bluuebunny/crossref_metadata_2025_split huggingface dataset:
Differential modulation of NMDA‐induced calcium transients by arachidonic acid and nitric oxide in cultured hippocampal neurons
Authors: Richards D. A. , Bliss T. V. P. , Richards C. D. 
Published: June 2003

AbstractWe have examined the effect of arachidonic acid on the transient increases in intracellular Ca2+ evoked by NMDA and AMPA in cultured hippocampal pyramidal cells loaded with Fura‐2 AM. Repeated brief pulses of NMDA elicited Ca2+ transients that showed a modest run down. This run down was enhanced if the preparation was shielded from UV light and was reduced by conducting the experiments in the presence of the nitric oxide synthase inhibitor l‐nitroarginine (100 µm). Arachidonic acid (2 µm) enhanced the Ca2+ transients evoked by NMDA but not those evoked by AMPA. Other C20 unsaturated fatty acids did not alter the time course of the response to NMDA. These experiments suggest that elevated intracellular Ca2+ activates nitric oxide synthase and the resulting synthesis of nitric oxide depresses the Ca2+ response to NMDA while arachidonic acid augments these responses. Therefore two substances implicated in synaptic plasticity (arachidonic acid and nitric oxide) differentially modulate NMDA‐mediated Ca2+ entry into hippocampal neurons.
Laminar differences in plasticity in area 17 following retinal lesions in kittens or adult cats
Authors: Waleszczyk W. J. , Wang C. , Young J. M. , Burke W. , Calford M. B. , Dreher B. 
Published: June 2003

AbstractCircumscribed retinal lesions in adult cats result in a reorganization of circuitry in area 17 such that neurons in the lesion projection zone (LPZ) can now be activated, not from their original receptive fields (RFs) but from regions of normal retina adjacent to the lesion (‘ectopic’ RFs). We have studied this phenomenon further by making circumscribed monocular retinal lesions in 8‐week‐old kittens and recording responses to visual stimuli of neurons in the LPZ of area 17 when these cats reached adulthood. These responses have been compared with those in adult‐lesioned cats either of relatively short postlesion survival (2–24 weeks) or long postlesion survival (3.5–4.5 years). In both kitten‐lesioned and adult‐lesioned animals most LPZ neurons recorded from the supragranular layers (II and III) not only exhibited new ectopic RFs when stimuli were presented via the lesioned eye but the RF properties (e.g. the sizes of excitatory RFs, orientation and direction selectivities, velocity preferences and upper cut‐off velocities) were often indistinguishable from those seen when stimuli were presented via the nonlesioned eye. Similarly, in both kitten‐lesioned and adult‐lesioned animals, most LPZ neurons recorded from the granular and infragranular layers (IV, V, VI), like those recorded from the supragranular layers, were binocular. However, in adult‐lesioned but not in kitten‐lesioned animals, the responses and the upper cut‐off velocities of LPZ cells recorded from the granular and infragranular layers to stimuli presented via ectopic RFs tended to be, respectively, substantially weaker and lower than those for stimuli presented via the nonlesioned eye. The age‐related laminar differences in reorganizational plasticity of cat striate cortex correlate with the lamino‐temporal pattern of distribution of N‐methyl‐d‐aspartate glutamate receptors in striate cortex.
Involvement of post‐synaptic kainate receptors during synaptic transmission between unitary connections in rat neocortex
Authors: Ali Afia B. 
Published: June 2003

AbstractThe properties of functional kainate receptor‐mediated EPSCs were studied in acute slices from 19–35‐day‐old rats. EPSCs elicited in pyramidal and fast‐spiking cells in layers 2/3 and 5 of the rat motor cortex by extracellular single shock stimulus in the presence of GYKI 53655 and D‐2‐amino‐5‐phosphopentanoic resulted in a residual current. This current was not enhanced by cyclothiazide but was blocked by 6‐cyano‐7‐nitroquinoxalin‐2,3‐dione and is thought to be mediated by kainate receptors. These kainate receptor‐mediated currents displayed a wide range of time courses depending on which pre‐synaptic fibres were activated. With paired recordings, unitary EPSCs elicited in pyramidal cells were almost totally blocked by GYKI 53655 and D‐2‐amino‐5‐phosphopentanoic. However, when L‐transpyrrolidine‐2,4‐dicarboxylate (PDC), a glutamate uptake blocker, was introduced in the bath, the amplitude of kainate receptor‐mediated currents, which is resistant to GYKI 53655 and D‐2‐amino‐5‐phosphopentanoic, was revealed. The rise and decay time constants of the kainate receptor‐mediated currents were identical to control EPSCs. PDC was not required to reveal the kainate receptor‐mediated currents elicited in fast‐spiking cells which also displayed similar rise and decay time constants to the control EPSCs. Excitatory input onto pyramidal and fast‐spiking cells in the neocortex mediated by kainate receptors contributed between 14 and 40% of the total control unitary EPSCs which displayed identical time courses to the AMPA receptor‐mediated component of the EPSCs. Post‐synaptic kainate receptors at connected pyramidal cell synapses may be located extra‐synaptically.
Electrophysiological properties of the utricular primary transducer are modified during development under hypergravity
Authors: Chabbert Christian , Brugeaud Aurore , Lennan Georges , Lehouelleur Jacques , Sans Alain 
Published: June 2003

AbstractThe electrophysiological development of hair cells between birth and the eight postnatal day (P8) was studied in the utricular macula of rats gestated in nest boxes mounted upon a centrifuge, subjecting the animals to a gravitational force of 2G. Whole‐cell voltage‐clamp recordings were made on cells in the acutely isolated epithelium. Cells were accessed through a tear in the epithelium, no enzymatic dissociation procedures were employed. Under artificially enhanced gravity, the whole cell conductance was dramatically altered in the two types of hair cells. Significant increases occurred from P3–4 in the type I cells while in the type II cells, the effect was delayed until P7–8. Fourfold and threefold increases of the mean slope conductance were observed at P7–8 in the type I and type II hair cells, respectively. These results indicate that the electrophysiological properties of a primary transducer such as utricle may be modified by variation of the primary stimulus during development.
Sound presentation rate is represented logarithmically in human cortex
Authors: Sable Jeffrey J. , Gratton Gabriele , Fabiani Monica 
Published: June 2003

AbstractThe encoding of temporal information is critical to auditory processing. Since the mismatch negativity component of the auditory event‐related brain potential is thought to reflect properties of auditory sensory memory, we used it to examine the representation of acoustic time intervals in the human cortex. The mismatch negativity occurs in response to deviations in acoustic regularities, which are stored in sensory memory. We used 16 stimulus conditions, randomly presenting short trains of tones with fixed onset‐to‐onset intervals of 100, 200, 300 or 400 ms (all tones in the study were identical). The first four intervals between the tones established the acoustic regularity on each train (i.e. the ‘standard’). The fifth tone in each train was preceded by an interval that varied randomly among the same four intervals. If this interval was different from the standard for that trial, it violated the acoustic regularity (i.e. it was a ‘deviant’). The mismatch response to the fifth tone differed significantly among stimulus conditions and was proportional to the absolute value of the logarithm of the deviant/standard interval ratio. This indicates that short acoustic time intervals are represented with a ratio scale in the human cortex. When the fifth tone occurred 100 ms after the fourth, it elicited a somewhat different, although proportional response, supporting the hypothesis that a special integration mechanism may exist for very short time intervals.
Molecular characterization of Enterococcus faecalis two‐component signal transduction pathways related to environmental stresses
Authors: Le Breton Yoann , Boël Grégory , Benachour Abdellah , Prévost Hervé , Auffray Yanick , Rincé Alain 
Published: June 2003

SummaryA key issue in the comprehension of the Enterococcus faecalis stress response is to understand how this bacterium is able to modulate its gene expression in accordance to environmental conditions. Through bio‐informatic analysis of the E. faecalis V583 genome, nine two‐component systems and a single orphan response regulator were identified. A transcriptional study gave evidence of four systems whose expression is induced by at least one environmental stress. In addition, gene disruption experiments allowed the isolation of eight response regulator mutants. Insertional inactivation of the response regulator gene err 05 resulted in growth default and cell morphology alterations; and also in expression default of the sagA gene, this latter being recently shown involved in E.  faecalis stress resistance toward numerous lethal  treatments (Y. Le Breton, A. Mazé, A. Hartke, S. Lemarinier, Y. Auffray and A. Rincé (2002) Current Microbiol 45: 434–439). Disruption of the err 04, err 08 or err 18 genes resulted in sensitivity towards heat. Finally, the err 10 mutant was shown to be more sensitive to acid pH and NaCl whereas its growth was less affected by bile salts or heat. We also demonstrated that the heat resistance phenotype of the err 10 mutant was correlated with an increase of the heat shock proteins DnaK and GroEL level.
Specificity in the settlement – modifying response of bacterial biofilms towards zoospores of the marine alga Enteromorpha
Authors: Patel Pratixa , Callow Maureen E. , Joint Ian , Callow James A. 
Published: June 2003

SummaryPrevious studies have shown that the rate of settlement of zoospores of the green alga Enteromorpha is stimulated by mixed microbial biofilms and that the number of zoospores settling is positively correlated with the number of bacteria in the biofilm. In the present study the specificity of this relationship has been investigated. Ninety‐nine strains of marine bacteria were isolated from natural biofilms on rocks and the surface of Enteromorpha plants. Isolates were screened by denaturing gradient gel electrophoresis (DGGE) to eliminate replicates and 16S rDNA sequencing identified a total of 37 unique strains. Phylogenetic analysis revealed that the isolated bacterial strains belonged to three groups γ‐Proteobacteria (28 strains), Cytophaga‐Flavobacteria‐Bacteroid (CFB) group (six strains) and α‐Proteobacteria (one strain). Two strains were unassigned, showing < 93% sequence similarity with the CFB group. The main genera of γ‐Proteobacteria were Pseudoalteromonas (14 strains), Vibrio (five strains), Shewanella (five strains), Halomonas (three strains) and Pseudomonas (one strain). Spore settlement experiments were conducted on single‐species biofilms, developed for different times on glass slides. The effect of correcting spore settlement values for biofilm density was evaluated. Results showed that the effect of bacterial strains on spore settlement was strain‐ but not taxon‐specific and activity varied with the age of the biofilm. However, most of the strains belonging to genera Vibrio and Shewanella showed stimulation. Pseudoalteromonas strains showed a range of effects including settlement‐inhibiting, paralysing and lysing activities. Spatial analysis of bacterial density in the presence and absence of spores revealed a range of different types of association between spores and bacteria. Overall, the spatial association between spores and bacteria appears to be independent of the overall quantitative influence of bacterial cells on spore settlement.
Characterization of a Vibrio cholerae phage isolated from the coastal water of Peru
Authors: Talledo Miguel , Rivera Irma N. G. , Lipp Erin K. , Neale Angela , Karaolis David , Huq Anwar , R. Colwell Rita 
Published: June 2003

SummaryA Vibrio cholerae bacteriophage, family Myoviridae, was isolated from seawater collected from the coastal water of Lima, Peru. Genome size was estimated to be 29 kbp. The temperate phage was specific to V. cholerae and infected 12/13 V. cholerae O1 strains and half of the four non‐O1/non‐O139 strains tested in this study. Vibrio cholerae O139 strains were resistant to infection and highest infection rates were obtained in low nutrient media amended with NaCl or prepared using seawater as diluent.
A δ13C‐based carbon flux model for the hydrothermal vent chemoautotrophic symbiosis Riftia pachyptila predicts sizeable CO2 gradients at the host–symbiont interface
Authors: Scott Kathleen M. 
Published: June 2003

SummaryThe chemoautotrophic symbiosis Riftia pachyptila has extremely 13C‐enriched δ13C values. Neither isotopic discrimination by the RubisCO enzyme of their bacterial endosymbionts, nor the δ13C value of CO2 at their hydrothermal vent habitat, suffice to explain biomass δ13C values in this organism, which range from − 9 to − 16‰. However, these 13C‐enriched δ13C values are consistent with the presence of 13C‐enriched CO2 within the symbiont cytoplasm. Such a 13C‐enriched pool of CO2 is expected when the rate of CO2 fixation by RubisCO, which fixes 12CO2 more rapidly than 13CO2, approaches the rate of exchange between intracellular and extracellular CO2 pools. Rapid CO2 fixation rates will also generate concentration gradients between these two pools. In order to estimate the size of these concentration gradients, an equation was derived, which describes the δ13C of tubeworm biomass in terms of the size of the CO2 gradient between the hydrothermal vent environment and the symbiont cytoplasm. Using mass balance equations for CO2 exchange and fixation by the symbionts and the tubeworm host, this model predicts that a CO2 concentration gradient of up to 17‐fold between the symbiont cytoplasm and the environment is sufficient to explain even the most 13C‐enriched R. pachyptila biomass. This model illustrates how both physical and enzymatic factors can act to influence the δ13C of intracellular CO2, which, in turn, highlights the danger of assigning a carbon fixation pathway to an autotroph based solely on its biomass δ13C value.
Bacterial recovery from ancient glacial ice
Authors: Christner Brent C. , Mosley‐Thompson Ellen , Thompson Lonnie G. , Reeve John N. 
Published: June 2003

SummaryIce that forms the bottom 18 m of a 308 m ice core drilled from the Guliya ice cap on the Qinghan‐Tibetan plateau in Western China is over 750 000 years old and is the oldest glacial ice known to date. Fourteen bacterial isolates have been recovered from samples of this ice from ∼296 m below the surface (mbs). Based on 16S rDNA sequences, these are members of the α‐ and β‐proteobacterial, actinobacterial and low‐G + C Gram‐positive bacterial lineages. 16S rDNA molecules have also been amplified directly, cloned and sequenced from the ice‐core melt water. These originated from Pseudomonas and Acinetobacterγ‐proteobacterial species. These results demonstrate that bacteria can be recovered from water ice that has frozen for time periods relevant to biological survival through terrestrial ice ages or during interplanetary transport.
Structure and activity of multiple nitrifying bacterial populations co‐existing in a biofilm
Authors: Gieseke Armin , Bjerrum Lotte , Wagner Michael , Amann Rudolf 
Published: June 2003

SummaryA biofilm from a nitrifying pilot‐scale sequencing batch reactor was investigated for effects of varying process conditions on its microscale activity and structure. Microsensor measurements of oxygen, substrates and products of nitrification were applied under incubation at different ammonium and oxygen concentrations which reflected various situations during a treatment cycle. A high net N loss was observed under high ammonium (HA) concentrations in contrast to low ones. Additionally, results indicated inhibition of nitrite‐oxidizing bacteria (NOB), but not of ammonia‐oxidizing bacteria (AOB) by free ammonia under HA conditions. Diversity, spatial distribution, and abundance of nitrifying bacteria as analysed by fluorescence in situ hybridization (FISH) revealed six different nitrifying populations with heterogeneous distributions. Nitrosococcus mobilis formed conspicuous microcolonies locally surrounded by cells of the dominating N. europaea/eutropha‐related AOB population. A third less abundant population was affiliated to N. oligotropha. Nitrite‐oxidizing bacteria of the genera Nitrobacter and Nitrospira (with at least two distinct populations) showed a large scale heterogeneity in their distribution. Nitrospira spp. were also found in deeper inactive layers where they might persist rather than thrive, and act as seed population when detached. Results of functional and structural analyses are discussed with respect to specific niches of individual populations in this system.
The gene cassette metagenome is a basic resource for bacterial genome evolution
Authors: Holmes Andrew J. , Gillings Michael R. , Nield Blair S. , Mabbutt Bridget C. , Nevalainen K. M. Helena , Stokes H. W. 
Published: June 2003

SummaryLateral gene transfer has been proposed as a fundamental process underlying bacterial diversity. Transposons, plasmids and phage are widespread and have been shown to significantly contribute to lateral gene transfer. However, the processes by which disparate genes are assembled and integrated into the host regulatory network to yield new phenotypes are poorly known. Recent discoveries about the integron/gene cassette system indicate it has the potential to play a role in this process. Gene cassettes are small mobile elements typically consisting of a promoterless orf and a recombination site. Integrons are capable of acquisition and re‐arrangement of gene cassettes and of the expression of their associated genes. The potential of the integron/gene cassette system is thus largely determined by the diversity contained within the cassette pool and the rate at which integrons sample this pool. We show here using a polymerase chain reaction (PCR) approach by which the environmental gene cassette (EGC) metagenome can be directly sampled that this metagenome contains both protein‐coding and non‐protein coding genes. Environmental gene cassette‐associated recombination sites showed greater diversity than previously seen in integron arrays. Class 1 integrons were shown to be capable of accessing this gene pool through tests of recombinational activity with a representative range of EGCs. We propose that gene cassettes represent a vast, prepackaged genetic resource that could be thought of as a metagenomic template for bacterial evolution.
Rice seedling whole exudates and extracted alkylresorcinols induce stress‐response in Escherichia coli biosensors
Authors: Miché Lucie , Belkin Shimshon , Rozen Rachel , Balandreau Jacques 
Published: June 2003

SummaryA set of Escherichia coli sensor strains was used to evaluate the stress exerted on surrounding bacteria by germinating rice seed exudates. These biosensor strains contain Vibrio fischeri luxCDABE genes fused to the promoters of different genes involved in bacterial responses to environmental stresses. They provided clear evidence for a stress exerted by rice exudates, as shown by the induction of the universal stress protein gene uspA as well as genes of the heat shock regulon, grpE, lon and dnaK. The oxidative stress gene katG, and the post‐transcriptional ompF regulator encoded by micF were also activated. The lack of derepression of recA, uvrA and alkA indicated that damage to the DNA was not induced in the E. coli strains tested. Interestingly, resorcinolic lipids extracted from rice root seedlings induced the same promoters as whole exudates, suggesting that these compounds may contribute to the stress exerted by seedling exudates. The results obtained with E. coli biosensors thus indicate that, in vivo, exudates may also exert a selective pressure on root‐colonizing bacteria.
Glutamine synthetase from the marine cyanobacteria Prochlorococcus spp.: characterization, phylogeny and response to nutrient limitation
Authors: El Alaoui Sabah , Diez Jesús , Toribio Fermín , Gómez‐Baena Guadalupe , Dufresne Alexis , García‐Fernández Jose M. 
Published: June 2003

SummaryThe regulation of glutamine synthetase (EC 6.3.1.2) from Prochlorococcus was previously shown to exhibit unusual features: it is not upregulated by nitrogen starvation and it is not inactivated by darkness (El Alaoui et al. (2001) Appl Environ Microbiol 67: 2202–2207). These are probably caused by adaptations to oligotrophic environments, as confirmed in this work by the marked decrease in the enzymatic activity when cultures were subjected to iron or phosphorus starvation. In order to further understand the adaptive features of ammonium assimilation in this cyanobacterium, glutamine synthetase was purified from two Prochlorococcus strains: PCC 9511 (high‐light adapted) and SS120 (low‐light adapted). We obtained ∼ 100‐fold purified samples of glutamine synthetase electrophoretically homogeneous, with a yield of ∼ 30%. The estimated molecular mass of the subunits was roughly the same for both strains: 48.3 kDa. The apparent Km constants for the biosynthetic activity were 0.30 mM for ammonium, 1.29 mM for glutamate and 1.35 mM for ATP; the optimum pH was 8.0. Optimal temperature was surprisingly high (55°C). Phylogenetic analysis of glnA from three Prochlorococcus strains (MED4, MIT9313 and SS120) showed they group closely with marine Synechococcus isolates, in good agreement with other studies based on 16 S RNA sequences. All of our results suggest that the structure and kinetics of glutamine synthetase in Prochlorococcus have not been significantly modified during the evolution within the cyanobacterial radiation, in sharp contrast with its regulatory properties.
Medical Management of Advanced Dementia
Authors: Tariot Pierre N. 
Published: June 2003

A cure for Alzheimer's disease (AD) is still far off, and clinicians face the burden of caring for patients at all stages of dementia for the foreseeable future. Those with advanced disease suffer neurological symptoms and signs that include incontinence; problems with gait and mobility; marked cognitive, language, and functional impairment; and in about 90% of patients, significant behavior problems. Dementia precludes the ability to initiate meaningful activities or social interactions. Whether patients are resident in the community or living in a nursing home, this composite reflects a highly complex medical and neuropsychiatric management challenge. Predictable medical conditions also must be addressed (i.e., those that accompany dementia, such as parkinsonism, and those that are prevalent in any aging population, such as hypertension).Clinicians can better address these problems with awareness of current treatment options. Placebo‐controlled trials of some psychotropic agents have shown modest favorable effects on behavior problems. Use of acetylcholinesterase inhibitors (AChEIs) to treat cognitive impairment and secondary behavioral symptoms derives primarily from results of placebo‐controlled clinical trials. Trials in patients with moderate to severe AD, outpatients as well as nursing home residents, show overall effects similar to those seen in outpatients with milder dementia. Treatment with AChEIs may delay institutional placement. Memantine has shown benefit in trials in moderate to severe dementia, although it is not yet approved in the United States. Emerging data have expanded physicians' ability to use pharmacotherapy in patients with advanced dementia. Physicians need to enact the principle that something can be done for our afflicted parents and grandparents.