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PubMed1990

Genetic and developmental analysis of irreC, a genetic function required for optic chiasm formation in Drosophila.

Irregular chiasm C (irreC) is an X-linked genetic function necessary for the correct projection of visual fibers in the optic chiasms of Drosophila optic ganglia. In addition to a severe disorganization of the inner optic chiasm irreC mutants display a subtle phenotype in the outer optic chiasm, in which some bundles of axons that leave the posterior equatorial part of the lamina on their way to the anterior medulla take a long detour before eventually finding their specific targets in the medulla neuropile. Deletion and recombination mapping of two irreC alleles (one P-element induced, the other associated with an inversion) have yielded a precise cytogenetic location in 3C4-5. A complex complementation pattern between roughest (rst) and irreC alleles indicates that both genetic functions are structurally and/or functionally closely interrelated. Flies in which the irreC locus is completely deleted by overlapping deficiencies are viable and their defects in the optic chiasms are similar to those seen in the two alleles. The defects in the outer and inner optic chiasms are not epigenetically connected and mosaic analyses have shown them to be independent from the genotype of the compound eye. Although the larval visual nerve looks normal, we have found that in the optic lobes of irreC mutants a group of early differentiating larval neurons is misplaced, suggesting a pioneering function of these cells during organization of the outer optic chiasms.

Animals↗
PubMed1984

Properties of visual cortical cells of the intact and the deafferented hemisphere of unilateral optic tract sectioned acute and chronic adult cats.

Single unit recording from visual cortex areas 17 and 18 and in the border region between them was performed on adult cats with unilateral optic tract section (OTX) either on the day of the operation (acute) or three to six months postoperatively (chronic). Visual activity from both hemispheres was analyzed with respect to the responsiveness level, the ocular dominance distribution and selectivity to orientation and direction. The results showed almost a complete absence of visual responsiveness in the deafferented hemisphere and a considerable reduction of responsiveness in the intact hemisphere. Following surgery an increase in visually responsive cells was found in the intact hemisphere as postoperative recovery continued. In addition, a reduction in the proportion of cells selective for orientation and direction was also found in the intact hemisphere of the OTX animals as compared to the control cats. Furthermore, cortical binocularity was not affected in the intact hemisphere of all OTX cats. We conclude that an almost total absence of interhemispheric callosal transfer of visual functions from the intact to the deafferented hemisphere is induced as a result of the unilateral OTX in adult cats. Moreover, the fact that the absence of cortical binocularity in the hemisphere receiving direct geniculate input was not disrupted, indicates the absence of callosal transfer from the deafferented to the intact hemisphere.

Animals↗
PubMed1991

Complementary global maps for orientation coding in upper and lower layers of the cat striate cortex and their possible functions.

Preferred stimulus orientations of striate cortical cells in the cat were analyzed for possible isotropic or anisotropic distributions. We separated the data twice, into central (0-5 degrees) vs. peripheral subgroups and into upper vs. lower layer cells. In the central group, absolute orientations were counted; in the periphery, a radial test was adopted by normalizing the preferred stimulus orientation of a cell to the line connecting the receptive field center to the retinal center. We found that in the center, vertical and horizontal orientations are overrepresented. In the periphery, the histograms show complementary anisotropies for upper and lower layers, favoring a map for radial orientation detection in upper layers and a more concentric map for orientation detection in lower layers. These results are possibly related to the probabilities of different optic flow fields on the retina under natural conditions of stimulation. They are discussed as possible neuronal structures supporting figure-ground discrimination, the distinction of self motion from object motion, and the location of objects in three-dimensional space.

Animals↗
PubMed1999

A direct demonstration of both structure and function in the visual system: combining diffusion tensor imaging with functional magnetic resonance imaging.

The relationships between functional activation patterns and the structural properties of brain pathways have not been widely studied. The recently developed magnetic resonance imaging technique of diffusion tensor imaging (DTI) allows a full characterization of water molecule mobility in three dimensions, providing new structural information that is not available from other in vivo imaging techniques. The directional bias of diffusion (anisotropy) may be derived from the diffusion tensor, and is related to fiber tract integrity and orientation. Since DTI and functional magnetic resonance imaging (fMRI) both require rapid (generally echoplanar) imaging it is possible to obtain geometrically matched images from the two modalities. fMRI and DTI were combined in a visual system study using photic stimulation to demonstrate the feasibility of combining the two methods and to investigate the structural properties of activated regions compared to the white matter tracts. Blood oxygenation level-dependent (BOLD) fMRI activation maps were directly overlayed upon fractional anisotropy (FA) maps, avoiding registration and spatial transformation by carefully matching acquisition parameters. Activated regions had lower FA than optic radiation white matter, supporting the hypothesis that most BOLD signal change occurs within the relatively isotropic cortical grey matter. The combination of these modalities in future studies may provide further insights into relationships between brain structure and function in both health and disease.

Adult↗
PubMed2003

Intensity modulated radiation therapy: film verification of planar dose maps.

A new slow response radiographic film (Kodak EDR) is compared with a more traditional faster responding dosimetry film (Kodak XV) in an intensity modulated radiation therapy x-ray field. Dose profiles derived from the two films are compared with doses obtained using a radiotherapy dose planning system (Philips-Pinnacle) which calculates planar dose using a collapsed cone convolution algorithm. Comparisons of the dose maps delivered from film with the Pinnacle dose maps are useful to ensure accurate dose delivery. The Pinnacle dose maps agreed with measurement using both film types to within +/- 3% (in the umbral region) at depths ranging from d(max) to 15 cm. Both XV and EDR films can be used to verify IMRT. EDR film is better suited for dosimetry for combined field dose maps due to its useful dose range of 1-5 Gy. We found XV to be more suitable for individual field dose maps (dose range 0-1 Gy) as no scaling of monitor units were required to achieve acceptable optical density response.

Algorithms↗
PubMed1997

Diffusion-weighted MRI of myelination in the rat brain following treatment with gonadal hormones.

Previous studies have demonstrated the ability of high-resolution diffusion-weighted MRI to show maturation of white-matter structures in the developing rat brain. The purpose of this study was to investigate the influence of gonadal steroid hormones on the rate of this development. Starting from their second postnatal day, 16 rat-pups of either sex were repeatedly treated with subcutaneous implants containing 17-beta estradiol or delta-androstene 3,17 dione, respectively. Serial T1-, T2- and diffusion-weighted MRI was performed weekly for 8 weeks using a 4.7 T unit. Maturation of anterior optic pathways and hemisphere commissures was assessed. Diffusion-weighted images were processed to produce "anisotropy index maps", previously shown to be sensitive to white-matter maturation. Compared with untreated rat-pups, estrogen-treated animals showed accelerated, and testosterone-treated animals delayed maturation on anisotropy index maps and histological sections. In all animals, maturational changes appeared earlier on anisotropy index maps than on other MRI sequences or on myelin-sensitive stained sections. Diffusion-weighted imaging, and the construction of spatial maps sensitive to diffusion anisotropy, seem to be the most sensitive approach for the detection of maturational white-matter changes, and thus may hold potential for early diagnosis of temporary delay or permanent disturbances of white-matter development.

Androstenediol↗
PubMed2005

Modelling of light pollution in suburban areas using remotely sensed imagery and GIS.

This paper describes a methodology for modelling light pollution using geographical information systems (GIS) and remote sensing (RS) technology. The proposed approach attempts to address the issue of environmental assessment in sensitive suburban areas. The modern way of life in developing countries is conductive to environmental degradation in urban and suburban areas. One specific parameter for this degradation is light pollution due to intense artificial night lighting. This paper aims to assess this parameter for the Athens metropolitan area, using modern analytical and data capturing technologies. For this purpose, night-time satellite images and analogue maps have been used in order to create the spatial database of the GIS for the study area. Using GIS advanced analytical functionality, visibility analysis was implemented. The outputs for this analysis are a series of maps reflecting direct and indirect light pollution around the city of Athens. Direct light pollution corresponds to optical contact with artificial night light sources, while indirect light pollution corresponds to optical contact with the sky glow above the city. Additionally, the assessment of light pollution in different periods allows for dynamic evaluation of the phenomenon. The case study demonstrates high levels of light pollution in Athens suburban areas and its increase over the last decade.

Air Pollutants↗
PubMed1997

Spatial and temporal visualization of gases and vapours in air using computed tomography. Numerical studies.

Numerical studies were performed to evaluate a new method for human exposure assessment and source monitoring, based upon optical remote sensing (ORS) and computed tomography (CT). With an ORS-CT system, two-dimensional maps of chemical concentrations in air, with good spatial and temporal resolution, can be created over a confined space such as a workplace room. The ORS-CT system was evaluated using 15 simulated test maps that model the generation and dispersion of contaminant plumes over time. A program simulated field measurements from these maps assuming different remote sensing scan times. Using these measurements, reconstructed maps were generated and compared with original maps. Qualitative and quantitative methods were used to evaluate the effect on reconstruction quality of sample time, number of iterations used by the maximum likelihood expectation maximization reconstruction algorithm and sample density. For this study, scanning an entire room in 10 min was adequate for exposure evaluation, source monitoring and leak detection.

Air Pollutants↗
PubMed1994

Results of excimer laser photorefractive keratectomy for the correction of myopia.

PURPOSE: This report summarizes the authors' 3-year experience with excimer laser photorefractive keratectomy on 240 eyes of 161 patients. METHODS: With constant laser emission parameters, nitrogen flow across the cornea was used on 79 eyes, whereas 161 eyes had no nitrogen flow. Of the 240 eyes, 74 were operated on without suction ring fixation. Postoperative pain management included patching and oral analgesics in 77 eyes and the use of topical diclofenac or ketorolac and a therapeutic soft contact lens in 163 eyes. Follow-up ranged from 1 month (206 eyes) to 36 months (10 eyes). RESULTS: At 3 months, 88% (144 eyes) had uncorrected visual acuity of 20/40 or better; 86% (151 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 10% (17 eyes) lost two or more lines of best-corrected visual acuity. At 12 months, 89% (122 eyes) achieved uncorrected visual acuity of 20/40 or better, 79% (115 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 4% (6 eyes) lost two or more lines of best-corrected visual acuity. At 24 months, 92% (44 of 48 eyes) had uncorrected visual acuity of 20/40 or better, 86% (44 of 51 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and 5% (2 eyes) lost two or more lines of best-corrected visual acuity. At 36 months, 90% (9 eyes) achieved an uncorrected visual acuity of 20/40 or better, 90% (9 eyes) had corrected visual acuity to within +/- 1 diopter of intended correction, and no eyes lost two or more lines of best-corrected visual acuity. CONCLUSIONS: The results obtained with one procedure are within accepted standards of accuracy for refractive surgery, and there is the potential for refinement of the final optical correction. Complication rates are low and are not vision threatening. They included increased intraocular pressure, epithelial "map dot" changes, and recurrent corneal erosion syndrome, "central islands," and others. Photorefractive keratectomy appears to be a safe procedure over the short and medium term.

Adult↗
PubMed2003

Optical analysis of acute spontaneous epileptiform discharges in the in vivo rat cerebral cortex.

We examined the spatiotemporal patterns of spontaneous epileptiform activity observed in the in vivo rat cerebral cortex using an optical recording technique of detecting transmembrane voltage changes. The surface of the cerebral cortex was exposed under anesthesia and stained with a fluorescent voltage-sensitive dye, RH414. Acute spontaneous epileptiform discharges were induced by application of a GABA(A) receptor antagonist, bicuculline. Changes in the intensity of fluorescence were recorded from the cerebral cortex using a 464-channel optic fiber photodiode system. We succeeded in recording spontaneous epileptiform discharges, and constructed their initiation-site maps. We found that the initiation site was neither unique nor randomly located, but exhibited a multimodal distribution pattern. The incidence of epileptiform discharges was different between the initiation sites, and some sites showed dominance in the induction of spontaneous epileptiform discharges.

Animals↗
PubMed2003

Monet's painting under the microscope.

An oil painting by Claude Monet, Port-Goulphar, Belle-Ile 1887 (collection of the Art Gallery of New South Wales), was examined to determine both the identity of the pigments used by the artist in this painting and his technique of mixing colors and laying paint on the canvas. The extremely complex construction of the painting was revealed by optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and X-ray mapping (XRM) analysis of cross sections of paint flakes excised from damaged regions of Port-Goulphar, Belle-Ile. Nine different pigments were found on the painting. Many of the identified colors were modern pigments that became available only late in the 19th century as a result of scientific advances in pigment chemistry. Although similar colors were available in a natural mineral form, they lacked the vivid color of their manufactured counterparts. The use of these new synthetic metallic oxide colors by Monet accounts for the brilliance of his paintings. In addition, a separation between successive paint layers was observed in some areas of paint chip cross sections, indicating that oil-based paint was applied to paint that had dried, and consequently, Port-Goulphar, Belle-Ile was painted over a long period of time. This observation is contrary to the general perception of Monet's technique of painting freely and quickly.

Electron Probe Microanalysis↗
PubMed2005

Novel algorithm for tomographic reconstruction of atmospheric chemicals with sparse sampling.

Numerical studies were performed to evaluate a new air monitoring method for reconstructing chemical exposures and source emissions, based upon optical remote sensing (ORS) and computed tomography (CT). With an ORS-CT system, two-dimensional maps of chemical concentrations can be created that have good spatial and temporal resolution. The mathematical algorithm used to compute the distribution is critical for accurate and useable reconstructions of the concentrations. In this research, a novel reconstruction method was tested that uses maximum likelihood expectation maximization (MLEM) combined with two techniques called grid-translation and multi-grid (GT-MG). To evaluate this method, computer simulations were performed using 120 test maps of varying complexity and a simulated ORS system with four instruments and a total of 40 path-integrated measurements. The results were quantitatively compared with two previously used reconstruction methods (single-grid and grid-translation). Results using the GT-MG method were dramatically improved over previously used methods. Quantitatively, peak exposure errors were reduced by up to 85% and artifacts were dramatically minimized.

Air Pollutants↗
PubMed1980

Cell movements in Xenopus eye development.

The vertebrate eye develops morphological markers, such as the ventral choroid fissure, which define its anatomical polarity in relation to the body. Also, retinal nerve fibres behave as though regionally differentiated by forming ordered, topographical maps of the visual field in the brain. It has long been held that these two features of eye polarity--its structure and the neural specificity of the ganglion cells--are labile in the early eye vesicle and become determined relative to body axes at a subsequent stage of development. Contrary to these earlier findings, recent experiments show that the structure and connectivity of the eye are already determined by the time it first appears as a distinct eye vesicle; surgical construction of eye pigmentation chimaeras suggested that normal tectal maps, previously reported after early eye rotations, may have arisen from neural retina cells recruited from the optic stalk after the operation. In agreement, using a radioactive tag which marks neural retina as well as pigment epithelium, I report here that during normal development in Xenopus laevis, cells in the ventral retina, where the choroid fissure forms, move into position from the optic stalk region during eye-cup formation. Depending on developmental stage, surgical eye rotations may intercept their movement and this provides a simple explanation of results previously taken to indicate a change from a labile to a determined state of eye polarity.

Animals↗
PubMed2000

Influence of ceramic and stainless steel brackets on the notching of archwires during clinical treatment.

The surface topography of 100 clinically used archwires of stainless steel, beta-, or nickel-titanium were investigated that had contacted either ceramic or stainless steel brackets. One group consisted of two sets: 60 wires with no treatment records accessed to bias analyses, and 40 wires for which extensive clinical records were available, half of which were used with ceramic or stainless steel brackets. A control group consisted of two sets: 30 unused wires comprised of five round and rectangular wires of each alloy, and four wires that were ligated and immediately removed from patients' mouths. After ultrasonic cleaning, each wire was inspected under an optical and/or a scanning electron microscope. Notches were categorized with regard to frequency, patterns, and severity, and mapped as a function of wire aspect (lingual, facial, and occlusal/gingival) and anatomical regions (molar, premolar, canine, and incisor). From these data the average severity of notch patterns and a notching index were derived. Although no recognizable defect patterns were observed in the control group, seven basic patterns were recognized for each wire cross-sectional shape in the clinically used wires. These wires appeared most damaged on their lingual aspect and least damaged on their facial aspect. With regard to anatomical regions, notching was prevalent in the anterior regions and sparse in the molar regions. The notch activity and the severity were nearly three times greater from ceramic brackets than from stainless steel brackets. Over one-third of all notches documented in ceramic bracket cases had severity numbers of 3 and penetrated at least one-quarter of each wire's dimension, However, over two-thirds of all notches documented in stainless steel bracket cases had severity numbers of 1. From these tabulations a theory of notch formation was proposed in which vertical movement from tooth or wire during mastication caused fretting wear, and horizontal movement during orthodontic procedures such as space closure, tipping, or bodily movement caused sliding wear.

Ceramics↗
PubMed1999

Improper orientational ordering regime and tricritical behavior in a lyotropic liquid crystal.

Optical microscopy, deuteron quadrupolar NMR, x-ray diffraction, and electrical conductivity techniques have been used to map the phase diagram and to measure the nematic order parameter variation (S) in ternary mixtures of pentadecafluorooctanoate acid ammonium salt (APFO), heavy water (D2O), and ammonium chloride (NH4Cl). A phenomenological model with an isotropic parent phase and a single primary segregation order parameter is elaborated on to describe in consistent terms the linear dependence of S(T) through the whole nematic stability region as well as the existence of a tricritical point at the nematic-to-lamellar phase transition line.

Journal Article↗
PubMed1974

The influence of centrally applied noradrenaline on shivering and body temperature in the pigeon.

1. Noradrenaline (NA) was injected in a volume of 1.0 mul. through chronically implanted cannula into the hypothalamus of the unanaesthetized pigeon.2. In doses of 1-15 mug NA caused complete inhibition of shivering of dose-dependent duration. Histological mapping of the brain showed that NA was exerting its inhibitor action in the region above the optic chiasma bordering on the posterior hypothalamus and the anterior preoptic nucleus.3. At low ambient temperature, the NA induced inhibition of the cold tremor caused a fall of core temperature which lasted as long as shivering was inhibited. Shivering induced by local cooling of the spinal cord, and by the combined cooling of the skin and the spinal cord, was likewise inhibited by the cerebral application of NA. There was no evidence of an adjustment of the temperature set-point by NA.4. A rapid rise in skin temperature of the unfeathered feet, whenever NA was injected indicated a reduction in peripheral vasomotor tone.

Animals↗
PubMed1996

Inferotemporal cortex and object vision.

Cells in area TE of the inferotemporal cortex of the monkey brain selectively respond to various moderately complex object features, and those that cluster in a columnar region that runs perpendicular to the cortical surface respond to similar features. Although cells within a column respond to similar features, their selectivity is not necessarily identical. The data of optical imaging in TE have suggested that the borders between neighboring columns are not discrete; a continuous mapping of complex feature space within a larger region contains several partially overlapped columns. This continuous mapping may be used for various computations, such as production of the image of the object at different viewing angles, illumination conditions, and articulation poses.

Animals↗
PubMed2006

Local and average gloss from flat-faced sodium chloride tablets.

The purpose of this study was to detect local gloss and surface structure changes of sodium chloride tablets. The changes in surface structure were reflected by gloss variation, which was measured using a diffractive optical element-based glossmeter (DOG). By scanning a surface area, we constructed a 2-dimensional gloss map that characterized the tablet's surface structure. The gloss variation results were compared with scanning electron microscopy (SEM) images and average surface roughness values that were measured by conventional diamond stylus profilometry. The profilometry data showed a decrease in tablet surface roughness as a function of compression force. In general, a smoother surface contributes to higher average gloss values. The average gloss values for this material, in contrast, showed a decrease as a function of the compression force. The sequence of particle fragmentation and deformation together with crack formation in sodium chloride particles resulted in a loss of gloss for single sodium chloride particles at the tablet surfaces, which could be detected by the DOG. These results were supported by the SEM images. The results show that detailed information regarding tablets' surface structure changes can be obtained by detection of local gloss variation and average gloss.

Microscopy, Electron, Scanning↗

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