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PubMed1992

Total internal reflection fluorescence microscopy (TIRFM). II. Topographical mapping of relative cell/substratum separation distances.

A simplified model of TIRF optics was used to quantitate the relative membrane/substratum separation distances from the spatial pattern of TIRF image brightness. Phase-contrast and total internal reflection fluorescence microscopy (TIRFM) images were collected of bovine aortic endothelial cells (BAEC) plated onto glass microscope slides for 15 min, 30 min and 24 h. BAEC adherent for 15 min showed an absence of a focal contact morphology, with the region of closest apposition beneath the cell center. After 30 min, multiple contacts with the surface were established and the morphology became more irregular. BAEC attached for 24 h showed well-defined focal contact regions aligned in characteristically striated patterns. The relative distance between closest and farthest membrane/substratum separations are consistent with reported distance between focal and matrix contacts. Topographical maps of membrane/substratum separation distances over the entire ventral surface of the plated cells were constructed to demonstrate the utility of quantitative TIRF microscopy.

Animals↗
PubMed1987

A sharp retinal image increases the topographic precision of the goldfish retinotectal projection during optic nerve regeneration in stroboscopic light.

Locally-correlated neural activity appears to play a key role in refining topographically mapped projections. The retinotectal projection of the goldfish normally regains a high degree of spatial precision after regeneration of a cut optic nerve, but it fails to do so if retinal ganglion cell activity is blocked by tetrodotoxin, or if local correlations in activity are masked by the synchronizing effect of stroboscopic light. A sharp retinal image is not normally needed for a sharp map because local correlation occurs even in darkness or diffuse light, but the possibility that a sharp image might restore local correlation and sharpen the map in stroboscopic light, though taken into account in earlier experiments, has not previously been tested. The precision of the retinotectal map was therefore studied, by retrograde transport of WGA-HRP from a standard tectal injection site and quantitative analysis of the labelled ganglion cell distribution, after regeneration of a cut optic nerve for 83-84 days in either continuous stroboscopic light or normal diurnal light. The lens of the eye was either ablated to blur the retinal image or sham-operated. Two different strobe flash patterns used in previous experiments were also compared. With the lens ablated, stroboscopic light impaired map refinement significantly, confirming previous results. A rapid, irregular flash pattern averaging about 5 Hz was rather more effective than a regular 1 Hz pattern. With the lens intact, however, neither pattern had any detectable effect. The significant gain in precision resulting from a sharp retinal image in these circumstances suggests that common mechanisms could underlie both the internal refinement of the retinotectal map and such directly experience-sensitive processes as the experimental realignment of binocular maps in the frog Xenopus, and of auditory and visual maps in the barn owl.

Animals↗
PubMed2002

Regional variations in myocardial tissue oxygenation mapped by near-infrared spectroscopic imaging.

Near-infrared fibre-optic single point spectroscopy has been widely exploited to provide information regarding blood volume and oxygenation in vivo, but it does not provide any information on regional differences in perfusion. We have combined the chemical sensitivity of spectroscopy with the spatial sensitivity of imaging to generate maps of regional cardiac oxygenation. Spectroscopic images were acquired for isolated, arrested, blood-perfused porcine hearts (n=4) over the wavelength range 650 and 1050 nm. Spectroscopic images were acquired during normal perfusion, regional ischemia (occlusion of left anterior descending artery) global ischemia, and reperfusion. Hemoglobin (Hb) and myoglobin (Mb) content and oxygenation were determined by reconstructing the tissue spectra measured at each pixel as weighted sums of water, oxy- and deoxy-Hb (and -Mb) absorptivity spectra. The spectroscopic images acquired during regional ischemia clearly revealed increased deoxy-(Hb+Mb) levels and decreased oxy-(Hb+Mb) levels in the ischaemic regions relative to the normally-perfused regions. Global ischemia produced a dramatic decrease in oxy-(Hb+Mb) levels and a moderate increase in deoxy-(Hb+Mb). These images confirm that blood oxygenation can be mapped in cardiac tissue by near-infrared spectroscopic imaging.

Animals↗
PubMed1977

[Responses of neurons in the nucleus isthmi region of the frog to optic nerve stimulation].

Neuronal responses were studied in the nucleus isthmi area of Rana temporaria. The animals were immobilized by diplacine, a curare-like drug. Single neurons in this area had no background activity. After single-pulse electric stimulation of the contralateral optic nerve these neurons discharged as a rule with one action potential only, its minimal latency being 20-110 msc. The latencies decrease significantly when the stimulus intensities were increased from threshold to maximal, indicating development of summation process in the corresponding afferent pathway. Only 14 per cent (7 of 57) of neurons responded to stimuli exciting myelinated optic fibres and not exciting the ummyelinated ones. All the nucleus isthmi neurons discharged with unstable latency; this means that these neurons were excitated not antidromically. The functional role of nucleus isthmi in Anurans is discussed.

Animals↗
PubMed2003

Optoacoustic diffraction tomography: analysis of algorithms.

We consider the problem of using the photoacoustic effect to image the optical properties of tissue. A region of tissue is assumed to be illuminated by frequency-modulated light that creates an ultrasonic wave of the same frequency. This wave is detected on a passive array of receiving transducers distributed over a circular or a cylindrical aperture. If the frequency is swept over a broad band (or, equivalently, if we illuminate with a pulse and Fourier transform the response), then a spatial map of a parameter that depends on the optical absorption coefficient of the tissue can be recovered. Analytical inversion formulas are derived in both two and three dimensions. The effects of band-limited data on image quality are also investigated.

Algorithms↗
PubMed2006

Multipoint holographic optical velocimetry in microfluidic systems.

We show how holographic optical trapping can be used for the multipoint measurement of fluid flow in microscopic geometries. An array of microprobes can be simultaneously trapped and used to map out the fluid flow in a microfluidic device. The optical traps are alternately turned on and off such that the probe particles are displaced by the flow of the surrounding fluid and then retrapped. The particles' displacements are monitored by digital video microscopy and directly converted into velocity field values. This technique enables the measurement of a two-dimensional flow field at points arbitrarily distributed in a three-dimensional volume. The validity of the technique is demonstrated for the case of the flow around a spinning sphere and the flow at the outlet of a microchannel.

Journal Article↗
PubMed1996

Activation and repolarization patterns are governed by different structural characteristics of ventricular myocardium: experimental study with voltage-sensitive dyes and numerical simulations.

INTRODUCTION: Substantial progress has been made in our understanding of transmural activation across ventricular muscle through studies of excitation patterns and potential distributions. In contrast, repolarization sequences are poorly understood because of experimental difficulties in mapping action potential durations (APDs) using extracellular electrodes. METHODS AND RESULTS: Langendorff-perfused guinea pig hearts and isolated coronary-perfused left ventricular sheet preparations were stained with the voltage-sensitive dye RH-421 and optical APs were recorded with a photodiode array. Epicardial maps were constructed using a triangulation method applied to matrices of activation and repolarization times determined from (dF/dt)max and (d2F/dt2)max' respectively. Numerical simulations were carried out based on: (1) a modified Luo-Rudy model; (2) the three-dimensional architecture of ventricular fibers; and (3) the intrinsic spatial distribution of APDs. In ventricular sheets, epicardial stimulation elicited elliptical activation patterns with the major axis aligned with the longitudinal axis of epicardial fibers. When the pacing electrode was progressively inserted from epicardium to endocardium, the major axes rotated gradually, clockwise by 45 degrees, and the eccentricity decreased from 2 to 1.14. Repolarization showed a relatively uniform pattern, independent of pacing site, beginning at the apex and spreading to the base. CONCLUSION: In experiments and simulations, the helical rotation of epicardial excitation isochrones caused by pacing at increasing depth in the myocardium correlated with the helical three-dimensional architecture of ventricular fibers. In contrast, repolarization was independent of the activation sequence and was mainly guided by spatial differences in APDs between apex and base.

Action Potentials↗
PubMed1993

Relationship between intrinsic connections and functional architecture revealed by optical imaging and in vivo targeted biocytin injections in primate striate cortex.

In primate primary visual cortex, neurons sharing similar response properties are clustered together forming functional domains that appear as a mosaic of patches or bands, often traversing the entire cortical depth from the pia to the white matter. Similarly, each cortical site connects laterally through an extensive network of intrinsic projections that are organized in multiple clusters (patches) and reach distances of up to a few millimeters. The relationship between the functional domains and these laterally connected patches has remained a controversial issue despite intensive research efforts. To investigate this relationship, we obtained high-resolution functional maps of the cortical architecture by in vivo optical imaging. Subsequently, extracellular injections of the sensitive anterograde tracer biocytin were targeted into selected functional domains. Within the ocular dominance system, we found that long-range intrinsic connections tended to link the monocular regions of same-eye ocular dominance columns. Furthermore, we discovered that binocular domains formed a separate set of connections in area V1; binocular regions were selectively connected among themselves but were not connected to strictly monocular regions, suggesting that they constitute a distinct columnar system. In the other subsystem subserving orientation preference, patches of intrinsic connections tended to link domains sharing similar orientation preferences. Analyses of the precision of these connections indicated that in both functional subsystems, < 15% of the connections were between domains having orthogonal response properties. However, their selectivity was limited; approximately 30% +/- 10% of the interconnected patches contained neurons exhibiting orientation tuning that differed from those found at the injection sites by at least 45 degrees. At short range (up to 400 microns from the injection site), this casual trend seemed markedly accentuated; the local, synaptic-rich axonal and dendritic arbors crossed freely through columns of diverse functional properties. These complex sets of connections can endow cortical neurons with a rich diversity of response properties and broad tuning.

Animals↗
PubMed2006

Scanning near-field optical data contrast measurement: a tomographylike near-field reconstruction.

A method for the reconstruction of near-field optical signals is proposed to produce a tomographylike map of the field above the nanostructures being studied. The data obtained through lock-in detection are processed employing Chebyshev's polynomial function of the distance between the probe and the sample. The method is first applied to numerically generated near-field evanescent data, with three different decreasing lengths, and then applied to an experimental signal. Therefore the contrast of the signal above nanostructures is discussed to underline the discrepancy between the scanning near-field optical microscopy data and the reconstructions.

Journal Article↗
PubMedDate not supplied

[Electrophysiologic studies of the pathways of visual afferentation in the forebrain of the dogfish Squalus acanthias].

Afferent visual projections to the pallium of the telencephalon have been investigated in immobilized conscious dogfish Squalus acanthias using electrophysiological recording the evoked potentials and neuronal reactions elicited by electric stimulation of the optic nerve. Analysis and comparison of the parameters of the components of the evoked potentials in the telencephalon and tectum opticum indicate the existence of two visual subsystems (the retino-thalamo-telencephalic and the retino-tecto-thalamo-telencephalic ones) in the dogfish.

Animals↗
PubMed1991

Autoradiographic study of the retinal projections in the Chinese pangolin, Manis pentadactyla.

Autoradiography was used to investigate the optic system of the Chinese pangolin, Manis pentadactyla. The pattern of retinal projections in the Chinese pangolin is similar to that described in other mammals. Each retina projects bilaterally to the suprachiasmatic nucleus, dorsal and ventral lateral geniculate nuclei, pretectal area, and superior colliculus (SC). Only contralateral projections are found to the medial, lateral, and dorsal accessory optic nuclei. The large lateral nucleus receives a dense projection from the retina and forms a compact mass on the dorsolateral area of the cerebral peduncle. The lamination of the SC could not be clearly demonstrated in the brain of the Chinese pangolin.

Animals↗
PubMedDate not supplied

[Visual projections in to the brain of the sturgeon Acipenser güldenstädti].

Visual projections have been studied after unilateral lesion of the optic nerve. Degenerated fibers and terminals, as well as fibers labelled by horseradish peroxidase were found contralaterally in the lateral geniculate thalamic nucleus, the second (stratum opticum) and the third (stratum fibrosum et griseum superficiale) layers of the midbrain tectum. In other brain structures (lateral ventrothalamic nucleus, in the pretectal area--cortical nucleus, pretectal nucleus, posterior comissure nucleus) the density of degeneration of optic fibers was significantly lower. Separate fragments of degeneration were found in the fourth layer of the tectum. Ipsilaterally, thalamic, pretectal and tectal visual projections of the same localization were found, although they were less massive than at the opposite side.

Animals↗
PubMed2000

Chiral action at a distance: remote substituent effects on the optical activity of calyculins A and B.

[structure--see text] Calyculins A and B differ only by the (E)- vs (Z)-configuration at C(2). Yet, they show a large difference in optical rotations. We demonstrate a new strategy that provides a physical analysis of this long-range chiro-optical effect by Boltzmann-averaged atomic contribution mapping. The polarizability characteristics of the CN substituent rather than the perturbation of the stereogenic centers or the introduction of asymmetry into the polyene chain give rise to the remarkable difference in rotation angles.

Biological Factors↗
PubMed1998

First evidence of diversity in eutherian chiasmatic architecture: tree shrews, like marsupials, have spatially segregated crossed and uncrossed chiasmatic pathways.

In the optic chiasm of mammals, axons either cross the midline to the opposite side of the brain or remain uncrossed. In the eutherian species studied to date, uncrossed axons in the caudal nerve are found in all regions. In the chiasm, they are dispersed through the hemichiasm, with many axons approaching the midline and then turning back to enter the same side of the brain as the originating eye. In marsupials, by contrast, uncrossed axons never approach the midline; instead, they remain grouped in the lateral nerve and chiasm. The impression gained from these data is that there is a major difference in chiasmatic architecture between eutherian and marsupial mammals. Therefore, the mechanisms by which axons choose their route through the chiasm was also thought to differ between the two major groups of mammals. However, the present study shows that the chiasm of a highly visual eutherian mammal, the tree shrew, is similar to that found in marsupials, with uncrossed axons confined to lateral regions and not approaching the midline. However, unlike marsupials, in the tree shrew, optic fascicles in the chiasm are often separated by thick collagen bundles. It is probable that the chiasmatic structure described to date for eutherian mammals is not ubiquitous, as was previously thought, and theories explaining the mechanisms by which axons chose their route through the chiasm during development will have to be expanded.

Animals↗
PubMed1987

Double-stranded cucumovirus associated RNA 5: which sequence variations may be detected by optical melting and temperature-gradient gel electrophoresis?

Sequence variants of the double-stranded form of satellite RNAs of cucumber mosaic virus (dsCARNA 5) were analyzed for the possibility to experimentally detect minor nucleotide sequence changes. Denaturation maps (helix-probability versus position of the nucleotide in the sequence versus temperature) were calculated applying the Poland algorithm. Optical denaturation curves and temperature-gradient gel mobility curves were simulated using the denaturation maps and were compared with experimental results from optical melting and temperature-gradient gel electrophoresis (Tien Po et al., accompanying paper). Melting of the dsRNAs starts from both ends of the molecule in two transitions of low co-operativity, continues in the right part in a highly co-operative transition, and is finished in another highly co-operative transition including strand-separation. Whereas all parts of the molecule contribute uniformly to the optical melting curve, opening of the ends predominates in the retardation transition in gel electrophoresis. Detailed discussion of the influence of base pair changes in the sequence shows that a single base pair change may be detected by temperature-gradient gel electrophoresis, if it is located in certain favorable locations, whereas its detection in optical melting curves is possible only in very special cases. The systematic differences found in the accompanying paper between necrogenic and non-necrogenic dsCARNA 5 could be interpreted on the basis of such nucleotide sequence differences.

Base Composition↗