PubMed Health⌕ Search

Biomedical subjects

K E Dow

Publications and source records attributed to K E Dow.

At least 37 records · Page 2Linked to original sources
PubMed1993

Regenerative neurite growth modulation associated with astrocyte proteoglycans.

Adherent GFAP-positive cells of neocortical origin in vitro produce and release members of three families of sulphated proteoglycans and a sulphated protein that copurifies with heparan sulphate proteoglycan (HSPG). Conditioned medium (CM) and the proteoglycans contained in the CM have neurite growth-promoting activity when immobilized on defined substrates of growth but not when in the nonimmobilized compartment. On a poly-D-lysine substrate, the rank ordering of specific neurite growth activity based on protein concentration was 330 kDa HSPG >> 100 kDa HSPG/chondroitin sulphate (CS) PG mixture or hybrid > 330 kDa CSPG > 50 kDa CSPG/dermatan sulphate (DS) PG mixture or hybrid and the 31 kDa sulphoprotein. Astrocyte CM lost its growth facilitatory activity when prepared and released by astrocytes in the presence of soluble mediators of inflammation. Loss of activity could not be explained by qualitative or quantitative alterations of released proteoglycans but appeared to be associated with the presence of an inhibitor. The sulphoprotein that copurified with HSPG was a potent inhibitor of HSPG-mediated neurite growth.

Animals↗
PubMed1992

Effects of 4-deoxy-L-threo-pentose, a novel carbohydrate, on neural cell proteoglycan synthesis and function.

A novel carbohydrate, 4-deoxy-L-threo-pentose (4-deoxyxylose), was synthesized by way of reductive dechlorination of a chlorodeoxy sugar. This carbohydrate, an analogue of xylose which is required for the initiation of glycosaminoglycan (GAG) synthesis, was used to explore the function of GAG side chains in neurite outgrowth on a laminin substrate. 4-Deoxyxylose inhibited the incorporation of 35SO4 into the GAGs of neuronal and astrocytic proteoglycans, with no effect being seen on the incorporation of [3H]glucosamine into proteoglycan. Direct analysis of the heparan sulphate fraction from such cells using nitrous acid digestion confirmed that the GAGs were undersulphated. No inhibition of either 35SO4 or [3H]glucosamine incorporation was observed in primary mouse hepatocytes exposed to 4-deoxyxylose. 4-Deoxyxylose produced a direct dose-dependent inhibition of neurite outgrowth by sensory neurons, and medium conditioned by neurons or astrocytes in the presence of 4-deoxyxylose displayed less laminin-complexed neurite-promoting activity than medium conditioned in its absence. These data suggest that 4-deoxyxylose inhibits neurite outgrowth by altering the sulphation of the GAGs of heparan sulphate proteoglycans.

Animals↗
PubMed1992

Neurite growth modulation associated with astrocyte proteoglycans: influence of activators of inflammation.

Of the three classes of sulphated proteoglycans produced by type 1 astrocytes in vitro and released into conditioned medium, only heparan sulphate (HS) was associated with enhanced neurite growth by sensory neurons following pretreatment of a laminin substratum. Astrocyte-conditioned medium (ACM) produced in the presence of certain inflammatory mediators had reduced titers of neurite-promoting activity. The low activity ACM contained inhibitors of neurite growth. Heparan sulphate proteoglycans may modulate neurite growth when complexed to constituents of the extracellular milieu either directly or by interacting with other growth-promoting or growth-inhibitory factors.

Animals↗
PubMed1992

Influence of N-linked oligosaccharides on the processing and neurite-promoting activity of proteoglycans released by neurons in vitro.

Inhibitors of enzymes involved in processing of N-linked oligosaccharides were used to examine biosynthesis and the neurite-promoting activity of proteoglycans produced by and released from dissociated chick embryo spinal cord neurons in vitro. In the cell compartment and in conditioned medium both castanospermine and swainsonine inhibited 3H-glucosamine incorporation into glycoprotein but only castanospermine reduced 3H-glucosamine incorporation into heparan sulphate and chondroitin sulphate proteoglycans. All of the neurite-promoting activity of neuron-conditioned medium that complexed to laminin was associated with heparan sulphate proteoglycans as determined by heparitinase digestion. Neuron-conditioned medium prepared in the presence of castanospermine displayed a 38 +/- 6% (mean +/- SD) reduction in 3H-glucosamine incorporation into heparan sulphate proteoglycans and a 30 +/- 5% reduction in substrate-attached neurite-promoting activity compared to control conditioned medium and to conditioned medium prepared in the presence of swainsonine. When neurons were coincubated with castanospermine, neurite growth on a laminin substrate was 50 +/- 10% of control growth or growth in the presence of swainsonine. However, when neuron-conditioned medium was used to pretreat the laminin substrate the inhibitory effect on neurite growth produced by castanospermine coincubation was reversed. Influences on neuronal processing of N-linked oligosaccharides alter neurite growth directly and also alter the neurite-promoting activity of neuron-conditioned medium by inhibiting the synthesis of heparan sulphate proteoglycans. These studies provide further evidence for an autocrine role for heparan sulphate proteoglycans in neurite growth.

Animals↗
PubMed1991

Neurite formation on laminin: effects of a galactosyltransferase on primary sensory neurons.

Avian embryonic sensory neurons from ED8 chick possess a trypsin-labile cell surface galactosyltransferase (GalTase) activity that glycosylates laminin in the presence of uridine 5' galactose (UDPgal). In a 4 h biological assay concentration dependent partial inhibition of neurite growth on laminin was observed in the presence of (i) alpha-lactalbumin, a specific inhibitor of the enzyme, (ii) N-acetylglucosamine (GlcNac), the appropriate acceptor substrate, or its polymer chitotriose, and (iii) UDPgal, the catalytic substrate. Prior exposure of substrate-immobilized laminin to glycosidase partially inhibited neurite growth. Alpha-lactalbumin did not influence cell adhesion at saturating concentrations for inhibition of neurite formation. Neurite growth on fibronectin was not inhibited by prior exposure to glycosidase or by alpha-lactalbumin, and fibronectin was not an appropriate substrate for glycosylation by the sensory neurons. These observations extend the catalogue of domains of laminin that subserve neurite growth, and define in functional terms a class of neuronal receptors that interact with lactosaminoglycan-type oligosaccharides of laminin.

Acetylglucosamine↗
PubMed1991

Characterization of glycosaminoglycans produced by primary astrocytes in vitro.

Quantitative 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 interactions.

Animals↗
PubMed1991

Domains of neuronal heparan sulphate proteoglycans involved in neurite growth on laminin.

A single neuronal cell assay of neurite growth was utilized to determine types and domains of neuronal proteoglycans involved in neurite growth on laminin. Perturbations of biosynthesis and processing, enzymatic digestion with specific lyases, and competition with glycosaminoglycan side chains produced complementary data consistent with a molecular model implicating glycosaminoglycan (GAG) residues of heparan sulphate proteoglycans (HSPGs) in neurite growth. The observations suggest that HSPGs promote neurite growth on laminin by bridging between binding domains for HSPGs on laminin and on the neuronal cell surface, and that the bridge is tethered at both ends by non-covalent interactions between the binding domains and GAG side chains. Sulphation of the GAGs of HSPGs appears to be critical to the tethering and/or neurite growth-promoting activity of neuronal HSPGs.

Animals↗
PubMed1991

Molecular interactions modulating neuronal survival and growth.

The extracellular environment of the neuron provides a heterogeneous milieu of survival and growth modulating molecular species subserving regulatory signals that operate in development, mediate activity-dependent enduring changes in synaptic connectivity, and promote or inhibit survival and axonal regeneration following insult. Parallel distributed processing networks in neurons, activated by these molecular species, can likely be recruited selectively to serve specific needs of the organism.

Animals↗
PubMed1990

Functional interactions of neuronal heparan sulphate proteoglycans with laminin.

Quantitative biosynthetic studies using cellular extracts and neuron conditioned medium demonstrated that heparan sulphate proteoglycans (HSPGs) comprised 20-25% of the sulphated proteoglycans produced by neurons while the remainder consisted of chondroitin sulphate proteoglycans (CSPGs). When chromatographic fractions containing guanidine extracted and partially purified proteoglycans from culture medium conditioned by neurons (NCM) were used to pretreat a laminin substrate, neurite formation by sensory neurons was enhanced. Enhanced neurite promoting activity was not apparent if, during the pretreatment of the laminin substrate with NCM, heparan sulphate glycosaminoglycans (HS) were present. To determine the molecular basis of cell surface HSPG interactions with immobilized laminin, adhesion and neurite growth by dissociated sensory neurons were quantified at 4 h in vitro--a time at which there was no apparent contribution of released proteoglycans to neurite growth. Whereas adhesion was not influenced, neurite growth was partially inhibited in a dose-dependent manner if the sensory neurons were coincubated with HS, and if the cells were pretreated, prior to seeding, with heparitinase. The inhibitory effect produced by coincubation with saturating concentrations of HS was no longer apparent if the cells had been pretreated with heparitinase. These findings distinguish quantitatively between neurite growth on laminin and on laminin-HSPG complexes, and suggest that some neuronal cell surface and released HSPGs are involved in neurite growth by virtue of non-covalent interactions with glycosaminoglycan binding domains of laminin.

Animals↗
PubMed1990

Specific effects of ethanol on neurite-promoting proteoglycans of neuronal origin.

Quantitative analysis of proteoglycan synthesis and release by neurons indicated that of the total incorporation of 35SO4 and [3H]glucosamine into proteoglycan, approximately 75% was chondroitin sulphate while approximately 25% was heparan sulphate. Using a biological assay it has been shown that heparan sulphate proteoglycans (HSPGs) in conditioned medium promote neurite outgrowth from sensory neurons when complexed to a laminin substrate. Culture media conditioned in the presence of ethanol did not enhance neurite formation over control levels. Co-incubation of neurons with beta-D-xyloside, an inhibitor of proteoglycan synthesis, reduced neurite outgrowth after 20 h in culture and the combination of ethanol and beta-D-xyloside produced no further inhibition than with either ethanol or beta-D-xyloside used alone. If the laminin substrate was coated with medium conditioned by neurons, the direct inhibitory effects on process formation seen when ethanol was co-incubated with neurons were no longer observed. Ethanol inhibited the incorporation of 35SO4 and [3H]glucosamine into HSPG by neurons while having little or no effect on incorporation into chondroitin sulphate. These results suggest that inhibition of neuronal synthesis of HSPGs by ethanol is responsible for the decrease in neurite promoting activity of medium conditioned in the presence of ethanol.

Animals↗
PubMed1990

Ethanol inhibits NMDA-stimulated neurite growth by sensory neurons in vitro.

N-methyl-D-aspartate (NMDA) produced dose dependent neurite growth from 8 day chick embryo sensory neurons in-vitro on a laminin substrate. NMDA-stimulated neurite growth was blocked by the competitive antagonist D-2-amino-5-phosphonovaleric acid (APV), by an antagonist of the glycine modulatory site kynurenate, and by the NMDA ion channel antagonist Mg2+. Ethanol blocked the NMDA-mediated neurotrophic effect in a manner that was additive with the effects of Mg2+, but non-additive with the inhibitory influences of APV and kynurenate. Thus the influences of ethanol were mediated at the NMDA receptor/modulatory site. These observations have implications for the understanding of adverse influences of ethanol on neuronal development and connectivity and on activity-dependent enduring changes in synaptic changes in synaptic function.

2-Amino-5-phosphonovalerate↗
PubMed1988

Differential effects of anticonvulsants on developing neurons in vitro.

The effects of four anticonvulsants, phenobarbital, diphenylhydantoin (DPH), carbamazepine and valproic acid, on dissociated cultures of embryonic chick dorsal root ganglia (DRG) neurons were examined. DPH and valproic acid inhibited process formation in a dose-dependent manner and reduced neuronal production of substrate attached neurite promoting activity (SANPA). Less inhibition of process formation occurred with phenobarbital and carbamazepine and these two anticonvulsants had no effect on SANPA production. Substrate attachment of neurons, their survival and receptor interactions of DRG neurons with nerve growth factor were not influenced by any of the four anticonvulsants. These data suggest a rank ordering of direct toxic effects of anticonvulsants on developing neurons. The mechanisms of this neurotoxicity may include decreased neuronal production of autostimulating neurite promoting factors.

Animals↗
PubMed1988

Neuronal proteoglycans: biosynthesis and functional interaction with neurons in vitro.

Glycosaminoglycans (GAGs) with electrophoretic mobilities on cellulose acetate similar to heparin (H), heparan sulfate (HS), and chondroitin sulfate (CS) were detected in cell extracts and in conditioned medium of high-density, neuron-enriched cultures labeled with 35SO4. Heparitinase digestion revealed that heparan sulfate proteoglycans (HSPGs) were heterogeneous in charge density and were responsible for neurite outgrowth activity for sensory neurons in conditioned medium. In the presence of beta-D-xyloside, an inhibitor of proteoglycan assembly, there was an increase of released GAGs with the mobility of CS and heavily sulfated HS but a decrease in neurite outgrowth activity on a laminin substrate at times greater than 14 hr. In the presence of beta-D-xyloside or the monoclonal antibody HNK-1 (Leu 7), which recognizes a neuronal cell surface epitope, there was a time-dependent inhibition of process formation that was half-maximal at 7-8 hr and independent of laminin concentration or cell adhesion to the laminin substrate. The kinetics and magnitude of the inhibitory effects of beta-D-xyloside and HNK-1 (Leu 7) were similar, and the influence of HNK-1 (Leu 7) could no longer be observed in the presence of beta-D-xyloside. Pretreatment of the laminin substrate with conditioned medium from high-density neuron cultures resulted in an increased rate of neurite formation compared with untreated laminin. Where the laminin substrate had been pretreated with conditioned medium, maximal inhibition by HNK-1 (Leu 7) was apparent from the earliest times. However, if the conditioned medium had been digested with heparitinase, neither enhanced neurite outgrowth nor the inhibitory influence of HNK-1 (Leu 7) were observed. The present biosynthetic and functional studies suggest that neurons are one source of HSPGs. These data complement and extend earlier studies suggesting a role for HSPGs in neurite formation. The experiments also provide evidence for modulation of laminin by HSPGs which interact with laminin and promote neurite outgrowth that is mediated by a cell surface receptor at or in juxtaposition to the HNK-1 (Leu 7) epitope.

Animals↗
PubMed1985

Ethanol neurotoxicity: effects on neurite formation and neurotrophic factor production in vitro.

The effects of ethanol on chick embryo sensory and spinal cord neurons growing on one of several biological substrates (poly-D-lysine, laminin, or neuron-produced neurite-promoting materials) were examined. Ethanol inhibited process formation by the neurons in a dose-dependent manner and inhibited the production of neurotrophic factors. Neuronal attachment to the substrates, survival of attached neurons, and receptor interactions of sensory neurons with nerve growth factor were not influenced by ethanol. It appears that ethanol alters certain metabolic characteristics of developing neurons.

Animals↗
PubMed1984

Some observations on vinca alkaloid and ethanol neurotoxicity using dissociated neuronal cultures.

Dissociated neuronal cultures have become a popular tool to address a number of questions in neurobiology. These culture systems may provide useful paradigms to approach problems related to in vivo neurotoxicity of xenobiotics. The clinical spectra of vinca neurotoxicity and alcohol teratogenesis is reviewed, and some observations on the use of dissociated cultures to study neuronal toxicity of vinca alkaloids and alcohol are presented.

Abnormalities, Drug-Induced↗
PubMed1984

Synergistic effect of triiodothyronine and dexamethasone on male and female fetal rat lung surfactant synthesis.

It has previously been reported that morphologic and functional indices of fetal lung maturation are delayed in male rabbit fetuses, and these differences cannot be overcome by glucocorticoid treatment. Since thyroid hormone also stimulates surfactant production we have studied the effects of triiodothyronine (T3) and dexamethasone on saturated phosphatidylcholine (SPC) synthesis by day 20 male and female rat lung. Control male lung slices incorporated significantly less 3H-choline into SPC than females; surgery on day 17 markedly stimulated 3H-choline incorporation into SPC by both sexes, but the sex difference persisted. The optimal dose of T3 inhibited SPC synthesis by both sexes while dexamethasone was stimulatory. When T3 and dexamethasone were given together they had a greater effect than that of dexamethasone or T3 alone. Based on these results we conclude that the male deficit in pulmonary surfactant production may be overcome by the synergistic effects of T3 and dexamethasone.

Animals↗
PubMed1983

Evidence for epithelial-mesenchymal interactions mediating glucocorticoid effects in developing chick liver. Fibroblast-hepatocyte factor.

When trypsin-dissociated liver cells from 17-day chick embryos were grown in regular minimum essential medium, mixed hepatocyte-fibroblast cultures resulted. When D-valine was substituted for L-valine in this medium, fibroblast growth was suppressed, leaving virtually pure hepatocyte cultures. Tyrosine aminotransferase activity is induced by cortisol in mixed cultures. No induction of enzyme activity is observed with cortisol exposure to hepatocytes, grown in D-valine. However, when cortisol-containing medium is conditioned by pre-incubation with mixed cells and then transferred to hepatocytes, tyrosine aminotransferase activity is induced. Enzyme activity is also induced in mixed cells incubated in D-valine medium in the presence of cortisol. It appears that a substance produced in the presence of fibroblasts exposed to cortisol is capable of inducing tyrosine aminotransferase activity in hepatocytes. This activity, which we have termed fibroblast hepatocyte factor, is heat stable, of low molecular weight, and antigenically different from fibroblast pneumonocyte factor, a factor similar to that produced by lung fibroblasts exposed to cortisol.

Animals↗