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At least 1,099 records · Page 61Linked to original sources
PubMed2000

FimE-catalyzed off-to-on inversion of the type 1 fimbrial phase switch and insertion sequence recruitment in an Escherichia coli K-12 fimB strain.

We have investigated the capacity of a well-defined Escherichia coli fimB strain, AAEC350 (a derivative of MG1655), to express type 1 fimbriae under various growth conditions. The expression of type 1 fimbriae is phase-variable due to the inversion of a 314-bp DNA segment. Two tyrosine recombinases, FimB and FimE, mediate the inversion of the phase switch. FimB can carry out recombination in both directions, whereas the current evidence suggests that FimE-catalyzed switching is on-to-off only. We show here that AAEC350 is in fact capable of off-to-on phase switching and type 1 fimbrial expression under aerobic static growth conditions. The phase switching is mediated by FimE, and allows emerging fimbriate AAEC350 to outgrow their non-fimbriate counterparts by pellicle formation. Following inversion of the phase switch, this element can remain phase-locked in the on orientation due to integration of insertion sequence elements, viz. IS1 or IS5, at various positions in either the fimE gene or the phase switch.

Agglutination↗
PubMed2004

Exercise level and energy expenditure in the TAKE 10! in-class physical activity program.

This study evaluated the effectiveness of an innovative, classroom-based physical activity prevention program designed to integrate academic curriculum elements along with a physical activity program in providing moderate-to-vigorous intensity physical activity. A convenience sample of three public school classrooms (one first, third, and fifth grade class) was observed implementing the TAKE 10! program while monitored by either CSA accelerometers or digital pedometers. Pedometer step counts and CSA data were recorded for each student and activity. As calculated from CSA data, average MET levels during the activities were 5.72-7.05 (first grade), 5.51-6.77 (third grade), and 4.98-7.19 (fifth grade), and levels were not different between grades (p > 0.05). Average caloric expenditure (Kcal) per 10-minute session was 25.6-27.8 (first grade), 27.6-33.9 (third grade), and 29.7-42.9 (fifth grade). Measured pedometer step counts per session ranged from 644-931 in first grade, 659-1, 376 in third grade, and 1002-1041 in fifth grade. TAKE 10! sessions for all three grades produced exercise levels in the moderate intensity range throughout full duration of the session. Classroom-based physical activity promotion provides a useful strategy to promote meaningful physical activity among school children.

Child↗
PubMed1998

Human olfactory bulb: aging of glomeruli and mitral cells and a search for the accessory olfactory bulb.

The aims of this study on the human olfactory bulb were two. First morphometry of the bulbs revealed marked declines during aging in the numbers of mitral cells and glomeruli, the bulb's principal integrative and relay elements. Numbers of glomeruli and mitral cells in each bulb of the young adult human were found to be approximately 8,000 and 40,000, respectively; these numbers declined steadily with age at an approximate rate of 10% per decade, so that in the ninth and tenth decades less than 30% of these elements remain in place. Such a marked decline with aging is suggested to underlie in part the decline in olfactory abilities (odor detection and identification) of humans with aging. In a separate study a systematic search for presence of an accessory olfactory bulb in the adult and aging bulbs was undertaken. No positive evidence for such an organized formation was found in the various regions of the adult bulbs of different age groups. The implications of these negative findings for the recent theories on human vomeronasal function and pheromonal perception are discussed.

Adult↗
PubMed1999

Interactions of presynaptic Ca2+ channels and snare proteins in neurotransmitter release.

N- and P/Q-type Ca2+ channels are localized in high density in presynaptic nerve terminals and are crucial elements in neuronal excitation-secretion coupling. In addition to mediating Ca2+ entry to initiate transmitter release, they are thought to interact directly with proteins of the synaptic vesicle docking/fusion machinery. These Ca2+ channels can be purified from brain as a complex with SNARE proteins, which are involved in exocytosis. In addition, N-type and P/Q-type Ca2+ channels are colocalized with syntaxin in high-density clusters in nerve terminals. The synaptic protein interaction (synprint) sites in the intracellular loop II-III (LII-III) of both alpha 1B and alpha 1A subunits of N-type and P/Q-type Ca2+ channels bind to syntaxin, SNAP-25, and synaptotagmin. Ca2+ has a biphasic effect on the interactions of N-type Ca2+ channels with SNARE complexes, stimulating optimal binding in the range of 10-30 microM. PKC or CaM KII phosphorylation of the N-type synprint peptide inhibits interactions with SNARE complexes containing syntaxin and SNAP-25. Introduction of the synprint peptides into presynaptic superior cervical ganglion neurons reversibly inhibits EPSPs from synchronous transmitter release by 42%. At physiological Ca2+ concentrations, synprint peptides significantly reduce transmitter release in injected frog neuromuscular junctions in cell culture, consistent with detachment of 70% of the docked vesicles from Ca2+ channels as analyzed by a theoretical model. Together, these studies suggest that presynaptic Ca2+ channels not only provide the Ca2+ signal required by the exocytotic machinery, but also contain structural elements that are integral to vesicle docking, priming, and fusion processes.

Animals↗
PubMed1979

Numerical solution of coupled transport equations applied to corneal hydration dynamics.

1. A quantitative basis for the currently accepted theory on the regulation of corneal hydration was derived using the technique of finite element analysis to integrate a set of coupled flow equations. The model was based on non-equilibrium thermodynamics and incorporated the transport and permeability properties of the corneal epithelium and endothelium as well as the gel properties of the central connective tissue layer. 2. Considerable errors were introduced in the prediction of corneal hydration dynamics (unsteady-state behaviour) unless allowance was made for the development of trans-stromal gradients in pressure and solute concentration. 3. Thickness of in vitro rabbit corneal epithelium and stroma were measured with an automatic specular microscope during responses to changes in the osmolarity of the tear-side bathing medium. The time course of these experiments was fitted with the mathematical model to obtain a set of membrane phenomenological coefficients and transport rates. 4. The model with the redetermined membrane parameters was tested by predicting the influence of other variations in boundary conditions with excellent match to several well-documented experimental observations, including an explanation for the slight stromal swelling observed in hibernating mammals. 5. The regulation of corneal stromal hydration can be explained accurately by balance between the dissipative flows across the serial array of corneal layers and the active HCO3 transport by the endothelium, supporting the earlier 'pump-leak' hypothesis. 6. It was found that stromal retardation of fluid flow, as well as gradients in solute concentration, significantly influences the dynamics of corneal stroma hydration. Tissue gel properties may be a more important factor in coupled transport across cell layers than generally appreciated.

Animals↗
PubMed2002

Spatial coherence analysis applied to aberration correction using a two-dimensional array system.

Complex degree of coherence functions are computed using synthetic and measured ultrasound data to demonstrate noteworthy aspects of coherence analysis in the context of aberration correction. Coherence functions calculated from synthetic data illustrate the importance of proper normalization of the constituent cross-correlation integrals when weak elements and receiver directivity are significant factors. The synthetic data also show that a spike can occur at the zero-lag position of the coherence function when the signal-to-noise ratio is reduced by element directivity near the edges of a large aperture. The latter observation is confirmed by experimental data acquired through tissue-mimicking distributed aberration phantoms using a low f-number two-dimensional array system. The coherence of data acquired at neighboring elements is not changed by time-shift compensation of transmit and receive focusing, but time-shift compensation does improve the coherence of echoes measured over larger separations. The resulting increase in coherence widths evaluated at levels between 0.2 and 0.5 is correlated with narrower -10 dB and -20 dB effective widths in focuses visualized using single-transmit images. Iterative focus compensation methods may benefit from aberration estimation algorithms that take advantage of these longer-range correlations in random-scattering waveforms.

Artifacts↗
PubMed1995

Temporal information transformed into a spatial code by a neural network with realistic properties.

Neurons exhibit a wide range of properties in addition to postsynaptic potential (PSP) summation and spike generation. Although other neuronal properties such as paired-pulse facilitation (PPF) and slow PSPs are well characterized, their role in information processing remains unclear. It is possible that these properties contribute to temporal processing in the range of hundreds of milliseconds, a range relevant to most complex sensory processing. A continuous-time neural network model based on integrate-and-fire elements that incorporate PPF and slow inhibitory postsynaptic potentials (IPSPs) was developed here. The time constants of the PPF and IPSPs were estimated from empirical data and were identical and constant for all elements in the circuit. When these elements were incorporated into a circuit inspired by neocortical connectivity, the network was able to discriminate different temporal patterns. Generalization emerged spontaneously. These results demonstrate that known time-dependent neuronal properties enable a network to transform temporal information into a spatial code in a self-organizing manner--that is, with no need to assume a spectrum of time delays or to custom-design the circuit.

Electric Stimulation↗
PubMed2006

Characterization of the global transcriptional responses to different types of DNA damage and disruption of replication in Bacillus subtilis.

DNA damage and perturbations in DNA replication can induce global transcriptional responses that can help organisms repair the damage and survive. RecA is known to mediate transcriptional responses to DNA damage in several bacterial species by inactivating the repressor LexA and phage repressors. To gain insight into how Bacillus subtilis responds to various types of DNA damage, we measured the effects of DNA damage and perturbations in replication on mRNA levels by using DNA microarrays. We perturbed replication either directly with p-hydroxyphenylazo-uracil (HPUra), an inhibitor of DNA polymerase, or indirectly with the DNA-damaging reagents mitomycin C (MMC) and UV irradiation. Our results indicate that the transcriptional responses to HPUra, MMC, and UV are only partially overlapping. recA is the major transcriptional regulator under all of the tested conditions, and LexA appears to directly repress the expression of 63 genes in 26 operons, including the 18 operons previously identified as LexA targets. MMC and HPUra treatments caused induction of an integrative and conjugative element (ICEBs1) and resident prophages (PBSX and SPbeta), which affected the expression of many host genes. Consistent with previous results, the induction of these mobile elements required recA. Induction of the phage appeared to require inactivation of LexA. Unrepaired UV damage and treatment with MMC also affected the expression of some of the genes that are controlled by DnaA. Furthermore, MMC treatment caused an increase in origin-proximal gene dosage. Our results indicate that different types of DNA damage have different effects on replication and on the global transcriptional profile.

Bacillus Phages↗
PubMed2001

Integron integrases possess a unique additional domain necessary for activity.

Integrons are genetic elements capable of integrating genes by a site-specific recombination system catalyzed by an integrase. Integron integrases are members of the tyrosine recombinase family and possess the four invariant residues (RHRY) and conserved motifs (boxes I and II and patches I, II, and III). An alignment of integron integrases compared to other tyrosine recombinases shows an additional group of residues around the patch III motif. We have analyzed the DNA binding and recombination properties of class I integron integrase (IntI1) variants carrying mutations at residues that are well conserved among all tyrosine recombinases and at some residues from the additional motif that are conserved among the integron integrases. The well-conserved residues studied were H277 from the conserved tetrad RHRY (about 90% conserved), E121 found in the patch I motif (about 80% conserved in prokaryotic recombinases), K171 from the patch II motif (near 100% conserved), W229 and F233 from the patch III motif, and G302 of box II (about 80% conserved in prokaryotic recombinases). Additional IntI1 mutated residues were K219 and a deletion of the sequence ALER215. We observed that E121, K171, and G302 play a role in the recombination activity but can be mutated without disturbing binding to DNA. W229, F233, and the conserved histidine (H277) may be implicated in protein folding or DNA binding. Some of the extra residues of IntI1 seem to play a role in DNA binding (K219) while others are implicated in the recombination activity (ALER215 deletion).

ATP-Binding Cassette Transporters↗
PubMed2005

Swine and poultry pathogens: the complete genome sequences of two strains of Mycoplasma hyopneumoniae and a strain of Mycoplasma synoviae.

This work reports the results of analyses of three complete mycoplasma genomes, a pathogenic (7448) and a nonpathogenic (J) strain of the swine pathogen Mycoplasma hyopneumoniae and a strain of the avian pathogen Mycoplasma synoviae; the genome sizes of the three strains were 920,079 bp, 897,405 bp, and 799,476 bp, respectively. These genomes were compared with other sequenced mycoplasma genomes reported in the literature to examine several aspects of mycoplasma evolution. Strain-specific regions, including integrative and conjugal elements, and genome rearrangements and alterations in adhesin sequences were observed in the M. hyopneumoniae strains, and all of these were potentially related to pathogenicity. Genomic comparisons revealed that reduction in genome size implied loss of redundant metabolic pathways, with maintenance of alternative routes in different species. Horizontal gene transfer was consistently observed between M. synoviae and Mycoplasma gallisepticum. Our analyses indicated a likely transfer event of hemagglutinin-coding DNA sequences from M. gallisepticum to M. synoviae.

Animals↗
PubMed2006

Predominance of clones carrying Panton-Valentine leukocidin genes among methicillin-resistant Staphylococcus aureus strains isolated in Japanese hospitals from 1979 to 1985.

We examined 97 strains of methicillin-resistant Staphylococcus aureus (MRSA) isolated between 1979 and 1985, the period of time when the appearance of MRSA strains increased, and we determined that these strains are distinct from the MRSA clones predominating in today's Japanese hospitals. Type IV staphylococcal cassette chromosome mec (SCCmec) strains were the most frequent, comprising 53.6% of all strains, followed by type I (22.7%) and type II (21.6%) SCCmec strains. Among the type IV SCCmec strains, the frequencies of two new subtypes, type IV.3 (IVc) and type IV.4 (IVd), were very high, comprising 38.1 and 10.3% of all strains, respectively. Forty-four of the 97 strains (45.3%) were Panton-Valentine leukocidin (PVL) positive. Among the PVL-positive strains, sequence type 30 (ST30)-SCCmec type IV strains producing type 4 coagulase were the most frequent. This is in striking contrast to the MRSA strains isolated in the 1990s, most of which were ST5-SCCmec type II strains producing type 2 coagulase and positive for the toxic shock syndrome toxin 1 gene. We also identified a new PVL-carrying prophage lysogenized in a type IV.3 SCCmec strain, 81/108. phi108PVL was distinct from the three extant PVL-carrying phages and was presumed to be carried by ST30-type IV.3 SCCmec strains isolated in Japan. These results provide genetic bases for the transition of MRSA clones in Japan that is commonly considered the transition from coagulase type 4 MRSA strains to coagulase type 2 MRSA strains. The results also suggested that MRSA strains that predominated between 1979 and 1985 were generated from PVL-positive methicillin-susceptible S. aureus strains through the integration of SCCmec elements.

Bacterial Toxins↗
PubMed2006

Analysis of longitudinal data: the integration of theoretical model, temporal design, and statistical model.

This article argues that ideal longitudinal research is characterized by the seamless integration of three elements: (a) a well-articulated theoretical model of change observed using (b) a temporal design that affords a clear and detailed view of the process, with the resulting data analyzed by means of (c) a statistical model that is an operationalization of the theoretical model. Two general varieties of theoretical models are considered: models in which the time-related change of primary interest is continuous, and those in which it is characterized by movement between discrete states. In addition, two general types of temporal designs are considered: the longitudinal panel design and the intensive longitudinal design. For each general category of theoretical models, some of the analytic possibilities available for longitudinal panel designs and for intensive longitudinal designs are discussed. The article concludes with brief discussions of two issues particularly relevant to longitudinal research--missing data and measurement--and a few words about exploratory research.

Humans↗
PubMed2005

Superimposing polymorphism: the case of a point mutation within a polymorphic Alu insertion.

The COL3A1 Alu insertion is a member of the AluY subfamily. It has been found to be absent in non-human primates and polymorphic in worldwide human populations. The integration of the element into the human genome seems to have preceded the initial migration(s) of anatomically modern humans out of the African continent. Although the insertion has been detected in populations from all the continents, its highest frequency values are located within sub-Saharan Africa. The sequence alignment of the COL3A1 insertion from several African individuals revealed a bi-allelic single nucleotide polymorphism (SNP) at the downstream terminus of the element's poly-A tract. Once discovered, a selective PCR procedure was designed to determine the frequency of both alleles in 19 worldwide populations. The A-allele in this binary SNP experiences a clinal increase in the eastward direction from Africa to Southeast Asia and Mongolia, reaching fixation in the two latter regions. The T variant, on the other hand, exhibits a westward clinal increase outside of Africa, with its lowest frequency in Asia and achieving fixation in northern Europe. The presence of this internal SNP extends the usefulness provided by the polymorphic Alu insertion (PAI). It is possible that superimposing polymorphisms like this one found in the COL3A1 locus may accentuate signals from genetic drift events allowing for visualization of recent dispersal patterns.

Africa↗
PubMed2005

Auditory stream segregation in the songbird forebrain: effects of time intervals on responses to interleaved tone sequences.

For both humans and other animals, the abilities to integrate separate sound elements over time into coherent perceptual representations, or 'auditory streams', and to segregate these auditory streams from other interleaved sounds are critical for hearing and vocal communication. In humans and European starlings (Sturnus vulgaris) the ability to perceptually segregate a simple interleaved tone sequence comprised of two alternating tones differing in frequency (ABA-ABA-ABA-...) into separate auditory streams of A and B tones is promoted at larger frequency separations (DeltaF) between the A and B tones. In humans, segregating A and B tones into different streams also appears to be promoted at shorter interstimulus intervals (ISI) between tones within a stream (e.g., between consecutive A tones). Here, we used the ABA experimental paradigm to investigate the influence of different time intervals between A and B tones in repeated ABA triplets on neural responses in the starling forebrain. The main finding from the study is that a DeltaF-dependent effect of ISI had a large influence on the relative responses to A and B tones. Responses to B tones were suppressed, relative to A-tone responses, when the A and B tones were more similar in frequency (smaller DeltaFs) and occurred at shorter ISIs. We attribute these suppressive effects to physiological forward masking and suggest that forward masking functions as a mechanism for segregating neural responses to interleaved tones in tonotopic space. We discuss the relevance of our physiological data with respect to previous electrophysiological studies of auditory stream segregation in mammals and previous perceptual studies in humans.

Animals↗
PubMed2003

Safety and efficacy of endovascular cooling and rewarming for induction and reversal of hypothermia in human-sized pigs.

BACKGROUND AND PURPOSE: Numerous studies indicate that mild hypothermia provides substantial neuroprotection. However, current systems transfer insufficient heat to rapidly vary core temperature. We thus evaluated the safety and efficacy of endovascular cooling and rewarming for the induction and reversal of hypothermia. METHODS: In 10 anesthetized pigs (weight, 66+/-2 kg), a heat-exchange balloon catheter was inserted into the inferior vena cava and used to cool to a core temperature of 32 degrees C and then rewarm to normothermia. Control animals had 38 degrees C saline infused. Venous blood was sampled before, during, and after cooling. Three animals in each group were killed 1 week later, and the lungs and inferior vena cava were removed for gross and microscopic examination. In 5 additional animals, cardiac output was measured during cooling to 32 degrees C. RESULTS: Body temperature in the hypothermic animals decreased at a rate of 4.5+/-0.4 degrees C/h. Animals were subsequently rewarmed to 36.0+/-0.04 degrees C at 2.5+/-0.2 degrees C/h. There was no difference in heart rate between hypothermic and control animals, whereas systolic pressure decreased during cooling. Cardiac output was well maintained during cooling. There were no thermal effects on blood elements or blood vessels. CONCLUSIONS: The endovascular heat-exchange system effectively cooled and rewarmed pigs with large thermal mass without producing any adverse effects on blood elements, blood vessel integrity, or cardiovascular function.

Animals↗
PubMed2006

The role of spatial phase in texture segmentation and contour integration.

It has been recently argued that the visual system possesses just two phase "detector" mechanisms, namely, +cosine and -cosine (P. C. Huang, F. A. Kingdom, & R. F. Hess, 2006). This suggests rather limited access to the rich distribution of receptive field phase that neurophysiologists tell us are represented in the different response profiles of striate simple cells. Whereas that study has suggested that striate receptive field phase is not directly available to perception for the detection/discrimination of localized stimuli, here we investigate whether such information might be used in more integrative striate or extrastriate functions such as texture segregation or contour integration. Specifically, given that simple cells have different local absolute phase response profiles, we ask whether a network of simple cells with similar phase preferences interact in such a way as to extract textures, contours, or both based on phase alone. Two novel texture segmentation experiments and one contour integration experiment were carried out with the intention of providing an answer to the question of how useful is local absolute spatial phase for texture segmentation and contour integration. The results support the possibility of two phase mechanisms (+/-cosine) for global texture segmentation, as well as for contour integration, when the elements that make up a given contour are orthogonal to contour paths.

Form Perception↗
PubMed2000

Horizontal mergers in the United States health field: some practical realities.

During the past decade, 'merger mania' has been a striking trend in the US health field as a strategy to improve the integration of services, to reduce expenses, and to increase the ability of providers to manage risk-based payment. However, during the past quarter of a century limited operational and fiscal evidence has been published in both the health and general management literature that strongly supports the efficacy of horizontal mergers. This article further argues that a likely scenario over the next decade, in spite of disappointments among these mergers in effecting significant cost reductions, is for the US health networks to continue acquiring additional providers and insurers. After these alliances gain significant market penetration, they are expected to behave as oligopolists. For these mergers to eventually achieve their earlier projected savings, the health field's leadership will be forced to implement cost-cutting measures such as: more vigorously coordinating the network's key clinical services to reduce competition for revenues among the partners within an alliance, closing superfluous hospitals and centralizing expensive tertiary services, encouraging surplus physicians to relocate to under-served areas, and providing direction to carefully integrate the best elements of what the competitive and regulatory strategies are able to offer to improve access, social equity, quality of care, and to reduce total health expenditures.

Canada↗
PubMed1996

Overview of Hospice and Palliative Care in Oncology.

BACKGROUND: The concept of palliative care in oncology has not yet reached the forefront of American medicine, and hospice care may be underused. METHODS: Data on increasing needs for palliative care and the development of the hospice movement are compared with practice behavior patterns of physicians in regard to palliative care. RESULTS: Hospice/palliative care has grown from an alternative health care movement to an accepted part of the American health field. Limitations of hospice/palliative care include health professionals' discomfort with care of the terminally ill as well as difficulties in predicting limited prognoses that may hinder access to such care. CONCLUSIONS: Hospice/palliative care principles should be integrated into other elements of cancer control to ensure comprehensive care for all cancer patients.

Journal Article↗