17 research outputs found
Effect of sintering temperature on properties of transparent YSZ-ceramics prepared by spark plasma sintering
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
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Anomalous alterations affecting microglia in the central nervous system of a fetus at 12 weeks of gestation: case report
We report here on the first documented case of profound alterations specifically affecting the microglial population within the nervous system during the fetal period. This case, derived at gestational week 12, was one amongst a series of second trimester brains currently being investigated with respect to microglial colonization of the human fetal brain. No significant pathological alterations could be identified upon gross macroscopy or following microscopic analysis of serial brain sections stained with cresyl fast violet (Nissl). By contrast, sections stained immunohistochemically to detect MHC class II (CR3/43) and CD68 (PG-M1) antigens revealed a marked pathological change in the morphology and density of microglia within the CNS. Specifically, labeled cells within the rostral telencephalon were clearly hypertrophied and emitted numerous, branched processes in all directions, appearing in an atypical 'hyper-ramified' state uncharacteristic of microglia found in normal brains at this age. However, cells located elsewhere in the CNS (for example in the thalamus and internal capsule) appeared in a less differentiated state (small, rounded cells lacking processes) when compared to those within normal age-matched control brains. The total density and distribution of these labeled cells far outnumbered that seen in normal development. As far as we are aware, such an anomaly specifically affecting microglia, has not been documented previously. Consequently, this case represents the first of its kind, and the remarkable observations outlined in this study bear considerable significance from a neuropathological standpoint for future investigations into pathological changes affecting microglia in the central nervous system during the fetal period
Distribution and morphology of GFAP-positive astrocytes in the human fetal brain at second trimester
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
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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Brain macrophages and microglia in human fetal hydrocephalus [poster presentation]
Whereas several studies have addressed the activation of microglia (the resident mononuclear phagocytes of the brain) and macrophages within the nervous system in experimental animal models of congenital and induced hydrocephalus, little is known of their state of activation or regional distribution in human fetal hydrocephalus. This investigation aimed to address such questions. Ten human fetal cases [20-36 gestational weeks (GW) at postmortem] previously diagnosed with hydrocephalus on ultrasound examination in utero, and 10 non-hydrocephalic controls (22-38 GW at postmortem) were assessed immufcnohistochemically with antibodies directed against MHC class II and CD68 antigens, and lectin histochemistry with Lycopersicon esculentum (tomato lectin). Adjacent sections were also immunoreacted with an antiserum to laminin to detect cerebral blood vessels. Eight out of the 10 hydrocephalus cases showed numerous CD68 and tomato lectin-positive macrophages located at focal regions along the ependymal lining of the lateral ventricles (particularly within the occipital horn). However, only five of these cases demonstrated MHC class II positive macrophages associated with the ventricular lining. Microglial reactivity within periventricular regions could also be identified using the lectin in four cases, two of which were also immunoreactive with CD68 (but not with MHC class II). By comparison, in control cases five out of 10 fetal brains (aged between 20 and 24 GW) showed few or no ependymal or supraependymal macrophages. One case at 28 GW, and cases at 32 and 38 GW (two of which were diagnosed with intrauterine hypoxic-ischemia) did, however, show some MHC class II (CD68 negative) cells located at the ependymal surface. Nevertheless, these were not as numerous or intensely immunoreactive as in the hydrocephalus cases. Microglia interspersed throughout the intermediate zone and circumscribing the basal ganglia were within normal confines in all cases examined. Hydrocephalic cases additionally showed focal regions of hypovascularization or alterations in the structure and orientation of capillaries within periventricular areas, compared to controls. The macrophage response detected at the ependymal lining of the ventricles and within the periventricular area in hydrocephalus may be related both to the severity of hydrocephalus and the age of the fetus
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Brain macrophages and microglia in human fetal hydrocephalus
Whereas several studies have addressed the activation of microglia (the resident mononuclear phagocytes of the brain) and macrophages within the nervous system in experimental animal models of congenital and induced hydrocephalus, little is known of their state of activation or regional distribution in human fetal hydrocephalus. This investigation aimed to address such questions. Ten human fetal cases [20-36 gestational weeks (GW) at postmortem] previously diagnosed with hydrocephalus on ultrasound examination in utero, and 10 non-hydrocephalic controls (22-38 GW at postmortem) were assessed immufcnohistochemically with antibodies directed against MHC class II and CD68 antigens, and lectin histochemistry with Lycopersicon esculentum (tomato lectin). Adjacent sections were also immunoreacted with an antiserum to laminin to detect cerebral blood vessels. Eight out of the 10 hydrocephalus cases showed numerous CD68 and tomato lectin-positive macrophages located at focal regions along the ependymal lining of the lateral ventricles (particularly within the occipital horn). However, only five of these cases demonstrated MHC class II positive macrophages associated with the ventricular lining. Microglial reactivity within periventricular regions could also be identified using the lectin in four cases, two of which were also immunoreactive with CD68 (but not with MHC class II). By comparison, in control cases five out of 10 fetal brains (aged between 20 and 24 GW) showed few or no ependymal or supraependymal macrophages. One case at 28 GW, and cases at 32 and 38 GW (two of which were diagnosed with intrauterine hypoxic-ischemia) did, however, show some MHC class II (CD68 negative) cells located at the ependymal surface. Nevertheless, these were not as numerous or intensely immunoreactive as in the hydrocephalus cases. Microglia interspersed throughout the intermediate zone and circumscribing the basal ganglia were within normal confines in all cases examined. Hydrocephalic cases additionally showed focal regions of hypovascularization or alterations in the structure and orientation of capillaries within periventricular areas, compared to controls. The macrophage response detected at the ependymal lining of the ventricles and within the periventricular area in hydrocephalus may be related both to the severity of hydrocephalus and the age of the fetus
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Microglia in the cerebral wall of the human telencephalon at second trimester
We have recently begun to gain a clearer understanding of the phasing and patterns of colonization of the developing human brain by microglia. In this study we investigated the distribution, morphology and phenotype of microglia specifically within the wall of the human telencephalon from 12 to 24 gestational weeks (gw), a period that corresponds to the development of thalamocortical fibres passing through the transient subplate region of the developing cerebral wall. Sections from a total of 45 human fetal brains were immunoreacted to detect CD68 and MHC class II antigens and histochemically reacted with RCA-1 and tomato lectins. These markers were differentially expressed by anatomically discrete populations of microglia in the cerebral wall: two cell populations were noted during the initial phase of colonization (12–14 gw): (i) CD68++ RCA-1+ MHC II– amoeboid cells aligned within the subplate, and (ii) RCA-1++ CD68– MHC II– progenitors in the marginal layer and lower cortical plate that progressively ramified within the subplate, without seemingly passing through an ‘amoeboid’ state. At this stage microglia were largely absent from the germinal layers and the intermediate zone. From 14 to 15 gw, however, MHC class II positive cells were also detected within germinal layers and in the corpus callosum, and these cells, which coexpressed CD68 antigen (a marker associated with phagocytosis), further populated the lower half of the telencephalon from 18 to 24 gw. These findings are discussed in relation to developmental events that take place during the second trimester within the wall of the telencephalon