摘要:

AbstractIn the developing retina, the microvessels form by differentiation of endothelial precursor cells in a process referred to as vasculogenesis. Experiments using in vivo and in vitro model systems were designed to determine the specific influence of astrocytes on this process. Immunolocalization analyses of retinal vasculogenesis in vivo showed that astrocytes spread within the nerve fiber layer of the neonatal rat retina just ahead of the forming vessels. Then, endothelial precursor cells align themselves in register with the astrocytes. In contact with astrocytes, precursor cells differentiate as vascular endothelium, as indicated by lumen formation and patency to red blood cells. Experiments in vitro using cell culture and conditioned medium approaches showed that cell‐cell contact between rat brain astrocytes and bovine retinal endothelial cells results in release of soluble factors, inhibiting endothelial cell growth and inducing morphological differentiation in capillary‐like structures. Thus, it is suggested that astrocytes lay down the pattern for vasculogenesis and induce the elongation and alignment of endothelial precursor cells into a prevascular meshwork. In contact with astrocytes, precursor cells differentiate as vascular endothelium. Furthermore, this cell‐cell contact with astrocytes apparently inhibits endothelial cell growth and stimulates their elongation, alignment, and morphogenic differentiation by means of the release or activation of soluble, growth factor‐like substances. © 1995 Wiley

ISSN:0894-1491    

DOI:10.1002/glia.440150102

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

年代:1995

数据来源: WILEY

摘要:

AbstractA qualitative and quantitative light and electron microscopic analysis of the glial cells in the supraventricular part of the corpus callosum of the neonatal and adult homozygous athymic nude (nu/nu) and normal BALB/c (+/+) mice was carried out to determine the possible contribution of nude gene mutation to glial cell development. Quantitative cell counts using toluidine blue stained serial callosal sections of 0.5 μm thickness showed that the overall glial cell population was significantly reduced in both neonatal and adult athymic mice. The number of glioblasts, astrocytes and microglia of 5‐day‐old athymic mouse was reduced by 10%, 27%, and 39%, respectively, when compared to the 5‐day‐old normal mouse. The frequency of necrotic cells in the neonatal athymic mouse increased by 70% when compared with the normal mouse. In the 13‐week‐old adult athymic mouse, the number of oligodendrocytes, astrocytes, and microglia decreased by 19%, 31%, and 33%, respectively, when compared to normal mouse. There was no significant difference in the area covered by the corpus callosum in 5‐day‐old and adult nude mice versus the normal ones of corresponding ages. Except for microglia and astrocytes, the ultrastructural features of the other glial cell types in both strains were comparable. Most of the microglial cells of the neonatal normal mouse were round and were selectively marked by Mac‐1 monoclonal antibody at their plasma membrane. The immunoreactivity appeared to be more intense in the normal than the athymic mouse, suggesting a down regulation of CR3 receptors and reduced phagocytic activity of this cell type in the athymic mouse. It is proposed that the increased number of necrotic cells in the neonatal athymic mouse may be attributed to the delay in the removal of dead cells normally phagocytosed by microglia. The microglia in both strains of mouse showed comparable lectin staining intensity at the plasma membrane, indicating that their glycoprotein binding receptors to lectin remained unchanged. Some astrocytes in the adult athymic mice showed hypertrophy. The reduced number of glial cells may be the direct result of genetic mutation or consequential to the lack of certain trophic factors arising from the genetic mutation. Thus, the reduction of microglial cells in both neonatal and adult athymic mice may be due to the lack of thymic hormones which, together with lymphokines have been shown to affect the maturation of bone marrow derived cells including monocytes, the putative precursor cells of microglia. The reduction in the number of glioblasts and astrocytes may be attributed to the diminution of T lymphocytes or consequential to the reduction of microglia which are known to secrete interleukin‐1 that would influence gliogenesis and produce specific growth factors for promoting astrocyte proliferation. Last, as interaction exists between astrocytes and oligodendrocytes, the products of astrocytes may affect the development of oligodendrocytes and vice vasa. The present findings point to a relation between glial cell development and immune network system. ©

ISSN:0894-1491    

DOI:10.1002/glia.440150103

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

年代:1995

数据来源: WILEY

摘要:

AbstractLoss of function mutations at theNF1locus may act intrinsically in Schwann cells to cause the formation of benign Schwann cell tumors (neurofibromas) in patients with type 1 neurofibromatosis. To identify contexts in Schwann cells in which such mutations may play an important role, we measured the levels ofNF1mRNA and neurofibromin in rat sciatic nerve during development, after axotomy, and in cultured rat Schwann cells.NF1mRNA was present in developing sciatic nerve throughout the period of active Schwann cell proliferation and myelination. After nerve transection, no alteration inNF1message level was detected, but neurofibromin levels increased, as assessed by immunohistochemistry and Western blotting, suggesting that, in vivo, neurofibromin expression in Schwann cells is post‐transcriptionally induced during Wallerian degeneration. Cultured rat Schwann cells constitutively expressedNF1mRNA and neurofibromin. Schwann cell proliferation induced by exposure to serum and forskolin was not associated with changes inNF1mRNA or neurofibromin expression, whereas Schwann cell proliferation induced by extracts of embryonic brain membranes was associated with increasedNF1message and neurofibromin expression. Thus, Schwann cells, both in vivo and in vitro, expressNF1mRNA constitutively; the expression ofNF1mRNA and neurofibromin is modulated by only some mitogenic stimuli in Schwann cells. © 1995 Wiley‐Liss,

ISSN:0894-1491    

DOI:10.1002/glia.440150104

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

年代:1995

数据来源: WILEY

摘要:

AbstractAn affinity column prepared with noxiustoxin (NTx), a K+channel blocker from the venom of the Mexican scorpionCentruroides noxius, was used to purify a functional channel from a detergent extract of Schwann cell membrane of the giant axon of the squidLoligo vulgaris. The purified protein was reconstituted as a functional unit in a planar lipid bilayer and tested with a sequence of potentials to obtain information about single‐channel amplitude and kinetics. The reconstituted channel showed delayed rectifier behavior with a slope conductance of 10 pS under 5:1 asymmetric KCl concentrations and a clear tendency to open under negative potentials. The zero‐current potential was +36 mV, which fitted well with the Nernst equation for the CIS/TRANS K+‐concentration ratio of 5:1. The channel also showed a strong sensitivity to tetraethylammonium and its activity was inhibited by NTx, as expected from the purification procedure. The behavior of this protein in the presence of 0.5 mM ATP (cis side) was also tested, significantly increasing current fluctuations across the membrane. In order to compare the modulation of the Schwann cell K+channel with that of the axonal K+channel, a purified protein from the squid axon membrane was also tested in the presence of ATP. This 10–11 pS, delayed rectifier channel from the squid giant axon (Prestipino et al.,FEBS Lett. 250:570–574, 1989) was also tested in the presence of ATP and showed a similar rise in activity. © 1995 Wiley

ISSN:0894-1491    

DOI:10.1002/glia.440150105

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe effect of cholinergic agonists and antagonists on the intracellular free Ca2+concentration ([Ca2+]i) of leech neuropile glial cells was investigated by use of iontophoretically injected fura‐2. In neuropile glial cells, cholinergic agonists induced a marked increase in [Ca2+]ithat was inhibited by d‐tubocurarine, α‐bungarotoxin, strychnine, and atropine. The efficacy of the various agonists and antagonists indicates that the [Ca2+]iincrease is mediated by the nicotinic acetylcholine (ACh) receptors that have been characterized previously in these cells by using electrophysiological methods. In the presence of high agonist concentrations, [Ca2+]ipartly recovered, suggesting that the ACh receptors desensitize.The [Ca2+]iincrease induced by cholinergic agonists was abolished in Ca2+‐free solution, which indicates that it is caused by Ca2+influx from the external medium. The agonist‐induced [Ca2+]iincrease was partly preserved in Na+‐free solution, whereas the agonist‐induced membrane depolarization was strongly suppressed. The agonist‐induced [Ca2+]iincrease was also partly preserved in the presence of 5 mM Ni2+, which almost abolished the K+‐induced [Ca2+]iincrease mediated by voltage‐dependent Ca2+channels. It is concluded that at low agonist concentrations the [Ca2+]iincrease in leech neuropile glial cells is mediated exclusively by the ion channels associated with the nicotinic ACh receptors. At high agonist concentrations, voltage‐dependent Ca2+channels activated by the concomitant membrane depolarization also contribute to the agonist‐induced Ca2+influx

ISSN:0894-1491    

DOI:10.1002/glia.440150106

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

年代:1995

数据来源: WILEY

摘要:

AbstractVoltage dependent potassium currents were recorded using the whole‐cell mode of the patch‐clamp technique for the first time from endfeet of Müller cells dissociated from the frog retina. Recordings from intact cells and isolated endfeet indicate that the inward rectifier potassium channel is the dominant ion channel in these cells and that the density of these channels is highest in the endfoot as has been previously reported for several other species. The present study uses rapid changes in [K+]oto understand the behavior of these channels in buffering [K+]oin the retina. With rapid changes in [K+]o, it was found that, at a membrane potential of −90 mV, which is close to EK, increasing [K+]ofrom 3 to 10 mM produced an inward K+current 5.48 ± 0.89 SD (n = 9) times larger than outward current induced by decreasing [K+]ofrom 3 to 1 mM. The outward current was maximal at a holding potential of about −80 mV and exhibited inactivation at more positive potentials. At −40 mV both the inward and outward currents are markedly reduced. The current voltage curve for the inward current was linear at holding potentials from −50 mV to −140 mV. Using 20 mV voltage steps, it was found that the voltage dependent K+currents were unaffected by the addition of 2 mM Cd2+, a blocker of Ca2+‐activated potassium currents, decreasing [Cl−]ofrom 120 mM to 5 mM or the substitution of 30 mM Na+by TEA. The addition of 5 mM [Cs+]oblocked only the inward current. Both the outward and inward currents disappeared in the absence of intracellular and extracellular K+; 0.3 mM [Ba2+]oblocked the inward current completely and strongly inhibited the outward current in a time and voltage dependent manner. We conclude that at physiological [K+]oand membrane potential, the K+channels in the Müller cell endfoot are well suited to carry K+both inward and outward across the membrane as required for spatial buffering. ©

ISSN:0894-1491    

DOI:10.1002/glia.440150107

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe mitotic activity astrocytes in the adult central nervous system (CNS) is of interest due to their roles in gliosis and tumorigenesis, and their potential in aiding recovery of function following injury or disease. The posterior pituitary offers a potentially powerful model to study proliferation in vivo, since its resident astrocytes, called pituicytes, have been reported to divide concurrently with hormone release from the neurosecretory terminals there. Our aim in this study was to confirm and characterize this proliferative response during dehydration and rehydration in fully adult animals, using contemporary techniques. Adult male rats were given 2% saline in substitution for water for 0–9 days. Proliferation of pituicytes was quantified in tissue sections triple‐labeled with the proliferation marker, 5‐bromodeoxyuridine (BrdU), the astrocyte marker glial fibrillary acidic protein (GFAP), and the DNA marker 4,6, diamidino‐2‐phenylindole, HC1 (DAPI). A robust proliferative response began within three days of dehydration and continued at a constant rate thereafter. In animals allowed to rehydrate, this response continued. After 9 days of dehydration, approximately 35% of pituicytes had participated in mitosis. While cell density remained constant across conditions, a reversible increase in posterior pituitary area was seen, suggesting that some cell death also occurs simultaneously. A significant proportion of non‐pituicytes also underwent similar changes. These results indicate that pituicytes in the adult posterior pituitary retain characteristics necessary for reentering the cell cycle in response to local factors present during neurosecretory activity. We hypothesize that this proliferative response is directly related to the morphological changes previously reported for these cells under activating conditions. © 1995 Wil

ISSN:0894-1491    

DOI:10.1002/glia.440150108

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

年代:1995

数据来源: WILEY

摘要:

AbstractCombinations of cytokines and/or phorbol ester induce expression of Type II nitric oxide synthase (NOS) mRNA in astrocyte cultures via protein kinase mediated pathways (Simmons and Murphy: GLIA 11:227, 1994; Feinstein et al.: J Neurochem 62:811,1994). Agonists that activate receptors linked to protein kinases did not reproduce this effect of cytokines in astrocytes. On the contrary, ATP and glutamate treatment of astrocytes prior to a combination of interleukin‐1ß and interferon‐γ markedly reduced (30–50%) subsequent NOS mRNA expression. The effect was not seen if treatment coincided with or followed cytokine activation, suggesting that ATP and glutamate were not destabilizing NOS mRNA. The effects of ATP and glutamate were additive and could be mimicked by selective receptor agonists, but were insensitive to a specific inhibitor of protein kinase C. The inhibition of cytokine‐induced NOS mRNA expression caused by these agents was not the result of interference with the activation/translocation of nuclear factor‐ϰB by interleukin‐1ß. These results suggest that exposure of astrocytes to ATP and glutamate, both of which increase markedly in a variety of neuropathologies, could modulate the subsequent responsiveness of these cells to NOS‐inducing stimuli. As such, this may be an important regulatory mechanism in the expression of Type II NOS in vivo. © 19

ISSN:0894-1491    

DOI:10.1002/glia.440150109

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

年代:1995

数据来源: WILEY

摘要:

AbstractVoltage‐gated ionic currents were studied in cultured trout oligodendrocyte precursor cells derived from larval trout brain with the whole‐cell mode of the patch‐clamp technique. These bipolar cells which carry the ganglioside epitope A2B5 on their surface differentiated in vitro into immature multipolar oligodendrocytes expressing the myelin glycoprotein IP2, which signifies the initial step of oligodendroglial development in fish CNS. Depolarization above ‐40 mV activated a fast transient sodium inward current that was eliminated by substituting Na+for choline and blocked in the presence of 1 μM TTX. The kinetics and the voltage‐dependence of inactivation (half‐maximal inactivation at ‐68 mV) resembled those of sodium currents described in mammalian oligodendrocyte precursor cells and CNS neurons. The expression of Na+channels was developmentally regulated, since high amplitudes were measured only in A2B5+cells with a characteristic bipolar morphology of glial progenitors. Depolarizing voltage steps, additionally elicited outward potassium currents that were sensitive to external 4‐AP. In a subpopulation of cells this outward current consisted of a sustained and a transient component. The amplitude of both components were dependent on the prepulse potential. © 199

ISSN:0894-1491    

DOI:10.1002/glia.440150110

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

年代:1995

数据来源: WILEY

ISSN:0894-1491    

DOI:10.1002/glia.440150111

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

年代:1995

数据来源: WILEY