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PubMed1998

Determination of orientational order parameters from 2H NMR spectra of magnetically partially oriented lipid bilayers.

The partial orientation of multilamellar vesicles (MLVs) in high magnetic fields is known to affect the shape of 2H NMR spectra. There are numerical methods for extracting either the orientational order parameters of lipid molecules for a random distribution of domain orientations in the sample, or the distribution of orientations for a known set of spectral anisotropies. A first attempt at determining the orientational order parameters in the presence of an unknown nonrandom distribution of orientations is presented. The numerical method is based on the Tikhonov regularization algorithm. It is tested using simulated partially oriented spectra. An experimental spectrum of a phospholipid-ether mixture in water is analyzed as an example. The experimental spectrum is consistent with an ellipsoidal shape of MLVs with a ratio of semiaxes of approximately 3.4.

Algorithms↗
PubMed1999

Orientation of the tetranuclear manganese cluster and tyrosine Z in the O(2)-evolving complex of photosystem II: An EPR study of the S(2)Y(Z)(*) state in oriented acetate-inhibited photosystem II membranes.

Inhibitory treatment by acetate, followed by illumination and rapid freezing, is known to trap the S(2)Y(Z)(*) state of the O(2)-evolving complex (OEC) in photosystem II (PS II). An EPR spectrum of this state exhibits broad split signals due to the interaction of the tyrosyl radical, Y(Z)(*), with the S = 1/2 S(2) state of the Mn(4) cluster. We present a novel approach to analyze S(2)Y(Z)(*) spectra of one-dimensionally (1-D) oriented acetate-inhibited PS II membranes to determine the magnitude and relative orientation of the S(2)Y(Z)(*) dipolar vector within the membrane. Although there exists a vast body of EPR data on isolated spins in oriented membrane sheets, the present study is the first of its kind on dipolar-coupled electron spin pairs in such systems. We demonstrate the feasibility of the technique and establish a rigorous treatment to account for the disorder present in partially oriented 1-D membrane preparations. We find that (i) the point-dipole distance between Y(Z)(*) and the Mn(4) cluster is 7.9 +/- 0.2 A, (ii) the angle between the interspin vector and the thylakoid membrane normal is 75 degrees, (iii) the g(z)()-axis of the Mn(4) cluster is 70 degrees away from the membrane normal and 35 degrees away from the interspin vector, and (iv) the exchange interaction between the two spins is -275 x 10(-)(4) cm(-)(1), which is antiferromagnetic. Due to the sensitivity of EPR line shapes of oriented spin-coupled pairs to the interspin distance, the present study imposes a tighter constraint on the Y(Z)-Mn(4) point-dipole distance than obtained from randomly oriented samples. The geometric constraints obtained from the 1-D oriented sample are combined with published models of the structure of Mn-depleted PS II to propose a location of the Mn(4) cluster. A structure in which Y(Z) is hydrogen bonded to a manganese-bound hydroxide ligand is consistent with available data and favors maximal orbital overlap between the two redox center that would facilitate direct electron- and proton-transfer steps.

Electron Spin Resonance Spectroscopy↗
PubMed2006

Molecular orientation distributions in a biaxially oriented poly(L-lactic acid) film determined by polarized Raman spectroscopy.

Molecular orientation distributions in the crystalline and amorphous regions of a biaxially oriented poly(L-lactic acid) film were analyzed fully by polarized Raman spectroscopy. Raman bands at 926 and 875 cm(-1) were chosen for the determination of the most probable molecular orientation distribution functions for the crystalline and amorphous regions in the film. It was revealed that the PLLA molecules were oriented biaxially in both the crystalline and amorphous regions. The orientation distribution normal to the film surface was found to be broader in the amorphous regions than in the crystalline regions. Furthermore, a predominant unidirectional molecular orientation was observed in the crystalline regions, whereas the molecular orientation distribution in the amorphous regions was isotropic in the plane parallel to the film surface. The different behavior of the crystalline and amorphous regions suggests that each region underwent different deformation mechanisms during the film formation.

Biocompatible Materials↗
PubMed1998

Multiple groups of orientation-selective visual mechanisms underlying rapid orientated-line detection.

Visual search for an edge or line element differing in orientation from a background of other edge or line elements can be performed rapidly and effortlessly. In this study, based on psychophysical measurements with ten human observers, threshold values of the angle between a target and background line elements were obtained as functions of background-element orientation, in brief masked displays. A repeated-loess analysis of the threshold functions suggested the existence of several groups of orientation-selective mechanisms contributing to rapid orientated-line detection; specifically, coarse, intermediate and fine mechanisms with preferred orientations spaced at angles of approximately 90 degrees, 35 degrees, and 10 degrees-25 degrees, respectively. The preferred orientations of coarse and some intermediate mechanisms coincided with the vertical or horizontal of the frontoparallel plane, but the preferred orientations of fine mechanisms varied randomly from observer to observer, possibly reflecting individual variations in neuronal sampling characteristics.

Adult↗
PubMed1991

Relation of cortical cell orientation selectivity to alignment of receptive fields of the geniculocortical afferents that arborize within a single orientation column in ferret visual cortex.

Neurons in the primary visual cortex of higher mammals are arranged in columns, and the neurons in each column respond best to light-dark borders of particular orientations. The basis of cortical cell orientation selectivity is not known. One possible mechanism would be for cortical cells to receive input from several lateral geniculate nucleus (LGN) neurons with receptive fields that are aligned in the visual field (Hubel and Wiesel, 1962). We have investigated the relationship between the arrangement of the receptive fields of geniculocortical afferents and the orientation preferences of cortical cells in the orientation columns to which the afferents provide visual input. Radial microelectrode penetrations were made into primary visual cortex of anesthetized adult sable ferrets. Cortical cells were recorded throughout the depth of the cortex, and their orientation preferences were determined. Cortical cell responses were then eliminated by superfusion of the cortex with either kainic acid (Zahs and Stryker, 1988) or muscimol. After the drug treatment, responses from many single units with distinct receptive fields were recorded. These responses were presumed to be those of geniculocortical afferents, because they had the response properties characteristic of LGN neurons, and because they could be recorded only in cortical layers that receive geniculate input. In 16 of 18 cases, the afferent receptive fields recorded in a single penetration covered an elongated region of visual space. In these penetrations, the best-fit line through the centers of the afferent receptive fields generally paralleled the preferred orientation of cortical cells recorded at the same site in cortex. These results are consistent with the Hubel and Wiesel (1962) model for the construction of oriented visual cortical receptive fields from geniculate inputs with aligned receptive fields.

Afferent Pathways↗
PubMedDate not supplied

Code 50: an orientation matrix to track orientation cost.

Estimates of staff orientation costs can range from $20,000-50,000 per person. The Director of Finance and the Director of Nursing Education and Research developed a system to track the orientation process to determine the actual costs. Head nurses and educators approached the orientation process differently; therefore, there was no consistency as to the time allotted for orientation. Although competency-based orientation tools were used for all new orientees, the average amount of time for new orientees to become productive ranged from 3-9 months. By creating the orientation matrix, a unique pay class (code 50) was assigned for all new orientees, and a computer program was developed to track costs. The overtime hours for orientees dropped to 159 from 941, resulting in an 83% reduction in overtime hours. The matrix ensured a more cost effective approach to orientation.

Clinical Competence↗
PubMed1994

Does orientation-independent object recognition precede orientation-dependent recognition? Evidence from a cuing paradigm.

Object recognition may entail an incremental normalization process before access to canonical orientation representations, but is this process guided by prior access to object-centered representations? In Experiment 1, the authors showed observers figure-ground stimuli known to reflect access to, and output from, stored shape representations. The stimuli appeared in each of 6 different orientations, preceded by cues providing either (a) no information, (b) upright shape information only, (c) upright shape information plus orientation information (separately), or (d) shape information in the same orientation as the upcoming figure-ground test stimulus. Contrary to predictions by a postaccess account, the cues failed to eliminate orientation dependency in shape recognition. The results favor a preaccess account of the normalization process within the context of canonical orientation representations.

Adult↗
PubMed1975

The orientation anisotropy and orientation constancy: a visual evoked potential study.

Two experiments were conducted on the orientation anisotropy in which averaged visual evoked potentials (VEPs) were recorded from the occipital scalp. The first experiment confirmed the findings of Maffei and Campbell (1970) that obliquely oriented gratings alternated back and forth produced smaller-amplitude VEPs than when the gratings were oriented horizontally or vertically. Since no asymmetry was found in VEPs produced by a Julesz figure presented under identical conditions, it was concluded that direction of displacement could not have been contributing to the effect. In a second experiment head tilt of the subject was manipulated together with grating orientation and the results indicated that the orientation anisotropy is retinally rather than gravitationally referenced. It was concluded that the site of orientation constancy is located either at higher levels of the primary visual system or in the second visual system.

Adult↗
PubMed2005

Effects of hand orientation and delay on the verbal judgment of haptically perceived orientation.

We examined the haptic perception of orientations of a single bar throughout the horizontal plane using a verbal response: participants were to assign a number of minutes to the orientation of a bar defined with respect to the stimulus table. Performance was found to be systematically biased. Deviations were consistent with, yet much smaller than, those resulting from haptic motor matching tasks. The size and direction of the deviations were found to correlate with hand orientation, and not to depend on spatial location per se, suggesting a role for hand-centred reference frames in biasing performance. Delaying the response by 10 s led to a small improvement only of right-hand perceptions, indicating different hemispheric involvement in processes involved in retaining and/or recoding of haptic orientation information. Also the haptic oblique effect was found with the current verbal response. Importantly, it was affected neither by hand orientation nor by delay, suggesting that the oblique effect is independent of the aforementioned deviations in orientation perception.

Adult↗
PubMed1995

Human perceptual learning in identifying the oblique orientation: retinotopy, orientation specificity and monocularity.

1. Human perceptual learning in discrimination of the oblique orientation was studied using psychophysical methods. Subjects were trained daily to improve their ability to identify the orientation of a circular 2.5 deg diameter unidimensional noise field. Dramatic improvements in sensitivity to contour orientation occurred over a period of 15-20 days. The improved performance persisted for several months. Improvement was more evident between daily sessions than within sessions. This was partly due to fatigue interfering with the learning effect. Moreover, a consolidation period seemed to be required. 2. Improvement was restricted to the position of the stimulus being trained. This position dependency of the learning effect proved very precise. After training at a specific stimulus position, merely displacing the stimulus to an adjacent position caused a marked increase in thresholds. 3. No transfer of the training effect was observed between orientations. Following a shift of 90 deg away from the trained orientation, performance fell, even below the initial level. 4. We observed complete to almost complete transfer between the two eyes. 5. Our results suggest plastic changes at a level of the visual processing stream where input from both eyes has come together, but where generalization for spatial localization and orientation has not yet occurred.

Discrimination, Psychological↗
PubMed1980

Orientation of the hemes of high potential cytochromes relative to photosynthetic membranes, as shown by the linear dichroism of oriented preparations.

The orientations of high potential cytochromes with respect to photosynthetic membranes was investigated in spinach chloroplasts and in Rhodopseudomonas viridis. The general approach consists in detection with polarized light of photoinduced absorbance changes related to the oxidation of the cytochromes. The orientation of cytochrome c-558 was measured at room temperature in chromatophores and whole cells of Rps. viridis, oriented on glass slides and in a magnetic field, respectively. The orientation of cytochrome b-559 of green plants was detected at 77 K in magnetically oriented chloroplasts. In both cases the dichroic ratio for the alpha band shows that the heme plane makes an angle greater than 35 degrees C with the membrane plane. Moreover, the dichroic ratio is not constant throughout the alpha and beta bands, for both cytochrome c-558 and b-559. Linear dichroism spectra of oriented pure horse heart cytochrome c and cytochrome c2 of Rhodopseudomonas sphaeroides in stretched polyvinyl alcohol films show that the variations of the dichroic ratio in the alpha and beta bands can be explained by the occurrence of x- and y-polarized transitions absorbing at slightly different wavelengths.

Chloroplasts↗
PubMed1993

Measuring orientation of actin filaments within a cell: orientation of actin in intestinal microvilli.

Orientational distribution of actin filaments within a cell is an important determinant of cellular shape and motility. To map this distribution we developed a method of measuring local orientation of actin filaments. In this method actin filaments within cells are labeled with fluorescent phalloidin and are viewed at high magnification in a fluorescent microscope. Emitted fluorescence is split by a birefringent crystal giving rise to two images created by light rays polarized orthogonally with respect to each other. The two images are recorded by a high-sensitivity video camera, and polarization of fluorescence at any point is calculated from the relative intensity of both images at this point. From the value of polarization, the orientation of the absorption dipole of the dye, and thus orientation of F-actin, can be calculated. To illustrate the utility of the method, we measured orientation of actin cores in microvilli of chicken intestinal epithelial cells. F-actin in microvillar cores was labeled with rhodamine-phalloidin; measurements showed that the orientation was the same when microvillus formed a part of a brush border and when it was separated from it suggesting that "shaving" of brush borders did not distort microvillar structure. In the absence of nucleotide, polarization of fluorescence of actin cores in isolated microvilli was best fitted by assuming that a majority of fluorophores were arranged with a perfect helical symmetry along the axis of microvillus and that the absorption dipoles of fluorophores were inclined at 52 degrees with respect to the axis. When ATP was added, the shape of isolated microvilli did not change but polarization of fluorescence decreased, indicating statistically significant increase in disorder and a change of average angle to 54 degrees. We argue that these changes were due to mechanochemical interactions between actin and myosin-I.

Actins↗
PubMed2001

Practising orientation identification improves orientation coding in V1 neurons.

The adult brain shows remarkable plasticity, as demonstrated by the improvement in fine sensorial discriminations after intensive practice. The behavioural aspects of such perceptual learning are well documented, especially in the visual system. Specificity for stimulus attributes clearly implicates an early cortical site, where receptive fields retain fine selectivity for these attributes; however, the neuronal correlates of a simple visual discrimination task remained unidentified. Here we report electrophysiological correlates in the primary visual cortex (V1) of monkeys for learning orientation identification. We link the behavioural improvement in this type of learning to an improved neuronal performance of trained compared to naive neurons. Improved long-term neuronal performance resulted from changes in the characteristics of orientation tuning of individual neurons. More particularly, the slope of the orientation tuning curve that was measured at the trained orientation increased only for the subgroup of trained neurons most likely to code the orientation identified by the monkey. No modifications of the tuning curve were observed for orientations for which the monkey had not been trained. Thus training induces a specific and efficient increase in neuronal sensitivity in V1.

Animals↗
PubMed2005

What does pressure decide to cook with orientationally disordered plastic phase of cubane: an orientational glass or crystal?

The effect of pressure on the structure and reorientational motion of molecules in orientationally disordered (OD) crystalline phase of cubane has been investigated in detail using variable shape molecular simulations in constant-pressure constant-temperature ensemble. Complete orientational ordering occurs at a pressure of 1.0 GPa and the OD phase transforms to an orientationally ordered phase at this pressure. The transition is associated with a kink in the variation of structural parameters such as cell parameters, unit-cell volume, and interaction energy. This transition is also associated with an anomaly in specific heat. Above this transition pressure, the structural quantities display only smaller changes with further increase in pressure. The structure of high-pressure orientationally ordered (HPOO) phase has been characterized using radial distribution functions and orientational distribution function. From detailed analysis of the structure of HPOO phase we conclude that it is isostructural with low-temperature orientationally ordered phase. The OD phase has four times larger compressibility than the HPOO phase.

Journal Article↗
PubMed1973

Orientation of intermediates in the bleaching of shear-oriented rhodopsin.

Cattle rhodopsin can be highly oriented by shearing a wet paste of digitonin micelles of this visual pigment between two quartz slides. This orients the rhodopsin micelles so that their chromophores lie mainly parallel to the direction of shear. In such preparations the orientation of rhodopsin and intermediates of its bleaching by light have been measured with plane-polarized light from -195 degrees C to room temperature. The chromophore maintains essentially the same orientation as in rhodopsin in all the intermediates of bleaching: bathorhodopsin (prelumirhodopsin), lumirhodopsin, and metarhodopsins I and II. When, however, the retinaldehyde chromophore is hydrolyzed from opsin in the presence of hydroxylamine, the retinaldehyde oxime that results rotates so as to lie mainly across the direction of shear. That is, the retinal oxime, though free, orients itself upon the oriented matrix of the opsin-digitonin micelles. These experiments show the rhodopsin-digitonin micelle to be markedly asymmetric, with the chromophore lying parallel to its long axis. The asymmetry could originate in the formation of the micelle, in rhodopsin itself, or by its linear polymerization under the conditions of the experiment. If rhodopsin itself is markedly asymmetric, for which there is some evidence, then, since in the rod outer segments its chromophores lie parallel to the disk membranes, the molecules themselves must lie with their long axes parallel to the membranes.

Animals↗
PubMed2000

CGG/CCG repeats exhibit orientation-dependent instability and orientation-independent fragility in Saccharomyces cerevisiae.

An expansion to >200 CGG/CCG repeats (hereafter called CGG) in the 5' region of the FMR1 gene causes fragile X syndrome, and this locus becomes a folate-sensitive fragile site. We used Saccharomyces cerevisiae as a model system to study the stability and fragility of CGG repeats. Tracts of (CGG)(81)and (CGG)(160)were integrated onto a yeast chromosome in both orientations relative to the nearest replication origin. Tracts of this length are pre-mutation alleles in humans, with a high probability of expansion in future generations. The CGG tracts in yeast colonies showed a length-dependent instability with longer tracts being more prone to contraction than shorter tracts. In addition, there was an orientation bias for tract stability with tracts having fewer contractions when the CCG strand was the template for lagging strand synthesis. Expansions of the CGG tracts also occurred in an orientation-dependent manner, although at a lower frequency than contractions. To determine whether CGG tracts are fragile sites in yeast, the CGG tracts were flanked by direct repeats, and the rate of recombination between the repeats determined. Strains carrying the (CGG)(160)tract in either orientation had a large increase in their rate of recombination compared with a no-tract control strain. Because this increase was dependent on genes involved in double-strand break repair, recombination was likely to be initiated by CGG tract-induced breakage between the direct repeats. The observation of orientation-dependent instability and orientation-independent fragility suggests that at least some aspects of their underlying mechanisms are different.

Chromosome Fragile Sites↗
PubMed2000

Orientational ordering in fluids with partially constrained molecule orientations

Molecular orientations in anisotropic fluids can be partially constrained as a result of electric or magnetic fields or interface influences. A statistical approach for the investigation of the orientational ordering in such systems is proposed. The long-range correlations are taken into account consistently. The method is illustrated for the well-known thermotropic nematic model in an infinite disorienting field W, when the molecules are constrained to orient perpendicularly to the field direction. For this problem the analytical solution of the anisotropic Ornstein-Zernike equation is obtained, and the asymptotic expression for the long-range correlations on large distances is given. The phase diagram and elastic constants are calculated for W-->infinity and are compared with the usual case of a uniaxial nematic ordering at W=0. In the case W-->infinity when the temperature decreases the orientational phase transition of the second order becomes the one of the first order at a tricritical point. The disorienting field W increases much the region of an ordered fluid. It is shown that at a given pressure the orientational ordering temperature for W-->infinity is higher about 1.2-1.5 times than the one at W=0. The orientational ordering pressure is less about 4-5 times than the pressure of the uniaxial nematic ordering (W=0) at the same temperature. The disorienting field increases elastic properties of the model under consideration.

Journal Article↗
PubMed2003

Perceptual dominance of oriented faces mirrors the distribution of orientation tunings in inferotemporal neurons.

In three experiments participants viewed pairs of overlapping transparent faces, with one face upright and the other oriented, and they reported which face was dominant. In each trial, an upright face was presented with a face at 45, 90, 135 or 180 degrees, with transparency set using a linear weighted algorithm, so that relative contrast across faces was biased in favour of oriented faces. Exposure duration was restricted in experiment 1 to 250, 500 or 1000 ms, but was unlimited in experiments 2 and 3. Adults were tested in experiments 1 and 2 and children aged 6-9 years of age were tested in experiment 3. Irrespective of exposure duration, the results showed the probability of dominance being ceded by oriented faces to upright faces was a function of orientation. In comparable conditions, the function found with young children was flatter than with adults. These patterns, and those of earlier perceptual studies, can be explained by the distribution of different orientation tunings found in physiological studies of inferotemporal cortex in macaques.

Adult↗