bluuebunny/crossref_metadata_2025_split huggingface dataset:
Is there really a drift paradox?
Authors: Humphries Stuart , Ruxton Graeme D. 
Published: March 2003

Summary

Recent explanations for the persistence of freshwater invertebrates in the face of downstream drift (the so‐called ‘drift paradox’) have centred largely on recolonization by upstream flight by preovipositing adults.
Such explanations do not cover the many important species often found in the drift that lack an aerial phase. Here we demonstrate conclusively that long‐range aerial movements are not required to explain the drift paradox.
We show that small‐scale movements along the streambed of the order of centimetres, combined with density dependence at some stage of the lifecycle, are sufficient to maintain populations over geological timescales.
Further, we demonstrate that the principal previous modelling study of the drift paradox was parameterized in a way that is more compatible with such small‐scale movements than the long‐range flight for which it was intended.
A metadata classification schema for semantic content analysis of videos
Authors: Shotton D. M. , Rodríguez A. , Guil N. , Trelles O. 
Published: March 2003

SummarySimple ancillary metadata, such as those encompassed by the 15 elements of the Dublin Core, may be sufficient and entirely appropriate for basic coarse‐granularity cross‐domain resource discovery. However, they are insufficient and inappropriate for content description of complex data types such as videos, which require more detailed relational models. We propose a metadata classification schema for the characterization of items and events in videos that permits subsequent query by content. Following MPEG‐7 nomenclature, metadata intrinsic to the information content of the video are defined as either structural or semantic, where structural metadata are numerical feature primitives produced by analysing the colour, shape, texture, structure and motion within the video frames, whereas semantic metadata describe the locations and timings of individual items and particular actions or events in the video, and are thus of higher information value. In this paper, the semantic metadata required to describe the visual information content of videos are defined and classified into four distinct classes: Media Entities; Content Items; Events; and Supplementary Items, and three types of property tables are defined: Identity Tables; Spatio‐Temporal Position Tables; and Event Tables, in which these metadata may be stored in a relational database.
Neuroprotection by adenosine A2A receptor blockade in experimental models of Parkinson's disease
Authors: Ikeda Ken , Kurokawa Masako , Aoyama Shiro , Kuwana Yoshihisa 
Published: March 2003

AbstractAdenosine A2A receptors are abundant in the caudate‐putamen and involved in the motor control in several species. In MPTP‐treated monkeys, A2A receptor‐blockade with an antagonist alleviates parkinsonian symptoms without provoking dyskinesia, suggesting this receptor may offer a new target for the antisymptomatic therapy of Parkinson's disease. In the present study, a significant neuroprotective effect of A2A receptor antagonists is shown in experimental models of Parkinson's disease. Oral administration of A2A receptor antagonists protected against the loss of nigral dopaminergic neuronal cells induced by 6‐hydroxydopamine in rats. A2A antagonists also prevented the functional loss of dopaminergic nerve terminals in the striatum and the ensuing gliosis caused by MPTP in mice. The neuroprotective property of A2A receptor antagonists may be exerted by altering the packaging of these neurotoxins into vesicles, thus reducing their effective intracellular concentration. We therefore conclude that the adenosine A2A receptor may provide a novel target for the long‐term medication of Parkinson's disease, because blockade of this receptor exerts both acutely antisymptomatic and chronically neuroprotective activities.
Mitochondrial permeability transition and calcium dynamics in striatal neurons upon intense NMDA receptor activation
Authors: Alano Conrad C. , Beutner Gisela , Dirksen Robert T. , Gross Robert A. , Sheu Shey‐Shing 
Published: March 2003

AbstractDeregulation of the intracellular Ca2+ homeostasis by NMDA receptor activation leads to neuronal cell death. Induction of the mitochondrial permeability transition pore (MPT) by Ca2+ is a critical event in mediating cell death. In this study, we used fluorescent Ca2+ indicators to investigate the effect of high concentrations of NMDA on cytosolic and mitochondrial Ca2+ concentrations ([Ca2+]c and [Ca2+]m, respectively) in cultured striatal neurons. Exposure to NMDA resulted in an immediate, sustained increase in [Ca2+]c followed by a secondary increase in [Ca2+]c. This second increase of [Ca2+]c was prevented by pretreatment with N‐methyl‐valine‐4‐cyclosporin (NMV‐Cys). Exposure of neurons to NMDA also resulted in an increase in [Ca2+]m that was followed by a precipitous decrease in the rhod‐2 signal. This decrease followed the time frame of the secondary increase in [Ca2+]c. Preincubation of the neurons with NMV‐Cys prevented the decrease in rhod‐2 fluorescence. These dynamic changes in the rhod‐2 signal and [Ca2+]m in response to NMDA were confirmed by using confocal microscopy. The presented results indicate that MPT can be detected in living neurons using fluorescent Ca2+ indicators, which would allow the study of the physiological role of MPT in cell death.
Multiple mechanisms of transmitter release evoked by ‘pathologically’ elevated extracellular [K+]: involvement of transporter reversal and mitochondrial calcium
Authors: Raiteri Luca , Stigliani Sara , Zedda Luca , Raiteri Maurizio , Bonanno Giambattista 
Published: March 2003

AbstractThe release of [3H]GABA evoked by depolarization with various concentrations of KCl was studied using superfused rat cerebrocortex synaptosomes. Elevating [K+] produced release of [3H]GABA over basal which was increasingly less dependent on external Ca2+ but more sensitive to the GABA transporter blocker SKF 100330 A. Accordingly, the sensitivity to clostridial toxins of the depolarization‐evoked amino acid release was inversely correlated to the concentration of KCl used. However, at 50 mm K+, one‐third of the stimulated release remained which was external Ca2+‐independent but insensitive to SKF 100330 A. This release was prevented by BAPTA, thapsigargin or dantrolene; it also was inhibited by blocking in mitochondria the ATP production with oligomycin, the H+‐dependent Ca2+ uniporter with RU 360, the Na+/Ca2+ exchanger with CGP 37157 or by lowering extraterminal [Na+]. In fluorescence experiments with fura‐2/AM, 50 mm K+ (in␣Ca2+‐free medium) caused elevation of cytosolic [Ca2+] that was sensitive to thapsigargin or CGP 37157; these compounds produced partially additive effects. When exocytosis was monitored with the fluorescent dye acridine orange, the fluorescence elicited by 50 mm K+ was sensitive to thapsigargin or CGP 37157, which produced additive effects, and to low‐Na+ media. To conclude, extracellular K+ concentrations occurring in the CNS in certain pathological conditions provoke GABA release by mechanisms different from classical exocytosis. These include carrier‐mediated release and internal Ca2+‐dependent exocytosis; in the latter, mitochondrial Ca2+ seems to play a primary role.
Protease‐activated receptor‐2 (PAR‐2) in brain microvascular endothelium and its regulation by plasmin and elastase
Authors: Dömötör Eszter , Bartha Katalin , Machovich Raymund , Adam‐Vizi Vera 
Published: March 2003

AbstractProtease‐activated receptors (PARs) mediate cell activation after proteolytic cleavage of their extracellular amino terminus. We have reported earlier that primary cultures of rat brain capillary endothelial (RBCE) cells express at least two receptors for thrombin: PAR‐1 and PAR‐3. In the present study we show that PAR‐2 activation by trypsin or by the PAR‐2 agonist peptide (SLIGRL) evokes [Ca2+]i signal in RBCE cells. Taking advantage of RBCE cells expressing PAR‐1 and PAR‐2, we show that trypsin activates both receptors. The relative agonist activity of trypsin and thrombin on PARs of RBCE cells compared with that of SLIGRL were 112% and 48%, respectively, whereas the potency of trypsin was 105‐fold higher than that of SLIGRL. Because under pathological conditions other proteases such as plasmin or leukocyte elastase may reach the cells of the blood–brain barrier, we investigated the effect of these proteases on RBCE cells. Elastase evoked a small increase in [Ca2+]i but preincubation of cells with elastase dose‐dependently reduced the trypsin‐induced [Ca2+]i signal. Plasmin had a 30% inhibitory effect on the trypsin‐induced response, and reduced the SLIGRL signal by 20%. It is concluded that PAR‐2 is functional in brain capillary endothelium, and that the main␣fibrinolytic proteases, plasmin and elastase, may regulate PAR‐2 signalling under pathological conditions.
Hypoxia induces mitochondrial DNA damage and stimulates expression of a DNA repair enzyme, the Escherichia coli MutY DNA glycosylase homolog (MYH), in vivo, in the rat brain
Authors: Lee Heung‐Man , Wang Cheng , Hu Zhaoyong , Greeley George H. , Makalowski Wojciech , Hellmich Helen L. , Englander Ella W. 
Published: March 2003

AbstractHypoxia‐associated, acutely reduced blood oxygenation can compromise energy metabolism, alter oxidant/antioxidant balance and damage cellular components, including DNA. We show in vivo, in the rat brain that respiratory hypoxia leads to formation of the oxidative DNA lesion, 8‐hydroxy‐2′‐deoxyguanosine (oh8dG), a biomarker for oxidative DNA damage and to increased expression of a DNA repair enzyme involved in protection of the genome from the mutagenic consequences of oh8dG. The enzyme is a homolog of the Escherichia coli MutY DNA glycosylase (MYH), which excises adenine residues misincorporated opposite the oxidized base, oh8dG. We have cloned a full‐length rat MYH (rMYH) cDNA, which encodes 516 amino acids, and by in situ hybridization analysis obtained expression patterns of rMYH mRNA in hippocampal, cortical and cerebellar regions. Ensuing hypoxia, mitochondrial DNA damage was induced and rMYH expression strongly elevated. This is the first evidence for a regulated expression of a DNA repair enzyme in the context of respiratory hypoxia. Our findings support the premise that oxidative DNA damage is repaired in neurons and the possibility that the hypoxia‐induced expression of a DNA repair enzyme in the brain represents an adaptive mechanism for protection of neuronal DNA from injurious consequences of disrupted energy metabolism and oxidant/antioxidant homeostasis.
Characterization of the cocaine‐ and amphetamine‐regulated transcript (CART) peptide gene promoter and its activation by a cyclic AMP‐dependent signaling pathway in GH3 cells
Authors: Dominguez Geraldina , Lakatos Anita , Kuhar Michael J. 
Published: March 2003

AbstractCocaine‐ and amphetamine‐regulated transcript (CART) peptides are regulated neuropeptides that play a role in a variety of physiological processes. CART mRNA is also highly regulated as its levels change in response to psychostimulant drugs and leptin. To understand the mechanisms involved in regulating CART mRNA levels, the mouse CART 5′‐flanking regulatory region was studied. The sequence of 3.4 kb of the mouse CART 5′‐flanking region revealed a proximal promoter that contains a cluster of transcription factor binding sites, including an overlapping STAT/CRE/AP1 site. In addition, the 5′‐most 320 bp of the CART promoter shares 83% nucleotide identity between mouse and human. Three luciferase expressing constructs containing varying amounts of CART 5′ upstream sequence were generated and tested for promoter activity. Transient transfection of GH3 cells with constructs containing 641 and 3451 bp of upstream sequence displayed strong promoter activity, producing 29‐fold and 51‐fold stimulation, respectively, while, a construct containing 102 bp of upstream sequence displayed a 5.4‐fold increase in activity. A␣construct containing the composite STAT/CRE/AP1 site was responsive to cyclic AMP induction by forskolin in GH3 cells. Forskolin treatment also resulted in a 4.5‐fold increase in CART mRNA levels after 6 h and the addition of H89, an inhibitor of protein kinase A, reduced the levels by 50%. These studies indicate that the CART proximal promoter lies within the 5′‐most 641 bp and that in GH3 cells the CART gene is regulated via a cyclic AMP‐dependent pathway.
Dβ3, an atypical nicotinic acetylcholine receptor subunit fromDrosophila: molecular cloning, heterologous expression and coassembly
Authors: Lansdell Stuart J. , Millar Neil S. 
Published: March 2003

AbstractInsect nicotinic acetylcholine receptors (nAChRs) play a central role in mediating neuronal synaptic transmission and are the target sites for the increasingly important group of neonicotinoid insecticides. Six nicotinic acetylcholine receptor (nAChR) subunits (four α‐type and two β‐type) have been cloned previously from the model insect speciesDrosophila melanogaster. Despite extensive efforts, it has not been possible to generate functional recombinant nAChRs by heterologous expression of any combination of these six subunits. It has, however, been possible to express functional hybrid receptors whenDrosophilaα subunits are co‐expressed with vertebrate β subunits. This has led to the assumption that successful heterologous expression might require an, as yet, uncloned β‐type insect subunit. Examination of the recently completedDrosophilagenomic sequence data has identified a novel putative nAChR β‐type subunit. Here we report the molecular cloning, heterologous expression and characterization of this putativeDrosophilanAChR subunit (Dβ3). Phylogenetic comparisons with other ligand‐gated ion channel subunit sequences support its classification as a nAChR subunit but show it to be a distantly related member of this neurotransmitter receptor subunit family. Evidence that the Dβ3 subunit is able to coassemble with otherDrosophilanAChR subunits and contribute to recombinant nAChRs has been obtained by both radioligand binding and coimmunoprecipitation studies in transfectedDrosophilaS2 cells.
Signals in abscission
Authors: Taylor Jane E. , Whitelaw Catherine A. 
Published: March 2003

SummaryAbscission is the term used to describe the process of natural separation of organs from the parent plant. This may be part of the highly programmed development of a plant, or in response to environmental stress. It enables temperate plants to overwinter and hence survive, but in agricultural or horticultural environments premature abscission can lead to significant crop losses. Abscission is the culmination of changes in gene expression, which result in the loosening of adjacent cell walls within the zone and subsequent cell separation. For many years it has been recognized that the balance between the plant hormones ethylene and auxin determine where, and when, separation takes place. As we begin to understand the mechanisms by which plant growth regulator signals are perceived and transduced, we can begin to understand how the process of abscission itself may be induced and regulated. This review details what we know of the signals that lead to the differentiation of zone cells; the environmental signals that promote cell separation, and the possible intracellular signalling events that culminate in organ shedding.

Contents

Summary
323

I.
Introduction
323

II.
Differentiation of the abscission zone
324

III.
Environmental and developmental signals that induce abscission
327

1. Senescence
327

2. Photoperiod
327

3. Water stress
328

4. Wounding and pathogen attack
328

5. Ozone
329

IV.
Inter‐ and intracellular signals
329

1. Role of ethylene and auxin
330

2. Mechanisms of plant hormone signal perception
330

3. Roles of other hormones and components of signal transduction
333

V.
Conclusions
335

Acknowledgements
336

References
336
Pollen competition between cultivated and wild rice species (Oryza sativaandO. rufipogon)
Authors: Song Zhiping , Lu Baorong , Zhu Yingguo , Chen Jiakuan 
Published: March 2003

Summary Post‐pollination competition is reported here in cultivated rice (Oryza sativa) and a perennial wild rice (O. rufipogon) to investigate the occurrence of crop‐to‐wild gene flow. Wild and cultivated rice (variety Minghui‐63) were grown in a common garden in Hunan province, China, and crop‐specific genetic markers were used to detect hybridization following hand‐pollinations. Using 11 sequential pollination treatments, the effects of the relative timing of pollination on the success of foreign pollen was investigated. Foreign pollen from the crop resulted in lower pollen germination, fewer pollen tubes per style, and a significant reduction of seed set, demonstrating a disadvantage of foreign pollen even in the absence of pollen competition. When 1 : 1 pollen mixtures were applied, only 2% of the resulting seeds were hybrids, revealing a much stronger disadvantage of foreign pollen when competing with conspecific pollen. Testing the effects of the relative timing of pollination on the success of foreign pollen suggested that conspecific pollen is often more successful than foreign pollen. Nonetheless, hybridization is possible following the deposition of pollen mixtures, especially when foreign pollen arrives earlier than conspecific pollen. Pollen competition between wild and cultivated rice could slow the rate of crop‐to‐wild gene flow, but even if pollen competition was ubiquitous it would not prevent gene flow from the crop.
Growth, nitrogen uptake, and resource allocation in the two tripartite lichens Nephroma arcticum and Peltigera aphthosa during nitrogen stress
Authors: Dahlman Lena , Näsholm Torgny , Palmqvist Kristin 
Published: March 2003

Summary

Lichen responses towards nitrogen stress, both increased exposure and deprivation of N, were investigated by measuring N uptake, growth, ergosterol, chitin and Chla in two tripartite nitrogen‐fixing species, Nephroma arctium and Peltigera aphthosa.
The lichens were irrigated with different N forms, enriched in 15N to assess N uptake, during 3 months in the field, with a total N dosage of 500 mg m−2. Nitrogen deprivation was induced by removing the nitrogen‐fixing cephalodia.
The lichens took up 11–134 mg N m−2 of the added N, corresponding to 1–4% of their total thallus N. Uptake was 4 times higher for NH4+ than for NO3−, and the highest 15N concentrations were found in newly synthesized tissue. Both forms of N stress affected thallus expansion rates in both species.
It is concluded that the two lichens were able to maintain a balanced tissue N concentration despite large variations in N supply, and that assimilated N might be transported to growing apices. Alternatively, N assimilation from external sources might be greater in the margins than in the mature thallus. Thallus expansion was sensitive to N stress, apparently being tightly coupled to N assimilation.
Reading a CO2 signal from fossil stomata
Authors: Beerling D. J. , Royer D. L. 
Published: March 2003

SummaryThe inverse relationship between atmospheric CO2 and the stomatal index (proportion of epidermal cells that are stomata) of vascular land plant leaves has led to the use of fossil plant cuticles for determining ancient levels of CO2. In contemporary plants the stomatal index repeatedly shows a lower sensitivity atmospheric CO2 levels above 340 ppm in the short term. These observations demonstrate that the phenotypic response is nonlinear and may place constraints on estimating higher‐than‐present palaeo‐CO2 levels in this way. We review a range of evidence to investigate the nature of this nonlinearity. Our new data, from fossil Ginkgo cuticles, suggest that the genotypic response of fossil Ginkgo closely tracks the phenotypic response seen in CO2 enrichment experiments. Reconstructed atmospheric CO2 values from fossil Ginkgo cuticles compare well with the stomatal ratio method of obtaining a quantitative CO2 signal from extinct fossil plants, and independent geochemical modelling studies of the long‐term carbon cycle. Although there is self‐consistency between palaeobiological and geochemical CO2 estimates, it should be recognized that the nonlinear response is a limitation of the stomatal approach to estimating high palaeo‐CO2 levels.
Recent experience with human immunodeficiency virus transmission by cellular blood products in Germany: antibody screening is not sufficient to prevent transmission
Authors: Dreier J. , Götting C. , Wolff C. , Petersen N. , Kleesiek K. 
Published: March 2003

Background and ObjectivesA case of transfusion‐related human immunodeficiency virus‐1 (HIV‐1) transmission was not detected by standard HIV antibody screening.Materials and MethodsIn a look‐back procedure, the preceding donations were extensively analyzed by nucleic acid amplification technology (NAT) screening and alternative serological tests.ResultsThe chain of infection could be demonstrated by the analysis of HIV‐specific amplicon sequences from the donor and the recipient.ConclusionThis case report clearly indicates that the remaining risk of transfusion‐related transmission of HIV could be severely reduced, not only by the use of NAT screening but even by HIV antigen screening or more sensitive HIV antibody assays.
Serum immunoglobulin E response in calves infected with the lungworm Dictyocaulus viviparus and its correlation with protection
Authors: Kooyman F. N. J. , Yatsuda A. P. , Ploeger H. W. , Eysker M. 
Published: March 2003

SummaryProtection of a primary Dictyocaulus viviparus infection was measured against a homologueous challenge infection in two independent experiments and this was correlated with serum immunoglobulin (Ig)E responses. A primary infection of 30 third stage larvae (L3) of D. viviparus on day 0 protects calves for 70% against a challenge infection of 2000 L3 on day 35 compared to calves with no primary infection. The variation in post mortem worm counts within this group (n = 6) was very large with mean worm counts of 145 (range 3–446) lungworms. Parasite specific IgA, IgE, IgG1 and IgG2 and total IgE levels in serum were measured by ELISA. Parasite specific IgA, IgG1 and IgG2 were elevated after infection, but correlation with protection was only found with IgG1 levels on day 42 and with IgG2 levels on day 70. IgE was measured in a sandwich ELISA using antisheep IgE that cross‐reacts with cattle IgE. No parasite specific IgE could be detected. However, total serum IgE was elevated after infection and total serum IgE levels before and on the day of challenge correlated with protection (P < 0·05). Total serum IgE also correlates with peripheral eosinophil counts between days 14 and 28 after primary infection. Western blots with three different parasite antigen preparations, L1, excretory/secretory products and crude worm adult antigens, were used to detect parasite specific IgE in sera depleted of IgG and IgM. These depleted sera from protected calves contained parasite specific IgE, while sera from nonprotected calves were negative. A band of approximately 100 kDa was recognized in all three antigens. In a second experiment, primary doses of 30, 60, 120, 240, 480 and 960 L3 of D. viviparus were used and necropsy was 11 days after challenge. This experiment confirmed the correlation between protection and total IgE levels before and on the day of challenge. The rapid and strong IgE responses in protected animals after such a low infection might be caused by the specific characteristics of the lungworm antigens or by the somatic migration of the worm and might be involved in the rapid development of protection against lungworm reinfections in cattle.