摘要:

AbstractAlthough previous studies have revealed that the prenatal rat ventricular zone contains separate progenitor cells for neurons, astrocytes, and oligodendrocytes during the development of the cerebral cortex as early as the beginning of neurogenesis (Luskin et at., 1993; Grove et al., 1993), it is still unclear whether there are bipotential progenitor cells in the neonatal telencephalic subventricular zone which give rise to both astrocytes and oligodendrocytes during the peak of gliogenesis. To investigate this possibility, discrete groups of clonally related cells, generated by infecting progenitor cells of the neonatal subventricular zone with a retroviral lineage tracer, were analyzed ultrastructurally.An intracerebral injection of retrovirus encoding the reporter geneE. coliß‐galactosidase (lacZ) was made into the subventricular zone of newborn rats. Two weeks later their brains were perfused, sectioned, and histochemically reacted with X‐Gal to identify at the light microscopic level clones of lacZ‐positive cells. The sections were processed for electron microscopy to enable the identity of clonally related cells to be assessed at the ultrastructural level.All of the clones analyzed contained cells of the same phenotype and could be divided into four distinct types: immature cell clones situated in the subependymal zone surrounding the lateral ventricle, oligodendrocytes clones, and white or gray matter astrocyte clones. Not all of the cells in every clone displayed ultrastructural features of a mature cell. Rather, in some glial clones the lacZ‐positive cells appeared to be at different stages of differentiation. However, we never encountered clones which contained both macroglial subtypes or clones containing neurons. Although the existence of bipotential progenitor cells cannot be completely dismissed, our results indicate the absence of progenitor cells in vivo in the neonatal subventricular zone which divide and generate astrocytes and oligodendrocytes. © 1994 Wiley

ISSN:0894-1491    

DOI:10.1002/glia.440110302

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

年代:1994

数据来源: WILEY

摘要:

AbstractLipopolysaccharide (LPS) or a combination of interferon (IFN)‐γ and interleukin (IL)‐1β can induce a calcium‐independent nitric oxide synthase (iNOS) in astrocyte cultures (Simmons and Murphy: J Neurochem 59:897, 1992; Eur J Neurosci 5:825,1993; Galea et al: Proc Natl Acad Sci USA 89:10945,1992). This induction can be measured by assaying cyclic GMP levels in the cultures, which correlates with, but is more sensitive than, measurement of nitrite accumulation. To study potential second‐messenger systems involved in the induction of iNOS, phorbol 12‐myristate 13‐acetate (PMA), a protein kinase C (PKC) activator, and various protein kinase inhibitors were employed. PMA induced a time‐, dose‐, and L‐arginine‐dependent increase in cyclic GMP, which could be inhabited by dexamethasone or actinomycin D. This induction could be dramatically increased by concurrent treatment with IFN‐y. The presence of iNOS mRNA could be demonstrated by hybridization with a specific cDNA probe. H7 (a non‐specific serine/threonine kinase inhibitor) but not H89 (a more specific PKA inhibitor) prevented induction by all agents. However, downregulation of PKC or pretreatment with the PKC inhibitor calphostin C did not prevent the induction by LPS or cytokines, suggesting that PKC is not necessary for iNOS induction by these mediators. Additionally, genistein (a nonspecific tyrosine kinase inhibitor) could prevent induction by all agents, but the more specific inhibitor, tyrphostin, attenuated only NOS induction by LPS. These results suggest that activation ofPKC can lead to, but is not necessary for, the induction of NOS in astrocytes and that there is a potential role for tyrosine kinases in NOS induction by LPS. This complex control of induction of iNOS, seemingly requiring activation of multiple pathways for maximal effect, might represent a safeguard to prevent production of potentially toxic nitric oxide (NO) under normal physiological condition

ISSN:0894-1491    

DOI:10.1002/glia.440110303

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe microanatomy of ensheathing and early myelinating rat oligodendrocytes was analyzed through electron microscopic examination of serial sections. The study included cells in the spinal cord (SC) ventral funiculus and the corpus callosum (CC), containing early myelinating, prospective large axons and late myelinating, prospective small axons, respectively. The results show that ensheathment commences fetal day (F) 19 in the SC and 12 days postnatally (P12) in the CC. By then, multipolar SC and CC oligodendrocytes provide axons with uncompacted cytoplasmic sheaths. The average number of axons ensheathed by each such cell was 7 in the SC and 13 in the CC. The mean diameter of the ensheathed axons was 0.69 μm in the SC and 0.36 μm in the CC. The formation of compact myelin had clearly been initiated at birth in the SC and at P17 in the CC. At that stage, the mean number of myelinated axons per analyzed oligodendrocyte was 3 in the SC and 15 in the CC. The mean diameter of the myelinated axons was 1.02 μm in the SC and 0.54 μm in the CC. These observations show that myelin‐related rat oligodendrocytes are morphologically heterogeneous. It also seems that this heterogeneity is related to time of onset of myelination and prospective axon diameter. Further, the data suggest that some oligodendrocytes reduce the number of sheaths initially elaborated before formation of compact myelin. © 1994 Wiley‐L

ISSN:0894-1491    

DOI:10.1002/glia.440110304

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

年代:1994

数据来源: WILEY

摘要:

AbstractVoltage‐gated ionic currents were recorded from cultured trout astrocytes with the whole‐cell variation of the patch‐clamp technique. In a subpopulation of astrocytes depolarizations above −40 m V activated a fast transient inward current that was identified as a sodium current by ion substitution experiments, its current reversal potential, and its TTX‐sensitivity. Regarding threshold of activation, peak current voltage, and amplitude this current closely resembled those previously described for mammalian astrocytes. Voltage‐dependence of inactivation and kinetics, however, markedly differed from the “glial‐like” sodium current occurring in mammalian hippocampal or optic nerve astrocytes, since the sodium current of trout astrocytes exhibited a faster time course of activation and decay and a more depolarized steady‐state inactivation curve with midpoints close to −60 mV. During a period of 2 weeks in culture the biophysical properties of the sodium current did not change significantly, albeit a continuous decrease in current density was observed. At depolarizing voltage steps positive to −40 mV, additionally voltage‐gated potassium outward currents were evoked, which could be separated into a steady‐state current with delayed rectifier properties and an inactivating component resembling the A‐type current. Moreover, in a subpopulation of astrocytes an inward potassium current was elicited at hyperpolarizing potentials, which exhibited biophysical features consistent with the potassium inward rectifier of mammalian astro

ISSN:0894-1491    

DOI:10.1002/glia.440110305

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

年代:1994

数据来源: WILEY

摘要:

AbstractThyroid hormones and retinoic acid (RA) are important modulators of growth, development, and differentiation. Type III deiodinase (D‐III), which catalyzes thyroid hormones degradation in the brain and in cultured astroglial cells, is induced in astroglial cells by multiple pathways, including cAMP, 12.0‐tetradecanoylphorbol‐13‐acetate (TPA), fibroblast growth factors, and thyroid hormones themselves. In the present study, the effects of retinoids on D‐III activity were examined in astroglial cells cultures in a chemically defined medium devoid of hormones and growth factors. Incubation of astroglial cells with 5 μM all‐trans‐RA caused up to 200‐fold increase in D‐III activity, which reached a plateau after 48 h. The retinoid‐induced increase in D‐III activity was concentration dependent (0.5 μM all‐trans‐RA and 9‐cis‐RA producing half‐maximal effect). Retinol was effective at physiological concentrations (1 and μM). The 48 h effects of 5 μM all‐trans‐RA and 10 nM thyroid hormones on D‐III activity were at least additive. Addition of 2 nM acidic fibroblast growth factor or 1 mM 8‐bromo‐cAMP for the last 8 h of a 48 h incubation with 5 μM all‐trans‐RA did not alter the induction by all‐trans‐RA, whereas 0.1 μM TPA in the same conditions produced an additive effect with all‐trans‐RA. All‐trans‐RA (5 μM) had little or no effect on type II deiodinase, the enzyme which catalyzes the activation of thyroxine to 3,5,3′‐triiodothyronine. The potent action of retinoids on the enzyme responsible for thyroid hormones degradation in the brain may protect the brain from the effects of 3,5,3′‐tri

ISSN:0894-1491    

DOI:10.1002/glia.440110306

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

年代:1994

数据来源: WILEY

摘要:

AbstractUptake of radiolabelled L‐arginine was studied in four different kinds of glial cultures, in astroglia‐rich primary cultures derived from neonatal rat and mouse brains, in pure murine astrocyte cultures, and in rat glioma cells C6‐BU‐1. A saturable component of uptake was found in all cases with KMvalues between 15 and 35 μM and Vmaxvalues between 0.8 and 2.5 nmol · min−1· (mg protein)−1. In addition, in all cell types a non‐saturable component dominated total uptake at high concentrations of extracellular arginine. Rates of uptake of arginine were not affected when Na+or Cl−were absent from the incubation buffer. Carrier‐mediated uptake of arginine was reduced by depolarizing concentrations of K+and strongly inhibited by an excess of lysine or ornithine. Histidine, asparagine, glutamine, citrulline, creatine, NG‐nitro‐L‐arginine, NG‐monomethyl‐L‐arginine, or L‐canavanine inhibited L‐arginine transport to various degrees. Uptake of arginine was not reduced in the presence of serine or alanine, cysteic acid, N‐methyl‐α‐aminoisobutyric acid, or 2‐aminobicyclo‐(2.2.1)‐heptane‐2‐carboxylic acid. Rates of uptake of arginine were increased when cells had been preloaded with lysine. Preincubation of primary cultures, but not glioma cells, with bacterial lipopolysaccharide stimulated transport of arginine by increasing the Vmaxvalue of uptake. This stimulation was dependent on protein synthesis. The results suggest that, at physiological concentrations, arginine is taken up into the glial cells with the help of the transport system “y+” for basic amino acids. In glial primary cultures, uptake of arginine appears to be regulated by compounds which also exert in

ISSN:0894-1491    

DOI:10.1002/glia.440110307

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

年代:1994

数据来源: WILEY

摘要:

AbstractA recent study demonstrated oxytocin (OT) receptors on hypothalamic cultured astrocytes (Di Scala‐Guenot and Strosser, 1992). The attempt in the present paper was to determine a possible intracellular calcium mobilization induced by OT receptor activation in these cells. Using the microspectrofluorimetric technique with fura‐2 as calcium indicator, brief applications of OT on single astrocytes induced a transient and reversible dose‐dependent increase of intracellular calcium concentration ([Ca2+]i) in most of the cells tested. In a few cells, OT application triggered intracellular calcium oscillations. Repetitive applications of OT generally produced a decreasing calcium signal, suggesting a desensitization of the receptor. OT‐induced calcium release was prevented by a prior or simultaneous application of an OT antagonist. The origin of the calcium mobilization was assessed during conditions where no extracellular calcium was available. Neither removal of extracellular calcium nor addition of a calcium channel blocker, cadmium 100 μM, in the bathing solution, did affect the calcium response to OT, demonstrating that release of intracellular calcium is solely involved in the OT‐induced [Ca2+]iincrease. The OT‐induced calcium mobilization was abolished after thapsigargin application (100 nM). This indicates that the calcium response to OT application was principally associated with activation of the IP3‐sensitive calcium stores. Taken together these results demonstrate that OT receptors previously detected on hypothalamic cultured astrocytes are functional receptors which transduction pathways involve calcium mobilization from IP3‐sensitive stores. © 199

ISSN:0894-1491    

DOI:10.1002/glia.440110308

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

年代:1994

数据来源: WILEY

摘要:

AbstractVariations in intracellular free calcium concentration (Δ[Ca2+]i) were measured in intact and isolated human astrocytoma cells (U373 MG) loaded with fura‐2 acetoxymethylester. Microperfusion of 50 nM substance P (SP), applied for 1 s, increased [Ca2+]iby 351 nM from a stable basal level of [Ca2+]iof 26 nM. The peak Δ[Ca2+]iinduced by SP was dose dependent with a threshold of 10‐3nM, an ED50of 1.3 nM and a maximal effect for concentrations of SP greater than 100 nM. The NKI receptor agonist, [Sar9Met(O2)11]SP, mimicked the effect of SP, while the NK2and NK3selective receptor agonists, [N110]NKA(4‐10) and senktide, respectively, had no effect. The Δ[Ca2+]iinduced by SP was unaffected by 100 μM cadmium or by removal of extracellular calcium ions. Caffeine up to 30 mM had no effect on [Ca2+]i. In contrast, thapsigargin increased resting [Ca2+]iby 92 nM and reduced the Δ[Ca2+]iinduced by SP. A pertussis treatment (500 ng/ml‐24 h) did not modify the Δ[Ca2+]iinduced by SP.We conclude that SP, acting on a NK1 receptor, mobilizes cytosolic calcium from an intracellular calcium pool which can be partially depleted by thapsigargin. © 1994 W

ISSN:0894-1491    

DOI:10.1002/glia.440110309

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

年代:1994

数据来源: WILEY

摘要:

AbstractPhosphotyrosine and protein tyrosine phosphatase antibodies have been used to assess the distribution and potential functions of tyrosine phosphorylation systems in normal brain and cell cultures, as well as in a model of neural degeneration. Western blot and immunohistochemical analysis showed that a panel of antiphosphotyrosine antibodies recognizing different tyrosine phosphorylated substrates all selectively labeled ramified microglia in sections of brain tissue. This significantly extends our previous observation (GLIA 2:412‐419, 1989) that a single, limited, phosphotyrosine antibody served as a histological marker for microglia. The present results show that tyrosine phosphorylation of a variety of substrates is quantitatively enriched in microglia compared to other neural cell types. We also show that the protein tyrosine phosphatase, CD45, is constitutively expressed by ramified microglia in vivo and by ameboid microglia in vitro. Thus, the major enzymes constituting tyrosine phosphorylation systems are present in normal microglia. Neuronal degeneration in the trigeminal nucleus, caused by a introduction of the neurotoxic lectin, ricin, into the peripheral nerve, is accompanied by a robust upregulation of phosphotyrosine signal in ramified microglial adjacent to the nucleus and in ameboid microglia in the degenerating nucleus. The presence of phosphotyrosine in ramified microglia is consistent with a role for tyrosine phosphorylation systems in the activation of microglia and in the signaling events accompanying conversion of resting microglia to the ameboid form. © 1994 Wiley‐Liss,

ISSN:0894-1491    

DOI:10.1002/glia.440110310

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

年代:1994

数据来源: WILEY

ISSN:0894-1491    

DOI:10.1002/glia.440110301

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

年代:1994

数据来源: WILEY