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At least 1,423 records · Page 79Linked to original sources
PubMed2006

Application of two-dimensional spectral surface plasmon resonance to imaging of pressure distribution in elastohydrodynamic lubricant films.

What we believe to be a novel two-dimensional spectral surface plasmon resonance imaging technique determining pressure distribution in elastohydrodynamic lubricant films is presented. This technique makes use of the spectral characteristics associated with the surface plasmon resonance (SPR) effect, and it provides more spectral information in refractive index mapping than conventional contrast SPR imaging. Two-dimensional imaging is demonstrated and applied to a highly pressurized liquid lubricant trapped inside an elastohydrodynamic lubrication (EHL) dimple. The hydrostatic pressure inside the EHL dimple causes a localized change of the refractive index of the lubrication oil. This also results in a shift in the spectral SPR absorption dip. By monitoring the color changes within the SPR image and calibrating with lubricants of known refractive index profiles, we can obtain a direct measurement of the refractive index distribution within the EHL dimple. PB 2400 lubricant dimples were studied in our experiments. The proposed SPR imaging approach is irrespective of the absolute lubricant film thickness h, therefore overcoming the major limitations of a conventional optical interference technique. With further development of the two-dimensional refractive index mapping technique, widespread applications in various fields are possible, including high-throughput sensors and the detection of bioaffinity interactions.

Journal Article↗
PubMed2000

Modulatory effects of the nucleus of the basal optic root on rotundal neurons in pigeons.

The present paper reports for the first time in birds the modulatory effects of the nucleus of the basal optic root (nBOR) on visual neurons in the nucleus rotundus in particular and those of the accessory optic system on the tectofugal pathway in general. Pharmacological blockade of the nBOR by lidocaine led to a decrease or increase in visual responsiveness of rotundal cells, suggesting excitatory or inhibitory actions of the nBOR on rotundal cells. These results were confirmed by changes in the excitability of rotundal cells following electrical stimulation of the nBOR. Response latency measurements implied that there might be at least two pathways from the nBOR to the nucleus rotundus, one being a direct excitatory pathway and the other an indirect inhibitory pathway possibly mediated by the subpretectal nucleus and the interstitio-pretecto-subpretectal nucleus, which have been thought to send inhibitory afferents to the nucleus rotundus. Taken together with previous neuroanatomical and immunocytochemical studies, it is suggested that modulatory interactions might exist between the nBOR and the nRt in particular and between the accessory optic system and the tectofugal pathway in general in birds.

Animals↗
PubMed1996

Visual projection map specified by topographic expression of transcription factors in the retina.

Topographical maps of neuronal connectivity occur in various brain regions. In the visual system of birds, retinal ganglion-cell axons from the anterior retina connect to a posterior part of the optic tectum, and posterior retinal axons connect to the anterior part, thereby establishing a point-to-point projection map. The chemoaffinity theory predicts that the orderly retinotectal projection is generated by a topographical arrangement of molecules. We report here that we have found several genes topographically expressed along the nasotemporal (anterior-posterior) axis in the embryonic chicken retina. Among these, two transcriptional regulators, belonging to the winged-helix family are expressed in a mutually exclusive manner in either the nasal or temporal part of the retina. Misexpression of each factor causes misprojection on the tectum along the rostrocaudal axis, showing that topographical expression of these transcription factors controls formation of the retinotectal map.

Alkaline Phosphatase↗
PubMed1982

Central visual pathways and the distribution of sleep in 24-hr and 1-hr light-dark cycles.

The role of the central visual pathways in determining the distribution of sleep in light-dark (LD) cycles in the circadian and ultradian range was examined. EEG, EMG, and brain temperature were recorded under 24-hr (LD 12:12 or LD 10:14) and 1-hr (LD 0.5:0.5) cycles in rats which received either (1) no lesion, (2) primary optic tract lesions, (3) lesions of dorsal and lateral terminal nuclei of the accessory optic system, (4) lesions of medial terminal nucleus of the accessory optic system, or (5) retinohypothalamic tract-suprachiasmatic nucleus lesions. Under 24-hr cycles, about 40% of sleep occurred in the dark in intact rats. Retinohypothalamic tract-suprachiasmatic nucleus lesions abolished this entrainment of sleep to the LD cycle. Under 1-hr cycles, 90% of REM sleep occurred in the dark periods in intact rats. While primary optic tract lesions attenuated this response, it was not completely abolished by any of the visual system lesions. The characteristic LD distributions of sleep in circadian and ultradian cycles may therefore be under separate neural control by the central visual system.

Animals↗
PubMed1996

Retinotopy of the human retinal nerve fibre layer and optic nerve head.

The organisation of the primate nerve fibre layer and optic nerve head with respect to eccentricity or the positioning of central and peripheral axons remains controversial. Crystals of the carbocyanine dyes DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), or DiA (4-[4-didecylaminostryryl]-N-methylpridiniumiodide) were used to trace retinal ganglion cell axons within the nerve fibre layer, optic nerve head, and optic nerve. The present study demonstrated that peripheral retinal axons were scattered throughout the vitreal-scleral depth of the nerve fibre layer. This scattered distribution was maintained as the fibres passed through the optic nerve head and into the optic nerve. Axons of the arcuate bundles showed a bias towards the scleral portions of the nerve fibre layer and a variable degree of fibre scatter across the nerve fibre layer which was not as evident in labelling from other retinal regions. There was a rough topographic representation within the optic nerve head according to retinal circumference such that both peripheral and central fibres were mixed within a wedge extending from the periphery to the centre of the nerve. Foveal fibres occupied a large proportion of the temporal aspect of the optic nerve head and nerve, whereas fibres from areas temporal to the fovea appeared to be displaced to more superior and inferior regions. Consistent with the scleral bias seen in the retina, arcuate fibres maintained a peripheral position as they passed through the optic nerve head and occupied a more peripheral position in the nerve. The present results suggest that any degree of order present within the optic nerve is not an active process; optic axons are not instructed to establish a retinotopic order within the initial portions of the visual pathway.

Adult↗
PubMed2001

Fast intracellular motion in the living cell by video rate reflection confocal laser scanning microscopy.

Fast intracellular motion (FIM) was first revealed by back scattered light (BSL) imaging in video rate confocal scanning laser microscopy (VRCSLM), beyond the limits of spatial and temporal resolution obtainable with conventional optical microscopy. BSL imaging enabled visualisation of intra and extracellular motion with resolution in space down to 0.2 microm and in time to 1/25th of a second. Mapping the cell space at 0.2 microm x 0.2 microm (XY = in instantaneous best focal plane) x 0.5 microm (Z = height/depth, optic axis direction) volume steps revealed a communication layer above the known contact layer and an integrated dynamic spatial network (IDSN) towards the cell centre. FIM was originally observed as localised quasichaotic dancing (dithering) or reflecting patches/spots in the cell centre, faster in the darker nuclear space. Later, a second type of FIM was recognised which differed by the presence of a varied proportion of centrifugal and centripetal directional movements and/or jumping of patches/spots in the cell centre and outside the nuclear space. The first type is characteristic for cells in slightly adverse conditions while the second type has so far only been found in eutrophic cells. Temporal speeding up and coarsening of FIM, followed by slowing and eventually cessation at cell death, was found on exposure to strong stressors. It was concluded that the state of FIM provides instantaneous information about individual cell reactions to actual treatment and about cell survival. A putative switch between the first and second type FIM could be considered as an indicator of timing of cellular processes. The significance of FIM for the biology of the cell is seen in the rapid assessment of the condition of an individual live cell investigated by combination of various methods. Requirements for further development of this approach are outlined.

Animals↗
PubMed1997

Reproducibility of retinal and optic nerve head blood flow measurements with scanning laser Doppler flowmetry.

PURPOSE: To evaluate the interobserver variability and the reproducibility of retinal and optic nerve head capillary blood flow measurements performed with a new noninvasive equipment, the scanning laser Doppler flowmeter (Heidelberg Engineering, Heidelberg, Germany). METHODS: Blood flow measurements were performed during three independent sessions in six patients with glaucoma and five normal subjects using the scanning laser Doppler flowmeter (SLDF), which allows the visualization of perfused capillaries and vessels of the retina and optic nerve head and enables the quantification of capillary blood volume, flow, and velocity in any selected area of the perfusion map. To evaluate the interobserver variability in selecting the areas in the perfusion map to be measured, three observers tried to locate the same areas in the perfusion map of images obtained during the first session. To evaluate the reproducibility of the measurements, the observers measured correspondent areas in the peripapillary retina and in the optic nerve head of images from the three sessions. Areas of different sizes (10 x 10 pixels and 4 x 4 pixels) were measured. RESULTS: The agreement between readings performed by the three observers was very good, with the reliability coefficient for the various parameters varying from 0.90 to 0.98. The reproducibility of retinal and lamina cribrosa measurements with the 10 x 10 pixel square target was good (reliability coefficient for the different parameters ranging from 0.70 to 0.85) and much better than the reproducibility of the 4 x 4 pixel target. The measurements performed in the neuroretinal rim area also had poor reproducibility. The measurements from the patients with glaucoma tended to be more reproducible than those from normal subjects. CONCLUSIONS: The SLDF allows reproducible blood perfusion measurements of retinal and lamina cribrosa areas when a target square of 10 x 10 pixels is used.

Adult↗
PubMed1992

Retinal projections in the cane toad, Bufo marinus.

The location and extent of retinorecipient areas in the cane toad, Bufo marinus, were established by anterograde transport of cobaltic-lysine complex from the cut optic nerve. Most of the labeled optic axons travelled in the marginal optic tract, while others were in the axial optic tract, and/or the basal optic tract. Retinal projections terminated in both contralateral and ipsilateral targets. In addition to the optic tectum, the main visual center, retinorecipient areas included the suprachiasmatic nucleus, rostral visual nucleus, neuropil of Bellonci, corpus geniculatum thalamicum, ventrolateral thalamic nucleus (dorsal part), posterior thalamic neuropil, uncinate neuropil, pretectal nucleus lentiformis mesencephali and basal optic nucleus. While all of these retinorecipient areas receive optic fibers from both eyes, the ipsilateral retinal projections were observed to be generally sparser than those from the contralateral retina. A sparse optic fiber projection covers the surface of the ipsilateral optic tectum and is most prominent rostromedially and caudolaterally. The position and the extent of each of the retinorecipient areas were determined in relation to a three-dimensional coordinate system. Morphometric analysis showed that 85.3% of the retinorecipient area is in the contralateral optic tectum, 10.4% in contralateral non-tectal areas, 1.6% in the ipsilateral optic tectum and 2.7% in ipsilateral non-tectal areas. The presence of an ipsilateral tectal projection and the well defined pretectal visual neuropil complex may be related to the highly developed visual behavior and visual acuity of Bufo marinus.

Animals↗
PubMed2006

Retroviral misexpression of cVax disturbs retinal ganglion cell axon fasciculation and intraretinal pathfinding in vivo and guidance of nasal ganglion cell axons in vivo.

The transcription factor cVax (Vax2) is expressed in the ventral neural retina and restricted expression is a prerequisite for at least three prominent aspects of retinal dorsal-ventral patterning: polarized expression of EphB/B-ephrin molecules, the retinotectal projection and the distribution of rod photoreceptors across the retina. In the chick retina, the fasciculation pattern of ganglion cell axons also differs between the dorsal and ventral eye. To investigate the molecular mechanisms involved, the nerve fiber layer was analyzed after retroviral misexpression of several factors known to regulate the positional specification of retinal ganglion cells. Forced cVax expression ventralized the fasciculation pattern and caused axon pathfinding errors near the optic disc. Ectopic expression of different ephrin molecules indicated that axon fasciculation is, at least in part, mediated by the EphB system. Finally, we report that retroviral misexpression of cVax increased the pool of EphA4 receptors phosphorylated on tyrosine residues and altered the guidance preference of nasal axons in vitro. These results identify novel functions for cVax in intraretinal axon fasciculation and pathfinding as well as suggest a mechanism to explain how restricted cVax expression may influence map formation along the dorso-ventral and antero-posterior axes of the optic tectum.

Animals↗
PubMed2002

Large-aperture automatic focimeter for the measurement of optical power and other optical characteristics of ophthalmic lenses.

We propose an optical apparatus enabling the measurement of spherical power, cylindrical power, and optical center coordinates of ophthalmic lenses. The main advantage of this new focimeter is to provide a full bidimensional mapping of the characteristics of ophthalmic glasses. This is made possible thanks to the use of a large-area and high-resolution position-sensitive detector. We describe the measurement principle and present some typical mappings, particularly for progressive lenses. We then discuss the advantages in terms of speed and versatility of such a focimeter for the measurement of complex lens mappings.

Equipment Design↗
PubMed2005

A continuous smooth map of space in the primary visual cortex of the common marmoset.

We examined the fine-scale mapping of the visual world within the primary visual cortex of the marmoset monkey (Callithrix jacchus) using differential optical imaging. We stimulated two sets of complementary stripe-like locations in turn, subtracting them to generate the cortical representations of continuous bands of visual space. Rotating this stimulus configuration makes it possible to map different spatial axes within the primary visual cortex. In a similar manner, shifting the stimulated locations between trials makes it possible to map retinotopy at an even finer scale. Using these methods we found no evidence of any local anisotropies or distortions in the cortical representation of visual space. This is despite the fact that orientation preference is mapped in a discontinuous manner across the surface of marmoset V1. Overall, our results indicate that space is mapped in a continuous and smooth manner in the primary visual cortex of the common marmoset.

Animals↗
PubMedDate not supplied

Near-infrared imaging of the human breast: complementing hemoglobin concentration maps with oxygenation images.

We have previously reported a comparison between edge-corrected near-infrared optical mammograms and those that have undergone a further image-processing step based on a spatial second derivative. In this work, we go a step further by combining the second-derivative images from four wavelengths (690, 750, 788, and 856 nm) to obtain oxygenation-index images. While the spatial second derivative improves contrast and allows for visibility of fine structures in the images, thereby improving the sensitivity to tumor detection, additional information is needed to avoid false-positive results. The oxygenation-index images are introduced to address this issue. Oxygenation information may help discriminate benign from malignant breast lesions, thereby effectively complementing single-wavelength optical mammograms that display optically dense regions within the breast with high sensitivity.

Aged↗
PubMed2004

Competitive interactions between retinal ganglion axons for tectal targets explain plasticity of retinotectal projection in the servomechanism model of retinotectal mapping.

The mechanism of topographic mapping of retinal ganglion cells to the midbrain was previously elucidated by the servomechanism model, which is based on the fact that cells expressing Eph-receptors respond specifically to surface expressing membrane-bound ephrin-ligands at a critical level. The retina has increased nasal-to-temporal gradient of Eph receptor-density, and the optic tectum/superior colliculus has increased rostral-to-caudal gradient of membrane-bound ephrin-ligand. An axon from the retina has an identification tag of a certain level of Eph-receptor density depending on its retinal position, and adheres to the site on the tectum/superior colliculus expressing ephrin-ligands at a critical ligand-density level. The servomechanism model rigidly defines positions of axon terminals on the midbrain. However, optic nerve regeneration experiments combined with halved retina or tectum show a plastic or flexible mapping (expansion, compression and transposition of tectal projections). To reconcile the discrepancy between the rigid model and the plastic behavior, competition between retinal axon terminals for a target site was introduced to the servomechanism. The servomechanism/competition model succeeded in computer simulations of the plastic mapping of retinal axons on the tectum. Recent experiments of upregulated ligand-density on the tectum during nerve regeneration and the role of axonal competition are discussed.

Algorithms↗
PubMed2002

Salt-sensitive hypertension in conscious rats induced by chronic nitric oxide blockade.

This study examined the effects of alterations in salt-intake on blood pressure (BP) in rats chronically treated intravenously with or without the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) (8.6 mg/kg/day). The changes in mean arterial pressure (MAP), the renal cortical and medullary blood flow (CBF and MBF), and the sodium balance were determined by implanted optical fibers and laser-Doppler flow measurement techniques in the conscious rats. The results showed that high salt intake (7.4 mEq/day) elevates CBF (139% +/- 15%), but has no significant effect on MAP or MBF in control rats; in L-NAME-treated rats, high salt intake elevates MAP, produces no change in CBF, and decreases MBF (51% +/- 14%), as well as increasing the sodium balance (0.26 +/- 0.23 mEq/day to 1.29 +/- 0.47 mEq/day). The present experiments indicated that NO appears to maintain the MBF during high salt intake and to prevent the changes in MAP, and, in the absence of NO, salt-sensitive hypertension develops. Nitric oxide plays an important role in the development of salt-sensitive hypertension with the change of MBF.

Animals↗
PubMed2002

Evaluation of optical quality of corneas using corneal topographers.

PURPOSE: To review the evaluation of the optical quality of the cornea by corneal topography. METHODS AND RESULTS: Color-coded maps show qualitatively the characteristics and severity of irregular astigmatism at the entrance pupil. Topographic indices such as the surface regularity index and predicted corneal acuity are derived from computation of the corneal power distribution, and they are highly correlated with high-contrast visual acuity. Fourier analysis can be used to represent the irregular and regular astigmatism components simultaneously. Zernike polynomials can be used to calculate higher-order wavefront aberrations due to the corneal surface. CONCLUSION: Evaluation of the optical properties of the cornea using a corneal topographer is useful for assessing quality of vision.

Astigmatism↗
PubMed2005

3D modelling, gene expression mapping and post-mapping image analysis in the developing human brain.

As human brain development proceeds, there are complex changes in size and shape, most notably in the developing forebrain. Molecular technologies enable us to characterise the gene expression patterns that underlie these changes. To interpret these patterns the location of expression must be identified and, often, gene expression patterns compared for several genes or across several developmental stages. To facilitate interpretation we have generated a set of three-dimensional models using a recently developed technique, optical projection tomography. The models act as a framework onto which gene expression patterns are mapped and anatomical domains identified using custom-designed software, MAPaint. Here, we demonstrate their use to compare forebrain development at two embryonic stages (Carnegie stages 18 and 21; 44 and 52 days post conception, respectively) and as a means of recording, storing and visualising gene expression data for three example genes EMX1, EMX2 and OTX2. Anatomical domains were also mapped to the models and the comparison of gene expression and anatomical data is demonstrated at Carnegie stage 21. The three-dimensional models and sophisticated software facilitate the analysis and visualisation of morphological changes and gene expression patterns during early brain development and can be applied to the development of other complex structures.

Brain↗
PubMed2006

Combined diffuse optical tomography (DOT) and MRI system for cancer imaging in small animals.

Recently, there has been a great amount of interest in developing multi-modality imaging techniques for oncologic research and clinical studies with the aim of obtaining complementary information and, thus, improving the detection and characterization of tumors. In this present work, the details of a combined MR-diffuse optical imaging system for dual-modality imaging of small animals are given. As a part of this effort, a multi-spectral frequency domain diffuse optical tomography system is integrated with an MRI system. Here, a network analyzer provides the rf modulation signal for the laser diodes and measures the amplitude and the phase of the detected signals. Photomultiplier tubes are utilized to measure low-level signals. The integration of this optical imaging system with the 4T MRI system is realized by incorporating a fiber adaptive interface inside the MR magnet. Coregistration is achieved by a special probe design utilizing fiducial markers. A finite element algorithm is used to solve the diffusion equation and an inverse solver based on this forward solver is implemented to calculate the absorption and scattering maps from the acquired data. The MR a priori information is used to guide the optical reconstruction algorithm. Phantom studies show that the absorption coefficient of a 7 mm inclusion in an irregular object located in 64 mm phantom is recovered with 11% error when MR a priori information is used. ENU induced tumor model is used to test the performance of the system in vivo.

Algorithms↗