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At least 235 records · Page 13Linked to original sources
PubMed2000

Automated Talairach atlas labels for functional brain mapping.

An automated coordinate-based system to retrieve brain labels from the 1988 Talairach Atlas, called the Talairach Daemon (TD), was previously introduced [Lancaster et al., 1997]. In the present study, the TD system and its 3-D database of labels for the 1988 Talairach atlas were tested for labeling of functional activation foci. TD system labels were compared with author-designated labels of activation coordinates from over 250 published functional brain-mapping studies and with manual atlas-derived labels from an expert group using a subset of these activation coordinates. Automated labeling by the TD system compared well with authors' labels, with a 70% or greater label match averaged over all locations. Author-label matching improved to greater than 90% within a search range of +/-5 mm for most sites. An adaptive grey matter (GM) range-search utility was evaluated using individual activations from the M1 mouth region (30 subjects, 52 sites). It provided an 87% label match to Brodmann area labels (BA 4 & BA 6) within a search range of +/-5 mm. Using the adaptive GM range search, the TD system's overall match with authors' labels (90%) was better than that of the expert group (80%). When used in concert with authors' deeper knowledge of an experiment, the TD system provides consistent and comprehensive labels for brain activation foci. Additional suggested applications of the TD system include interactive labeling, anatomical grouping of activation foci, lesion-deficit analysis, and neuroanatomy education.

Anatomy, Artistic↗
PubMed2007

Effects of adaptation in maintaining high sensitivity over a wide range of backgrounds for Escherichia coli chemotaxis.

An allosteric model is developed to study the cooperative kinase response of wild-type (wt) Escherichia coli cells to the chemoattractant MeAsp in different ambient MeAsp concentrations. The model, together with wt dose response data, reveals the underlying mechanism for E. coli's ability to maintain high sensitivity over a wide range of backgrounds. We find: 1), Adaptation tunes the system to the steepest part of the dose response curve, where the sensitivity to a given type of stimulus is amplified by the number of corresponding receptors in the (mixed) functional receptor complex. A lower bound on the number of Tar receptor dimers (Na) in the complex Na>approximately 6 is obtained from the measured sensitivity. 2), Accurate adaptation synchronizes the kinase activities from different (uncoupled) receptor complexes in a single cell and is crucial in maintaining the high Hill coefficient in the (population averaged) kinase response curve. 3), The wide dynamic range of the high sensitivity can be explained in our model by either having a very small ratio between ligand dissociation constants of the inactive and the active receptors C=0.006, Na=6, and a (methylation level independent) dissociation constant for the inactive Tar receptor K=18.2 microM or by having K and/or Na increase with receptor methylation level together with a larger value of C>0.01. Specific experiments are suggested to distinguish these two scenarios. 4), The receptor occupancy in a wt cell should also adapt and exhibit a slow (approximately logarithmic) dependence on the ligand concentration in the adapted state; this general prediction can be tested experimentally to verify/falsify our model.

Adaptation, Physiological↗
PubMed2006

High dynamic range image rendering with a Retinex-based adaptive filter.

We propose a new method to render high dynamic range images that models global and local adaptation of the human visual system. Our method is based on the center-surround Retinex model. The novelties of our method is first to use an adaptive filter, whose shape follows the image high-contrast edges, thus reducing halo artifacts common to other methods. Second, only the luminance channel is processed, which is defined by the first component of a principal component analysis. Principal component analysis provides orthogonality between channels and thus reduces the chromatic changes caused by the modification of luminance. We show that our method efficiently renders high dynamic range images and we compare our results with the current state of the art.

Algorithms↗
PubMed2005

Male sterility at extreme temperatures: a significant but neglected phenomenon for understanding Drosophila climatic adaptations.

The thermal range for viability is quite variable among Drosophila species and it has long been known that these variations are correlated with geographic distribution: temperate species are on average more cold tolerant but more heat sensitive than tropical species. At both ends of their viability range, sterile males have been observed in all species investigated so far. This symmetrical phenomenon restricts the temperature limits within which permanent cultures can be kept in the laboratory. Thermal heat sterility thresholds are very variable across species from 23 degrees C in heat sensitive species up to 31 degrees C in heat tolerant species. In Drosophila melanogaster, genetic variations are observed among geographic populations. Tropical populations are more tolerant to heat induced sterility and recover more rapidly than temperate ones. A genetic analysis revealed that about 50% of the difference observed between natural populations was due to the Y chromosome. Natural populations have not reached a selection limit, however: thermal tolerance was still increased by keeping strains at a high temperature, close to the sterility threshold. On the low temperature side, a symmetrical reverse phenomenon seems to exist: temperate populations are more tolerant to cold than tropical ones. Compared to Mammals, drosophilids exhibit two major differences: first, male sterility occurs not only at high temperature, but also at a low temperature; second, sterility thresholds are not evolutionarily constrained, but highly variable. Altogether, significant and sometimes major genetic variations have been observed between species, between geographic races of the same species, and even between strains kept in the laboratory under different thermal regimes. In each case, it is easily argued that the observed variations correspond to adaptations to climatic conditions, and that male sterility is a significant component of fitness and a target of natural selection.

Adaptation, Physiological↗
PubMed1966

Temporal course of thermal adaptation.

Previous methods for measuring the range and temporal course of adaptation to thermal stimuli are difficult to use. A technique requiring subjects to adjust the temperature of the stimulator to maintain a just-de-tectable sensation is described. Complete adaptation occurs to temperatures within the range between 28 degrees and 37.5 degrees C in about 25 minutes.

Humans↗
PubMed1998

Identification, cloning and initial characterisation of FeuPQ in Brucella suis: a new sub-family of two-component regulatory systems.

To cause disease, Brucella species have to adapt to a range of different environments. Environmental sensing and adaptive responses in bacteria often involve the concerted action of a two-component regulatory system, consisting of sensor and response regulator components. Amplification and sequence analysis of response regulators from Brucella species identified a response regulator sequence with 96% similarity to Rhizobium leguminosarum FeuP. In R. leguminosarum, the FeuPQ two-component system is involved in the regulation of iron uptake. A Brucella suis feuP isogenic mutant was constructed but was not attenuated in the murine brucellosis model. The survival and multiplication of the mutant in macrophages was also unaffected. The FeuPQ regulon represents a newly characterised sub-family of response regulators.

Amino Acid Sequence↗
PubMed1995

Vergence adaptation and the order of clinical vergence range testing.

When measuring horizontal relative vergence ranges, the conventional clinical procedure is to assess the base-in (or divergence) range before the base-out (or convergence) determination. The rationale for this order of testing is that the convergence responses stimulated during the base-out measurements may produce vergence adaptation (i.e., a fusional aftereffect), which may temporarily bias the subsequent base-in values in the base-out direction. However, the effect of reversing this order of testing (i.e, base-out before base-in) has not been directly evaluated. Accordingly, the present study compared distance base-in vergence ranges measured both before and after base-out testing at separate test sessions. Additionally, tonic vergence (TV) was assessed before and after each vergence range measurement. The results indicated that base-out vergence range testing stimulated vergence adaptation, and furthermore produced a statistically significant reduction in the subsequently measured base-in recovery value. However, the magnitude of this shift was less than the estimated degree of repeatability of the vergence range measurement. Therefore, a more appropriate order of testing would be to assess the heterophoria compensating range first in order to obtain accurate results during this more critical measurement.

Adaptation, Ocular↗
PubMed2006

Cold-loving microbes, plants, and animals--fundamental and applied aspects.

Microorganisms, plants, and animals have successfully colonized cold environments, which represent the majority of the biosphere on Earth. They have evolved special mechanisms to overcome the life-endangering influence of low temperature and to survive freezing. Cold adaptation includes a complex range of structural and functional adaptations at the level of all cellular constituents, such as membranes, proteins, metabolic activity, and mechanisms to avoid the destructive effect of intracellular ice formation. These strategies offer multiple biotechnological applications of cold-adapted organisms and/or their products in various fields. In this review, we describe the mechanisms of microorganisms, plants, and animals to cope with the cold and the resulting biotechnological perspectives.

Acclimatization↗
PubMed2005

Total lactate dehydrogenase activity of tail muscle is not cold-adapted in nocturnal lizards from cool-temperate habitats.

The dependence of metabolic processes on temperature constrains the behavior, physiology and ecology of many ectothermic animals. The evolution of nocturnality in lizards, especially in temperate regions, requires adaptations for activity at low temperatures when optimal body temperatures are unlikely to be obtained. We examined whether nocturnal lizards have cold-adapted lactate dehydrogenase (LDH). LDH was chosen as a representative metabolic enzyme. We measured LDH activity of tail muscle in six lizard species (n=123: three nocturnal, two diurnal and one crepuscular) between 5 and 35 degrees C and found no differences in LDH-specific activity or thermal sensitivity among the species. Similarly, the specific activity and thermal sensitivity of LDH were similar between skinks and geckos. Similar enzyme activities among nocturnal and diurnal lizards indicate that there is no selection of temperature specific LDH enzyme activity at any temperature. As many nocturnal lizards actively thermoregulate during the day, LDH may be adapted for a broad range of temperatures rather than adapted specifically for the low temperatures encountered when the animals are active. The total activity of LDH in tropical and temperate lizards is not cold-adapted. More data are required on biochemical adaptations and whole animal thermal preferences before trends can be established.

Adaptation, Physiological↗
PubMed2003

Horizontal acquisition of divergent chromosomal DNA in bacteria: effects of mutator phenotypes.

We examine the potential beneficial effects of the expanded access to environmental DNA offered by mutators on the adaptive potential of bacterial populations. Using parameters from published studies of recombination in E. coli, we find that the presence of mutators has the potential to greatly enhance bacterial population adaptation when compared to populations without mutators. In one specific example, for which three specific amino acid substitutions are required for adaptation to occur in a 300-amino-acid protein, we found a 3500-fold increase in the rate of adaptation. The probability of a beneficial acquisition decreased if more amino acid changes, or integration of longer DNA fragments, were required for adaptation. The model also predicts that mutators are more likely than nonmutator phenotypes to acquire genetic variability from a more diverged set of donor bacteria. Bacterial populations harboring mutators in a sequence heterogeneous environment are predicted to acquire most of their DNA conferring adaptation in the range of 13-30% divergence, whereas nonmutator phenotypes become adapted after recombining with more homogeneous sequences of 7-21% divergence. We conclude that mutators can accelerate bacterial adaptation when desired genetic variability is present within DNA fragments of up to approximately 30% divergence.

Data Interpretation, Statistical↗
PubMed2005

Modulation effect of the atmosphere in a pyramid wave-front sensor.

The pyramid wave-front sensor in its original form works with a mechanical modulation that adapts the linear range of the sensor to seeing and sensing conditions. For adaptive optics systems working in an astronomical context, the way in which the aberrations produced by the atmospheric turbulence, which are not seen by the sensor owing to its limited temporal bandwidth, act as modulators is shown. These aberrations have the same effect of increasing the linear range and localizing the measurement as does mechanical modulation. The effect of residual wave-front aberrations is estimated for some example conditions of telescope diameter, system bandwidth, wind velocity, and Fried parameter.

Journal Article↗
PubMedDate not supplied

[Structural changes in the nuclei of human lymphocytes under the effects of ionizing radiation within the range of doses that cause the adaptive response].

Low-level radiation either from external, or from incorporated sources is shown to cause a non-monotonous change in some intranuclear parameters of human peripheral blood lymphocytes. For instance, radiation induces changes in the parameters that characterize the location of perecentromeric regions within the interphase nucleus and a non-monotonous increase in nuclear sizes. The exposure to doses exceeding 5 cGy impairs the relationship between the nuclear sizes and location therein of the perecentromeric regions of interphase chromosomes which exist in the control and after exposure to 2.5 cGy. Differences between the dose ranges of 1.5-3.5 and 17-25 cGy are manifested by the kinetics of restoration of the pattern of distribution of lymphocyte nuclear sizes.

Adaptation, Biological↗
PubMed2003

Time course and extent of mechanotransducer adaptation in mouse utricular hair cells: comparison with frog saccular hair cells.

Whole cell transduction currents were recorded from hair cells in early postnatal mouse utricles in response to step deflections of the hair bundle. For displacement steps delivered by a stiff probe (1-ms rise time), half-maximal responses decayed monoexponentially with a mean time constant of 30 ms. Adaptation and other transduction properties did not vary systematically with hair cell type (I vs. II) or region (striola vs. extrastriola). Thus regional variation in the phasic properties of utricular afferents arises through other mechanisms. When bundles were deflected by a fluid jet, which delivers force steps, transduction currents decayed about 3-fold more slowly than during displacement steps. A simple model of myosin-mediated adaptation predicts such slowing through forward creep of the bundle during a force step. For a faster stiff probe (rise time 200 micros), step responses of both mouse utricular and frog saccular hair cells decayed with two exponential components, which may correspond to distinct feedback processes. For half-maximal responses, the two components had mean time constants of 5 and 45 ms (mouse) and 2 and 18 ms (frog). The fast and slow components dominated the decay of responses to small and large stimuli, respectively. Adaptation shifts the instantaneous operating range in the direction of the adapting step. In frog saccular hair cells, the operating range shift is a constant percentage of the displacement. In mouse utricular hair cells, the percentage shift increases for large displacements, extending the range of background stimuli over which adaptation can restore instantaneous sensitivity.

Adaptation, Physiological↗
PubMed2000

Effect of eugenol-containing sealer on marginal adaptation of dentine-bonded resin fillings.

AIM: Eugenol is claimed to interfere with the polymerization of composite resins and to affect shear bond strengths of dentine-bonded composite restorations. Eugenol-based sealers are used during root canal treatment in teeth that may require build-ups or extensive restorations. Unfortunately, the adverse effect of eugenol has mostly been assessed in shear bond tests and this variable may be clinically inappropriate. The current study evaluate the effect of eugenol in a eugenol-based endodontic sealer on marginal adaptation of composite resin restorations with and without thermo-mechanical stress. METHODOLOGY: Thirty Class V cavities with half of the cavity margins in dentine and half of the cavity margins in enamel were prepared in extracted human premolars and then divided into 5 groups. Teeth in group 1 were not contaminated with eugenol. Cavities in groups 2-4 were contaminated with a eugenol-based sealer (Tubli-Seal, Kerr) and cleaned with: (i) sandblasting, (ii) bur finishing alone or (iii) bur finishing combined with swabbing with alcohol. These 4 groups were temporized for 6 weeks (Ketac, ESPE), whilst group 5 received no eugenol, was not temporized and acted as the control. Cavities were restored with Tetric Ceram using Syntac Classic (Vivadent) as a dentine-bonding agent. The specimens were then thermo-mechanically stressed. The percentages of marginal adaptation in dentinal and enamel margins were assessed in a SEM at x200 magnification before and after stress using a replica method. Mean percentages of marginal adaptation were calculated and compared using a two way-ANOVA (influence of eugenol and cleaning procedure) and non-parametric tests. RESULTS: Marginal adaptation in enamel exceeded 95% and 92% in all specimens before and after thermo-mechanical stress, respectively. Before stress, marginal adaptation in dentine ranged from 92.3 +/- 7.9% to 95.7 +/- 6.2% in groups 1-5. After stress, the percentage of marginal adaptation in dentine decreased significantly overall (P < 0.05, range 39.8 +/- 21.1% to 82.9 +/- 13.7%). The effect of contamination with eugenol was not significant (P > 0.05): in contrast, there was a significantly beneficial effect when the entire cavity was finished with burs (P < 0.01). CONCLUSIONS: Under the conditions of this study, the eugenol containing sealer did not significantly impair marginal adaptation in dentinal margins of mixed Class V restorations when bur finishing was employed before placement. However, no other cleaning method was sufficient to produce acceptable figures of marginal adaptation.

Analysis of Variance↗
PubMedDate not supplied

[Morphophysiological adaptation to feeding in Aplysia dactylomela (Rang, 1828)].

Hemoglobin content in radular muscle and relative weight of the main viscera were determined in Aplysia dactylomela. We propose that relatively low concentration of tissue hemoglobin as well as low heart and ctenidium indices are due to the mode of the mollusk nutrition. Nutrition by biting algae fragments requires less muscular effort than, for instance, scrapping off overgrowth from substrate and, hence, is accompanied by lower indices.

Adaptation, Physiological↗
PubMed2005

Enzootic transmission of Trypanosoma cruzi and T. rangeli in the Federal District of Brazil.

The Federal District of Brazil (DF) lies within the Cerrado biome, where open shrubland (savannas) is interspersed with riverside gallery forests and permanent swamps (veredas). Trypanosoma cruzi-infected native triatomines occur in the area, but the enzootic transmission of trypanosomatids remains poorly characterized. A parasitological survey involving sylvatic triatomines (166 Rhodnius neglectus collected from Mauritia flexuosa palms) and small mammals (98 marsupials and 70 rodents, totaling 18 species) was conducted in 18 sites (mainly gallery forests and veredas) of the DF. Parasites were isolated, morphologically identified, and characterized by PCR of nuclear (mini-exon gene) and kinetoplast DNA (kDNA). Six R. neglectus, seven Didelphis albiventris and one Akodon cursor were infected by trypanosomes; wild reservoir infection is documented for the first time in the DF. kDNA PCR detected T. cruzi in five R. neglectus and mini-exon gene PCR revealed T. cruzi I in isolates from D. albiventris. Parasites infecting one bug yielded T. rangeli KP1+ kDNA amplicons. In spite of the occurrence of T. cruzi-infected D. albiventris (an important wild and peridomestic reservoir) and R. neglectus (a secondary vector displaying synanthropic behavior), a low-risk of human Chagas disease transmission could be expected in the DF, considering the low prevalence infection recorded in this work. The detection of T. rangeli KP1+ associated with R. neglectus in the DF widens the known range of this parasite in Brazil and reinforces the hypothesis of adaptation of T. rangeli populations (KP1+ and KP1-) to distinct evolutionary Rhodnius lineages.

Animals↗
PubMedDate not supplied

Does the neurotransmitter transporter underlie adaptation at a histaminergic photoreceptor synapse?

Using autoradiographic and biochemical techniques, we studied the sodium-dependent forward and reverse transport of the neurotransmitter histamine in an arthropod photoreceptor in order to test whether the transporter plays a central role in visual signal transfer at this synapse. In particular, we asked whether the histamine transporter might be the important factor in synaptic adaptation, the process by which the operating range of the synapse adapts to increasing depolarizations of the photoreceptor in increasing background light. Drugs known from electrophysiological observations to interfere with synaptic adaptation blocked the uptake of [3H]histamine into photoreceptors. These drugs also blocked the sodium (Na)-triggered efflux of [3H]histamine, previously loaded into photoreceptors, via the histamine transporter. Several lines of evidence showed that efflux of [3H]histamine did not occur via calcium-dependent exocytosis. First, efflux occurred when the preparation was bathed in calcium (Ca)-free/EGTA salines or in cobalt (Co)-containing salines. Even more importantly, efflux could be elicited from axons, whose membranes must contain the transporter protein since they take up [3H]histamine independently from the presynaptic terminals. Since both adaptation and the histamine transporter are blocked by the same agents, the transporter may underlie adaptation by maintaining the cleft histamine concentration in a particular range independent of light intensity. We also characterized the transporter further and found that it is partially dependent on chloride ions, and that neither [3H]norepinephrine nor [3H]dopamine are transported (at 20 microM), adding to evidence that the transporter is highly selective for histamine.

Adaptation, Physiological↗