract, the secondary cultures contained greater than 99.5% Schwann cells. These purified populations have been maintained in culture for as long as 150 days (6 passages) and retained the Ran-1 marker. The cultured Schwann cells expressed the S100 antigen, as shown by indirect immunofluorescence and complement fixation, and receptors for cholera toxin. They did not express the large external transformation sensitive protein, the glial fibrillary acidic protein, or receptors for tetanus toxin.

Animals↗

PubMed1979

[Electron microscopic study of the structural variability of activated Schwann cells].

The structural variability of Schwann cell is studied on transsectioned sciatic nerves of rats using the electron microscope. Corresponding to histological and cytological changes in the proximal nerve stump and in the growing sprouts processes of regression and progression take place in different phases of nerve regeneration. Under this conditions the Schwann-cells can show a considerably varying ultrastructural cytology. Besides typical Schwann cells modulations can be distinguished differing in their organelle composition, such as light-cells, macrophage-like cells and highly synthetic active and roliferative forms. The importance of these cell modulations is discussed in relation to the functional properties of Schwann cells.

Animals↗

PubMed1977

Identification of the Schwann cell as a peripheral nervous system cell possessing a differentiation antigen expressed by a human lung tumor.

Recent studies of the plasma membrane antigens of a human lung tumor (oat cell carcinoma) indicated that the tumor expressed at least two normal differentiation antigens undetectable in normal respiratory epithelium. One antigen was characteristic of certain endodermally derived epithelial cells of the digestive system; the other antigen was characteristic of certain neural crest-derived cells in the peripheral nervous system. The present studies were undertaken to identify the reactive cell type in the peripheral nervous system. Since similar cells in the rat peripheral nervous system expressed a cross-reactive form of this antigen, and since pure cultures of different rat nerve cell type were available, the following approach was possible. Cultures of pure neurons, pure Schwann cells, pure fibroblasts, neurons and Schwann cells, and neurons, Schwann cells, and fibroblasts were assayed for this antigen with rabbit anti-oat cell carcinoma plasma membrane antiserum absorbed with normal lung and liver. The indirect immunofluorescence method on both whole, viable cell and fixed cell substrates was used. Only Schwann cells expressed the antigen; Schwann cells in the presence of neurons expressed the antigen much more strongly than did pure Schwann cells. It was concluded that the oat cell carcinoma of the lung expressed a differentiation antigen present on Schwann cells.

Animals↗

PubMedDate not supplied

The Schwann cell: a reappraisal of its role in the peripheral nervous system.

The Schwann cell is clearly essential for the maintenance of axonal integrity--yet we know little of the regulatory mechanisms governing its behaviour at any point in its life cycle, or of the nature of its interaction with the axons with which each Schwann cell is associated. In this article, the involvement of the Schwann cell in myelinogenesis, aspects of Schwann cell-axon recognition, the experimentally-demonstrable 'bipotentiality' of the Schwann cell and the possible functional significance of the proliferative response of the Schwann cell that occurs after injury are discussed. The isolation and preparation of pure populations of Schwann cells which can be injected or implanted into a damaged nerve, coupled possibly with the localized application of drugs to manipulate the cellular responses to injury within the nerve, represent interesting areas of recent research which may be applied in planning methods of therapeutic intervention in the treatment of peripheral nerve injury.

Animals↗

PubMed1979

Anin vivo method to prepare normal Schwann cells free of axons and myelin.

A viable population of undifferentiated Schwann cells may be prepared from chronically denervated peripheral nerves. Nerve transection stimulates a sequence of cellular events in distal stumps leading to removal of axons and myelin, and proliferation of Schwann cells. Sealing the ends of nerve stumps prevents reinnervation and leaves daughter Schwann cells residing in longitudinal columns. Schwann cells may be harvested from the endoneurial tissue of the nerve stumps 5-12 weeks after nerve transection. Unlike myelinating cells prepared from intact tissue, where function has been specified by associated axons, Schwann cells obtained from denervated stumps are functionally naive. Their usefulness in analyzing axonal regulation of myelinogenesis and mitosis is therefore suggested.

Animals↗

PubMed1978

Infantile neuroaxonal dystrophy. Schwann cell inclusion in the peripheral nerve.

Abnormal Schwann cell inclusion is reported in biopsied peripheral nerve in a case of infantile neuroaxonal dystrophy. In addition to non-specific dystrophic changes of the axons, the Schwann cells contained several distinct bodies which were composed of stacks of irregularly disposed membranes; in some instances, transformed Schwann cell cytoplasm was distined with similar bodies. This change has not been reported on this condition and its significance is briefly discussed.

Biopsy↗

PubMed1975

Unmyelinated fibres and Schwann cells of sural nerve in neuropathy.

Electron micrographs of 45 sural nerves from patients with acquired (22) or heredodegenerative neuropathy (23) were analysed with respect to the number of unmyelinated nerve fibres, 37 nerves with respect to the number of Schwann cell sub-units and of structures connected with Schwann cells. Findings were compared with those in 6 nerves from control subjects and referred to the total number rather than to the number per mm2 to eliminate error due to increase in the transverse endoneurial area, present in more than half the diseased nerves. Ninety-one per cent of the diseased nerves showed one or several abnormalities in unmyelinated fibres of their Schwann cells. The best indicator of fibre loss was an increase in the number of Schwann cell sub-units devoid of axons, found in more than half the nerves. This was the only abnormality related with decrease in number of myelinated fibres. The increase in number of empty Schwann cell sub-units was due both to loss of unmyelinated nerve fibres and to proliferation of Schwann cells. Proliferation was indicated by the higher incidence of Schwann cell nuclei in cross-sections of diseased nerves than in controls. The earliest sign of involvement was an increase in number of profiles and of small isolated Schwann cell projections, observed in 33 of 37 diseased nerves, as the only abnormality in 7 nerves. The number of unmyelinated nerve fibres by itself was of little value to indicate loss of fibres, since regeneration often replaced or more than replaced degenerated fibres. Regeneration was indicated by an increase in number or incidence of small unmyelinated fibres, present in nearly half of 45 diseased nerves; and by an increased in the total number, present in a third of the nerves. An increase in the number of collagen pockets and of fibres undergoing degeneration (loss of organelles) and a decrease in the number of unmyelinated fibres per Schwann cell sub-units was present in only a quarter to a third of diseased nerves and was not related to other criteria of loss of fibres or of regneration.

Adolescent↗

PubMed1979

Migration of Schwann cells and wrapping of neurites in vitro: a function of protease activity (plasmin) in the growth medium.

In vitro conditions were defined under which Schwann cells, from a population of dissociated embryonic chicken spinal cord cells, migrate along the growing neuronal fibers and wrap bundles as well as individual axons, in a pattern similar to that found in a developing peripheral nervous system in vivo. The migration of Schwann cells and their wrapping of nerve fibers was found to be a function of plasmin activity in the growth medium. It was determined that at least one cell type among the spinal cord cells is producing plasminogen activator, the enzyme that activates the plasminogen that is a constituent of any serum. It is concluded that, to achieve wrapping of neurons by Schwann cells in culture, it is essential to have an active plasmin-generating system in the medium. It is hypothesized that the Schwann cell produces plasminogen activator. The possible role of both the Schwann cell and the plasminogen possible role of both the Schwann cell and the plasminogen activator in the formation of the neuromuscular junction is discussed.

Animals↗

PubMedDate not supplied

Atypical axon-Schwann cell relationships in the common peroneal nerve of the dystrophic mouse: an ultrastructural study.

Several atypical features of myelination of the peripheral nervous system are reported in common peroneal nerve of dystrophic mice (129 Re J dy/dy): (i) central nervous system-like contact between myelin sheaths of adjacent nerve fibres; (ii) nodes and internodes of myelinated fibres enwrapped with cytoplasmic processes of Schwann cells from adjacent nerve fibres; (iii) Schwann cells of adjacent nerve fibres co-operating in formation of a single myelin sheath; and (iv) a single Schwann cell myelinating two separate axons. In view of the presence of similar features of myelination in the central nervous system, where the myelin producing cells lack basement membrane, we suggest that in the dystrophic peripheral nerves the development of these features can be attributed to the partial deficiency of the Schwann cell basement membrane. Two types of widened nodes of Ranvier are also identified: (i) nodes with paranodal damage; and (ii) nodes without paranodal damage. In addition, abnormal features of myelination are described which are likely to represent altered Schwann cell/axon relationships during demyelination and remyelination and/or decreased myelinating ability of Schwann cells. We interpret these findings as indicating a metabolic disorder of Schwann cells. They provide an experimental model for the investigation of factors involved in the origin and maintenance of the structural organization of peripheral nerve.

Animals↗

PubMed1976

Separation of functional Schwann cells and neurons from normal peripheral nerve tissue.

A method has been devised for obtaining viable cultures of normal sensory neurons and normal Schwann cells from rat dorsal root ganglia, using cytosine arabinoside and fluorodeoxyuridine for control of non-neuronal cell proliferation. These cultures were used to demonstrate (a) that Schwann cells could be generated and maintained in culture free of fibroblast contamination, (b) that Schwann cells could exist in either a quiescent or proliferative state, depending on the absence of neurons, (c) that sensory ganglia could be obtained that would provide an outgrowth of axons entirely free of non-neuronal cells even in the absence of antimitotic agents, and (d) that quiescent Schwann cells, induced to proliferate by 'bare' axons, could ensheath and, in time, myelinate some of these axons.

Animals↗

PubMed1979

[Ultrastructure of tumors arising from Schwann cells].

Ultrastructural changes have been studied using 67 tumors originated from the Schwann cells. Tumors were induced by means of methylnitrosourea injection with a week intervals. Both benign (fascicular and reticular) and malignant neurinomes were obtained. Main morphological changes were found in the Schwann cells. The tumor cell ultrastructure appeared to be definetely related to the degree of the tumor maturity. The results obtained may suggest that the fine structure of neurogenic tumors is also characteristic of their normal prototype--the Schwann cells.

Animals↗

PubMed1979

Aberrant axon-Schwann cell junctions in dystrophic mouse nerves.

'Amyelinated' axons in the spinal roots of dystrophic mouse nerves lack typical nodal and paranodal membrane specializations. However, at the periphery of the amyelinated bundles some of the naked axons form aberrant junctions with Schwann cells belonging to neighbouring myelinated axons. These junctions are characterized by a narrow intercellular cleft containing regularly-spaced densities that closely resemble the 'transverse bands' found at paranodal axoglial junctions with respect to both configuration and spacing. In addition, the Schwann cells sometimes extend fingerlike projections towards amyelinated axons in regions where the axolemma has a dense cytoplasmic undercoating. Such regions resemble nodes of Ranvier, where Schwann cell processes interlace over the axolemma. Freeze-fracture replicas show no typical nodal or paranodal membrane specializations in the amyelinated fibres where they are apposed to each other. However, isolated paracrystalline patches of membrane occur corresponding to the aberrant junctions between amyelinated axons and Schwann cells at the periphery of the bundles. The observations show that structural differentiation of the axolemma occurs only where axons are in intimate contact with myelinating cells and does not develop independently in the amyelinated regions. Sodium channels, which are normally concentrated in the specialized nodal membrane, are, therefore, probably distributed uniformly along the amyelinated axon segments that show no sign of such regional differentiation. In addition, it is shown that Schwann cells are capable of forming specialized junctions with more than one axon at the same time.

Animals↗

PubMed1978

Schwann cell abnormalities in 2,5-hexanedione neuropathy.

Distinctive cytoplasmic alterations of Schwann cells were observed by electron microscopy in rats and mice with peripheral neuropathy induced by chronic exposure to 2,5-hexanedione. Pronounced enlargement of Schwann cells was due to accumulation of 100 angstrom cytoplasmic filaments and endoplasmic reticulum and was most often observed after 12--15 weeks exposure to 2,5-hexanedione. Examination of teased nerve fibres revealed segmental demyelination and remyelination involving axons of normal diameter as well as giant axons. The filament disorder induced by 2,5-hexanedione administration is not limited solely to axoplasmic contents. Possible mechanisms of demyelination are discussed and the changes are compared to those observed in human neuropathy for which 2,5-hexanedione appears to be the closest experimental model.

Animals↗

PubMed1979

Do Schwann cells produce collagen type III?

The fact that collagen from both normal nerve endoneurium and Schwann cell tumours present characteristics of collagen type III, suggests that Schwann cells produce this type of collagen.

Animals↗

PubMed1979

Lepromatous leprosy as a model of Schwann cell pathology and lysosomal activity.

A brief illustrated account is presented of the light microscopic pathology, histochemistry of lysosomal enzymes, and fine structural changes in the nerves of patients with untreated or treated lepromatous leprosy. Predominant bacillation of the Schwann cells of unmyelinated fibres, degeneration of their axons, prominence of phagolysosomes, and disappearance of these cells with endoneurial collagenosis were observed on electronmicroscopic examination of the index branch of the radial cutaneous nerve. Although there were changes in the blood vessels and proliferation of perineurium, bacillation of endothelial or perineurial cells was much less conspicuous. Intact and degenerating forms of M. leprae were found in both treated and untreated patients, fragmenting or crumpled forms being more frequent in the treated. Both groups of patients also showed increased lysosomal enzyme activity, evidenced by single or paired paranodal spots of acid phosphatase and beta-glucuronidase in Schwann cells in histochemical preparations of the nerve. There was lesser activity, and activity in fewer cells, in the case of beta-glucuronidase than of acid phosphatase. Diffuse beta-glucuronidase activity was found in the wall of empty-looking oval chambers in the Schwann cells, and acid-fast bacilli were seen in these chambers. In teased fibre preparations, both axonal degeneration and segmental demyelination were found. In semi-thin araldite sections, the myelinated fibre density was either preserved or reduced; large diameter fibres were more frequently depleted, with tall peaks of smaller fibres seen on plotting diameter spectra.

Axons↗