17 research outputs found

    Effect of sintering temperature on properties of transparent YSZ-ceramics prepared by spark plasma sintering

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    Transparent yttria-stabilized zirconia (YSZ) ceramics were sintered with the spark plasma sintering (SPS) method at different temperatures. The influence of sintering temperature (1200-1400°С) on the ceramics microstructure and mechanical properties was investigated and discussed

    Distribution and morphology of GFAP-positive astrocytes in the human fetal brain at second trimester

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    Background: Various studies have shown that a close physical and functional relationship exists between astrocytes and microglia during development. The maturation of astrocytes can be followed by their specific expression of glial fibrillary acidic protein (GFAP). Although there have been several reports on the expression of GFAP in the developing brain, these are mainly descriptive and have not defined clearly the regional distribution patterns of these cells during fetal development. Aim: This study set out to analyse the regional distribution and morphology of GFAP-expressing astrocytes during the latter half of the second trimester (19-23 gestational weeks) within five normal fetal brains, with a view towards comparing the findings with the microglial distribution and differentiation previously recorded throughout the same period. Results: A clear account of the morphology and regional distribution of GFAP-positive astrocytes is presented. Differentiating astrocytes (including radial glia and their processes) were found in the germinal layers, corpus callosum and cavum septum pellucidum, within neural tracts and surrounding the basal ganglia - areas known to be populated by microglia during the same period. The differentiation of astrocytes was predominant within the subplate and intermediate zone towards the end of the second trimester. Importantly, the differentiation of astrocytes within these regions followed a similar spatially interspersed pattern as reported for fetal microglia. However, astrocytes appeared to differentiate at a later stage within these regions than described for microglia. This will require further investigations for confirmation. Differentiated astrocytes were also found to associate with cortical blood vessels in a region-specific manner during the second trimester. Conclusions: These observations indicate that the differentiation and spatial distribution of astrocytes parallels those of microglia during the second trimester. It remains to be seen whether factors released by microglia can directly influence the differentiation of astrocytes in situ during development

    Transient structures of the human fetal brain: Subplate, thalamic reticular complex, ganglionic eminence

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    Morphological features of the subplate, the thalamic reticular complex and the ganglionic eminence, which represent three major transient structures of the human fetal forebrain, are summarized with special reference to their functional roles. The subplate harboring various neuronal types is an outstandingly wide zone subjacent to the cortical plate in the human fetal brain. Within the subplate various cortical afferents establish synaptic contacts for a prolonged period before entering the cortical plate. Therefore, the subplate is regarded as a "waiting compartment" which is required for the formation of mature cortical connections. Next to the thalamic reticular nucleus, within the fibers of internal capsule, the perireticular nucleus is located which has been established as a distinct entity during development. Its various neuronal types express a number of different neuroactive substances. Perinatally, the perireticular nucleus is drastically reduced in size. It is involved in the guidance of corticofugal and thalamocortical fibers. The ganglionic eminence is a conspicuous proliferative area that persists throughout nearly the entire fetal period. In the human fetal brain it extends medially upon the dorsal thalamic nuclei which receive precursor cells from the ganglionic eminence. Postmitotic cells in the marginal zone of the ganglionic eminence serve as an intermediate target for growing axons. On the whole, all three structures establish transient neural circuitries that may be essential for the formation of adult projections. The characteristics of the three transient structures are particularly relevant for developmental neuropathology as these structures may be damaged in disorders that preferentially occur in preterm infants
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