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At least 1,207 records · Page 67Linked to original sources
PubMed2005

Mechano-sensitive orientation of cortical microtubules during gravitropism in azuki bean epicotyls.

The orientation of cortical microtubules (cMT) during gravitropism was studied in epidermal cells of azuki epicotyls. The relative proportion of cells with longitudinal cMT increased in the upper epidermis, and those with transverse cMT increased in the lower epidermis. When epicotyls were kept straight during gravistimulation, no change in cMT orientation occurred in either the upper and lower epidermis. When epicotyls were forced to bend downward, cells with transverse cMT increased in the upper epidermis, and those with longitudinal cMT increased in the lower epidermis. When epicotyls were loaded with naphthylphthalamic acid, an inhibitor of auxin transport, both gravitropic bending and change in cMT orientation were inhibited. However, when a change in cMT orientation was induced by forced downward bending, cells with longitudinal cMT increased in the compressed (lower) side and those with transverse cMT increased in the extended (upper) side. It was suggested that cMT orientation was controlled by the bending of the epicotyl and not by a gravity signal per se. Loading with Gd3+, an inhibitor of the stretch-activated channel, did not inhibit gravitropic bending. However, it inhibited cMT reorientation induced by gravitropic bending and by forced bending. Involvement of the stretch-activated channel in mechano-sensitive orientation of cMT was suggested.

Fabaceae↗
PubMed2006

Optimized diffusion gradient orientation schemes for corrupted clinical DTI data sets.

OBJECT: A method is proposed for generating schemes of diffusion gradient orientations which allow the diffusion tensor to be reconstructed from partial data sets in clinical DT-MRI, should the acquisition be corrupted or terminated before completion because of patient motion. MATERIALS AND METHODS: A general energy-minimization electrostatic model was developed in which the interactions between orientations are weighted according to their temporal order during acquisition. In this report, two corruption scenarios were specifically considered for generating relatively uniform schemes of 18 and 60 orientations, with useful subsets of 6 and 15 orientations. The sets and subsets were compared to conventional sets through their energy, condition number and rotational invariance. Schemes of 18 orientations were tested on a volunteer. RESULTS: The optimized sets were similar to uniform sets in terms of energy, condition number and rotational invariance, whether the complete set or only a subset was considered. Diffusion maps obtained in vivo were close to those for uniform sets whatever the acquisition time was. This was not the case with conventional schemes, whose subset uniformity was insufficient. CONCLUSION: With the proposed approach, sets of orientations responding to several corruption scenarios can be generated, which is potentially useful for imaging uncooperative patients or infants.

Algorithms↗
PubMed2006

Prevalence and stability of sexual orientation components during adolescence and young adulthood.

Analyses of three waves (6 years) of the National Longitudinal Survey of Adolescent Health data explored the prevalence and stability of sexual orientation and whether these two parameters varied by biologic sex, sexual orientation component (romantic attraction, sexual behavior, sexual identity), and degree of component. Prevalence rates for nonheterosexuality varied between 1 and 15% and depended on biologic sex (higher among females), sexual orientation component (highest for romantic attraction), degree of component (highest if "mostly heterosexual" was included with identity), and the interaction of these (highest for nonheterosexual identity among females). Although kappa statistics testing for temporal stability across waves were significant, they failed to reach acceptable levels of agreement and could be largely attributable to the stability of opposite-sex rather than same-sex attraction and behavior. Migration over time among sexual orientation components was in both directions, from opposite-sex attraction and behavior to same-sex attraction and behavior and vice versa. To assess sexual orientation, investigators should measure multiple components over time or abandon the general notion of sexual orientation and measure only those components relevant for the research question.

Adolescent↗
PubMed2006

Separated local field NMR experiments on oriented samples rotating at the magic angle.

Biophysical studies on membrane proteins by solid state NMR (SSNMR) can be carried out directly in a membrane environment. Samples are usually prepared in form of multi-lamellar dispersions for magic angle sample spinning or as aligned multi-layers for orientation dependent NMR experiments without sample rotation. A new development is the application of MAS NMR to aligned samples (MAOSS; Magic Angle Oriented Sample Spinning). In combination with separated local field (SLF) experiments, size and orientation of heteronuclear dipolar couplings may be extracted from two-dimensional experiments which correlate dipolar couplings with isotropic chemical shifts. The orientation of these (1)H-X dipolar couplings can be directly related to the orientation of molecular groups in the sample. Here, we demonstrate the feasibility of these experiments on highly ordered polyethylene fibers which serve as model compound. Based on these data, the experiment is also applied to ordered multi-layers of bacteriorhodopsin (purple membrane) which is used as a model for aligned membrane proteins. We present a detailed analysis of different experimental designs with respect to angular sensitivity and the influence of residual sample disorder ("mosaic spread"). The results of the MAOSS-SLF experiment are discussed within the context of established solid state NMR experiments which are usually performed without sample rotation and we compare the data to orientation information obtained from X-ray diffraction.

Bacteriorhodopsins↗
PubMed1978

Photovoltages in suspensions of magnetically oriented chloroplasts.

The photovoltage of suspensions of magnetically oriented chloroplasts using polarized light of 680 nm has been measured. The magnitude of the photo e.m.f. depends on the polarization of the light and on its direction of propagation with respect to the oriented thylakoid planes. This photo e.m.f. is qualitatively attributed to the Dember effect which arises when inhomogeneous light absorption gives rise to a gradient of positive and negative charges along x , where x is the direction defined by the propagation vector of the light and which is also the direction joining the two electrodes. The photovoltage obtained with the planes of the oriented thylakoids parallel to x depends on the plane of polarization of the incident light and shows that (1) the magnitude of the photovoltage depends on the absorption coefficient (which itself is polarization dependent) and thus on the magnitude of the charge gradient produced by the inhomogeneously absorbed light, and (2) a charge gradient within the planes of the thylakoids can give rise to the macroscopic photovoltage. While our experimental observations are basically in agreement with those previously reported (Fowler, C.F. and Kok, B.(1974) Biochim. Biophys. Acta 357, 308-318 and Witt, H.T. and Zickler, A. (1973) FEBS Lett. 37, 307-310) for unoriented chloroplasts, their interpretation of the origin of this effect in terms of a transmembrane potential must be modified in view of our results obtained with oriented chloroplasts. The macroscopically observed photovoltage of oriented chloroplasts is due to the creation of charge gradients either parallel or perpendicular to the thylakoid planes by a flash of light, the diffusion of these charges and to differences in the mobilities of the negative and positive charges. This interpretation in terms of the Dember effect is completely consistent with the existence of a transmembrane electric field as proposed by Fowler and Kok, as well as by Witt and Zickler. However, macroscopic measurements of the photovoltage using either oriented or unoriented chloroplast suspensions cannot prove that a transmembrane voltage exists, as previously claimed.

Chloroplasts↗
PubMed1985

Oriented reconstitution of red cell membrane proteins and assessment of their transmembrane disposition by immunoquenching of fluorescence.

The two major membrane glycoproteins of human red cells, glycophorin and band 3, the anion exchange protein, were isolated from cells exofacially labeled with fluorescein and reconstituted into vesicles with defined transmembrane disposition. Uniform orientation of polypeptides was accomplished by two procedures: Vesicles with single protein units were obtained by a one-step dilution of a protein/detergent suspension with a vast excess of phospholipid. Vesicles with uniform orientation of protein were selected by affinity chromatography on derivatized Sepharoses (organomercurial, wheat germ agglutinin, aminoethyl or diethylaminoethyl). Vesicles with multiple protein units with uniform orientation were generated by vectorial immobilization of detergent solubilized proteins on the above affinity matrices and in situ formation of proteoliposomes by detergent substitution for phospholipid. The proteoliposomes were released from the column by addition of excess free ligand. The orientation of band 3 and glycophorin in the reconstituted vesicles was first assessed by immunofluorescence quenching, using anti-fluorescein antibodies, to quantitatively quench fluorescein residues exposed on the outer surface of vesicles. Further assessment was achieved by chromatographing the vesicles through various affinity and ionic matrices. Vesicle populations of higher than 90% homogeneity in protein orientation (right-side-out or inside-out) were obtained with both procedures. The above methods provide a convenient experimental tool for the oriented reconstitution of proteins and the evaluation of their transmembrane disposition.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1975

Behavioral deficits in cats following early selected visual exposure to contours of a single orientation.

The ability of adult cats, whose early visual experience was confined to contours of a single orientation (either vertical or horizontal), to resolve gratings of different orientations was studied by operant methods. Following selective visual exposure during part or all of the first 4 months of life, the cats were trained on a simultaneous discrimination between gratings of various orientations and blank fields of the same mean luminance. The spatial frequency of the gratings was systematically altered in order to obtain an estimate of acuity based upon extrapolation to chance levels of performance. Selectively deprived cats performed as well as normally reared cats on gratings having the same orientation as that of the stripes they saw as kittens, but their performance on gratings orthogonal to these was poorer. The deficits in acuity for gratings perpendicular to the experienced orientation varied between 0.26 and 0.87 of an octave. On the other hand, control cats whose early visual experience alternated between vertical and horizontal stripes, or who were reared in an environment containing randomly oriented contours, failed to show any difference in their acuity for vertical and horizontal gratings. The acuity deficits shown by the selectively deprived animals are long-standing since they remain unchanged even after 30 months of normal visual exposure. It is argued that these perceptual deficits are a consequence of the changes in cortical physiology that other investigators have described in cats who had undergone similar early visual deprivation. Taken together, these findings provide a basis for explaining a number of human perceptual disorders.

Animals↗
PubMed1994

Qualitative comparison of the bilayer-associated structures of diacylglycerol and a fluorinated analog based upon oriented sample NMR data.

sn-1,2-Dimyristoylglycerol (DMDAG) and sn-1,2-dimyristoyl-3-fluoropropanediol (DMFPD) were synthesized in carbonyl 13C-labeled and acyl chain perdeuterated forms. These compounds were reconstituted at low levels into both randomly dispersed dimyristoylphosphatidylcholine (DMPC) bilayers and magnetically orientable DMPC media. Samples were subjected to NMR analysis, leading to a substantial body of 2H quadrupolar splitting, 13C-13C and 13C-19F dipolar coupling and 13C chemical shift anisotropy data for both compounds. A number of measurements were also made for DMPC. The data acquired from magnetically oriented samples were found to be undesirably affected by the presence of artifacts related to the experimental use of the oriented lipid media. However, it was possible to draw a number of qualitative conclusions from the data and to correct the data so that they may ultimately prove useful in quantitative structural analyses of bilayer-associated DMDAG and DMFPD. Comparison of the DMDAG data with corresponding measurements of DMPC suggests a high degree of similarity between the two compounds within bilayers composed primarily of L alpha phase phosphatidylcholine, consistent with previous work (S.O. Smith et al. (1992) Biochemistry 31, 11660-11664). Comparison of the data for DMDAG and DMFPD suggests that the hydroxyl proton of DMDAG is involved in hydrogen bonding interactions, which appear to be largely responsible for maintaining the orientational inequivalence of its two acyl chains. Bilayer-associated DMFPD also appears to exhibit a higher degree of whole-molecule disorder than DMDAG, again suggestive of an important structural role for the hydroxyl proton of DMDAG. Finally, comparison of 13C-NMR data for oriented DMPC in the presence and absence of low levels of DMDAG and DMFPD indicated that neither compound induces a significant change in the averaged conformational state of DMPC comprising the bilayer matrix of the oriented samples.

Carbon Isotopes↗
PubMed1986

Fibroblasts on micromachined substrata orient hierarchically to grooves of different dimensions.

Contact guidance was studied by light, scanning (SEM) and transmission electron microscopy (TEM) in cultures of human gingival fibroblasts cultured on grooved surfaces. The grooves were originally produced in silicon wafers by micromachining, a process which is based on the methods used to fabricate microelectronic components, and the grooved surfaces were then replicated in Epon. Micromachining enables precise control of groove depth, groove spacing, and groove shape to be obtained. In silicon wafers with appropriate crystal orientation, a second smaller set of grooves, called the minor grooves, is found on the floor of the major grooves. The minor grooves are oriented at a 54 degree angle to the major grooves, so that cells cultured on such surfaces are concurrently exposed to grooves of different dimensions which direct cell migration in different directions. Marked fibroblast alignment with the major grooves was observed both within the grooves and in the intervening flat ridges between the grooves. In addition, shallow and closely spaced grooves in epon or titanium-coated polymer or silicon were also capable of orienting fibroblasts. Although the minor grooves were able to orient fibroblasts in the absence of any other orienting influence, when fibroblasts were concurrently exposed to major and minor grooves the cells aligned themselves with the major grooves. TEM showed that the cellular filamentous cytoskeletal elements reflected the orientation of the cell as a whole. Fibroblasts on grooved substrata appeared to have more filopodia and to round up more frequently than fibroblasts cultured on flat substrata. It is suggested that both the mechanical properties of the cytoskeleton as well as the durability of the cellular attachment to groove edges may play a role in the contact guidance effected by grooved surfaces produced by micromachining.

Cell Adhesion↗
PubMed1992

Collagen fiber orientation and geometry effects on the mechanical properties of secondary osteons.

The effects of collagen fiber orientation and osteon geometry on the mechanical properties of secondary osteons under axial compression/tension and combined loadings (compression, bending and torsion) were investigated using a composite-beam finite-element model. Three cross-sectional shapes of secondary osteons were studied to show the effect of geometry. The results of stiffness are presented using the tension and compression properties for each lamella. The model shows that the mechanical properties of osteons are enhanced in bending and torsion when collagen fibers are oriented within 30 degrees of the loading axis. Osteons with alternating lamellar orientation are not well adapted to resist torsional moments, but alternate collagen fiber orientation has virtually no effect on the bending stiffness of osteons. Fiber orientation affects the mechanical properties less significantly when osteons are non-circular. Collagen fiber orientation and osteon geometry interact to determine the mechanical behavior of the osteon, and may act in a compensatory manner in the adaptive process.

Adult↗
PubMed1995

Cell orientation response to cyclically deformed substrates: experimental validation of a cell model.

We have developed a stochastic model that describes the orientation response of bipolar cells grown on a cyclically deformed substrate. The model was based on the following hypotheses regarding the behavior of individual cells: (a) the mechanical signal responsible for cell reorientation is the peak to peak surface strain along the cell's major axis (p-p axial strain); (b) each cell has an axial strain threshold and the threshold is normally distributed in the cell population; (c) the cell will avoid any direction where the p-p axial strain is above its threshold; and (d) the cell will randomly orient within the range of directions where the p-p axial strains are less than the cell's threshold. These hypotheses were tested by comparing model predictions with experimental observations from stretch experiments conducted with human melanocytes. The cells were grown on elastic rectangular culture dishes subjected to unidirectional cyclic (1 Hz) stretching with amplitudes of 0, 4, 8, and 12%. After 24 h of stimulation, the distribution of cell orientations was determined by measuring the orientations of 300-400 randomly selected cells. The 12% stretch experiment was used to determine the mean, 3.5%, and the standard deviation, 1.0% of the strain threshold for the cell population. The Kolmogorov-Smirnov test was then used to determine if the orientation distributions predicted by the model were different from experimentally measured distributions for the 4 and 8% stretches. No significant differences were found between the predicted and experimental distributions (4%: p = 0.70; and 8%: p = 0.71). These results support the hypothesis that cells randomly orient, but avoid directions where the p-p axial strains are above their thresholds.

Algorithms↗
PubMed1984

Stimulus context and infant orientation discrimination.

In three experiments, the effect of additional "contextual" elements on the discrimination of the orientation of linear and curvilinear segments was investigated with 4-month-old infants. In Experiment 1, paired visual matrices (one which contained some irregularity in orientation of internal elements, vs one which contained no irregularities) were presented. Infants detected irregular matrices significantly better than chance, but such detection was not aided by contextual elements. Discrimination of orientation in Experiment 2 was assessed with a paired-comparison familiarization-novelty paradigm. It was found that the addition of elements here significantly aided discrimination of linear segment orientation, but not curvilinear segment orientation. Experiment 3 investigated why this effect was not found for curvilinear segments; after equating the curvilinear stimuli to linear ones used in Experiment 2 with respect to the closedness of figure, discrimination of curvilinear orientation was observed.

Female↗
PubMed1992

Structure of RecA-DNA complexes studied by combination of linear dichroism and small-angle neutron scattering measurements on flow-oriented samples.

By combining anisotropy of small-angle neutron scattering (SANS) and optical anisotropy (linear dichroism, l.d.) on flow-oriented RecA-DNA complexes, the average DNA-base orientation has been determined in RecA complexes with double-stranded (ds) as well as single-stranded (ss) DNA. From the anisotropy of the two-dimensional SANS intensity representation, the second moment orientation function S is obtained. Knowledge of S is crucial for the interpretation of l.d. spectra in terms of orientation of the DNA bases and the aromatic amino acid residues. The DNA-base planes are essentially perpendicular to the fibre axis of the complex between RecA and dsDNA in the presence of cofactor ATP gamma S. A somewhat tilted base geometry is found for the RecA-ATP gamma S complexes with single-stranded poly(dT) and poly(d epsilon A). This behaviour contrasts the RecA-ssDNA complex formed without cofactor which displays a poor orientation of the bases. Well-ordered bases in the ssDNA-RecA complex is possibly reflecting the role of RecA in preparing a nucleotide strand for base-pairing in the search-for-homology process. While the central SANS intensity is essentially independent of the pitch of the helical complex, a secondary intensity maximum, which becomes focused upon flow orientation, is found to be a sensitive measure of the pitch. The pitch values for the complexes compare well with cryo-electron microscopy results but are slightly larger than those seen for uranyl-stained samples.

Adenosine Triphosphate↗
PubMed1982

Contrast influence on perceived orientation.

When two gratings of slightly different orientation and equal contrast are presented dichoptically the observer perceives a unique fused grating at an orientation intermediate between the two (cyclofusion). We show here that if the contrast of the two gratings is different the perceived orientation of the fused grating depends on the relative contrast of the two monocular images. The results show that the perceived orientation varies linearly with the contrast difference, provided that the contrast values of the gratings presented to each eye are such as to give rise to a fused image. In these conditions, the perceived orientation is the average of the two monocular orientations, weighted with their contrast.

Depth Perception↗
PubMed1986

Periodicity in orientation discrimination and the unconfounding of visual information.

Orientation discrimination is a periodic function of mean orientation. Discrimination sensitivity (i.e. threshold-1) was measured at 7.5 deg increments around the clock for an 8 c/deg grating subtending 1.0 deg dia located 1.25 deg from the foveal centre. Discrimination sensitivity was best for horizontal and vertical orientations, but did not fall monotonically to minima at 45 deg and 135 deg. Instead it fell precipitously to minima at angles of only 20 deg to the horizontal and vertical, and there was a weak submaximum near 45 deg. This finding is consistent with the proposal that orientation discrimination is determined by the relative activity of broadly-tuned, orientation-sensitive neural elements, and that only a small number of elements are effective in any small retinal region. This idea can also explain why subjects do not confound a change of orientation with a simultaneous change of contrast or spatial frequency.

Discrimination, Psychological↗
PubMed1988

Interactions among spatial frequency and orientation channels adapted concurrently.

Interactions between size and orientation-specific mechanisms in the human visual system were investigated using a sequential adaptation technique. Subjects adapted to a vertical, 4 c/deg high-contrast (0.7) sinewave grating that was interleaved at a rate of 0.5 Hz with another adapting grating differing either in (1) spatial frequency or (2) orientation. Before and after adaptation contrast thresholds were measured for a vertical 4 c/deg sinewave test grating. The resultant elevation in contrast threshold was plotted as a function of the (1) spatial frequency or (2) orientation differences between the first and second adapting gratings. Maximum threshold elevation was found when both adapting gratings shared the same spatial frequency and orientation. Minimum elevations were found when the second grating's spatial frequency or orientation differed by approx. 1.5 octaves or 45 deg, respectively. Beyond these values threshold elevations reapproached the baseline value measured in a control condition, where the 4.0 c/deg adapting grating was interleaved with a blank. The minimum threshold elevations were 0.2-0.3 log units below the baseline level. The results suggest the existence of inhibitory interactions between neural mechanisms tuned to the size and orientation of retinal images.

Adaptation, Ocular↗
PubMed1991

Texture segregation and orientation gradient.

Rapid texture segregation is examined using filtered noise textures. The stimuli consist of a foreground region of filtered noise with one dominant texture orientation against a background region with a different dominant orientation. Shape discrimination of the foreground region is measured as a function of the difference in orientation between the two regions (delta theta), the distance over which the dominant orientation rotates from the background to the foreground value (delta chi), and the dominant spatial frequency of the textures (f). Performance declines with smaller delta theta, larger delta chi, and lower f. These effects are partially independent of viewing distance, which implies that it is the relative or object spatial frequency, not retinal spatial frequency, which determines performance in this task. We present a model consisting of channels tuned for orientation and spatial frequency which compute local oriented energy, followed by (texture) edge detection and a cross-correlator which performs the shape discrimination. Monte Carlo simulations of this model are in accord with the degradation in performance with increased delta chi and decreased delta theta.

Humans↗
PubMed1993

Anisotropies in the perception of stereoscopic surfaces: the role of orientation disparity.

We measured stereoscopic slant detection thresholds for surfaces slanting about a horizontal or a vertical axis. For random-dot covered surfaces, 1.25 deg of slant was required to detect slant about a horizontal axis, whereas 2.1 deg of slant was required to detect slant about a vertical axis. This anisotropy could be due to the fact that orientation disparities, which contain information about surface slant, are generally smaller for surfaces slanting about a vertical axis. To test this possibility, slant thresholds were measured for surfaces whose orientation disparity content was manipulated independently of the other slant information present. When the magnitude of orientation disparity was the same for surfaces slanting about a horizontal and a vertical axis, both surface orientations required about 1.5 deg of slant to be detected; thus the anisotropy became negligible. In contrast, when the orientation disparity content of a surface slanting about a vertical axis was zero, 3-4 deg of slant was required for detection; thus the anisotropy became larger. Under the conditions of these experiments, it appears that the visual system utilizes orientation disparities.

Depth Perception↗