bluuebunny/crossref_metadata_2025 huggingface dataset:
Columnar joint morphology and cooling rate: A starch‐water mixture experiment
Authors: Toramaru A. , Matsumoto T.
Published: February 2004

An analogue experiment using a starch‐water mixture has been carried out in order to understand the effect of cooling rate on the morphological characteristics of a basalt columnar joint. If the contraction of material is essential for the formation of columnar joint structure, the water loss rate by desiccation (hereafter referred to as desiccation rate) in the experiment is analogous to the cooling rate in solidifying basalt. In the experiment the desiccation rate is controlled by varying the distance between the starch‐water mixture and a lamp used as the heat source. We find that there are three regimes in the relation between joint formation and desiccation rate: (1) At desiccation rates higher than ∼1.4 × 10−2 (g cm−2 h−1) (normal columnar joint regime), the average cross‐sectional area S of a column is inversely proportional to the average desiccation rate, 〈〉 (i.e., S ∝ 〈〉−δ, with δ = 1). (2) Between that desiccation rate and a critical desiccation rate, 0.8 × 10−2 (g/cm2h), S approaches infinity as 〈〉 decreases close to a critical desiccation rate (i.e., exponent δ monotonically increases from unity to infinity) (critical regime). (3) Below the critical desiccation rate, no columnar structure forms (no columnar joint regime forms). Applying the present experimental result to the formation of basalt column, the basalt columnar cross‐sectional area is inversely proportional to the cooling rate with factors including elasticity, crack growth coefficient, thermal expansion, glass transition temperature, and crack density ratio at stress maximum. Also, it can be predicted that there exists a critical cooling rate below which the columnar joint does not form; the presence of a critical regime between the normal columnar jointing and no columnar jointing during a certain cooling rate range can also be predicted. We find that at higher cooling rate the preferred column shape is a pentagon, whereas at lower cooling rate it is a hexagon.
Methyl bromide and methyl chloride in the Southern Ocean
Authors: Yvon‐Lewis Shari A. , King Daniel B. , Tokarczyk Ryszard , Goodwin Kelly D. , Saltzman Eric S. , Butler James H.
Published: February 2004

Air and water concentrations of methyl bromide (CH3Br) and methyl chloride (CH3Cl) were measured in the Southern Ocean (latitudes 45°–67°S, longitudes 144°–139°E) from late October through mid‐December 2001. CH3Br and CH3Cl were undersaturated with mean saturation anomalies of −39 ± 11% and −37 ± 11% between 45° and 65°S. The minimum degradation rate constants needed to maintain these saturation anomalies are consistent with the observed total degradation rate constants, suggesting that there is no significant production of these gases in this region. Near the Antarctic coast (south of 65°S) the saturation anomalies for both gases decreased to approximately −80%, although CFC‐11 measurements suggest these extreme anomalies are associated with enhanced vertical mixing rather than with degradation in the surface waters.
Shoaling of subharmonic gravity waves
Authors: Battjes J. A. , Bakkenes H. J. , Janssen T. T. , van Dongeren A. R.
Published: February 2004

In this paper the energy budget of wave group‐induced subharmonic gravity waves in the nearshore region is examined on the basis of the energy equation for long waves in conjunction with analyses of a high‐resolution laboratory data set of one‐dimensional random wave propagation over a barred beach. The emphasis is on the growth of forced subharmonics and the deshoaling of the reflected free waves in the shoaling zone. The incident lower‐frequency subharmonics are nearly fully reflected at the shoreline, but the higher‐frequency components appear to be subject to a significant dissipation in a narrow inshore zone including the swash zone. The previously reported phase lag of the incident forced waves behind the short‐wave groups is confirmed, and its key role in the transfer of energy between the grouped short waves and the shoaling bound waves is highlighted. The cross‐shore variation of the local mean rate of this energy transfer is determined. Using this as a source function in the wave energy balance allows a very accurate prediction of the enhancement of the forced waves in the shoaling zone, where dissipation is insignificant. The phase lag appears to increase with increasing frequency, which is reflected in a frequency‐dependent growth rate, varying very nearly from the free‐wave variation ∼ h−1/4 (Green's law) for the lower frequencies to the shallow‐water equilibrium limit for forced subharmonics ∼h−5/2 for the higher frequencies. This observed frequency dependence is tentatively generalized to a dependence on a normalized bed slope, controlling whether a so‐called mild‐slope regime or a steep‐slope regime prevails, in which enhanced incident forced waves dominate over breakpoint‐generated waves or vice versa.
Geographical distribution and interseasonal variability of tropical deep convection: UARS MLS observations and analyses
Authors: Jiang Jonathan H. , Wang Bin , Goya Kenshi , Hocke Klemens , Eckermann Stephen D. , Ma Jun , Wu Dong L. , Read William G.
Published: February 2004

Tropical deep convection and its dynamical effect on the tropopause and stratosphere are investigated using a suite of data from the Upper Atmospheric Research Satellite (UARS) Microwave Limb Sounder (MLS), including upper tropospheric humidity, cloud radiance, and gravity wave measurements. For this purpose, geographical distributions of temperature, water vapor, and cloudiness in the tropical tropopause layer (TTL) are compared with corresponding maps of gravity wave variance in the stratosphere. In addition, ECMWF global wind divergent and velocity potential fields as well as NOAA outgoing longwave radiation and CMAP rainfall data are analyzed to help pinpoint the locations of deep convection. We found that high‐altitude clouds near the bottom of TTL (∼147 hPa) are usually surrounded by high‐humidity air, and their spatial pattern and seasonal variability are closely associated with regions of vigorous summertime deep convection. Upward propagating gravity waves generated from these convection regions are shifted poleward by prevailing stratospheric winds. We estimate that tropical deep convection lifts ∼5% of the cloud tops to altitudes above 100 hPa and that most of the extreme deep convection events occur in the Western Pacific and Indian monsoon regions. Low‐temperature regions in the TTL are associated with, but often drift away from, the center of deep convection. Regions of water vapor maxima near the bottom of TTL are located directly above the deep convection centers, but this moisture behavior is somewhat reversed at the top of the TTL. The integrated picture derived from this study implies that convective scale motions could be important in affecting short‐term dehydration processes in the TTL. Our results also suggest that the spatial organization and temporal development of tropical convective systems will be better monitored with the follow‐on Earth Observing System (EOS) Aura satellite instruments and lead to improved understanding of the complex interaction of tropical convection with large‐scale dynamic and thermodynamic conditions.
Diffuse emission of organic trace gases from the flank and crater of a quiescent active volcano (Vulcano, Aeolian Islands, Italy)
Authors: Schwandner Florian M. , Seward Terry M. , Gize Andrew P. , Hall P. Anthony , Dietrich Volker J.
Published: February 2004

Volcanoes discharge a range of inorganic major gas species (e.g., H2O, CO2, SO2, and CO) not only during eruptions but also during quiescent phases through fumarolic and diffuse degassing in their craters and on their flanks. The emission of organic trace gases from volcanoes is similarly not expected to be restricted to discrete fumarolic gas discharges alone. To test this hypothesis, we have sampled soil gas emissions for organic compounds and determined CO2 fluxes along a profile extending from the vegetated base of the active La Fossa cone (Vulcano Island, Italy) over the unvegetated volcanic flank and up into the crater rim and base and then continuing over fumarolic areas. The results indicate that the majority of volatile organic compounds in the soil gas show significant increases in concentration toward the crater and fumaroles and that diffuse emissions contribute significantly to the volcanic halocarbon source strength. Emissions of the halocarbon CFC‐11 (CCl3F) correlate well with soil CO2 fluxes measured on site (R2 = 0.89, slope = 1.42 ± 0.1) and both increase toward the crater and fumaroles. Other ozone‐depleting substances were found in concentrations significantly above those found in field and system blanks, including CH3Br, CH3Cl, CH3I, C2H5Br, and chlorinated benzenes. Abundances ranged from upper pptv to ppmv; for example, the maximum observed CFC‐11 concentrations were 1200 pptv in diffuse emissions and 3700 pptv in dry fumarolic gas (average dry air is 268 pptv). On the basis of these results the natural volcanic source strength of halocarbon emissions to the atmosphere requires reevaluation, and in some cases, correction to higher values. Global average fumarolic and diffuse halocarbon source strengths were estimated and scaled to known global volcanic fumarolic and diffuse CO2 flux data. Among these were CFC‐11 (8.56 ± 4.7 × 10−6 Tg y−1), CH3Br (0.98 ± 0.47 × 10−6 Tg y−1), CHCl3 (94.9 ± 27.6 × 10−6 Tg y−1), and CCl4 (3.41 ± 1.0 × 10−6 Tg y−1).
Relative humidity dependence of HONO chemistry in urban areas
Authors: Stutz Jochen , Alicke Björn , Ackermann Ralf , Geyer Andreas , Wang Shuhui , White Allen B. , Williams Eric J. , Spicer Chester W. , Fast Jerome D.
Published: February 2004

The role of nitrous acid, HONO, as a precursor for hydroxyl radicals in polluted urban air has been recognized for many years. The chemical processes leading to the formation of HONO are, however, still not well understood. Laboratory studies show that HONO formation occurs primarily on surfaces and is first order in NO2. Water also plays an important role in the conversion process. While the latter has been shown in the laboratory, little information is available regarding the influence of water on the NO2 and HONO chemistry in the real atmosphere. Here we present nocturnal DOAS measurements of HONO and NO2 from three field experiments. The observations show that [HONO]/[NO2] ratios between 10 and 30% relative humidity (RH) do not exceed 0.04, while values of up to 0.09 were observed at higher RH. These results are analyzed by interpreting the observed maximum [HONO]/[NO2] ratio at a given relative humidity as the pseudo steady state (PSS) between the heterogeneous NO2 to HONO conversion and the HONO loss on surfaces. Theoretical considerations show that the [HONO]/[NO2] ratio at the PSS is equal to the ratio of the heterogeneous NO2 to HONO conversion coefficient and the reactive HONO uptake coefficient, thus showing that these processes depend on the RH. This result implies that RH has to be considered in the parameterization of HONO formation in air pollution models.
Pore water pressure assessment in a forest watershed: Simulations and distributed field measurements related to forest practices
Authors: Dhakal Amod S. , Sidle Roy C.
Published: February 2004

A distributed shallow groundwater model related to slope stability is described to assess the spatial distribution of pore water pressure in steep forested terrain in British Columbia. Additionally, effects of timber harvesting and roads on measured changes in pressure head during rainstorms were evaluated for the first time to assess the need for incorporating different hydrological components in the event‐driven distributed model. Although explicit spatial quantification of pore water pressure requires many measurements for accurate prediction, model performance using average parameter values was reasonable when compared with pressure heads measured at nine spatially distributed sites. Increases in maximum pressure head (varying from 9 to 28 cm) between preharvesting (after road construction) and postharvesting rainstorm events were observed in seven of nine sites. The remaining two sites showed either a small decrease (≈5 cm) or similar peak pressure heads following harvesting. Peak pressure head evaluated at one piezometer located 46 m downslope of the road decreased substantially (≈50 cm) after road construction during moderate rainstorms and then recovered following harvesting. Piezometric responses in sites upslope of the road were not affected by road construction but did increase after harvesting. Moderate storms caused the largest relative increases in pressure head between preharvesting (after roads) and postharvesting conditions; such increases were small during large storms, lending support to the idea that timber harvesting in temperate forests enhances hydrologic response only during small and moderate storms. Since landslides in coastal Pacific Northwest are typically caused by large winter rainstorms, it appears more justified to include better spatial representation of soil physical and engineering parameters in the distributed shallow groundwater model compared to specifying evapotranspiration; road hydrology may, however, need to be included.
Fluid motion through an unsaturated fracture junction
Authors: Dragila Maria Ines , Weisbrod Noam
Published: February 2004

Fluid dynamics in unsaturated fracture intersections were experimentally investigated in a glass fracture‐analog at four different flow rates and compared with theoretical behavior estimates. The experimental system consisted of a vertical fracture that divided into two fracture branches. Visual data of fluid behavior were collected using digital stills and video. Two flow modes were analyzed: film flow and capillary droplets accompanied by snapping rivulets. Even under almost ideal experimental conditions, fluid dynamics at the intersection were extremely complicated and strongly influenced by flow mode, dynamics in the main fracture, contact angle of the advancing meniscus, and the presence of a capillary barrier at the intersection. Film flow moved into one or both branches through a capillary bridge that formed above the intersection. In droplet mode, rivulets reached lengths of up to 70 cm prior to snapping, and often stretched contiguously across the intersection and into both branches while maintaining its connection to the two droplet halves. Transition from droplet to film flow mode was observed at the intersection. There was a strong correlation between the length of the incoming droplet and the potential for a switch to occur. Liquid bridges were observed to form occasionally at the entrance of a fracture branch, which blocked further liquid entry. The temporal nature of these blockages further complicates temporal and spatial variability observed in flow in fracture systems.
Stochastic simulation of radionuclide migration in discretely fractured rock near the Äspö Hard Rock Laboratory
Authors: Cvetkovic V. , Painter S. , Outters N. , Selroos J. O.
Published: February 2004

We study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network. The rock volume is on a 100 m scale and is a replica of a thoroughly characterized site at the Äspö Hard Rock Laboratory, Sweden. Flow is driven by generic boundary conditions consistent with the natural gradient in the region. The emphasis is on the global effect of fracture‐to‐fracture hydraulic variability where individual fractures are assumed to be of uniform aperture. The transport measures are conditioned on two random variables: the water residence time (τ) and a parameter which quantifies the hydrodynamic control of retention (β). Results are illustrated for two radionuclides: technetium (strongly sorbing) and strontium (weakly sorbing). It is found that the assumption of streamline routing or full mixing at fracture intersections has comparatively little impact on transport. The choice of the cubic or quadratic hydraulic law (i.e., relation between transmissivity and aperture) strongly affects water residence times but has little impact on average transport since it does not affect the statistics of β. If the statistics of β are known, then the distribution of water residence time (τ) is of little importance for transport. We assess the applicability of a linearized model β = τ/bret using two different approaches to estimate the effective “retention” aperture 2bret: from transmissivity data and from fracture density and flow porosity data. Under some conditions, these conventional estimates may provide acceptable representation of transport. The results stress the need for further studies on upscaling of τ, β distributions as well as on estimating effective parameters for hydraulic control of retention.
Multifractal analysis of river networks: Sandbox approach
Authors: De Bartolo Samuele G. , Gaudio Roberto , Gabriele Salvatore
Published: February 2004

Two fixed‐size algorithms were used to investigate natural river networks: the box‐counting method and the sandbox method. The first produces good results for nonnegative moment orders, q, but suffers from border effects. The second solves border problems and is particularly adapted to negative moment orders for the reconstruction of the right side of the multifractal spectrum, f(α). In the box‐counting applications the influence of the mesh number was investigated in the range 20 to 100, for moment orders from 0 to 10, showing that the error in the assessment of the generalized fractal dimensions is not greater than 3%. The sandbox method was applied to the river networks for the first time, and the theoretical expression of the information entropy was derived. Results were obtained also for negative moment orders, showing that the analyzed river networks are multifractal and non‐plane‐filling structures. The sandbox method avoids border effects, as verified through an application to a square portion extracted from a river network. Result analysis suggests a dependence of the f(α) spectra from the lithologic characteristics of the source rocks.
Temporal dissection of Bax‐induced events leading to fission of the single mitochondrion in Trypanosoma brucei
Authors: Esseiva Anne Crausaz , Chanez Anne‐Laure , Bochud‐Allemann Natacha , Martinou Jean‐Claude , Hemphill Andrew , Schneider André
Published: February 2004

The protozoan Trypanosoma brucei has a single mitochondrion and lacks an apoptotic machinery. Here we show that expression of the proapoptotic protein Bax in T. brucei causes the release of cytochrome c, the depolarization of the mitochondrial membrane potential and mitochondrial fission. However, in contrast to mammalian cells, the three events are temporally well separated. The release of cytochrome c from the intermembrane space precedes mitochondrial fission, showing that it does not depend on mitochondrial fragmentation. Furthermore, halting Bax expression allows some cells to recover even after mitochondrial fission, the last recorded event, went to completion, indicating that all three Bax‐induced events are, in principle, reversible.
A comparison of cross‐hole electrical and seismic data in fractured rock
Authors: Herwanger J.V. , Worthington M.H. , Lubbe R. , Binley A. , Khazanehdari J.
Published: February 2004

Cross‐hole anisotropic electrical and seismic tomograms of fractured metamorphic rock have been obtained at a test site where extensive hydrological data were available. A strong correlation between electrical resistivity anisotropy and seismic compressional‐wave velocity anisotropy has been observed. Analysis of core samples from the site reveal that the shale‐rich rocks have fabric‐related average velocity anisotropy of between 10% and 30%. The cross‐hole seismic data are consistent with these values, indicating that observed anisotropy might be principally due to the inherent rock fabric rather than to the aligned sets of open fractures. One region with velocity anisotropy greater than 30% has been modelled as aligned open fractures within an anisotropic rock matrix and this model is consistent with available fracture density and hydraulic transmissivity data from the boreholes and the cross‐hole resistivity tomography data. However, in general the study highlights the uncertainties that can arise, due to the relative influence of rock fabric and fluid‐filled fractures, when using geophysical techniques for hydrological investigations.
Geophysical exploration for interlayer slip breccia gold deposits: example from Pengjiakuang gold deposit, Shandong Province, China
Authors: Qingdong Z. , Yuanchao S. , Tiebing L. , Guangming L. , Qirui Z. , Kunfa S. , Hongchen L. , Xiuying S. , Jinzhong Y.
Published: February 2004

Interlayer slipping breccia‐type gold deposit – a new type of gold deposit, defined recently in the northern margin of the Jiaolai Basin, Shandong Province, China – occurs in interlayer slip faults distributed along the basin margin. It has the features of large orebody thickness (ranging from 14 m to 46 m, with an average thickness of 30 m), shallow embedding (0–50 m thickness of cover), low tenor of gold ore (ranging from 3 g/t to 5 g/t), easy mining and ore dressing. This type of gold deposit has promising metallogenic forecasting and potential for economic exploitation.

A ground gamma‐ray survey in the Pengjiakuang gold‐ore district indicates that the potassium/thorium ratio is closely related to the mineralization intensity, i.e. the larger the potassium/thorium ratio, the higher the mineralization. The gold mineralized alteration zone was defined by a potassium/thorium ratio of 0.35. A seismic survey confirms the location of the top and bottom boundaries and images various features within the Pengjiakuang gold mineralization belt. The gold‐bearing shovel slipped belt dips to the south at an angle of 50–55° at the surface and 15–20° at depth. The seismic profile is interpreted in terms of a structural band on the seismic section characterized by a three‐layered model. The upper layer is represented by weakly discontinuous reflections that represent the overlying conglomerates. A zone of stronger reflections representing the interlayer slip fault (gold‐bearing mineralized zone) is imaged within the middle of the section, while the strongest reflections are in the lower part of the section and represent metamorphic rocks at depth. At the same time, the seismic reflection survey confirms the existence of a granite body at depth, indicating that ore‐forming fluids may be related to the granite. A CSAMT survey showed that the gold‐bearing mineralized zone is a conductive layer and contains a low‐resistivity anomaly ranging from 2 Ωm to 200 Ωm.
Nucleotide sequence identification of Cryphonectria hypovirus 1 infecting Cryphonectria parasitica on grafted American chestnut trees 12–18 years after inoculation with a hypovirulent strain mixture
Authors: Griffin G. J. , Robbins N. , Hogan E. P. , Farias‐Santopietro G.
Published: February 2004

Natural blight cankers on grafted American chestnut Castanea dentata trees were inoculated with one French‐derived hypovirulent Cryphonectria parasitica strain, with a predominantly orange‐pigmented colony phenotype and three Italian hypovirulent C. parasitica strains, with a predominantly white colony phenotype, in 1982 and 1983. Cryphonectria hypovirus 1 (CHV1) dsRNA was extracted from the four inoculated strains and from 11 predominantly white or orange pigmented C. parasitica isolates recovered from blight‐controlled cankers on the grafted trees during 1994–2000; cDNAs were made by reverse transcriptase‐polymerase chain reaction for two hypovirus regions: (i) an 844‐bp region in the helicase domain of open reading frame B (ORF B), designated OB and (ii) an 894‐bp region that included part of the 5′ non‐coding region and part (p29) of ORF A (5′OA). Nucleotide sequence analysis indicated that hypovirus isolates from the grafted trees and Italian inoculated strains had high homologies (identities) to each other and high homologies for OB (98.7–99.9%) and 5′OA (99.2–99.6%) to reference hypovirus, CHV1‐Euro7; homologies to reference hypovirus, CHV1‐EP713, were low (≤89.8%). In contrast, the hypovirus from the predominantly pigmented, French‐derived inoculated strain had high homologies for OB (99.1%) and 5′OA (99.7%) to reference CHV1‐EP713, and low homologies (87.7–89.7%) to the predominantly pigmented grafted‐tree isolates. These results provide strong evidence that hypoviruses present in the two predominantly pigmented isolates and nine predominantly white isolates of C. parasitica from the grafted trees were of Italian inoculated hypovirulent strain origin. For the Phe(25) through Gln(73) phenotype‐determinant region in p29 of 5′OA, hypovirus isolate amino acid sequences were dependent on whether they were CHV1‐Euro7 or CHV1‐EP713 hypoviruses, but predominantly white and predominantly pigmented phenotypes within CHV1‐Euro7 or within CHV1‐EP713 had identical amino acid sequences. Grafted‐tree hypovirus isolates infecting the predominantly pigmented C. parasitica isolates may originate from chance transmission and replication of a CHV1‐Euro7 hypovirus variant or variant mixture, possibly present in one or more of the Italian inoculated hypovirulent strains, such as Ep 49.
Diazepam‐induced adaptive plasticity revealed by α1 GABAA receptor‐specific expression profiling
Authors: Huopaniemi Laura , Keist Ruth , Randolph Ann , Certa Ulrich , Rudolph Uwe
Published: February 2004

Benzodiazepines are in wide clinical use for their sedative and tranquilizing actions, the former being mediated via α1‐containing GABAA receptors. The signal transduction pathways elicited beyond the receptor are only poorly understood. Changes of transcript levels in cerebral cortex induced by acute diazepam administration were therefore compared by microarray analysis between wild‐type and point mutated α1(H101R) mice, in which the α1 GABAA receptor subunit had been rendered insensitive to diazepam. In wild‐type animals, diazepam reduced the expression levels of the α subunit of the calcium/calmodulin‐dependent protein kinase II, as well as brain‐derived neurotrophic factor, MAP kinase phosphatase, transcription factor GIF, c‐fos and nerve growth factor induced gene‐A. None of these transcripts was changed in the α1(H101R) mice after treatment with diazepam. Thus, the sedative action of diazepam is correlated with a selective down‐regulation of transcripts involved in the regulation of neuronal plasticity and neurotrophic responses. Most transcript changes were transient except for the decrease of the CaMKIIα transcript which persisted even 40 h after the single dose of diazepam. This long‐term alteration is likely to contribute to the resetting of the neuronal responsiveness, which may be involved in rebound phenomena and, under chronic treatment, in the development of tolerance and dependence.
Identification of regulated genes during permanent focal cerebral ischaemia: characterization of the protein kinase 9b5/MARKL1/MARK4
Authors: Schneider Armin , Laage Rico , Von Ahsen Oliver , Fischer Achim , Rossner Moritz , Scheek Sigrid , Grünewald Sylvia , Kuner Rohini , Weber Daniela , Krüger Carola , Klaussner Bettina , Götz Bernhard , Hiemisch Holger , Newrzella Dieter , Martin‐Villalba Ana , Bach Alfred , Schwaninger Markus
Published: February 2004

Cerebral ischaemia induces transcriptional changes in a number of pathophysiologically important genes. Here we have systematically studied gene expression changes after 90 min and 24 h of permanent focal ischaemia in the mouse by an advanced fragment display technique (restriction‐mediated differential display). We identified 56 transcriptionally altered genes, many of which provide novel hints to ischaemic pathophysiology. Particularly interesting were two pro‐apoptotic genes (Grim19 and Tdag51), whose role in cerebral ischaemia and neuronal cell death has not been recognized so far. Among the unknown sequences, we identified a gene that was rapidly and transiently up‐regulated. The encoded protein displayed high homology to the MARK family of serine–threonine protein kinases and has recently been described as MARKL1/MARK4. Here we demonstrate that this protein is a functional protein kinase with the ability to specifically phosphorylate a cognate peptide substrate for the AMP‐kinase family. Upon overexpression in heterologous cells, the functional wild‐type protein, but not its kinase‐dead mutant, led to decreased cell viability. We conclude that the up‐regulation of this kinase during focal ischaemia may represent an interesting new target for pharmacological intervention.
Tau exon 10, whose missplicing causes frontotemporal dementia, is regulated by an intricate interplay of cis elements and trans factors
Authors: Wang Junning , Gao Qing‐Sheng , Wang Yingzi , Lafyatis Robert , Stamm Stefan , Andreadis Athena
Published: February 2004

Tau is a microtubule‐associated protein whose transcript undergoes complex regulated splicing in the mammalian nervous system. In humans, exon 10 of the gene is an alternatively spliced cassette which is adult‐specific and which codes for a microtubule binding domain. Mutations that affect splicing of exon 10 have been shown to cause inherited frontotemporal dementia (FTDP). In this study, we reconstituted naturally occurring exon 10 FTDP mutants and classified their effects on its splicing. We also carried out a comprehensive survey of the influence of splicing regulators on exon 10 inclusion and tentatively identified the site of action for several of these factors. Lastly, we identified the domains of regulators SWAP and hnRNPG, which are required for regulation of exon 10 splicing.
Iron accumulation, iron‐mediated toxicity and altered levels of ferritin and transferrin receptor in cultured astrocytes during incubation with ferric ammonium citrate
Authors: Hoepken Hans H. , Korten Till , Robinson Stephen R. , Dringen Ralf
Published: February 2004

The cellular uptake and storage of iron have to be tightly regulated in order to provide iron for essential cellular functions while preventing the iron‐catalysed generation of reactive oxygen species (ROS). In contrast to cells in other organs, little is known about the regulation of iron metabolism in brain cells, particularly in astrocytes. To investigate the regulation of iron metabolism in astrocytes we have used primary astrocyte cultures from the brains of newborn rats. After application of ferric ammonium citrate (FAC), cultured astrocytes accumulated iron in a time‐ (0–48 h) and concentration‐dependent (0.01–1 mm) manner. This accumulation was prevented if FAC was applied in combination with the iron‐chelator deferoxamine (DFX). Application of FAC to astrocyte cultures caused a strong increase in the cellular content of the iron storage protein ferritin and a decrease in the amount of transferrin receptor (TfR), which is involved in the transferrin‐mediated uptake of iron into cells. In contrast, application of DFX strongly increased the level of TfR. Both up‐regulation of ferritin content by iron application and up‐regulation of TfR content by DFX were prevented by the protein synthesis inhibitor cycloheximide (CHX). During incubation of astrocytes with FAC, a mild and transient increase in the extracellular activity of the cytosolic enzyme lactate dehydrogenase and in the concentration of intracellular ROS was observed. In contrast, prevention of protein synthesis by CHX during incubation with FAC resulted in significantly more cell loss and a persistent and intense increase in the production of intracellular ROS. These results demonstrate that both iron accumulation and deprivation modulate the synthesis of ferritin and TfR in astrocytes and that protein synthesis is required to prevent iron‐mediated toxicity in astrocytes.
Massive accumulation of N‐acylethanolamines after stroke. Cell signalling in acute cerebral ischemia?
Authors: Berger Christian , Schmid Patricia C. , Schabitz Wolf‐Ruediger , Wolf Margit , Schwab Stefan , Schmid Harald H. O.
Published: February 2004

We investigated levels and compositions of N‐acylethanolamines (NAEs) and their precursors, N‐acyl phosphatidylethanolamines (N‐acyl PEs), in a rat stroke model applying striatal microdialysis for glutamate assay. Rats (n = 18) were treated with either intravenous saline (control), NMDA receptor antagonist MK801 (1 mg/kg), or CB1 receptor antagonist SR141716A (1 mg/kg) 30 min after permanent middle cerebral artery occlusion (MCAO). MK801 significantly attenuated the release of glutamate in the infarcted striatum (79 ± 22 μmol/L) as compared with controls (322 ± 104 μmol/L). The administration of CB1 antagonist SR141716A had no statistically significant effect on glutamate release (340 ± 89 μmol/L), but reduced infarct volume at 5 h after MCAO significantly by approximately 40%, whereas MK801 treatment resulted in a non‐significant (18%) reduction of infarct volume. In controls, striatal and cortical NAE concentrations were about 30‐fold higher in the infarcted than in the non‐infarcted hemisphere, whereas ipsilateral N‐acyl phosphatidylethanolamine (N‐acyl PE) levels exceeded contralateral levels by only a factor of two to three. Treatment with MK801 or SR141716A, or glutamate release in the infarcted tissue, had no significant effect on these levels. NAE accumulation during acute stroke may be due to increased synthesis as well as decreased degradation, possibly by inhibition of fatty acid amide hydrolase (FAAH).
Opposite modulatory roles for adenosine A1and A2Areceptors on glutamate and dopamine release in the shell of the nucleus accumbens. Effects of chronic caffeine exposure
Authors: Quarta Davide , Ferré Sergi , Solinas Marcello , You Zhi‐Bing , Hockemeyer Jörg , Popoli Patrizia , Goldberg Steven R.
Published: February 2004

Previous studies have demonstrated opposing roles for adenosine A1and A2Areceptors in the modulation of extracellular levels of glutamate and dopamine in the striatum. In the present study, acute systemic administration of motor‐activating doses of the A2Areceptor antagonist MSX‐3 significantly decreased extracellular levels of dopamine and glutamate in the shell of the rat nucleus accumbens (NAc) and counteracted both dopamine and glutamate release induced by systemic administration of motor‐activating doses of either the A1receptor antagonist CPT or caffeine. Furthermore, exposure to caffeine in the drinking water (1 mg/mL, 14 days) resulted in tolerance to the effects of systemic injection of CPT or caffeine, but not MSX‐3, on extracellular levels of dopamine and glutamate in the NAc shell. The present results show: first, the existence of opposite tonic effects of adenosine on extracellular levels of dopamine and glutamate in the shell of the NAc mediated by A1and A2Areceptors; second, that complete tolerance to caffeine's dopamine‐ and glutamate‐releasing effects which develops after chronic caffeine exposure is attributable to an A1receptor‐mediated mechanism. Development of tolerance to the dopamine‐releasing effects of caffeine in the shell of the NAc may explain its weak addictive properties and atypical psychostimulant profile.
Rat brain arachidonic acid metabolism is increased by a 6‐day intracerebral ventricular infusion of bacterial lipopolysaccharide
Authors: Rosenberger Thad A. , Villacreses Nelly E. , Hovda Jonathan T. , Bosetti Francesca , Weerasinghe Gayani , Wine Robert N. , Harry G. Jean , Rapoport Stanley I.
Published: February 2004

In a rat model of acute neuroinflammation, produced by a 6‐day intracerebral ventricular infusion of bacterial lipopolysaccharide (LPS), we measured brain activities and protein levels of three phospholipases A2 (PLA2) and of cyclo‐oxygenase‐1 and ‐2, and quantified other aspects of brain phospholipid and fatty acid metabolism. The 6‐day intracerebral ventricular infusion increased lectin‐reactive microglia in the cerebral ventricles, pia mater, and the glial membrane of the cortex and resulted in morphological changes of glial fibrillary acidic protein (GFAP)‐positive astrocytes in the cortical mantel and areas surrounding the cerebral ventricles. LPS infusion increased brain cytosolic and secretory PLA2 activities by 71% and 47%, respectively, as well as the brain concentrations of non‐esterified linoleic and arachidonic acids, and of prostaglandins E2 and D2. LPS infusion also increased rates of incorporation and turnover of arachidonic acid in phosphatidylethanolamine, plasmenylethanolamine, phosphatidylcholine, and plasmenylcholine by 1.5‐ to 2.8‐fold, without changing these rates in phosphatidylserine or phosphatidylinositol. These observations suggest that selective alterations in brain arachidonic acid metabolism involving cytosolic and secretory PLA2 contribute to early pathology in neuroinflammation.
Neuroprotection of immortalized hippocampal neurones by brain‐derived neurotrophic factor and Raf‐1 protein kinase: role of extracellular signal‐regulated protein kinase and phosphatidylinositol 3‐kinase
Authors: Rössler Oliver G. , Giehl Klaus M. , Thiel Gerald
Published: February 2004

We have investigated the molecular mechanisms of neurotrophin‐mediated cell survival in HT22 cells, a murine cell line of hippocampal origin, expressing the brain‐derived neurotrophic factor (BDNF) receptor TrkB as well as the TrkB.T1 splice variant. Stimulation with BDNF protected HT22‐TrkB cells, but not HT22‐TrkB.T1 cells, against programmed cell death induced by serum deprivation. BDNF did not, however, provide protection against oxidative glutamate toxicity, indicating that serum deprivation‐induced cell death differs substantially from glutamate‐induced cell death. Using a pharmacological strategy to block either the extracellular signal‐regulated protein kinase (ERK) or the phosphatidylinositol 3‐kinase (PI3) pathway, we show that activation of PI3 kinase is required for the neuroprotective activity of BDNF in HT22 cells. To further analyse the role of ERK in neuroprotection we expressed an inducible ΔRaf‐1:ER fusion protein in HT22 cells. Activation of this conditionally active form of Raf‐1 induced a sustained phosphorylation of ERK, and protected the cells from serum withdrawal‐induced cell death. Inhibition of ERK activation at different time points revealed that a prolonged activation of ERK is essential to protect HT22 cells from cell death triggered by the withdrawal of serum, indicating that the duration of ERK activation is of major importance for its neuroprotective biological function.
Transthyretin is involved in depression‐like behaviour and exploratory activity
Authors: Sousa João Carlos , Grandela Catarina , Fernández‐Ruiz Javier , De Miguel Rosário , De Sousa Liliana , Magalhães Ana Isabel , Saraiva Maria João , Sousa Nuno , Palha Joana Almeida
Published: February 2004

Transthyretin (TTR), the major transporter of thyroid hormones and vitamin A in cerebrospinal fluid (CSF), binds the Alzheimer β‐peptide and thus might confer protection against neurodegeneration. In addition, altered TTR levels have been described in the CSF of patients with psychiatric disorders, yet its function in the CNS is far from understood. To determine the role of TTR in behaviour we evaluated the performance of TTR‐null mice in standardized tasks described to assess depression, exploratory activity and anxiety. We show that the absence of TTR is associated with increased exploratory activity and reduced signs of depressive‐like behaviour. In order to investigate the mechanism underlying these alterations, we measured the levels of cathecolamines. We found that the levels of noradrenaline were significantly increased in the limbic forebrain of TTR‐null mice. This report represents the first clear indication that TTR plays a role in behaviour, probably by modulation of the noradrenergic system.
Inhibiting Src family tyrosine kinase activity blocks glutamate signalling to ERK1/2 and Akt/PKB but not JNK in cultured striatal neurones
Authors: Crossthwaite Andrew J. , Valli Haseeb , Williams Robert J.
Published: February 2004

Glutamate receptor activation of mitogen‐activated protein (MAP) kinase signalling cascades has been implicated in diverse neuronal functions such as synaptic plasticity, development and excitotoxicity. We have previously shown that Ca2+‐influx through NMDA receptors in cultured striatal neurones mediates the phosphorylation of extracellular signal‐regulated kinase 1/2 (ERK1/2) and Akt/protein kinase B (PKB) through a phosphatidylinositol 3‐kinase (PI 3‐kinase)‐dependent pathway. Exposing neurones to the Src family tyrosine kinase inhibitor PP2, but not the inactive analogue PP3, inhibited NMDA receptor‐induced phosphorylation of ERK1/2 and Akt/PKB in a concentration‐dependent manner, and reduced cAMP response element‐binding protein (CREB) phosphorylation. To establish a link between Src family tyrosine kinase‐mediated phosphorylation and PI 3‐kinase signalling, affinity precipitation experiments were performed with the SH2 domains of the PI 3‐kinase regulatory subunit p85. This revealed a Src‐dependent phosphorylation of a focal adhesion kinase (FAK)–p85 complex on glutamate stimulation. Demonstrating that PI3‐kinase is not ubiquitously involved in NMDA receptor signal transduction, the PI 3‐kinase inhibitors wortmannin and LY294002 did not prevent NMDA receptor Ca2+‐dependent phosphorylation of c‐Jun N‐terminal kinase 1/2 (JNK1/2). Further, inhibiting Src family kinases increased NMDA receptor‐dependent JNK1/2 phosphorylation, suggesting that Src family kinase‐dependent cascades may physiologically limit signalling to JNK. These results demonstrate that Src family tyrosine kinases and PI3‐kinase are pivotal regulators of NMDA receptor signalling to ERK/Akt and JNK in striatal neurones.
Polyamine, Carbohydrate, and Proline Content Changes During Salt Stress Exposure of Aspen (Populus tremula L.): Involvement of Oxidation and Osmoregulation Metabolism
Authors: Jouve L. , Hoffmann L. , Hausman J.‐F.
Published: February 2004

Abstract: Excess salt in the soil solution affects the plant either through osmotic or ionic effects. Poplar trees, as fast growing pioneer tree species, are thought to be potential suitable candidates for afforestation on saline soils. Osmotic and oxidative stress induced by salinity could be reduced by the production and accumulation of compatible solutes and osmoprotectants in the plant. In this respect, metabolites of this type could be interesting markers for the improvement of salt stress tolerance in breeding programmes. Results have shown that Populus tremula was able to cope with up to 150 mM NaCl without any effect on plant survival. During stress application, the endogenous level of malondialdehyde did not vary significantly between the treatments, indicating that the level of lipid peroxidation was similar in the control and in the stressed plants. However, proline, spermine, sucrose, mannitol, and raffinose levels increased temporarily or throughout the salt treatment. All these molecules are more or less closely related to antioxidant or osmoprotectant mechanisms during stress, suggesting a key role for these compatible solutes, osmoprotectants, and their metabolism for salt stress resistance. The accumulation of free proline, sucrose and mannitol, and the transitory increase in spermine level observable during low and high NaCl application must be considered as general salt stress reaction markers.
Compatible and Incompetent Paxillus involutus Isolates for Ectomycorrhiza Formation in vitro with Poplar (Populus×canescens) Differ in H2O2 Production
Authors: Gafur A. , Schützendübel A. , Langenfeld‐Heyser R. , Fritz E. , Polle A.
Published: February 2004

Abstract: Isolates of Paxillus involutus (Batsch) Fr. collected from different hosts and environmental conditions were screened for their ability to form ectomycorrhizal symbiosis with hybrid poplar P.×canescens (= Populus tremula L. ×P. alba) in vitro. The ability to form ectomycorrhiza varied between the fungal isolates and was not correlated with the growth rate of the fungi on agar‐based medium. The isolate MAJ, which was capable of mycorrhiza synthesis under axenic conditions, and the incompetent isolate NAU were characterized morphologically and anatomically. MAJ formed a typical hyphal mantle and a Hartig net, whereas NAU was not able to penetrate the host cell walls and caused thickenings of the outer cell walls of the host. MAJ, but not NAU, displayed strong H2O2 accumulation in the outer hyphal mantle. Increases in H2O2 in the outer epidermal walls and adjacent hyphae of the incompetent isolate were moderate. No increases of H2O2 in response to the mycobionts were found inside roots. Suggested functions of H2O2 production in the outer hyphal mantle of the compatible interaction are: growth regulation of the host's roots, defence against other invading microbes, or increasing plant‐innate immunity. The system established here for P.×canescens compatible and incompetent fungal associations will be useful to take advantage of genomic information now available for poplar to study tree‐fungal interactions at the molecular and physiological level.
Genetic Variation of the Bud and Leaf Phenology of Seventeen Poplar Clones in a Short Rotation Coppice Culture
Authors: Pellis A. , Laureysens I. , Ceulemans R.
Published: February 2004

Abstract: Leaf phenology of 17 poplar (Populus spp.) clones, encompassing spring phenology, length of growth period and end‐of‐year phenology, was examined over several years of different rotations. The 17 poplar clones differed in their latitude of origin (45°30′N to 51°N) and were studied on a short rotation experimental field plantation, situated in Boom (province of Antwerpen, Belgium; 51°05′N, 04°22′E). A similar, clear pattern of bud burst was observed during the different years of study for all clones. Clones Columbia River, Fritzi Pauley, Trichobel (Populus trichocarpa) and Balsam Spire (Populus trichocarpa×Populus balsamifera) from 45°30′N to 49°N reached bud burst (expressed as day of the year or degree day sums) almost every year earlier than clones Wolterson (Populus nigra), Gaver, Gibecq and Primo (Populus deltoides×Populus nigra) (50°N to 51°N). This observation could not be generalised to end‐of‐season phenology, for which a yearly returning pattern for all clones was lacking. Late bud burst and early leaf fall of some clones (Beaupré, Boelare, IBW1, IBW2, IBW3) was brought about by increasing rust incidence during the years of observation. For these clones, the variability in leaf phenology was reflected in high coefficients of variation among years. The patterns of genetic variation in leaf phenology have implications for short rotation intensive culture forestry and management of natural populations. Moreover, the variation in phenology reported here is relevant with regard to the genetic mapping of poplar.
Vectors for RNAi Technology in Poplar
Authors: Meyer S. , Nowak K. , Sharma V. K. , Schulze J. , Mendel R. R. , Hänsch R.
Published: February 2004

Abstract: The potential of double‐stranded RNA interference (RNAi) technology was studied for down‐regulation of gene expression in poplar. A set of vectors was constructed generating RNAs capable of duplex formation of sequences specific for the β‐glucuronidase (GUS) reporter gene system. These gene cassettes are driven by the CaMV‐35S promoter. To address the question of gene silencing, we tested the functionality of these vectors, both in transient assays by transforming protoplasts with the RNAi constructs, and in stably transformed GUSexpressing poplar plants. Agrobacterium‐mediated transformation of those GUS‐expressing plants with a GUS‐specific RNAi construct showed a strong down‐regulation of the reporter gene. From these results we conclude that RNAi is also functional in poplar.