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PubMed1996

The orientation of the bi-leaflet CarboMedics valve in the mitral position determines left ventricular spatial flow patterns.

OBJECTIVES: In the mitral annulus bi-leaflet mechanical valves can be oriented in two ways: the anatomical orientation with the hinge line parallel to a line through the commissures of the native valve (90 degrees). The influence of this orientation on the left ventricular spatial flow pattern and valve leaflet opening was investigated in pigs. METHODS: In 9 pigs a CarboMedics mitral valve prosthesis was implanted in the ) degree position and in 9 pigs in the 90 degree orientation. Two dimensional echocardiographic and color Doppler recordings were performed before surgery, immediately after surgery and after 6 weeks. RESULTS: In the native valve the diastolic flow pattern was characterized by a central inflow and backflow away from the apex along the left ventricular wall. In the 0 degree orientation a diastolic flow pattern with an asymmetrical inflow was observed, resulting from a greater extension of the jet along the lateral wall compared to the jet along the interventricular septum. Mid-diastolic back-flow away from the left ventricular apex was directed towards the valve prosthesis. In the 2-dimensional echocardiographic recordings the opening angle of both prosthetic leaflets was different showing a larger opening angle of the posterior leaflet. In the 90 degree orientation a diastolic flow pattern with paradoxical flow directions was recorded, that could only be explained in a 3-dimensional way: one inflow jet along the anterior wall, one inflow jet along the posterior wall and back-flow away from the apex sandwiched in between the two inflow jets. In this orientation the 2-dimensional echocardiographic recordings showed symmetrical opening of the two leaflets of the prosthesis. CONCLUSIONS: The orientation of the CarboMedics bi-leaflet mechanical valve prosthesis in the mitral valve annulus determines the left ventricular spatial flow pattern. The flow pattern resulting from the 0 degree orientation, was associated with asymmetrical leaflet motion, while the 90 degree orientation flow pattern was associated with symmetrical leaflet motion. These findings may be of importance for prosthetic valve function as well as for left ventricular kinetics.

Animals↗
PubMed1989

Role of inhibition in the specification of orientation selectivity of cells in the cat striate cortex.

Mechanisms supporting orientation selectivity of cat striate cortical cells were studied by stimulation with two superimposed sine-wave gratings of different orientations. One grating (base) generated a discharge of known amplitude which could be modified by the second grating (mask). Masks presented at nonoptimal orientations usually reduced the base-generated response, but the degree of reduction varied widely between cells. Cells with narrow orientation tuning tended to be more susceptible to mask presence than broadly tuned cells; similarly, simple cells generally showed more response reduction than did complex cells. The base and mask stimuli were drifted at different temporal frequencies which, in simple cells, permitted the identification of individual response components from each stimulus. This revealed that the reduction of the base response by the mask usually did not vary regularly with mask orientation, although response facilitation from the mask was orientation selective. In some sharply tuned simple cells, response reduction had clear local maxima near the limits of the cell's orientation-tuning function. Response reduction resulted from a nearly pure rightward shift of the response versus log contrast function. The lowest mask contrast yielding reduction was within 0.1-0.3 log unit of the lowest contrast effective for excitation. The temporal-frequency bandpass of the response-reduction mechanism resembled that of most cortical cells. The spatial-frequency bandpass was much broader than is typical for single cortical cells, spanning essentially the entire visual range of the cat. These findings are compatible with a model in which weak intrinsic orientation-selective excitation is enhanced in two stages: (1) control of threshold by nonorientation-selective inhibition that is continuously dependent on stimulus contrast; and (2) in the more narrowly tuned cells, orientation-selective inhibition that has local maxima serving to increase the slope of the orientation-tuning function.

Animals↗
PubMed2003

Global orientation of bound MMP-3 and N-TIMP-1 in solution via residual dipolar couplings.

Crystal structures of catalytic domains of MMP-3 and MT1-MMP bound to TIMP-1 or TIMP-2, respectively, differ in the orientation of the TIMP in the MMP active site. The orientation in solution of N-TIMP-1 in the MMP-3 active site has been investigated using residual dipolar couplings (RDCs). Fitting of the RDCs to the X-ray structures of the complexes suggests general agreement with the orientation of crystalline MMP-3(DeltaC) and TIMP-1 and a large disparity from the orientation of crystalline MT1-MMP(DeltaC) and TIMP-2. Rigid body docking of MMP-3 and N-TIMP-1 X-ray coordinates using RDCs and intermolecular NOEs provided a time-averaged orientation in solution differing from the crystal structure by a 5 degrees rotation toward the MT1-MMP(DeltaC)/TIMP-2 orientation. The slight discrepancy in orientations in solution and crystal lies within the experimental uncertainties. Intermolecular NOEs used in the docking corroborated the accuracy of mapping the interface by a paramagnetic NMR footprinting assay, a potential alternative source of contacts for docking. Some uncertainty in the N-TIMP-1 orientation in the MMP-3 active site, coupled with microsecond to millisecond fluctuations of the MMP-binding ridge of N-TIMP-1 in the complex and flexibility in MMP-3(DeltaC) S(1)' to S(3)' subsites, leaves open the possibility that N-TIMP-1 might dynamically pivot a few degrees or more in the arc toward the MT1-MMP(DeltaC)/TIMP-2 orientation. Differing TIMP orientations in MMP active sites are more likely to result from structural differences in TIMP AB hairpin loops than from crystal packing artifacts.

Antineoplastic Agents↗
PubMed1999

How accurate is the family history method for assessing siblings' sexual orientation?

Previous studies investigating the familial nature of sexual orientation have often relied on the reports of siblings. They have generally obtained extremely high accuracy rates for proband rating of the sexual orientation of siblings. However, participants in these studies have probably been unusually open about their sexual orientation, and thus it is uncertain if more representative participants would have as accurate knowledge about their families. An unselected sample of twins from the Australian Twin Registry rated their own, their cotwins', and their siblings' sexual orientations. We examined accuracy of heterosexual and homosexual probands' assessments of their twins' sexual orientations, as well as cotwins' agreement about other siblings' orientations. Concordance between twins' ratings of their cotwins' orientations with the cotwins' self-rated orientations was considerably lower than that found in previous studies, as was the level of agreement between members of a twin pair in the assessment of other siblings' sexual orientations. Marital history as a proxy variable for determining the sexual orientation of older subjects did not support its use with women, though its use for older men received some weak support.

Adult↗
PubMed1998

The layout of orientation and ocular dominance domains in area 17 of strabismic cats.

In the primary visual cortex of strabismic cats, the elimination of correlated activity between the two eyes enhances the segregation of the geniculocortical afferents into alternating ocular dominance domains. In addition, both tangential intracortical fibres and neuronal synchronization are severely reduced between neurons activated by different eyes. Consequently, ocular dominance columns belonging to different eyes are functionally rather independent. We wondered whether this would also affect the organization of orientation preference maps. To this end, we visualized the functional architecture of area 17 of strabismic cats with both optical imaging based on intrinsic signals and double labelling of orientation and ocular dominance columns with [14C]2-deoxyglucose and [3H]proline. As expected, monocular iso-orientation domains had a patchy appearance and differed for the two eyes, leading to a clear segregation of the ocular dominance domains. Comparison of 'angle maps' revealed that orientation domains exhibit a pinwheel organization as in normally reared cats. Interestingly, the map of orientation preferences did not show any breaks at the borders between ocular dominance columns: iso-orientation domains were continuous across these borders. In addition, iso-orientation contours tended to cross the borders of adjacent ocular dominance columns at right angles. These data suggest that the basic relations between the layout of orientation maps and ocular dominance columns are not disturbed by artificial decorrelation of binocular input. Therefore in cat area 17, the orientation map does not seem to be modified by experience-dependent changes of thalamic input connections. This suggests the possibility that use-dependent rearrangement of geniculocortical afferents into ocular dominance columns is due to Hebbian modifications whereby postsynaptic responsivity is constrained by the scaffold of the orientation map.

Animals↗
PubMed2001

Differences between the sexes and age-related changes in orienteering speed.

The aim of this study was to assess the effects of the age and sex of the competitor on orienteering speed during competitive events. The results of the fastest three male and fastest three female competitors in each 5-year age band (21-79 years), from four national orienteering events, were analysed. The data for age and orienteering speed were log-transformed and regression analyses were conducted to determine the relationships between age and sex and orienteering speed. For comparison, data for the fastest Great Britain finisher in the 10,000-m track and 10-km cross-country events for age groups 40-69 years at the World Masters Championships were also analysed. The results showed that, before the age of 40 years, there was no substantial slowing in orienteering speed for males (0.5-4.2% per decade) but a moderate decline (4.7-10.0% per decade) for females. After the age of 45 years, the orienteering speed of males and females slowed by 13+/-2% and 16+/-4% per decade (mean +/- s), respectively, until around the age of 69, after which the deterioration was accentuated. The orienteering speed of the females was 81+/-4, 74+/-6 and 69+/-7% that of the males at ages 21, 45 and 65 years, respectively. The magnitudes of the age-related slowing of orienteering speed and of the difference in orienteering speed between males and females aged 45 years and over were greater than those reported for the other endurance running events. This may reflect the physical demands of running in orienteering terrain, tactical and cognitive aspects of the sport, or sociocultural aspects of the participating population.

Adult↗
PubMed1999

Grating orientation as a measure of tactile spatial acuity.

Recent studies have used grating orientation as a measure of tactile spatial acuity on the fingerpad. In this task subjects identify the orientation of a grooved surface presented in either the proximal-distal or lateral-medial orientation. Other recent results have suggested that there might be a substantial anisotropy on the fingerpad related to spatial sensitivity. This anisotropy was revealed using a task in which subjects discriminated between a smooth and a grooved surface presented at different orientations on the fingerpad. The anisotropy was substantial enough that it might permit subjects to discriminate grating orientation on the basis of intensive rather than spatial cues. The present study examined the possibility that anisotropy on the fingerpad might provide cues in a spatial acuity task. The ability of subjects to discriminate between a smooth and a grooved surface was measured under conditions that are typically used in grating orientation tasks. No evidence of anisotropy was found. Also, using a grating orientation task, separate estimates were made of sensitivity in the proximal-distal and lateral-medial orientations. Again no evidence of anisotropy was found. Consistent with changes in the density of innervation, grating orientation sensitivity was found to vary as a function of location on the fingerpad. The results support the view that grating orientation is a valid measure of spatial acuity reflecting underlying neural, spatial mechanisms.

Discrimination Learning↗
PubMed2005

Boundary cue invariance in cortical orientation maps.

We effortlessly perceive oriented boundaries defined by either luminance changes ('first-order' cues) or texture variations ('second-order' cues). Many neurons in mammalian visual cortex show orientation preference to both types of boundaries, but it is uncertain how they contribute to perceptual orientation cue-invariance at the neuronal population level. Using optical imaging in cat A 18, we observed highly similar orientation preference maps to first-order and a variety of second-order visual stimuli. Thus the neuronal representation of coarse-scale boundary orientation appears to be invariant to the characteristics (including local orientation) of the fine-scale textures by which those boundaries are defined. A common feature of second-order visual stimuli is that modulation shifts their Fourier energy for boundary orientation to the higher spatial frequencies of their constituent textures - our results suggest a common neural mechanism (demodulation) mediating visual processing of many kinds of texture boundary. The similarity between orientation maps to different stimuli implies that second-order responsive neurons are homogeneously distributed across the cortical surface. Such homogeneously cue-invariant orientation representation could provide a neural substrate for perceptual form-cue invariance, and reflect an optimal organization for encoding orientation information in natural scenes.

Animals↗
PubMed1991

Topographical Aspects of Intracortical Excitation and Inhibition Contributing to Orientation Specificity in Area 17 of the Cat Visual Cortex.

Intracortical mechanisms contributing to orientation and direction specificity were investigated with a method of local cortical inactivation. Single-unit activity was recorded in area 17 of the anaesthetized cat while a small volume of cortical tissue 400 - 2900 microm lateral to the recorded cell was inactivated by gamma-aminobutyric acid (GABA) microiontophoresis. Cells were stimulated with moving bars of variable orientation and changes of the response were monitored. Recording and inactivation sites were histologically verified. Statistically significant changes in orientation tuning during GABA-induced remote inactivation were observed in 80 of 145 cells (55%), and consisted in a reduced orientation specificity due to either increased (36%) or decreased (19%) responses. Increases of responses were more pronounced for the non-optimal orientations. This effect mainly occurred with GABA application at distances around 500 microm and is interpreted as loss of inhibition. Reduced orientation specificity as a result of decreasing response mainly to the optimal orientation was interpreted as loss of excitation. This effect most frequently occurred with inactivation at distances around 1000 microm. Loss of inhibition was also elicited from a distance of 1000 microm; such inhibition, however, affected only directionality, without inducing changes in orientation tuning. For several cells at distances >1000 microm from the inactivation site a temporal sequence consisting of a change in direction specificity followed by a reduction of orientation specificity, and finally by direct GABAergic inhibition of the cell under study, could be induced with gradually increasing ejecting currents. The results indicate that excitation and inhibition originating from populations of neurons at different horizontal distances differentially contribute to direction and orientation specificity of a given visual cortical cell.

Journal Article↗
PubMed2004

Determination of the left ventricular long-axis orientation from a single short-axis MR image: relation to BMI and age.

Accurate determination of imaging planes in relation to the left ventricular (LV) long-axis orientation is important for anatomical and functional evaluation as well as for serial comparisons with cardiac magnetic resonance (CMR) imaging. Therefore, a fast and reliable method to test the accuracy of CMR imaging for measuring the orientation of the LV long-axis was developed and validated. In addition, the relationship between LV long-axis orientation and body mass index (BMI), gender and age was assessed. Two approaches were used, a long-axis approach (based on a manually defined vector) and a short-axis approach (based on a calculated vector). The concordance between the two approaches was assessed in 72 healthy volunteers. The accuracy and precision of MR imaging for measuring three-dimensional orientations were tested using a LV phantom. The mean difference between the long- and short-axis approaches for measuring the LV long-axis orientation in the study population was 0 +/- 3 degrees, 0 +/- 2 degrees, and -1 +/- 3 degrees in the frontal, transverse and sagittal plane, respectively. BMI and age were shown to influence LV long-axis orientation, especially in the frontal and sagittal planes. A significant difference in LV long-axis orientation in the frontal and sagittal planes was found between genders. The correlation coefficient between MR-measured phantom orientation and true phantom orientation was >0.98 in all three orthogonal planes. These observations suggest that a single LV short-axis MR image can be used for measuring LV long-axis orientation in patients with no cardiac disease.

Adult↗
PubMed1982

Analysis of orientation bias in cat retina.

1. Responses of cat retinal ganglion cells to a drifting sinusoidal grating stimulus were measured as a function of the grating orientation and spatial frequency.2. The response at fixed frequency and contrast varied with orientation in the manner of a cosine function. A new measure was introduced to quantify this orientation bias in the response domain on an absolute scale of 0-100%. Under experimental conditions designed to maximize the effect, the mean bias for 250 cells was 16% and the range was 0-46%. In 70% of cells there was significant bias.3. Orientation bias varied with spatial frequency and was maximal near the high-frequency limit. The majority of biassed cells preferred the same orientation at high and low frequencies but in some cells a reversal occurred: the orientation which gave maximum response at high frequencies gave minimum response at low frequencies. The greatest variation of cut-off frequency with orientation was (2/3) octave.4. Orientation bias was due to neural, not optical, factors. Nevertheless, the phenomenon could often be imitated by deliberately introduced optical astigmatism of up to 4 dioptres for brisk-sustained units and over 10 dioptres for brisk-transient units.5. The grating orientation preferred by cells varied systematically with position in the visual field. The central tendency was for the grating which yielded maximum response to lie parallel to the line joining the cell to the area centralis. This generalization failed for units within 2 degrees of the centre of the area centralis.6. Analysis of orientation bias indicates a functional asymmetry of receptive fields such that the centre mechanism, and sometimes also the surround mechanism, is elongated along the line joining cell to area centralis.

Animals↗
PubMed2002

Laminar processing of stimulus orientation in cat visual cortex.

One of the most salient features to emerge in visual cortex is sensitivity to stimulus orientation. Here we asked if orientation selectivity, once established, is altered by successive stages of cortical processing. We measured patterns of orientation selectivity at all depths of the cat's visual cortex by making whole-cell recordings with dye-filled electrodes. Our results show that the synaptic representation of orientation indeed changes with position in the microcircuit, as information passes from layer 4 to layer 2+3 to layer 5. At the earliest cortical stage, for simple cells in layer 4, orientation tuning curves for excitation (depolarization) and inhibition (hyperpolarization) had similar peaks (within 0-7 deg, n = 11) and bandwidths. Further, the sharpness of orientation selectivity covaried with receptive field geometry (r = 0.74) - the more elongated the strongest subregion, the shaper the tuning. Tuning curves for complex cells in layer 2+3 also had similar peaks (within 0-4 deg, n = 7) and bandwidths. By contrast, at a later station, layer 5, the preferred orientation for excitation and inhibition diverged such that the peaks of the tuning curves could be as far as 90 deg apart (average separation, 54 deg; n = 6). Our results support the growing consensus that orientation selectivity is generated at the earliest cortical level and structured similarly for excitation and inhibition. Moreover, our novel finding that the relative tuning of excitation and inhibition changes with laminar position helps resolve prior controversy about orientation selectivity at later phases of processing and gives a mechanistic view of how the cortical circuitry recodes orientation.

Action Potentials↗
PubMed1996

Depletion of lysophosphatidic acid triggers a loss of oriented detyrosinated microtubules in motile fibroblasts.

We reported earlier that isolated plasma membranes trigger a number of responses comprising contact inhibition of motility, including loss of oriented detyrosinated microtubules (Glu MTs) from the lamella of motile fibroblasts. In this study, we show that the membranes trigger this loss of Glu MTs, not by binding to cells, but by removing an essential component from the medium necessary to maintain oriented Glu MTs. Preincubation of membranes with medium containing serum followed by removal of the membranes by sedimentation rendered the membrane-treated medium capable of triggering the loss of oriented Glu MTs. Membrane activity was inhibited by high concentrations of serum and removal of serum from medium triggered the loss of oriented Glu MTs similar to that triggered by membranes. These results suggest that the membranes trigger the loss of Glu MTs by inactivating factors in serum that are required for the maintenance of oriented Glu MTs. By fractionating serum, we have identified lysophosphatidic acid (LPA) as the principal serum factor that is responsible for supporting oriented Glu MTs. The activity of LPA to maintain oriented Glu MTs upon serum withdrawal was half maximal at 100 nM and no activity was observed with structurally related phospholipids. Serum LPA levels were sufficient to account for the ability of serum to support oriented Glu MTs. Enzymatic degradation of serum LPA strongly reduced the ability of serum to support oriented Glu MTs. That membranes degrade LPA was shown by the ability of membranes to block LPA's ability to maintain oriented Glu MTs, and by direct measurement of the loss of radiolabeled LPA after incubation with membranes in vitro. These results show that isolated plasma membranes trigger the loss of Glu MTs from the lamella of motile cells by degrading serum LPA. Coupled with earlier results showing that membranes trigger a number of contact inhibition responses, our data suggest a new model for contact inhibition of motility in which local degradation of LPA and/or interference with LPA-stimulated signalling pathways initiates a contact inhibition response in colliding cells.

Alkaline Phosphatase↗
PubMed2000

Partial experience with the arc of the sun is sufficient for all-day sun compass orientation in homing pigeons, Columba livia.

The ability of animals to learn to use the sun for orientation has been explored in numerous species. In birds, there is conflicting evidence about the experience needed for sun compass orientation to develop. The prevailing hypothesis is that birds need entire daytime exposure to the arc of the sun to use the sun as an orientation cue. However, there is also some evidence indicating that, even with limited exposure to the arc of the sun, birds, like insects, can use the sun to orient at any time of day. We re-examine this issue in a study of compass orientation in a cue-controlled arena. Two groups of young homing pigeons received different exposure to the sun. The control group experienced the sun throughout the day; the experimental group experienced only the apparent descent of the sun. After 8 weeks of sun exposure, we trained both groups in the afternoon to find food in a specific compass direction in an outdoor arena that provided a view of the sun but not landmarks. We then tested the pigeons in the morning for their ability to use the morning sun as an orientation cue. The control group and the experimental group, which was exposed to the morning sun for the first time, succeeded in orienting in the training direction during test 1. The orientation of the experimental group was no different from that of the control group, although the experimental first trial directional response latencies were greater than the control latencies. Subsequently, we continued training both groups in the afternoon and then tested the pigeons during the morning under complete cloud cover. Both groups displayed random directional responses under cloud cover, indicating that the observed orientation was based on the visibility of the sun. The data indicate that pigeons with limited exposure to the arc of the sun can, like insects, use the sun for orientation at any time of day.

Animals↗
PubMed2003

Integration of first- and second-order orientation.

The problem of how visual information such as orientation is combined across space bears on key visual abiities, such as texture perception. Orientation signals can be derived from both luminance and contrast, but it is not well understood how such information is pooled or how these different orientation signals interact in the integration process. We measured orientation discrimination thresholds for arrays of equivisible first-order and second-order Gabors. Thresholds were measured as the orientation variability in the arrays increased, and we estimated the number of samples (or efficiency) and internal noise of the mechanism being used. Observers were able to judge the mean orientation of arrays of either first- or second-order Gabors. For arrays of first-order and arrays of second-order Gabors, estimates of the number of samples used increased as the number of Gabors increased. When judging the orientation of arrays of either order, observers were able to ignore randomly oriented Gabors of the opposite order. If observers did not know which Gabor type carried the more useful orientation information, they tended to use the information from first-order Gabors (even when this was poorer information). Observers were unable to combine information from first- and second-order Gabors, though this would have improved their performance. The visual system appears to have separate integrators for combining local orientation across space for luminance- and contrast-defined features.

Discrimination, Psychological↗
PubMed2005

Optimizing oriented planar-supported lipid samples for solid-state protein NMR.

Sample orientation relative to the static magnetic field of an NMR spectrometer allows study of membrane proteins in the lipid bilayer setting. The straightforward preparation and handling of extremely thin mica substrates with consistent surface properties has prompted us to examine oriented phospholipid bilayer and hexagonal phases on mica. The spectral characteristics of oriented lipid samples formed on mica are as good as or better than those on glass. Nine solvents with varying dielectric constants were used to cast lipid films or for vesicle spreading; film characteristics were then compared, and static solid-state 31P-NMR was used to characterize the degree of orientation of the hydrated lipid species. Lipids with four headgroup chemistries were tested: 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPG), 1,2-dioleoyl-sn-glycero-3-phosphate (DOPA), and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE). Solvent affected orientation of POPG, DOPA, and DOPE, but not POPC. Film characteristics varied with solvent, with ramifications for producing homogeneous oriented lipid samples. POPC was used to optimize the amount of lipid per substrate and compare hydration methods. POPG did not orient reproducibly, whereas POPG-POPC mixtures did. DOPA showed 1-2 oriented states depending upon hydration level and deposition method. DOPE formed an oriented hexagonal phase that underwent a reversible temperature-induced phase transition to the oriented bilayer phase.

Aluminum Silicates↗
PubMed2006

Seasonal and cultivar-associated variation in oviposition preference of Oriental fruit moth (Lepidoptera: Tortricidae) adults and feeding behavior of neonate larvae in apples.

The Oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae) has become a pest of tree fruits since its introduction to the United States in the early twentieth century. Oriental fruit moth has historically been a major pest problem in peach production, and outbreaks in commercial apple (Malus spp.) orchards in the eastern United States were rare until the late 1990s. Recent outbreaks in Mid-Atlantic apple orchards have lead researchers to investigate host-associated effects on oriental fruit moth biology, behavior, and population dynamics. Studies were designed to assess cultivar level effects in apples on oviposition and larval feeding behavior of oriental fruit moth. In a mixed cultivar apple orchard, total oriental fruit moth oviposition and oviposition site preferences varied between cultivars. These preferences also varied over time, when sampling was repeated at various times of the growing season. Although most adult female oriental fruit moth preferentially oviposited in the calyx and stem areas of apple fruit, noticeable numbers of eggs also were laid on the sides of fruit, contradicting some previous reports. Oriental fruit moth females exhibited a strong ovipositional preference for fruit that were previously damaged by oriental fruit moth or codling moth, Cydia ponmonella (L.). The majority of newly hatched oriental fruit moth larvae were observed to spend <24 h on the surface of apple fruit before entry, and this behavior was observed on several apple cultivars. Neonate larvae exhibited a preference for entering fruit at either the stem or calyx ends, regardless of their initial site of placement. Our findings underscore the importance of adequate spray coverage and accurate timing of insecticide applications targeting oriental fruit moth.

Animals↗
PubMed2001

Theoretical and experimental dissection of gravity-dependent mechanical orientation in gravitactic microorganisms.

Mechanisms of gravitactic behaviors of aquatic microorganisms were investigated in terms of their mechanical basis of gravity-dependent orientation. Two mechanical mechanisms have been considered as possible sources of the orientation torque generated on the inert body. One results from the differential density within an organism (the gravity-buoyancy model) and the other from the geometrical asymmetry of an organism (the drag-gravity model). We first introduced a simple theory that distinguishes between these models by measuring sedimentation of immobilized organisms in a medium of higher density than that of the organisms. Ni2+-immobilized cells of Paramecium caudatum oriented downwards while floating upwards in the Percoll-containing hyper-density medium but oriented upwards while sinking in the hypo-density control medium. This means that the orientation of Paramecium is mechanically biased by the torque generated mainly due to the anterior location of the reaction center of hydrodynamic stress relative to those of buoyancy and gravity; thus the torque results from the geometrical fore-aft asymmetry and is described by the drag-gravity model. The same mechanical property was demonstrated in gastrula larvae of the sea urchin by observing the orientation during sedimentation of the KCN-immobilized larvae in media of different density: like the paramecia, the gastrulae oriented upwards in hypo-density medium and downwards in hyper-density medium. Immobilized pluteus larvae, however, oriented upwards regardless of the density of the medium. This indicates that the orientation of the pluteus is biased by the torque generated mainly due to the posterior location of the reaction center of gravity relative to those of buoyancy and hydrodynamic stress; thus the torque results from the fore-aft asymmetry of the density distribution and is described by the gravity-buoyancy model. These observations indicate that, during development, sea urchin larvae change the mechanical mechanism for the gravitactic orientation. Evidence presented in the present paper demonstrates a definite relationship between the morphology and the gravitactic behavior of microorganisms.

Animals↗