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PubMedDate not supplied

[Conformational analysis of cysteine-containing peptides and prospects of their application to 213Bi chelating in antitumor therapy].

The method of conformational analysis was applied to the spatial structures of peptide analogues of phytochelatins and some fragments of metallothioneins: (Cys-Gly)3, (Cys-Gly)3Asp, (Cys-Gly)3Glu, (Cys-betaAla)3, (Cys-gammaGlu)3, and (Cys-Gly-Gly)3. All the possible low-energy conformations of the molecules were revealed and the role of intra- and inter-residual interactions in the formation of their spatial structures was determined. A different tendency of the molecules under study for acceptance of conformations favorable for binding bismuth ions was shown. Low-energy structures providing an optimum binding of bismuth ion were shown to be most frequent for (Cys-betaAla)3 peptide. Among the analogues of peptide fragments of the metallothioneins, lacking in natural peptides, low-energy pentapeptide CCXXC fragments (where X = Gln, Asn, Phe, Tyr, and Gly) were revealed. In the alpha-helical conformations of these pentapeptides, the distance between the sulfur atoms corresponds to that in Bi2S3. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2006, vol. 32, no. 3; see also http://www.maik.ru.

Animals↗

PubMed2003

Dynamo effect in a driven helical flow.

The Roberts flow, a helical flow in the form of convectionlike rolls, is known to be capable of both kinematic and nonlinear dynamo action. We study the Roberts dynamo with particular attention being paid to the spatial structure of the generated magnetic field and its back-reaction on the flow. The dynamo bifurcation is decisively determined by the symmetry group of the problem, which is given by a subgroup of discrete transformations and a continuous translational invariance of the flow. In the bifurcation the continuous symmetry is broken while the discrete subgroup symmetry completely survives. Its actions help in understanding the spatial structures of the magnetic field and of the modified flow. In accordance with experimental observations, the magnetic field component perpendicular to the originally invariant direction is much stronger than the component in this direction. Furthermore, the magnetic field is largely concentrated in layers separating the convectionlike rolls of the flow and containing, in particular, its stagnation points, which are isolated for the modified flow while they are line filling for the original Roberts flow. The magnetic field is strongest near beta-type stagnation points, with a two-dimensional unstable and a one-dimensional stable manifold, and is weak near alpha-type stagnation points, with a two-dimensional stable and a one-dimensional unstable manifold. This contrasts with the usual picture that dynamo action is promoted at the alpha points and impeded at the beta points. Both the creation of isolated stagnation points and the concentration of strong fields at the beta points may be understood as a result of the way in which the Roberts dynamo saturates. It is also found that, while the original Roberts flow is regular, the modified flow is chaotic in the layers between the convectionlike rolls where the magnetic field is concentrated. This chaoticity, which results from the back-reaction of the magnetic field on the flow, appears to merely enhance magnetic diffusion rather than to strengthen the dynamo effect.

Journal Article↗

PubMed1995

Temporal structure in spatially organized neuronal ensembles: a role for interneuronal networks.

Network oscillations are postulated to be instrumental for synchronizing the activity of anatomically distributed populations of neurons. Results from recent studies on the physiology of cortical interneurons suggest that through their interconnectivity, they can maintain large-scale oscillations at various frequencies (4-12 Hz, 40-100 Hz and 200 Hz). We suggest that networks of inhibitory interneurons within the forebrain impose co-ordinated oscillatory 'contexts' for the 'content' carried by networks of principal cells. These oscillating inhibitory networks may provide the precise temporal structure necessary for ensembles of neurons to perform specific functions, including sensory binding and memory formation.

Animals↗

PubMed2005

The relative importance of spatial versus temporal structure in the perception of biological motion: an event-related potential study.

We investigated how the spatiotemporal structure of animations of biological motion (BM) affects brain activity. We measured event-related potentials (ERPs) during the perception of BM under four conditions: normal spatial and temporal structure; scrambled spatial and normal temporal structure; normal spatial and scrambled temporal structure; and scrambled spatial and temporal structure. As in a previous study, we identified two negative components at both occipitotemporal regions: N210 reflected general motion processing while N280 reflected the processing of BM. We analyzed the averaged ERPs in the 200-300 ms response time window and found that spatial structure had a substantial effect on the magnitude of the averaged response amplitude in both hemispheres. This finding suggests that spatial structure of point-lights elicits a stronger response in the occipitotemporal region than temporal structure for the BM perception.

Adolescent↗

PubMed1981

Sensilla of the cricket palp. Fine structure and spatial organization.

On the distal segment of the maxillary palp of the cricket Gryllus bimaculatus there is an extensive multimodal sensory field comprising approximately 5000 sensilla of nine morphologically distinguishable types: three types containing pores in their walls (5% of the total), three types with a pore at the tip (65%) and three types lacking pores (30%). The approximately 27,000 axons of their sense cells join in the distal palp segment to form two nerves. On the slightly smaller sensillum field on the tip of the labial palp, the same sensillum types are found in comparable density and proportion. By analogy with sensilla of which both structure and function are known, the structure of these three groups of sensillum types suggests that they function as olfactory, contact-chemoreceptive, and/or mechanoreceptive sensors. Moreover, the positioning of the sensilla on the tip of the palp is appropriate to these function. The cuticle of the pulp tip is elastically deformable; all sensory hairs are fixed via a special, presumably flexible socket suspension. These structural features could be an adaptation to stresses encountered during tactile activity of the palp.

Animals↗

PubMed2002

Differences in spatial autocorrelation between four sub-populations of Alnus trabeculosa Hand.-Mazz. (Betulaceae).

To investigate the spatial structure of Alnus trabeculosa Hand.-Mazz, we compared three sub-populations at Imaichi in Tochigi Prefecture and one sub-population at Juo in Ibaraki Prefecture, Japan. A total of 269 trees, covering 0.71 ha in total, were mapped and genetically analyzed using nine enzyme systems encoding 13 isozyme loci. There were no significant differences between the four sub-populations in terms of Na,Ne, H(o), H(e )and F(IS). However, according to spatial autocorrelation analysis, the Juo sub-population, which is younger than the others, showed an aggregation of multilocus genotypes, especially within 25 m radii. In contrast with the Juo sub-population, those in Imaichi showed no clear spatial structuring. In the three Imaichi sub-populations, gametic phase disequilibrium is attributable to heterogeneity of genotype frequencies, but in the Juo sub-population it seems to be due to other factors, connected with the composition of the trees in the sub-population and/or its founder population, gene flow and asexual propagation. To conserve as much as possible of the genes or genotypes in restricted areas, conservation of populations that do not show clear family structures, such as those in Imaichi, would be most effective.

Betulaceae↗

PubMed1998

Creating intracellular structural domains: spatial segregation of actin and tropomyosin isoforms in neurons.

Actin microfilaments play a direct role in a variety of cell processes. Distinct populations of microfilaments are associated with different cellular compartments, such as growth cones, filipodia, stress fibers, and lamellipodia. It is becoming clear that these different populations are often composed of different isoforms of the two core microfilament components, actin and tropomyosin. This is particularly true in neurons, where actin and tropomyosin isoforms are segregated into different intracellular compartments which correspond to functionally distinct regions of the neuron. Developmental regulation of this isoform sorting suggests a specific role for some isoforms in growth and for others in stabilization of neuronal structure. This provides a mechanism by which a neuron can create and independently regulate intracellular domains composed of microfilaments with different functional properties.

Actin Cytoskeleton↗

PubMed2001

Membrane binding motif of the P-type cardiotoxin.

Carditoxins (CTXs) from cobra snake venoms, the basic 60-62 residue all-beta sheet polypeptides, are known to bind to and impair the function of cell membranes. To assess the membrane induced conformation and orientation of CTXs, the interaction of the P-type cardiotoxin II from Naja oxiana snake venom (CTII) with perdeuterated dodecylphosphocholine (DPC) was studied using ( 1 )H-NMR spectroscopy and diffusion measurements. Under conditions where the toxin formed a well-defined complex with DPC, the spatial structure of CTII with respect to the presence of tightly bound water molecules in loop II, was calculated using the torsion angle dynamics program DYANA. The structure was found to be similar, except for subtle changes in the tips of all three loops, to the previously described "major" form of CTII in aqueous solution illustrated by the "trans" configuration of the Val7-Pro8 peptide bond. No "minor" form with the "cis" configuration of the above bond was found in the micelle-bound state. The broadening of the CTII backbone proton signals by 5, 16-doxylstearate relaxation probes, together with modeling based on the spatial structure of CTII, indicated a periphery mode of binding of the toxin molecule to the micelle and revealed its micelle interacting domain. The latter includes a hydrophobic region of CTII within the extremities of loops I and III (residues 5-11, 46-50), the basement of loop II (residues 24-29,31-37) and the belt of polar residues encircling these loops (lysines 4,5,12,23,50, serines 11,46, histidine 31, arginine 36). It is suggested that this structural motif and the mode of binding can be realized during interaction of CTXs with lipid and biological membranes.

Amino Acid Motifs↗

PubMed1999

Speed tuning in elementary motion detectors of the correlation type.

A prominent model of visual motion detection is the so-called correlation or Reichardt detector. Whereas this model can account for many properties of motion vision, from humans to insects (review, Borst and Egelhaaf 1989), it has been commonly assumed that this scheme of motion detection is not well suited to the measurement of image velocity. This is because the commonly used version of the model, which incorporates two unidirectional motion detectors with opposite preferred directions, produces a response which varies not only with the velocity of the image, but also with its spatial structure and contrast. On the other hand, information on image velocity can be crucial in various contexts, and a number of recent behavioural experiments suggest that insects do extract velocity for navigational purposes (review, Srinivasan et al. 1996). Here we show that other versions of the correlation model, which consists of a single unidirectional motion detector or incorporates two oppositely directed detectors with unequal sensitivities, produce responses which vary with image speed and display tuning curves that are substantially independent of the spatial structure of the image. This surprising feature suggests simple strategies of reducing ambiguities in the estimation of speed by using components of neural hardware that are already known to exist in the visual system.

Models, Theoretical↗

PubMed2004

Scanning tunneling microscopy of sulfur and benzenethiol chemisorbed on Ru(0001) in 0.1 M HClO4.

In situ scanning tunneling microscopy (STM) combined with linear sweep voltammetry was used to examine spatial structures of sulfur adatoms (SA) and benzenethiol (BT) molecules adsorbed on an ordered Ru(0001) electrode in 0.1 M HClO4. The Ru(0001) surface, prepared by mechanical polishing and electrochemical reduction at -1.5 V (vs RHE) in 0.1 M HClO4, contained atomically flat terraces with an average width of 20 nm. Cyclic voltammograms obtained with an as-prepared Ru(0001) electrode in 0.1 M HClO4 showed characteristics nearly identical to those of Ru(0001) treated in high vacuum. High-quality STM images were obtained for SA and BT to determine their spatial structures as a function of potential. The structure of the SA adlayer changed from (2 x mean square root of 3)rect to domain walls to (mean square root of 7 x mean square root of 7)R19.1 degrees and then to disordered as the potential was scanned from 0.3 to 0.6 V. In contrast, molecules of BT were arranged in (2 x mean square root of 3)rect between 0.1 and 0.4 V, while they were disordered at all other potentials. Adsorption of BT molecules was predominantly through the sulfur headgroup. Sulfur adatoms and adsorbed BT molecules were stable against anodic polarization up to 1.0 V (vs RHE). These two species were adsorbed so strongly that their desorption did not occur even at the onset potential for the reduction of water in 0.1 M KOH.

Journal Article↗

PubMedDate not supplied

[Spatial-temporal structure of the organization of goal-directed behavior under the action of delta 9-tetrahydrocannabinol].

The effect of delta-9-tetrahydrocannabinol (delta-9-THC) on the goal-directed behavior was studied by the pattern recognition theory methods on cats trained for a differentiated response, to structured visual stimuli. Administration of delta-9-THC was shown to cause noncoordination of certain neocortex regions as well as disagreement of temporal characteristics of the processes involved in the goal-directed behavior organization.

Animals↗

PubMed2006

Structural and spatially resolved studies on the hardening of a commercial resin-modified glass-ionomer cement.

A commercial photopolymerizable resin-modified glass-ionomer (Fuji II LC) was studied using a variety of nuclear magnetic resonance (NMR) techniques. (1)H and (19)F stray-field imaging (STRAFI) enabled to follow the acid-base reaction kinetics in self-cured (SC) samples. Gelation and maturation processes with 25 min and 40 h average time constants, respectively, were distinguished. In self- & photo-cured (SPC) samples, two processes were also observed, which occurred with 2 s and 47 s average time constants. (1)H, (27)Al and (29)Si magic angle spinning (MAS) NMR, (13)C cross-polarization (CP)/MAS NMR and (27)Al multiple quanta (MQ)MAS NMR spectroscopy were used to obtain structural information on the glass and cements that were either SC or SPC. The presence of methacrylate groups was identified in the solid component. Unreacted hydroxyl ethylmethacrylate (HEMA) was detected in self-cured cement. (27)Al data showed that approximately 28% and 20% of Al is leached out from glass particles in SC and SPC samples, respectively. The upfield shift detected in (29)Si MAS NMR spectra of the cements is consistent with a decrease in the number of Al species in the second coordination sphere of the silicon structures. Scanning electron microscopy (SEM) showed existence of 3D shrinkage of the cement matrix in photo-cured cements.

Glass Ionomer Cements↗

PubMed1997

Influence of boundary information on the perception of color.

The integration of color and form to produce a unified percept is a central problem in vision research. We know that the spatial arrangement of colored stimuli influences their detectability. In the gap effect, for example, a small gap between two colored fields enhances their discriminability [Opt. Acta 24, 159 (1977)]. Chromatic thresholds are also reduced when test fields are spatially demarcated. To explore the mechanisms underlying these types of effect, the influence of spatial structure on chromatic sensitivity for gratings was measured. For sine-wave and square-wave gratings modulated in different directions in color space, contrast sensitivity was measured by using a two-alternative forced-choice procedure with a QUEST staircase. Thin lines, of the same orientation as that of the grating, were superimposed on it at half-cycle intervals. The phase of the superimposed lines was varied. For S-cone modulated gratings, dark lines placed at the midpoints between peaks and troughs (90 degrees) increased sensitivity. As the phase of the lines moved toward the peaks (0 degree), their effect on sensitivity declined to zero. A similar but smaller effect was seen for isoluminant L- and M-cone modulated gratings. The superimposed lines always impaired contrast sensitivity for achromatic gratings, especially at a phase of 0 degree. Spatial structure superimposed on gratings can both facilitate and impair contrast sensitivity. In the presence of sharp boundaries, chromatic sensitivity is increased. This effect may depend more on the salience of boundaries, since isoluminant lines superimposed on S-cone modulated gratings and gray lines of similar cone contrast can facilitate detection if they are of sufficient contrast. Achromatic contrast sensitivity is reduced when the boundaries are present. The additional luminance information at the boundaries masks the grating. A simple model in which spatial integration is arrested at the positions of the superimposed lines fits only the isoluminant conditions. For both luminance and chromatic contrast the change in sensitivity depends on phase.

Color Perception↗

PubMed1988

Negative cortical DC shifts preceding and accompanying simultaneous and sequential finger movements.

Cortical DC shifts preceding and accompanying the execution of five different bimanual motor tasks were analysed in 20 subjects. All tasks required repetitive flexions and extensions of the two forefingers for a period of at least six seconds. The temporal and spatial structures organization varied in the different tasks: (1) Simultaneous agonistic performance (forefinger flexion on both sides), (2) simultaneous antagonistic performance (e.g. flexion of the right, extension of the left forefinger), (3) sequential agonistic performance, (4) sequential antagonistic performance, (5) uncoordinated flexions and extensions of the two forefingers. Compared to (1) and (2), conditions (3) and (4) included a temporal delay between the performance of the two forefingers; compared to (1) and (3), conditions (2) and (4) required the subjects to perform movements of opposite directions with their two forefingers. Effects of the temporal factor (T; simultaneous vs. sequential) and the spatial factor (S; agonistic vs. antagonistic) on cortical DC shifts were investigated. The voluntary initiation of each motor task was preceded by a Bereitschaftspotential (BP). The performance of the complex tasks (1-4) was accompanied by a slow negative DC potential shift (N-P). In general, the BP did not differ depending on the temporal or spatial structures of the tasks (1-4). However, amplitudes of N-P (i.e. during tasks) were influenced by the temporal factor with significantly larger amplitudes in sequential than in simultaneous tasks. This difference was not a global phenomenon in all recordings but was selectively found in the recordings over the fronto-central midline.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2002

Adaptive divergence in experimental populations of Pseudomonas fluorescens. I. Genetic and phenotypic bases of wrinkly spreader fitness.

A central feature of all adaptive radiations is morphological divergence, but the phenotypic innovations that are responsible are rarely known. When selected in a spatially structured environment, populations of the bacterium Pseudomonas fluorescens rapidly diverge. Among the divergent morphs is a mutant type termed "wrinkly spreader" (WS) that colonizes a new niche through the formation of self-supporting biofilms. Loci contributing to the primary phenotypic innovation were sought by screening a WS transposon library for niche-defective (WS(-)) mutants. Detailed analysis of one group of mutants revealed an operon of 10 genes encoding enzymes necessary to produce a cellulose-like polymer (CLP). WS genotypes overproduce CLP and overproduction of the polymer is necessary for the distinctive morphology of WS colonies; it is also required for biofilm formation and to maximize fitness in spatially structured microcosms, but overproduction of CLP alone is not sufficient to cause WS. A working model predicts that modification of cell cycle control of CLP production is an important determinant of the phenotypic innovation. Analysis of >30 kb of DNA encoding traits required for expression of the WS phenotype, including a regulatory locus, has not revealed the mutational causes, indicating a complex genotype-phenotype map.

Adaptation, Physiological↗

PubMed2003

Nuclear and chloroplast genetic structure indicate fine-scale spatial dynamics in a neotropical tree population.

Dicorynia guianensis is a canopy tree, endemic to the tropical rain forest of French Guiana. We compared generational and spatial genetic structure for maternally and biparentally inherited markers in two cohorts (adult and seedling) in order to infer processes shaping the distribution of genetic diversity. The study was conducted on a 40 ha study plot located at Paracou near Kourou, where 172 adults trees and 375 saplings were sampled. Aggregation of trees was therefore suggested at different distances, ranging from 100 to 400 m. There was a strong link between demographic and genetic spatial structures at small distances (less than 100 m) that is likely to be the consequence of restricted seed dispersal. Genetic differentiation was more pronounced between spatial aggregates than between cohorts. Despite the spatial differentiation, the species was able to maintain high levels of diversity for maternal genomes, suggesting rapid turnover of aggregates. Spatial autocorrelation was larger for chloroplast than nuclear markers indicating a strong asymmetry between pollen and seed flow. Fixation indices indicated a lower heterozygote deficiency for the adults, maybe because of gradual elimination of selfed trees. Genetic relatedness at lower distances was higher in adult trees than in saplings, as a result of generation overlapping in the adult cohort. Overall, our results confirm earlier biological knowledge about the dispersion mechanisms of the species, and lead to an enhanced role of spatial processes in the dynamics of genetic diversity of D. guianensis.

Cell Nucleus↗

PubMed2005

Spread of parasites in metapopulations: an experimental study of the effects of host migration rate and local host population size.

We established experimental metapopulations of the flour beetle, Tribolium castaneum, and its ectoparasitic mite, Acarophenax tribolii, to investigate the effects of host migration rate and local host population size on the spread of mite infections. Global prevalence across our metapopulations was less than half the observed within-patch prevalence, so that spatial structure alone afforded a great deal of protection to hosts against parasite infection. Our results showed further that migration played a determining role in occupancy, the number of patches infected within a metapopulation, while host population size played a determining role in local prevalence, the fraction of hosts infected within local patches. Local and global prevalence appeared to reach equilibrium levels on 2 different time-scales. Local host prevalence reached equilibrium values within 30 days of receiving an infected host migrant. Global prevalence increased more slowly and was clearly dependent upon occupancy, the number of host patches with at least 1 infected host, which in turn depended on the level of host migration among host patches. The effect of population size was not limited to local prevalence in patches without spatial structure but extended to sets of patches across the metapopulation. Lloyd's index of patchiness differed significantly between metapopulations with small versus large numbers of hosts. Although parasites were aggregated on hosts for both local patch sizes, they tended to aggregate to a much greater degree at the smaller host patch size. We discuss our empirical findings in light of current epidemiological theory.

Animals↗

PubMed1996

Relation of chemical structure to spatial distribution of sensory responses in rat olfactory epithelium.

1. Electroolfactogram (EOG) recordings were made in three configurations from the rat olfactory epithelium. Each configuration compared recordings in the dorsomedial recess of the epithelium with recordings in ventral or lateral parts of the epithelium. Most comparisons were made with simultaneous recordings. The exception was a series in which the dorsal recess and lateral space between the base of two turbinate bones were directly exposed for odor application and recording. The spatial distributions of maximal responses were largely independent of recording configuration. 2. Simultaneous recordings compared dorsomedial and lateral sites in the epithelium during stimulation with a series of 50 odorants. The odorants that evoked larger responses in the lateral sites were usually compounds that lacked oxygen containing functional groups (such as the carbonyl group). This was true for straight chain and cyclic alkanes, for terpine compounds, and for aromatic compounds. The major exception was cineole, a bicyclic compound. All compounds containing ketone groups evoked larger dorsomedial responses. The responses of aldehydes and esters depended upon whether they were attached to aliphatic or aromatic chains. 3. In the three types of preparation, the sites responding best to ketones were in the same expression zone of the epithelium according to published maps for the rat and mouse. The sites responding best to odors without functional groups were in the far lateral or ventral region and corresponded to one of the two most lateral and ventral expression zones. This fact suggests that the receptors in these regions have a preference for particular chemical properties. This level of analysis cannot determine whether all receptors in each zone have a stronger response to certain properties of these odorants or whether each zone contains different proportions of receptors with these properties.

Anesthesia, Inhalation↗