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HÉLÈNE VIGNOLLES 《Archive for History of Exact Sciences》2000,55(1):77-101
En dépit de la difficulté présentée par les mesures d'éclat, John Michell construisit au dix-huitième siècle une échelle de magnitude étonnante de précision et de rigueur. Mais il n'indique pas ses propres méthodes. Sans doute transposa-t-il aux étoiles les méthodes de Bouguer dont l'ouvrage faisait alors autorité en matière de photométrie. Son travail, dont il se contente d'exposer très brièvement les résultats sans en développer les principes, restera ignoré des autres astronomes. 相似文献
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Vogt J Glumm R Schlüter L Schmitz D Rost BR Streu N Rister B Suman Bharathi B Gagiannis D Hildebrandt H Weinhold B Mühlenhoff M Naumann T Savaskan NE Brauer AU Reutter W Heimrich B Nitsch R Horstkorte R 《Cellular and molecular life sciences : CMLS》2012,69(7):1179-1191
During development, axonal projections have a remarkable ability to innervate correct dendritic subcompartments of their target neurons and to form regular neuronal circuits. Altered axonal targeting with formation of synapses on inappropriate neurons may result in neurodevelopmental sequelae, leading to psychiatric disorders. Here we show that altering the expression level of the polysialic acid moiety, which is a developmentally regulated, posttranslational modification of the neural cell adhesion molecule NCAM, critically affects correct circuit formation. Using a chemically modified sialic acid precursor (N-propyl-D: -mannosamine), we inhibited the polysialyltransferase ST8SiaII, the principal enzyme involved in polysialylation during development, at selected developmental time-points. This treatment altered NCAM polysialylation while NCAM expression was not affected. Altered polysialylation resulted in an aberrant mossy fiber projection that formed glutamatergic terminals on pyramidal neurons of the CA1 region in organotypic slice cultures and in vivo. Electrophysiological recordings revealed that the ectopic terminals on CA1 pyramids were functional and displayed characteristics of mossy fiber synapses. Moreover, ultrastructural examination indicated a "mossy fiber synapse"-like morphology. We thus conclude that homeostatic regulation of the amount of synthesized polysialic acid at specific developmental stages is essential for correct synaptic targeting and circuit formation during hippocampal development. 相似文献
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Savaskan NE Rocha L Kotter MR Baer A Lubec G van Meeteren LA Kishi Y Aoki J Moolenaar WH Nitsch R Bräuer AU 《Cellular and molecular life sciences : CMLS》2007,64(2):230-243
Autotaxin is a secreted cell motility-stimulating exo-phosphodiesterase with lysophospholipase D activity that generates bioactive
lysophosphatidic acid. Lysophosphatidic acid has been implicated in various neural cell functions such as neurite remodeling,
demyelination, survival and inhibition of axon growth. Here, we report on the in vivo expression of autotaxin in the brain during development and following neurotrauma. We found that autotaxin is expressed in
the proliferating subventricular and choroid plexus epithelium during embryonic development. After birth, autotaxin is mainly
found in white matter areas in the central nervous system. In the adult brain, autotaxin is solely expressed in leptomeningeal
cells and oligodendrocyte precursor cells. Following neurotrauma, autotaxin is strongly up-regulated in reactive astrocytes
adjacent to the lesion. The present study revealed the cellular distribution of autotaxin in the developing and lesioned brain
and implies a function of autotaxin in oligodendrocyte precursor cells and brain injuries.
Received 18 September 2006; received after revision 30 October 2006; accepted 4 December 2006 相似文献
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