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At least 1,171 records · Page 65Linked to original sources
PubMed1999

The origin of organic matter in the Martian meteorite ALH84001.

Stable carbon isotope measurements of the organic matter associated with the carbonate globules and the bulk matrix material in the ALH84001 Martian meteorite indicate that two distinct sources are present in the sample. The delta 13C values for the organic matter associated with the carbonate globules averaged -26% and is attributed to terrestrial contamination. In contrast, the delta 13C values for the organic matter associated with the bulk matrix material yielded a value of -15%. The only common sources of carbon on the Earth that yield similar delta 13C values, other then some diagenetically altered marine carbonates, are C4 plants. A delta 13C value of -15%, on the other hand, is consistent with a kerogen-like component, the most ubiquitous form of organic matter found in carbonaceous chondrites such as the Murchison meteorite. Examination of the carbonate globules and bulk matrix material using laser desorption mass spectrometry (LDMS) indicates the presence of a high molecular weight organic component which appears to be extraterrestrial in origin, possibly derived from the exogenous delivery, of meteoritic or cometary debris to the surface of Mars.

Antarctic Regions↗
PubMed2002

White matter T(1) relaxation time histograms and cerebral atrophy in multiple sclerosis.

T(1) relaxation time (T(1)) provides a quantitative magnetic resonance imaging (MRI) parameter for evaluating tissue damage in the brain. We aimed to measure T(1) in the white matter of patients with multiple sclerosis (MS) and study relationships with cerebral atrophy, T(2) lesion load and clinical parameters. Twenty-six patients with relapsing-remitting MS and sixteen healthy controls were scanned with dual-echo T(2)-weighted, 3-dimensional (3-D) magnetization-prepared rapid acquisition gradient echo and whole brain, multi-slice inversion recovery (IR) sequences. White matter masks were defined on axial T(1) map slices using semi-automated seed growing and normalized 'total white matter' T(1) histograms generated. Atrophy data was obtained using the Cavalieri method of modern design stereology. T(2) lesion volume was also determined using seed growing.T(1) histogram-derived measures (median, peak height, peak position and standard deviation) in MS patients were significantly different (p < 0.0001) from controls. Median T(1) correlated significantly with supratentorial (r = 0.42, p = 0.036), lateral ventricle (r = 0.55, p = 0.004), and T(2) lesion volumes (r = 0.84, p < 0.0001), but not with clinical parameters. Total white matter T(1) provides a robust, quantitative measure of global disease burden in MS, and also correlates significantly with cerebral atrophy. Serial studies are required to determine its potential role as a surrogate marker of disease progression.

Adult↗
PubMed1998

Multiple system atrophy with severe involvement of the motor cortical areas and cerebral white matter.

We report multiple system atrophy (MSA) of 14 years' duration in a 75-year-old woman. Postmortem examination revealed pathological changes typical of MSA. Furthermore, neuronal loss with astrocytosis in the primary motor and premotor cortices, especially in the fifth and sixth layers, and extensive myelin and axonal loss in the frontal and parietal white matter were evident. There were numerous ubiquitin-positive oligodendroglial inclusions, which are characteristic of MSA, in these cortical and white matter lesions. These findings suggest that the motor cortical areas and cerebral white matter are sites of significant involvement in the MSA disease process and that inclusion-bearing oligodendroglial alterations contribute to the white matter degeneration.

Aged↗
PubMed1999

Magnetization transfer ratio in cerebral white matter lesions of Binswanger's disease.

We measured the magnetization transfer (MT) ratios in white matter lesions of Binswanger's disease (BD) and compared them with BD and with similar-appearing changes in non-demented elderly subjects and cerebral infarction. Four subject groups were studied: 30 patients with BD and periventricular hyperintensity (PVH) on MRI, 29 patients with ischemic cerebrovascular event with PVH but no dementia, 17 patients with old cerebral infarction, and 26 elderly control subjects. MT ratios were calculated for areas of PVH in BD and non-demented subjects, of infarction, and of normal-appearing white matter in controls. The decrease in MT ratios for areas in PVH of non-demented subjects and BD and in infarction compared with normal white matter in controls was 12, 20, and 35%, respectively. The MT ratio in PVH of BD was significantly lower than that in PVH of non-demented subjects, but not to the levels seen in areas of infarction. There was a significant high correlation between the Mini-Mental State Examination score and MT ratio for area of PVH (r = 0.790). MT ratio distinguishes PVH in BD patients from those in non-demented subjects, suggesting underlying histopathological differences. Tissue damage in white matter lesions of BD may be more severe than that in non-demented subjects, but not as much as with complete infarction.

Aged↗
PubMed2002

Natural organic matter (NOM) in a limed lake and its tributaries.

The chemistry of a limed lake and its main tributaries were studied for 3 years (1992-94) with an emphasis on natural organic matter (NOM). Increased transparency and decreased water colour indicated a general reduction of NOM in the lake. Increased A(254 nm)/A(410 nm) ratios in the epilimnion during summer and early autumn suggested degradation of higher molecular size organic matter into low molecular size NOM. Increase in ammonium and dissolved inorganic carbon concentrations in the lake was possibly due to the NOM degradation. Using budget calculations and the literature values, photodegradation and microbial activity were estimated to be the main mechanisms of the NOM removal. These mechanisms accounted for about 30-35% and 60-65% of the total loss of organic matter, respectively, in the summer and early autumn period. Low sedimentation rates indicate that co-precipitation of organic matter with calcium, aluminium and/or iron was of minor importance in these seasons.

Acid Rain↗
PubMed2002

Composition of particulate and dissolved organic matter in a disturbed watershed of southeast Brazil (Piracicaba River basin).

The elemental and isotopic composition of particulate and dissolved organic matter was investigated in the Piracicaba River basin, São Paulo State, Brazil. Comparison of riverine organic matter from the Piracicaba River basin, a region where rivers and streams receive urban sewage and industrial effluents, with data reported for the pristine Amazon system revealed significant differences associated with anthropogenic impacts. One important difference was N enrichment in the particulate organic material of the Piracicaba basin rivers, due to (a) urban and industrial effluents, and (b) enhanced phytoplankton growth, which results from the combination of nutrient enrichment and damming of sections of the rivers. Radiocarbon concentrations were overall more depleted (older 14C age) in the Piracicaba basin rivers than in the Amazon, which may reflect the importance of soil erosion in the former. Analyses of stable and radioactive carbon isotopes and lignin-derived compounds indicated that coarse particulate organic material is composed of a mixture of soil particles and degraded organic matter from C3 and C4 vascular plants. Fine particulate organic material was composed mainly of soil particles and phytoplankton cell remains, the latter especially during low water. Ultrafiltered dissolved organic matter was the most degraded fraction according to its lignin oxidation products, and showed the greatest influence of C4 plant sources.

Brazil↗
PubMed2003

Short- and long-term sorption/desorption of polycyclic aromatic hydrocarbons onto artificial solids: effects of particle and pore sizes and organic matters.

In order to elucidate the effect of nanopores and organic matters on sequestration of contaminants, short- and long-term sorption and desorption of naphthalene and pyrene in seven artificial solid-water systems were studied. Fast sorption occurred in every case; steady states were reached within 1-5h. Sorption constants varied drastically among the seven absorbents, ranging from 1.19 to 5.29 x 10(3) for naphthalene, and from 24.3 to 6.52 x 10(4) for pyrene. Slow sorption continued to take place in some cases, especially on absorbents containing humic matter. Desorption usually took place in two stages, fast and slow, on both unaged and aged absorbents. Irreversibility of desorption occurred for every absorbent except for silica particles modified with octadecyl silyl. Aging led to a reduction of fast desorption fraction due to entrapment of the chemicals into nanopores and partitioning of the chemicals into condensed areas of humic matters, and showed no effect on slow desorption and irreversibility of desorption. On the whole, entrapment into nanopores and partitioning into humic matters are considered to be important for sequestration of contaminants. Irreversibility of desorption is considered to be a more influencing factor than percentage of desorption for describing the extent of sequestration.

Adsorption↗
PubMed2003

UV-light induced mineralization of organic matter bound chlorine in Lake Bjän, Sweden--a laboratory study.

Surface water and aqueous solutions of isolated organic matter from a humic rich lake in southern Sweden were exposed to artificial UV radiation to investigate the UV light induced influence on organic matter bound chlorine in natural systems. It was found that the photodegradation of organic matter bound chlorine was more pronounced than the photodegradation of organic carbon. After 120 h of irradiation of the isolated organic matter, only 35% of the initial organochlorine was still in the solution compared to about 70% of the dissolved organic carbon (DOC). A similar result was obtained for unfractionated surface water. Furthermore, our results indicate that the loss of organic chlorine was mainly due to a mineralization of organic chlorine into chloride ions. The total decrease of organic chlorine after 120 h was 32 microg Cl(org) l(-1), of which the major part disappeared in the initial irradiation phase. A similar increase was observed in the chloride concentration (34 microg Cl(-) l(-1)).

Carbon↗
PubMed2001

Partitioning of copper onto suspended particulate matter in river waters.

Suspended particles and river water from the Susquehanna River, White Clay Creek and the Delaware River were collected to experimentally study the partitioning of copper. The effects of many factors that may influence the partitioning coefficient (Kd) including pH, total suspended solids (TSS), total copper concentration ([Cu]T), dissolved organic matter (DOM), particulate organic matter (POM), hardness, and ionic strength were investigated by performing batch adsorption experiments. The results implied that organic matter binding sites in both the aqueous and solid phases play the most important role in controlling copper partitioning. Other major factors governing the partitioning are pH and TSS. Kd increases with pH in the pH range 3-8. TSS increases caused decreases in Kd values, which may be attributed to the decrease in the quantity of available binding sites caused by interparticle interactions, rather than by the redistribution of organic matter between solid and solution phases with the variation of TSS. Kd decreases slightly when total Cu concentration increases; however, Kd can be considered to be independent of Cu concentration when TSS is high. The effects of calcium competition and ionic strength on partitioning are small.

Binding Sites↗
PubMed1999

Measured and modelled concentrations and vertical profiles of airborne particulate matter within the boundary layer of a street canyon.

Concentrations and vertical profiles of various fractions of airborne particulate matter (suspended particulate matter (SPM), PM10 and PM2.5) have been measured over the first three metres from ground in a street canyon. Measurements were carried out using automated near real-time apparatus called the Kinetic Sequential Sampling (KSS) system. KSS system is essentially an electronically-controlled lift carrying a real-time particle monitor for sampling air sequentially, at different heights within the breathing zone, which includes all heights within the surface layer of a street canyon at which people may breathe. Data is automatically logged at the different receptor levels, for the determination of the average vertical concentration profile of airborne particulate matter. For measuring the airborne particle concentration, a Grimm Dust Monitor 1.104/5 was used. The recorded data also allows for time series analysis of airborne particulate matter concentration at different heights. Time series data and hourly-average vertical concentration profiles in the boundary layer of the confines of a street are thought to be mainly determined by traffic emissions and traffic associated processes. Hence the measured data were compared with results of a street canyon emission-dispersion model in time and space. This Street Level Air Quality (SLAQ) model employs the plume-box technique and includes modules for simulating vehicle-generated effects such as thermally- and mechanically-generated turbulence and resuspension of road dust. Environmental processes, such as turbulence resulting from surface sensible heat and the formation of sulphate aerosol from sulphur dioxide exhaust emissions, are taken into account. The paper presents an outline description of the measuring technique and model used, and a comparison of the measured and modelled data.

Air Pollutants↗
PubMed2003

Progression of cerebral white matter lesions: 6-year results of the Austrian Stroke Prevention Study.

More than half of all elderly people have some degree of cerebral white matter lesions. However, the rate of progression of these lesions is uncertain. We aimed to assess the progression of lesions in community-dwelling volunteers aged 50-75 years without neuropsychiatric disease. We used MRI to grade and measure the total volume of white matter lesions in 296 volunteers at baseline, 3 years, and 6 years. 58 participants with no lesions and 123 with punctate abnormalities at baseline had a low tendency for lesion progression, whereas 14 participants with early confluent and nine with confluent lesions underwent median increases of 2.7 cm(3) (IQR 0.5-5.9) and 9.3 cm(3) (7.1-21.0), respectively, in lesion volume at 6 years. Lesion grade at baseline was the only significant predictor of lesion progression (p<0.0001). Punctate white matter lesions are not progressive and are thus benign, whereas early confluent and confluent white matter abnormalities are progressive, and thus malignant.

Aged↗
PubMed2003

Disturbance of oligodendrocyte development, hypomyelination and white matter injury in the neonatal rat brain after intracerebral injection of lipopolysaccharide.

Increasing data provide support for the hypothesis that brain inflammation plays an important role in injury to developing white matter. In the present study, inflammatory responses in the neonatal rat brain were investigated following lipopolysaccharide (LPS) administration at postnatal day 5. LPS-induced brain injury was examined in brain sections 24 h, 3 and 9 days after LPS injection. White matter rarefaction was observed in 50% of the rat brains (three out of six) 24 h after LPS injection. Lateral ventricle enlargement was found in 100% (four out of four) and 89% (eight out of nine) of rat brains 3 and 9 days after LPS administration, respectively. White matter necrosis was found in three out of nine brains injected with LPS on P14. None of these injuries was observed in any control rat brains. No histological changes in gray matter were noted in the LPS-injected rat brain. Proinflammatory cytokines, tumor necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) and interleukin-6 (IL-6), and inducible nitric oxide synthase (iNOS) in the rat brain were greatly induced after LPS administration. Activated astrocytes and microglia/macrophages were found in the affected rat brains. Double-labeling showed that IL-1beta and iNOS expressing cells were microglia/macrophages. Injury to or delayed development of immature oligodendrocytes (OLs) was evident by decreased immunostaining for both O4 and O1 antibodies, markers for developing immature OLs, in the LPS-injected as compared to the control rat brain. LPS also resulted in hypomyelination, as indicated by reduced myelin basic protein (MBP) immunostaining in the P8 rat brain. Co-administration of IL-1 receptor antagonist (IL-1Ra) with LPS reduced brain injury by improving myelination and subsequent reduction of lateral ventricle enlargement. These results indicate that developing OLs may be the target cells for LPS-induced brain injury and inflammatory cytokines are possible mediators of LPS-induced brain injury.

Animals↗
PubMed1999

Neuregulin and erbB receptor expression in normal and diseased human white matter.

Human white matter from non-neurologic cases, multiple sclerosis (MS) and other neurologic diseases (OND, inflammatory and non-inflammatory), was subjected to immunocytochemistry and Western blotting for expression of the neuregulin, glial growth factor-2 (GGF2), and its receptors, erbB2, erbB3 and erbB4. GGF2 has previously been shown to have mitogenic effects upon oligodendrocytes in vitro and an enhancing effect upon remyelination in animals with autoimmune demyelination. In all types of human white matter examined, expression of the ligand GGF2 and its three receptors was consistently found on oligodendrocytes, with higher levels being seen in cases of MS. Expression was also seen, albeit at lower levels, on astrocytes and microglial cells, the latter most commonly in MS and OND. In human lymph node tissue, some lymphocytes were positive for erbB2, erbB3 and erbB4. Western blots confirmed the presence of all three receptors in normal, MS and OND white matter. GGF2 and erbB receptor expression did not correlate with areas of remyelination and reactivity occurred throughout the tissue, with some increase in intensity at the edge of MS lesions. Examination of precursor oligodendrocyte immunoreactivity (with anti-PDGF-Ralpha and NG2), revealed widespread expression throughout both normal and diseased white matter. The presence of GGF2 and its receptors on oligodendrocytes and lymphocytes render this cell type a candidate for functional signaling via this pathway, perhaps in relationship to myelinating activity.

Blotting, Western↗
PubMed2001

Oligodendroglial cell death with DNA fragmentation in the white matter under chronic cerebral hypoperfusion: comparison between normotensive and spontaneously hypertensive rats.

We investigated the neuropathological and biochemical changes in the white matter of normotensive Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR) after bilateral carotid artery ligation (BCAL). One week after BCAL, both WKY and SHR showed white matter rarefaction and vacuolation with reduced oligodendrocytes, but there was no difference between WKY and SHR. On the other hand, vacuoles formed by oligodendroglial cell death were increased significantly from 2 to 4 weeks in the optic tract and fimbria fornix of hypoperfused SHR. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP in situ nick end labeling (TUNEL)-positive cells and lectin-positive microglia increased in number and intensities of staining more markedly in SHR than in WKY. In situ cell death detection ELISA supported these results quantitatively. RT-PCR represented the expression of TNF-alpha, TNF receptor 1 (p55), caspase-2 (Ich-1) and -3 (CPP32) mRNAs in both WKY and SHR brains after BCAL. Immunohistochemical analyses revealed that TNF-alpha, TNF receptor 1 (p55), Ich-1 and CPP32 immunoreactive cells could also be detected in the white matter regions of hypoperfused SHR. These results suggested that local production of TNF-alpha by the activated microglia might selectively induce oligodendroglial cell death through the death domain-containing TNF receptor 1 (p55), caspase-2 or -3 activation, resulting in white matter changes as a primary pathological feature.

Animals↗
PubMedDate not supplied

Age-induced white matter changes in the human brain: a stereological investigation.

In the present pilot study, age-related white matter changes were investigated by the use of design-based stereological methods. In the brains of elderly subjects, the total volume of the white matter and the total volume of the myelinated fibers therein were lower than in those of young subjects (15% and 17%, respectively), but the differences were not statistically significant. The total length of the myelinated fibers of the white matter in the elderly group of 86,000 km was, statistically, significantly decreased by 27% compared with 118,000 km in the young group. This loss of the total nerve fiber length was accompanied in particular by a decline of the myelinated fibers with a small diameter. The mean diameter of the myelinated fibers in the young group was significantly smaller than in the old group, but the relative size distributions of the myelinated fiber diameters between the young and old groups were similar. Our findings show that the atrophy of the human white matter during ageing is probably caused by a loss of myelinated fibers with a small diameter.

Adult↗
PubMed1999

The origin of organic matter in the Martian meteorite ALH84001.

Stable carbon isotope measurements of the organic matter associated with the carbonate globules and the bulk matrix material in the ALH84001 Martian meteorite indicate that two distinct sources are present in the sample. The delta 13C values for the organic matter associated with the carbonate globules averaged -26% and is attributed to terrestrial contamination. In contrast, the delta 13C values for the organic matter associated with the bulk matrix material yielded a value of -15%. The only common carbon sources on the Earth that yield similar delta 13C values, other then some diagenetically altered marine carbonates, are C4 plants. A delta 13C value of -15%, on the other hand, is consistent with a kerogen-like component, the most ubiquitous form of organic matter found in carbonaceous chondrites such as the Murchison meteorite. Examination of the carbonate globules and bulk matrix material using laser desorption mass spectrometry (LDMS) indicates the presence of a high molecular weight organic component which appears to be extraterrestrial in origin, possibly derived from the exogenous delivery of meteoritic or cometary debris to the surface of Mars.

Amino Acids↗
PubMed2000

Glutamine synthetase activities in spinal white and gray matter 7 days following spinal cord injury in rats.

The glial enzyme glutamine synthetase (GS) is critical for central nervous system catabolism of glutamate and glutamine production. Upregulation of GS is a hallmark of reactive astrocytosis, although such induction following spinal cord injury (SCI) has not been reported. This study's purpose was to determine if GS activity is increased following SCI. Experimental rats received a complete spinal transection at the T5 segment and control rats received a laminectomy only. GS activities were determined using an enzymatic microassay. Glutamine levels were resolved in semi-adjacent sections. At 7 days following SCI, GS activity increased an average of 170-190% in white matter and 15-25% in gray matter immediately adjacent to the transection, and 70-90% in white matter and 40-45% in gray matter from cervical and lumbar enlargements. Correlative increases in glutamine were observed also. These findings further characterize the astrocytic response to SCI, which may contribute to altered glutamine metabolism in injured spinal tissue.

Animals↗
PubMed2003

Plasma vitamin C, cholesterol and homocysteine are associated with grey matter volume determined by MRI in non-demented old people.

We studied 82 non-demented old people and, using MRI, derived measures of grey and white matter and intracranial volumes. Controlling for sex and intracranial volume, we related grey and white matter volumes to plasma concentrations of vitamins C, B(12), folate, homocysteine, cholesterol, triglycerides, high density and low density (LDL) lipoproteins, and to red blood cell folate and glycated haemoglobin concentrations (HbA1(c)). We found that lower grey matter volume was associated with lower plasma vitamin C and higher homocysteine, cholesterol and LDL. Lower blood cell folate was also associated with lower grey matter volume but HbA1(c) was not. These data are consistent with the putative benefits of dietary vitamin C and folate intake and the role of cholesterol in age related neurodegeneration.

Aged↗