摘要:

AbstractKainate (KA), quisqualate (QA), and α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid (AMPA) stimulated γ‐aminobutyric acid [3H]γ‐aminobutyric acid (GABA) release from cultured cerebellar type 2 astrocytes and from their bipotential precursors. The evoked release was prevented by the antagonist 6‐cyano‐2,3‐dihydroxy‐7‐nitro‐quinoxaline (CNQX). AMPA and QA applied together with KA at concentrations around or above their EC50s (20–50 μM) antagonized the stimulatory effect of KA on [3H]GABA release. On the other hand, the releasing action of KA was potentiated by concentrations of QA in the low micromolar range (2–5 μM), particularly when the concentration of KA was at the borderline of effectiveness (10 μM). KA and QA did not elevate intracellular cyclic GMP levels in astrocyte cultures, although guanylate cyclase was present in both type 2 and type 1 astrocytes. The inability of KA to elevate cyclic GMP levels in astrocytes was the only major difference in the behavior of this glutamate agonist between astroglial and neuronal cultures. The GABA transport inhibitor nipecotic acid or replacement of NaCl with LiCl abolished [3H]GABA uptake and also KA‐ and QA‐induced release of preaccumulated [3H]GABA. Therefore, [3H]GABA was released from type 2 astrocytes and their progenitors through its Na+‐dependent transport system, operating in an outward direction when the cells w

ISSN:0894-1491    

DOI:10.1002/glia.440040302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractWe have developed a novel in vitro method to analyze the diversification of glial cells during development. The primary advantage of the approach is that glial lineages are formed in discrete clones on a nitrocellulose substratum where the relationship of the progeny is strictly defined. This method facilitates the comparison of a large complement of astrocyte and oligodendrocyte lineages under controlled conditions. Clones were formed by plating a brain dissociate on nitrocellulose at very low density (5,000–40,000 cells/154 mm2). However, growth depended on diffusible factors produced by brain cells growing under the nitrocellulose support at high density (feeder layer). The cloning efficiency of cells from mouse forebrain (P0) was 1–3%. This means we can detect 100,000 to 300,000 clonal progenitors in the dissociate (107cells per forebrain) using the clonal culture technique. Cell phenotypes were determined by immunocytochemical staining with anti‐glial fibrillary acidic protein (GFAP) to label astrocytes and anti‐galactocerebroside (GC) and anti‐myelin basic protein (MBP) to label oligodendrocytes. There was a remarkable diversity of glia represented in different lineages. The number of astrocyte clones was greater than the number of oligodendrocyte clones but combined their total was 90%. Clone sizes were distributed over a wide range, which indicated that growth rates varied. Clones appeared compact or dispersed but astrocyte clones exhibited three different morphologies—fibroblast‐like, stellate, and elongated. Oligodendrocytes had different morphologies distinct from astrocytes. Although there were different glial lineages the cells in most clones were homogeneous, indicating the progeny had the same fate. However, a small number of the clones, approximately 2%, were heterogeneous and contained both astrocytes and oligodendrocytes. The application of this technique to glial lineages demonstrates that intrinsic factors have a role in determining cell fate since different clones formed under the same external conditions. Finally, these results are consistent with the existence of multiple glial progenitors or the continued presence of multipotential progenitors at the

ISSN:0894-1491    

DOI:10.1002/glia.440040303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractPrevious studies from our laboratory have shown that C‐6 glial cells in culture express astrocytic phentoypes with increasing cell passage. Early passage glial cells have been shown to respond to various factors by expressing either astrocytic or oligodendrocytic phenotype. In view of the numerous reports on the trophic effects of muscle‐derived factors on spinal cord neurons, we examined the effect of muscle‐dervied factors on C‐6 glial cells from both early and late passages. Soluble factors were obtained from either leg (LME) or breast (BME) muscle from 15‐day‐old chick embryos by homogenization followed by high velocity centrifugation. Both LME‐ and BME‐derived factors triggered the proliferation and differentiation of early passage glial cells as assessed by cell number and glutamine synthetase activity, respectively. Late passage glial cells responded to muscle‐derved factors with enhanced proliferation and only with a slight increase in glutamine synthetase activity. These findings indicate that glial cells of both early and late passages respond to signals produce

ISSN:0894-1491    

DOI:10.1002/glia.440040304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe concentrations of glial fibrillary acidic protein (GFAP) and its encoding mRNA in the cerebellum and hippocampal formation were assayed during the development of normal and hypothyroid rats. Neonatal hypothyroidism induced a significant reduction in the GFAP concentration in both regions from day 14. The reduction was especially marked on day 35 in the cerebellum (−43%) and the hippocampal formation (−55%). The immunocytochemical study of vimentin showed that the developmental disappearance of this protein from the Bergmann and internal astroprcytes is greatly delayed in the cerebellum of the hypothyroid rats. The reduction in GFAP concentration together with the delayed vimentin‐GFAP transition could explain how astrocyte morphogenesis is impaired by neonatal thyroid deficiency.The GFAP‐mRNA concentration in the hippocampal formation was reduced throughout the development of thyroid‐deficient rats, while the GFAP‐mRNA concentration in the cerebellum first increased between birth and day 14 to reach a peak well above the normal value (+78%) and decreased thereafter to reach 53% of the normal value by day 35. This transient increase in the cerebellar GFAP‐mRNA concentration may be related to the astroglial hyperplasia that occurs in these animals. The difference between the developmental profile of GFAP and its encoding mRNA, especially under pathological conditions, indicates that two distinct mechanisms control the synthesis or stability of the protein and its messenger RNA, as was previously found in the forebrain of the developi

ISSN:0894-1491    

DOI:10.1002/glia.440040305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractUnitary currents through single ion channels in the glial cells, which ensheath the abdominal stretch receptor neurons of the crayfish, were characterized with respect to their basic kinetic properties. In cell‐attached and excised patches two types of Ca++‐independent K+channels were observed with slope conductances of 57 pS and 96 pS in symmetrical K+solution.The 57 pS K+channel was weakly voltage‐dependent with a slope of the Povs. membrane potential relationship of +95 mV for an e‐fold change in Po. In addition to the main conductance level, the channel displayed conductance levels of 80 and 109 pS. In excised patches, channel activity of this “subconductance” K+channel showed “rundown” that could be prevented with 2 mM ATP‐Mg on the cytoplasmic side of the membrane.The 96 pS K+channel was strongly voltage‐dependent with a slope of +12 mV for an e‐fold change in Po. Averaged single‐channel currents elicited by voltage jumps proved the channel to be of the delayed rectifying type. Channel activity persisted in excised patches with minimal salt solution and in virtually Ca++‐free saline.Because of its dependence on intracellular ATP‐Mg, the subconductance K+channel is discussed as a target of modulation by transmitters or peptides via pho

ISSN:0894-1491    

DOI:10.1002/glia.440040306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe dependence of3[H]‐L‐glutamate uptake on the presence of sodium, chloride, or calcium ions or on a combination of the three was investigated in astrocyte primary cultures. A stimulating effect on glutamate uptake by each of the ions tested was found. In addition to the comparably small effect by calcium alone, calcium exhibits a synergistic effect on the sodium‐ and chloride‐dependent uptake. The sodium‐dependent transport accumulates the glutamate analogue D‐aspartate as well as L‐glutamate. L‐aspartate is taken up by about 50% of the values observed for L‐glutamate transport. Sodium‐dependent glutamate uptake is strongly inhibited by aspartate‐beta‐hydrox‐amate (AβH) and threo‐beta‐hydroxyasparatate (TβH). Quisqualate is less potent in inhibiting this uptake.In contrast, the chloride‐ and the calcium‐dependent uptake systems do not handle D‐ and L‐aspartate as substrates. AβH and TβH are only poor inhibitors of these transporters while quisqualate reduces glutamate uptake almost completely. Kinetic data of all uptake systems were estimated. High and low affinity components of each individual system are demonstrated by Eadie‐Hofstee analysis. Hill plots indicate that high and low affinity uptake may be due either to two respective uptake sites for Na+‐, Cl−‐, and Ca++‐dependent glutamate transport, or to two glutamate binding sites for each

ISSN:0894-1491    

DOI:10.1002/glia.440040307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe injection of the gliotoxic agent ethidium bromide (EB) into spinal white matter produces a CNS lesion in which it is possible to investigate the ability of transplanted glial cells to reconstruct a glial environment around demyelinated axons. This study demonstrates that transplanted mouse glial cells can repopulate EB lesions in rats provided tissue rejection is controlled. In X‐irradiated EB lesions in cyclosporin‐A‐treated rats, mouse oligodendrocytes remyelinated rat axons and, together with mouse astrocytes, re‐established a CNS environment. When transplanted into nonirradiated EB lesions in nude rats, mouse glial cells modulated the normal host repair by Schwann cells to remyelination by oligodendrocytes. In both X‐irradiated and non‐irradiated EB lesions, transplanted mouse glial cells behaved similarly to isogenic rat glial cell transplants (Blackemore and Crang Dev Neurosci, 1988;10:1–10; J Neurocytol, 1989;18:519–528). These findings indicate that the cell‐cell interactions involved in reconstruction of a glial environment are common to b

ISSN:0894-1491    

DOI:10.1002/glia.440040308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractQuantitative biosynthetic studies with cultures highly enriched for glial fibrillary acidic protein (GFAP+) cells of neonatal mammalian brain demonstrated production of four proteoglycans: hyaluronate (HA), heparan sulphate (HS), chondroitin sulphate (CS), and dermatan sulphate (DS). The glycosaminoglycans were present in cell conditioned medium and in the cellular compartment. There were qualitative differences in the subcellular disposition of the various proteoglycans. The ratio of HS to CS/DS in cell extracts was 1:1, while in medium this ratio was 1:6. All of the glycosaminoglycans were associated with core proteins that were integral to the cell membrane and associated with the cell surface by non‐covalent interactions involving glycosaminoglycans. Less than 20% of the HS was non‐covalently associated with the astrocyte cell surface reflecting in part the proportionately smaller amounts of this proteoglycan released to astrocyte conditioned medium. HS released to medium was undersulphated relative to that associated with cells.The astrocyte can contribute proteoglycans to the extracellular milieu and displays cell surface proteoglycans that have the potential to provide appropriate substrates for neuron adhesion, process extension, and other cell‐cell interac

ISSN:0894-1491    

DOI:10.1002/glia.440040309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractShort term and chronic dBcAMP effects on the expression of glial fibrillary acidic protein (GFAP) in astroglial primary cultures are investigated. Short (48 h) and long (more than 7 days) treatments with the cAMP derivative induce both cell shape changes and an increase in GFAP immunolabelling. Such effects are only associated with an increase in GFAP and in GFAP‐mRNA levels in the long term treatment. These results suggest that the short term effect of dBcAMP induces post‐translational modifications of the protein whereas the long term effect is associated with an increase in GFAP mRNA transcription and/or stabil

ISSN:0894-1491    

DOI:10.1002/glia.440040310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractBlood macrophages and brain macrophages (microglia) have been implicated in demyelination and destruction of the oligodendrocyte in multiple sclerosis (MS), a disease affecting primarily white matter of the central nervous system (CNS). In this study, we demonstrate that at high effector to target cell ratios, normal rat microglia exhibit a natural cytotoxicity against normal rat oligodendrocytes in vitro. The killing is not mediated by the release of soluble factors. The cytotoxic activity is upregulated by pretreatment of microglia with interferon gamma (IFNγ) or phorbol myristate acetate (PMA). Both the natural and induced cytotoxicities are inhibitable by transforming growth factor beta (TGFβ). The increase in numbers and apposition of primed or activated microglia to oligodendrocytes in MS lesions may give rise to natural or induced killing from which oligodendrocytes may be protected by TGF

ISSN:0894-1491    

DOI:10.1002/glia.440040311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY