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PubMedDate not supplied

Receptive field and orientation scatter studied by tetrode recordings in cat area 17.

The receptive-field positions and orientation preferences of neurons occupying the same tangential location in visual cortex are thought to be similar but to have an associated random scatter. However, previous estimates of this scatter may have been inflated by the use of subjective plotting methods, sequential recording of single units, and residual eye movements. Here we report measurements of receptive-field position and orientation scatter in cat area 17 made with tetrodes, which were able to simultaneously isolate and record up to 11 nearby neurons (ensembles). We studied 355 units at 72 sites with moving light and dark bars. Receptive-field sizes and positions were estimated by least-squares fitting of Gaussians to response profiles. We found that receptive-field position scatter was about half of the ensemble average receptive-field size. We confirmed previous estimates of orientation scatter, but calculations suggested that much of it may be accounted for by anatomical scatter in the positions of recorded neurons relative to the tetrode in a smooth map. Orientation tuning width was positively correlated with the degree of orientation scatter. Scatter was not independent in the two eyes: deviations from the local mean for both preferred orientation and receptive-field position were correlated although a significant amount of residual inter-ocular orientation and receptive-field position scatter was present. We conclude that cortical maps of orientation and receptive-field position are more ordered than was previously thought, and that random scatter in receptive-field positions makes a relatively small contribution to cortical point image size.

Animals↗
PubMed2005

Measurement and mapping of small changes of crystal orientation by electron backscattering diffraction.

We have explored the possibility of measuring small changes of orientation within grains by electron backscattering diffraction (EBSD), in the scanning electron microscope. Conventional orientation maps (using EBSD) index the orientation of each position on the sample separately. This does not give accurate results for small differences of orientation. We have studied methods of measuring small changes in orientation by measuring the change from one EBSD pattern to the next directly, without indexing either. Previous workers have measured the change of position of a zone axis in the EBSD pattern. We have compared this with an alternative method, which we show to be superior, of measuring the shift of the peaks in the Hough transform from one diffraction pattern to the next. This means that we are measuring the change of orientation of sets of crystal planes within the grain, rather than measuring the change of orientation of zone axes. We show that it is possible, with a standard EBSD configuration, to measure the shift of the Kikuchi bands to a precision of about a 10th of a pixel, which corresponds to a change of orientation in the sample of about 0.1 mrad (0.006 degrees ).

Journal Article↗
PubMed1992

Orientation factor in steady-state and time-resolved resonance energy transfer measurements.

Resonance energy transfer measurements provide a way to estimate distances between chromophores attached to different sites of macromolecules. There are two unknowns involved in resonance energy transfer measurements, the distance between two chromophores and their relative orientation. When static orientational disorder exists, the orientation factor, kappa 2, can vary from 0 to 4, leading to considerable uncertainty in estimation of distances. Fluorescence polarization anisotropy measurements can reduce the degree of uncertainty [Dale & Eisinger (1974) Biopolymers 13, 1573]. There may still be substantial error bounds for the average distance measurements. Time-resolved fluorescence measurements provide an "apparent" average distance and distance distribution containing contributions by both distance and orientation. The contribution of orientation to observed "apparent" average distance and distance distribution widths has been estimated for both simulated and real data. With a single unique distance as input in the simulation and with random but static orientation of donor and acceptor, the recovered average distance is very close to that of the input when the input distance is close to or larger than the Förster distance. The recovered width of apparent distance distribution can be substantial and it changes as a function of Förster distance to average distance ratio and as a function of Förster distance. Similar conclusions apply to the case where there is a real distance distribution. Motional averaging of the orientation was simulated by the Monte Carlo method to estimate the contribution of orientation when chromophores have certain degrees of mobility.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed2001

Kinetic preference for oriented DNA binding by the yeast TATA-binding protein TBP.

In solution, the TATA box binding protein from S. cerevisiae (yTBP) is only minimally oriented when bound to the adenovirus major late promoter (AdMLP) and the yeast CYC1 promoter. At equilibrium, approximately 60% of the complexes are assembled in the orientation observed within crystal structures; 40% are assembled in the opposite orientation. Here we use stopped-flow fluorescence resonance energy transfer (FRET) to study the association kinetics of the two TBP.TATA box orientational isomers. Kinetics were determined by monitoring FRET between a unique tryptophan residue engineered into either the C- or the N-terminal stirrup of the conserved C-terminal subunit of yeast TBP (yTBPc) and an aminocoumarin moiety appended either upstream or downstream of the TATA box. Together, these constructs permitted a simultaneous yet independent monitor of the kinetics of TBP binding in both orientations. Not only did our results provide an independent confirmation of the free energy difference between the two orientational isomers, but they also showed that the orientational binding preference at equilibrium is a result of a faster association rate when TBP binds DNA in the orientation observed in the crystal structure.

Coumarins↗
PubMed1994

13C NMR studies of wheat germ agglutinin interactions with N-acetylglucosamine at a magnetically oriented bilayer surface.

The orientation of synthetic 13C-labeled glycolipid receptors and their interaction with the plant lectin wheat germ agglutinin have been studied in an oriented membrane system using NMR spectroscopy. A series of 2-[1,2-13C2]acetamido-2-deoxy-beta-D-glucopyranosides were synthesized with between zero and four hydrophilic ethoxy units between the headgroup and an alkyl chain which anchors the receptors in the bilayers. The chemical shift anisotropy of the 13C carbonyl and a 13C-13C dipolar coupling between the labeled carbons provide information about the orientation and dynamics of the receptor headgroup in oriented membrane systems. It was found that the headgroups of the receptors with two, three, or four ethoxy units appeared isotropic when incorporated in the oriented bilayers, but those of the receptors with zero or one ethoxy units were significantly ordered by the bilayers. The average orientations consistent with measured spectral parameters were determined for the receptors with zero and one ethoxy units and were found to coincide with low-energy conformations from molecular modeling. When the plant lectin wheat germ agglutinin was added to the sample, only the receptors with two, three, or four ethoxy units separating the headgroup from the alkyl chain showed evidence of binding by the lectin. Although the 13C-labeled resonances broadened when the protein bound, no changes in dipolar couplings or chemical shift anisotropies could be detected, suggesting that the motion of the headgroup was slowed by protein binding, but average orientation and overall order changed little. Competition studies demonstrated that none of the lectin/receptor complexes are more stable than the complex of the lectin and N-acetylglucosamine in solution. These results suggest that the membrane does not stabilize the interactions of wheat germ agglutinin with these cell-surface receptors. Furthermore, molecular modeling demonstrates that the zero- and one-spacer receptors may not bind wheat germ agglutinin because the orientations of the N-acetyl groups in these receptors would result in significant steric contacts between the lectin/receptor complex and the membrane.

Acetylglucosamine↗
PubMed1988

Study of the specific heme orientation in reconstituted hemoglobins.

NMR studies of the recombination reaction of apohemoglobin derivatives with natural and unnatural hemes and of the heme-exchange reaction for reconstituted hemoglobin have revealed that the heme is incorporated into the apoprotein with stereospecific heme orientations dependent upon the heme peripheral 2,4-substituents and the axial iron ligand(s). Heme orientations also depend on whether recombination occurs at the alpha or beta subunit and on whether or not the complementary subunit is occupied by the heme. In the recombination reaction with the azido complex of deuterohemin, the alpha subunit of the apohemoglobin preferentially combines with the hemin in the "disordered" heme orientation, whereas protohemin is inserted in either of two heme orientations. Mesohemin inserts predominantly in the "native" heme orientation. For the beta subunit, specific heme orientation was also encountered, but the specificity was somewhat different from that of the alpha subunit. It was also shown that the specific heme orientation in both subunits is substantially affected by the axial heme ligands. These findings imply that apohemoglobin senses the steric bulkiness of both the porphyrin 2,4-substituents and the axial iron ligands in the heme-apoprotein recombination reaction. To gain an insight into the effect of the protein structure, the heme reconstitution reaction of semihemoglobin, demonstrating that the heme orientation in the reconstituted semihemoglobin with the azido-deuterohemin complex was in the native form, was also examined.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Effect of ADP on the orientation of spin-labeled myosin heads in muscle fibers: a high-resolution study with deuterated spin labels.

We have used electron paramagnetic resonance (EPR) to determine the effects of ADP on the orientational distribution of nitroxide spin labels attached to myosin heads in skinned rabbit psoas muscle fibers. To maximize the specificity of labeling, we spin-labeled isolated myosin heads (subfragment 1) on a single reactive thiol (SH1) and diffused them into unlabeled muscle fibers. To maximize spectral and orientational resolution, we used perdeuterated spin labels, 2H-MSL and 2H-IASL, eliminating superhyperfine broadening and thus narrowing the line widths. Two different spin labels were used, with different orientation relative to the myosin head, to ensure that the results are not affected by unfavorable probe orientation. In rigor, a very narrow three-line spectrum was observed for both spin labels, indicating a narrow orientational distribution, as reported previously (Thomas & Cooke, 1980). ADP induced very slight changes in the spectrum, corresponding to very slight (but significant) changes in the orientational distribution. These changes were quantified by a digital analysis of the spectra, using a two-step simplex fitting procedure (Fajer et al., 1990). First, the magnetic tensor values and line widths were determined by fitting the spectrum of a randomly oriented sample. Then the spectrum of oriented fibers was fit to a model by assuming a Gaussian distribution of the tilt angle (theta) and twist angle (phi) of the nitroxide principal axes relative to the fiber axis. A single-Gaussian distribution resulted in inadequate fits, but a two-component model gave excellent results. ADP induces a small (less than 5 degrees) rotation of the major components for both spin labels, along with a similarly small increase of disorder about the average positions.

Actin Cytoskeleton↗
PubMed2001

Orientation of amide-nitrogen-15 chemical shift tensors in peptides: a quantum chemical study.

Knowledge of the orientation of the nitrogen-15 chemical shift anisotropy (CSA) tensor is critical for a variety of experiments that provide information on protein structure and dynamics in the solid and solution states. Unfortunately, the methods available for determining the orientation of the CSA tensor experimentally have inherent limitations. Rotation studies of a single crystal provide complete information but are tedious and limited in applicability. Solid-state NMR studies on powder samples can be applied to a greater range of samples but suffer from ambiguities in the results obtained. Density functional gauge-including-atomic-orbitals (GIAO) calculations of the orientations of (15)N CSA tensors in peptides are presented here as an independent source of confirmation for these studies. A comparison of the calculated (15)N CSA orientations with the available experimental values from single-crystal and powder studies shows excellent agreement after a partial, constrained optimization of some of the crystal structures used in the calculation. The results from this study suggest that the orientation as well as the magnitudes of (15)N CSA tensors may vary from molecule to molecule. The calculated alpha(N) angle varies from 0 degrees to 24 degrees with the majority in the 10 degrees to 20 degrees range and the beta(N) angle varies from 17 degrees to 24 degrees in good agreement with most of the solid-state NMR experimental results. Hydrogen bonding is shown to have negligible effect on the orientation of (15)N CSA tensor in accordance with recent theoretical predictions. Furthermore, it is demonstrated that the orientation of the (15)N CSA can be calculated accurately with much smaller basis sets than is needed to calculate the chemical shift, suggesting that the routine application of ab initio calculations to the determination of (15)N CSA tensor orientations in large biomolecules might be possible.

Amides↗
PubMed2005

Orientational melting and reorientational motion in a cubane molecular crystal: a molecular simulation study.

Detailed molecular simulations are carried out to investigate the effect of temperature on orientational order in cubane molecular crystal. We report a transition from an orientationally ordered to an orientationally disordered plastic crystalline phase in the temperature range 425-450 K. This is similar to the experimentally reported transition at 395 K. The nature of this transition is first order and is associated with a 4.8% increase in unit cell volume that is comparable to the experimentally reported unit cell volume change of 5.4% (Phys. Rev. Lett. 1997, 78, 4938). An orientational order parameter, eta(T), has been defined in terms of average angle of libration of a molecular 3-fold axis and the orientational melting has been characterized by using eta(T). The orientational melting is associated with an anomaly in specific heat at constant pressure (C(P)) and compressibility (kappa). The enthalpy of transition and entropy of transition associated with this orientational melting are 20.8 J mol(-1) and 0.046 J mol(-1) K(-1), respectively. The structure of crystalline as well as plastic crystalline phases is characterized by using various radial distribution functions and orientational distribution functions. The coefficient of thermal expansion of the plastic crystalline phase is more than twice that of the crystalline phase.

Journal Article↗
PubMed2005

Influence of surfactant tail branching and organization on the orientation of liquid crystals at aqueous-liquid crystal interfaces.

We have examined the influence of two aspects of surfactant structure--tail branching and tail organization--on the orientational ordering (so-called anchoring) of water-immiscible, thermotropic liquid crystals in contact with aqueous surfactant solutions. First, we evaluated the influence of branches in surfactant tails on the anchoring of nematic liquid crystals at water-liquid crystal interfaces. We compared interfaces that were laden with one of three linear surfactants (sodium dodecyl sulfate, sodium dodecanesulfonate, and isomerically pure linear sodium dodecylbenzenesulfonate) to interfaces laden with branched sodium dodecylbenzenesulfonate. We carried out these experiments at 60 degrees C, above the Krafft temperatures of all the surfactants studied, and used the liquid crystal TL205 (a mixture of cyclohexane-fluorinated biphenyls and fluorinated terphenyls), which forms a nematic phase at 60 degrees C. Linear surfactants caused TL205 to assume a perpendicular orientation (homeotropic anchoring) above a threshold concentration of surfactant and parallel orientation (planar anchoring) at lower concentrations. In contrast, branched sodium dodecylbenzenesulfonate caused planar anchoring of TL205 at all concentrations up to the critical micelle concentration of the surfactant. Second, we used sodium dodecanesulfonate and a commercial linear sodium dodecylbenzenesulfonate to probe the influence of surfactant tail organization on the orientations of liquid crystals at water-liquid crystal interfaces. Commercial linear sodium dodecylbenzenesulfonate, which comprises a mixture of ortho and para isomers, has been previously characterized to form less ordered monolayers than sodium dodecanesulfonate at oil-water interfaces at room temperature. We found sodium dodecanesulfonate to cause homeotropic anchoring of both TL205 and 4'-pentyl-4-cyanobiphenyl (5CB, nematic at room temperature), whereas commercial linear sodium dodecylbenzenesulfonate caused predominantly planar and tilted orientations of both TL205 and 5CB. These results, when combined, lead us to conclude that (1) interactions between the aliphatic tails of surfactants and liquid crystals largely dictate the orientations of liquid crystals at aqueous-liquid crystal interfaces, (2) the interactions that orient the liquid crystals at these interfaces are sensitive to the branching and degree of disorder in the surfactant tails, and (3) differences in the chemical composition of TL205 and 5CB, most notably fluorination of TL205, lead to subtle differences in the orientations of these two nematic liquid crystals.

Crystallization↗
PubMed1998

Magnetic Field Orientation of Liquid Crystalline Epoxy Thermosets.

The effect of magnetic fields on the orientation and properties of 4,4'-bis(2,3-epoxypropoxy)-alpha-methylstilbene cured with sulfanilamide has been studied. This epoxy system is initially isotropic and forms a smectic A phase upon curing. A magnetic field was applied during the cure reaction, resulting in alignment of the molecules along the direction of the applied field. Measurement of the orientation parameter of the fully cured material by wide-angle X-ray scattering (WAXS) showed that orientation improved with an increase in field strength. The orientation parameters of the smectic layer normals calculated from the inner reflection of the WAXS pattern attained a maximum level of approximately 0.8 at a field strength of approximately 12 T. The orientation parameters calculated from the outer reflection of the WAXS pattern were considerably lower, possibly due to the presence of amorphous regions associated with domain boundaries or the loss of molecular alignment within the smectic layers due to topological restrictions of the cross-linking sites. Orientation resulted in an anisotropic linear thermal expansion coefficient after curing, although the overall volumetric expansion was constant. The elastic tensile modulus increased with the square of the orientation parameter, attaining a maximum value of 8.1 GPa, compared to 3.1 GPa for the unoriented material. The change in modulus with orientation could be fit with a simple model for the modulus of anisotropic materials.

Journal Article↗
PubMedDate not supplied

Establishment of hair bundle polarity and orientation in the developing vestibular system of the mouse.

The morphological development of the vestibular maculae in the mouse was studied in order to identify elements that may determine how hair-bundle polarity is established. Utricles and saccules develop in parallel. Hair-bundles first appear at embryonic day (E) 13.5. They are initially not polarised and have a kinocilium located at the centre of the cell surface surrounded by stereocilia. Polarisation is rapidly established as the kinocilium becomes eccentrically positioned. The orientation of these polarised bundles is initially not random. It varies systematically across the maculae and the general orientation in utricles is the opposite of that in saccules. At E15.5, in both maculae, hair-bundle orientation angles fall into two populations that differ by approximately 180 degrees defining a line of orientation reversal, the position of which varies little during subsequent maturation. Many more immature hair bundles appear at E15.5 suggesting a second wave of hair cell differentiation is initiated. Otoconial membrane is produced simultaneously across the entire width of both maculae, indicating directional growth of the overlying extracellular matrix is unlikely to influence hair-bundle orientation. Growth of both maculae occurs asymmetrically, essentially outwards from the striola, but it is most pronounced after orientation is defined. Microtubules are prominent in hair cells at the earliest stages of their differentiation, but are oriented parallel to the long axis of the cell and, thus, may not have a role in directing hair-bundle polarity. Microfilament assemblies that are aligned parallel to the apical surface and connect to the adherens junctions in supporting cells could provide a "framework" for hair-bundle orientation. The striated rootlets of ciliary centrioles that are aligned parallel to the cell surface with their tips associated with microfilament assemblies at adherens junctions were the only structural asymmetry identified that might influence the development of hair-bundle polarity.

Acoustic Maculae↗
PubMed1990

A multivariate analysis of adolescents' orientations toward physician use.

Health professionals know surprisingly little about the origins of the health beliefs and orientations they often seek to change, and they do not know about when, or if, changes in these orientations are likely to occur. This study is aimed at increasing our understanding of the origins and development of health beliefs and attitudes by focusing on the impact of parents' orientations toward physician utilization (inclination to consult a doctor when experiencing somatic symptoms) on the comparable orientations of their adolescent children. Hypotheses regarding direct parent-adolescent links are examined within a multivariate structural equations model relating demographics, adolescents' interpersonal competencies, and parental variables to adolescents' orientations toward physician utilization. Evidence for the development of these orientations is obtained by comparing influences across two groups of adolescents: 12- to 13-year-olds and 16- to 18-year-olds. Findings indicate that adolescents' orientations toward physician use are associated with those of their parents and that this link is generally stronger and more specific during late adolescence. The model also suggests that these orientations conform to social and cultural variables related to differences in social stratification.

Adolescent↗
PubMed2004

The affective structure of supportive parenting: depressive symptoms, immediate emotions, and child-oriented motivation.

This study investigated the maternal concerns and emotions that may regulate one form of sensitive parenting, support for children's immediate desires or intentions. While reviewing a videotape of interactions with their 1-year-olds, mothers who varied on depressive symptoms reported concerns and emotions they had during the interaction. Emotions reflected outcomes either to children (child-oriented concerns) or to mothers themselves (parent-oriented concerns). Child-oriented concerns were associated with fewer negative emotions and more supportive behavior. Supportive parenting was high among mothers who experienced high joy and worry and low anger, sadness, and guilt. However, relations depended on whether emotions were child or parent oriented: Supportive behavior occurred more when emotions were child oriented. In addition, as depressive symptoms increased, mothers reported fewer child-oriented concerns, fewer child-oriented positive emotions, and more parent-oriented negative emotions. They also displayed less supportive behavior. Findings suggest that support for children's immediate intentions may be regulated by parents' concerns, immediate emotions, and depressive symptoms.

Adult↗
PubMed2002

Goal orientation and ability: interactive effects on self-efficacy, performance, and knowledge.

This study examined the direct relationship of goal orientation--and the interaction of goal orientation and cognitive ability--with self-efficacy, performance, and knowledge in a learning context. The authors argue that whether a particular type of goal orientation is adaptive or not adaptive depends on individuals' cognitive ability. Consistent with previous research, learning orientation was positively related to self-efficacy, performance, and knowledge, whereas performance orientation was negatively related to performance only. The interactions between goal orientation and ability also supported several hypotheses. As expected, learning orientation was generally adaptive for high-ability individuals but had no effect for low-ability individuals. In contrast, the effects of performance orientation were contingent on both individuals' level of cognitive ability and the outcome examined.

Adaptation, Psychological↗
PubMed2005

Shaking hands with a computer: an examination of two methods of organizational newcomer orientation.

The current study investigated the effects of using a computer-based orientation program on organizational socialization and attitudinal outcomes. In a quasi-experimental field study, 261 newcomers either participated in a group, social-based orientation session or an individual, computer-based orientation session. Consistent with hypotheses, results indicated that participation in the computer-based orientation session led to lower levels of socialization in the more socially rich content areas, whereas the more information-based content areas were not affected. Levels of socialization mediated the effects of computer-based orientation on the more distal attitudinal outcomes of affective organizational commitment and job satisfaction. Computer-based orientation participation also negatively affected supervisor ratings of socialization. The results demonstrate the importance of newcomer orientations and socialization outcomes during organizational entry and that training method can be an important moderator of orientation practices.

Adult↗
PubMed1992

Orientation congruency effects in visual search.

Subjects searched for the letter E in a background of Ls and Fs in displays that had 1, 2, 4, 8, or 12 letters. The letters could be shown at one of six orientations (upright or rotated clockwise in 60 degrees increments). The displays were either congruent for orientation (all letters had the same orientation) or incongruent (letters in haphazard orientations except for the target on E-present trials). Search time increased linearly with the number of letters in the display, and more so for E-absent trials than for E-present trials. Letter orientation, in general, increased search time and produced an M-shaped function. Furthermore, orientation effects were attenuated in congruent displays relative to those produced by incongruent displays. The results demonstrated systematic orientation effects on the time to search for a simple pattern embedded in simple backgrounds, and provided converging evidence for the orientation-congruency effect found by Jolicoeur (1990b, Journal of Experimental Psychology: Human Perception and Performance, 16, 351-364).

Adult↗
PubMed2000

Induction of visual orientation modules in auditory cortex.

Modules of neurons sharing a common property are a basic organizational feature of mammalian sensory cortex. Primary visual cortex (V1) is characterized by orientation modules--groups of cells that share a preferred stimulus orientation--which are organized into a highly ordered orientation map. Here we show that in ferrets in which retinal projections are routed into the auditory pathway, visually responsive neurons in 'rewired' primary auditory cortex are also organized into orientation modules. The orientation tuning of neurons within these modules is comparable to the tuning of cells in V1 but the orientation map is less orderly. Horizontal connections in rewired cortex are more patchy and periodic than connections in normal auditory cortex, but less so than connections in V1. These data show that afferent activity has a profound influence on diverse components of cortical circuitry, including thalamocortical and local intracortical connections, which are involved in the generation of orientation tuning, and long-range horizontal connections, which are important in creating an orientation map.

Animals↗