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At least 1,639 records · Page 91Linked to original sources
PubMed1979

A route for direct retinal input to the preoptic hypothalamus: dendritic projections into the optic chiasm.

With the use of Golgi, horseradish peroxidase, and electron microscopic techniques, neurons within a broad region of the preoptic hypothalamus of the mouse were shown to have dendrites that projected well into the depths of the optic chiasm. Further experimental and ultrastructural investigation demonstrated synapses between these dendrites and retinal axonal boutons within the chiasm. All synapses located in the chiasm were classified as Gray's type I. The possible function of these dendritic projections is discussed.

Animals↗
PubMed1985

Growth cone-target interactions in the frog retinotectal pathway.

The growth cones of retinal ganglion cell axons were studied in the optic tract and tectum with horseradish peroxidase (HRP) histochemistry and electron microscopy. The ganglion cell growth cones has many morphological features similar to those described in vitro and in other in vivo systems. However, we found that some processes formed highly differentiated terminal arborizations, while retaining growth cones on many of their branches. In addition, ultrastructural examination of the tectal neuropil revealed that many ganglion cell axonal processes had characteristics of both growth cones and presynaptic endings. These findings are discussed in the context of the hypothesis of shifting connections and the evidence that retinotectal map formation involves several mechanisms, including a process that depends on the action potential activity in the optic fibers.

Animals↗
PubMed2005

Analyzing Sub-Classifications of Glaucoma via SOM Based Clustering of Optic Nerve Images.

We present a data mining framework to cluster optic nerve images obtained by Confocal Scanning Laser Tomography (CSLT) in normal subjects and patients with glaucoma. We use self-organizing maps and expectation maximization methods to partition the data into clusters that provide insights into potential sub-classification of glaucoma based on morphological features. We conclude that our approach provides a first step towards a better understanding of morphological features in optic nerve images obtained from glaucoma patients and healthy controls.

Algorithms↗
PubMed1994

A new approach to optical imaging applied to rat barrel cortex.

Several groups have described using intrinsic optical imaging to form images of activity patterns in the cortex. Because the signal is small, the general approach has been to use expensive camera equipment with a high dynamic range to make these measurements. However, by using signal averaging to compensate for lower dynamic range, images can be obtained using equipment already available in many laboratories. This modified technique has been used for imaging activity in 'barrel' cortex of the rat. A map of the representation of a single whisker as determined by the imaging technique corresponded well with a similar map made using standard electrophysiology. A map of several whiskers was made by overlaying images of single-whisker representations. The details of the images differ from those previously described. Possible mechanisms for the signal are discussed.

Animals↗
PubMed1998

Topography of diabetic macular edema with optical coherence tomography.

OBJECTIVE: This study aimed to develop a protocol to screen and monitor patients with diabetic macular thickening using optical coherence tomography (OCT), a technique for high-resolution cross-sectional imaging of the retina. DESIGN: A cross-sectional pilot study was conducted. PARTICIPANTS: A total of 182 eyes of 107 patients with diabetic retinopathy, 55 eyes from 31 patients with diabetes but no ophthalmoscopic evidence of retinopathy, and 73 eyes from 41 healthy volunteers were studied. INTERVENTION: Six optical coherence tomograms were obtained in a radial spoke pattern centered on the fovea. Retinal thickness was computed automatically from each tomogram at a total of 600 locations throughout the macula. Macular thickness was displayed geographically as a false-color topographic map and was reported numerically as averages in each of nine regions. MAIN OUTCOME MEASURES: Correlation of OCT with slit-lamp biomicroscopy, fluorescein angiography, and visual acuity was measured. RESULTS: Optical coherence tomography was able to quantify the development and resolution of both foveal and extrafoveal macular thickening. The mean +/- standard deviation foveal thickness was 174 +/- 18 microns in normal eyes, 179 +/- 17 microns in diabetic eyes without retinopathy, and 256 +/- 114 microns in eyes with nonproliferative diabetic retinopathy. Foveal thickness was highly correlated among left and right eyes of normal eyes (mean +/- standard deviation difference of 6 +/- 9 microns). Foveal thickness measured by OCT correlated with visual acuity (r2 = 0.79). A single diabetic eye with no slit-lamp evidence of retinopathy showed abnormal foveal thickening on OCT. CONCLUSIONS: Optical coherence tomography was a useful technique for quantifying macular thickness in patients with diabetic macular edema. The topographic mapping protocol provided geographic information on macular thickness that was intuitive and objective.

Adult↗
PubMed2005

Use of gene expression profiling to direct in vivo molecular imaging of lung cancer.

Using gene expression profiling, we identified cathepsin cysteine proteases as highly up-regulated genes in a mouse model of human lung adenocarcinoma. Overexpression of cathepsin proteases in these lung tumors was confirmed by immunohistochemistry and Western blotting. Therefore, an optical probe activated by cathepsin proteases was selected to detect murine lung tumors in vivo as small as 1 mm in diameter and spatially separated. We generated 3D maps of the fluorescence signal and fused them with anatomical computed tomography images to show a close correlation between fluorescence signal and tumor burden. By serially imaging the same mouse, optical imaging was used to follow tumor progression. This study demonstrates the capability for molecular imaging of a primary lung tumor by using endogenous proteases expressed by a tumor. It also highlights the feasibility of using gene expression profiling to identify molecular targets for imaging lung cancer.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1990

X- and Y-mediated synaptic potentials in neurons of areas 17 and 18 of cat visual cortex.

When a cuff-shaped electrode is placed on the optic nerve of the cat, X and Y axons, by virtue of their different diameters, exhibit different thresholds to electrical stimulation. Large-diameter Y axons have low thresholds, while smaller-diameter X axons have high thresholds. There is very little overlap between the two populations. Given this segregation, the strength of stimulation of the optic nerve required to evoke synaptic potentials in cortical neurons becomes a reliable indicator of the type of visual input a cortical neuron receives. Potentials with thresholds below the thresholds of X axons must be mediated by Y cells of the retina and LGN. Potentials with thresholds above the Y axons of the optic nerve must be mediated by X cells. From previous experiments, one would expect to find ample input via both types of axon to area 17 of the visual cortex. This was not the case. Of 58 neurons distributed throughout the layers of area 17 from which intracellular records were taken, in only four could substantial Y excitation be detected. Three of these four were located near the border with area 18. All four received large X inputs as well. The 24 neurons studied in area 18 all received large Y inputs but no detectable X input.

Animals↗
PubMed1983

A computer electron microscope plotter for mapping spatial distributions in biological tissues.

We have designed a computer-based electron microscope plotting system which maps the locations of organelles in tissue specimens and analyzes their distribution. The system includes: (1) two optical incremental shaft encoders which translate stage drive rotation to electrical pulses; (2) a Display/Control unit used to convert encoder pulses to binary code for computer input; (3) two 16-bit parallel interfaces for transferring data to the computer; (4) a Hewlett-Packard 9845T microcomputer, used to control data input and to store, graph, and analyze the plots. The software for the plotter is written in enhanced BASIC. The plotter system is driven by 4 programs called Trace, Plot, Analyze, and Density. The Trace program "draws" an outline of the edges of the tissue. The Plot program maps the positions of profiles within the tissue. The Analyze program compares trace and plot data and calculates the depth and medial-lateral distance of each plotted profile from the surfaces of the tissue. The Density program sorts and counts profile types, measures surface areas, and calculates profile densities. Commercial statistical software is used to analyze the data. Our laboratory uses the system to map the spatial distribution of synapses and neurons in the central nervous system. The plotting system will also be of value in other areas of neurobiology research.

Animals↗
PubMed1991

Biomagnetically localizable multipurpose catheter and method for MCG guided intracardiac electrophysiology, biopsy and ablation of cardiac arrhythmias.

A multipurpose catheter, specially designed to be biomagnetically localizable and the method for magnetocardiographic (MCG) guided intracardiac electrophysiological recordings, endomyocardial biopsy and ablation of cardiac arrhythmias are described. The catheter features two non-polarizable non-ferrous magnetic electrodes, arranged in such a way that, connected to an external current generator, an electromagnetic field of dipolar configuration can be generated in the heart. The connection is done with twisted pairs of non-ferrous magnetic conductors, to avoid the occurrence of spurious magnetic fields along the catheter during current injection to the electrodes. With this assembly the tip of the catheter can be localized (and driven close to an arrhythmogenic area) by MCG mapping. The same electrodes are feasible for monophasic action potential (MAP) recordings. One or more lumen allow fluid infusion, blood sampling, pressure measurements and introduction of steerable wires, pacing or ablation electrodes, bioptic devices, or optic fibers. On the basis of preoperative MCG three-dimensional localization of the arrhythmogenic substrate, the biomagnetically localizable catheter is driven, under fluoroscopic control, as close as possible to the suspected arrhythmogenic zone. MCG mapping is then performed under pacing, with adjustments of the catheter's tip, until the electrically induced magnetic field and catheter's localization parameters fit those generated by the spontaneous arrhythmia. MAP is recorded. The catheter position is accepted for ablation when electrophysiological abnormalities are identified in the MCG localized area.

Action Potentials↗
PubMed1982

Specificity of neural connections in the retinotectal system.

The existence of a retinotopic map raises the question of how such a map is formed during development. Since little is known about molecular mechanisms which may be involved in the formation of retinotopy, the structural aspects of this developmental process were studied to a greater detail in the chick. In the retina the following patterns of growth can be observed: (1) Ganglion cell formation starts in the centre and spreads towards the periphery. Thus, each cell is labelled by both its position and its time of origin. (2) Axons tend to grow towards the optic fissure by the shortest possible route, and more peripheral axons whose perikarya are born later than that of central ones tend to lie next to the inner limiting membrane. A regular change in the pattern of fibres, which we call transformation, occurs at the optic fissure. The incremental rings are transformed into crescents lying ventrally in the optic stalk at early stages of development. In the middle of the optic nerve retinotopy is re-established. Another transformation occurs shortly behind the chiasm. Except for these transformations, fibres run parallel to each other even across the chiasm. Thus, fibres arriving at the optic tectum are well organized. It is concluded that a multiplicity of factors contribute to the formation of the retinotectal map at any site of the visual pathway. The analysis of these factors may indicate how topographically organized projections develop.

Animals↗
PubMed2001

Fate map of the avian anterior forebrain at the four-somite stage, based on the analysis of quail-chick chimeras.

To better understand the topological organization of the primordia within the anterior forebrain, we made a fate map of the rostral neural plate in the chick. Homotopic grafts at the four-somite stage were allowed to survive for up to 9 days to enable an analysis of definitive brain structures. In some cases, the topography of the grafted neuroepithelia was compared with gene expression patterns. The midpoint of the anterior neural ridge maps upon the anterior commissure in the closed neural tube, continuing concentrically into the preoptic area and optic field. Non-neural epithelium just in front of this median ridge gives rise to the adenohypophysis. Areas for the presumptive pallial commissure, septum, and prosencephalic choroidal tissue lie progressively more posteriorly along the ridge, peripheral to the telencephalic entopeduncular and striatopallidal primordia (the subpallium), and the pallium (olfactory bulb, dorsal ventricular ridge, and cortical domains). Subpallial structures lie topologically anterior to the pallial formations, and both are concentric to the septum. Within the pallium, the major cortical domains (Wulst and caudolateral, parahippocampal, and hippocampal cortices) appear posterior to the dorsal ventricular ridge. The amygdaloid region appears concentrically across both the subpallial and pallial regions. This fate map shows that the arrangement of the prospective primordia in the neural plate is basically a flattened representation of topological relationships present in the mature brain, though marked phenomena of differential growth and selective tangential migration of some cell populations complicate the histogenetic constitution of the mature telencephalon.

Animals↗
PubMed1975

[Morpho-functional changes in the tegmentum mesencephali of turtles following enucleation].

Morpho-functional changes in the mesencephalic centre of the turtle (Emys orbicularis L.) were studied during optic nerve degeneration. It was observed that synaptic terminals in this centre undergoing the "dark" degeneration are associated with myelinated optic fibres and terminals undergoing the "light" one are associated with unmyelinated fibres. The first low amplitude component of the evoked potential disappears with degeneration of myelinated fibres of large diameter during the "dark" degeneration (4-5 months after enucleation). The first high amplitude component disappears with degeneration of the middle-sized myelinated fibres and the end of the "dark" degeneration (7 months after enucleation). The characteristics of the second high amplitude component which reflects the excitation of both thin myelinated and all unmyelinated fibres, begin to change with degeneration of unmyelinated fibres during "light" degeneration (2.5-3.5 months). This component disappears with degeneration of the thin myelinated fibres (7 months).

Animals↗
PubMed2005

Birefringence of the primate retinal nerve fiber layer.

The purpose of this study was to measure the peripapillary retinal nerve fiber layer (RNFL) thickness, phase retardation (PR), and depth-resolved birefringence (Deltan) of the normal primate eye using Enhanced Polarization-Sensitivity Optical Coherence Tomography (EPS-OCT). Both eyes of two rhesus monkeys were imaged with EPS-OCT. A multiple incident polarization state nonlinear fitting algorithm was used to determine RNFL phase retardation. RNFL thickness (RNFLT) was determined from the corresponding EPS-OCT intensity image and phase retardation per unit depth (PR/UD, proportional to Deltan) was calculated by dividing PR by RNFLT. Peripapillary area maps consisting of pixels uniformly distributed along a radius from 0.8 to 1.8 mm from the center of the optic nervehead were constructed for RNFLT, PR, and PR/UD. Average PR/UD in the superior and inferior quadrants was 18 degrees /100 mivrom (Deltan=4.2 x 10(-4)) and average PR/UD in the nasal and temporal quadrants was 6.3 degrees /100 microm (Deltan=1.5 x 10(-4)). Relative magnitude of PR radial gradient is similar to that of RNFLT radial gradient and no radial gradient was observed for PR/UD. Polarization-dependent amplitude attenuation per unit depth (PDAA/UD) was 0.02 rad/100 microm in thick RNFL regions. RNFL birefringence was higher in the arcuate bundles compared to nasal and temporal fibers (P=0.001). Birefringence was nearly equal in nasal and temporal quadrants. No statistically significant (P=0.01) radial gradient of birefringence was observed in any quadrant. RNFL birefringence is believed to originate from anisotropic structures within the cytoskeleton of the parallel axons. Birefringence differences presented in this study cannot be explained by the known axon diameter distribution around the optic nervehead and suggest other sources of the birefringence signal including neurotubules and neurofilaments.

Algorithms↗
PubMed2001

Prism adaptation to rightward optical deviation improves postural imbalance in left-hemiparetic patients.

Left-hemiparetic patients show predominant postural imbalance as compared to right-hemiparetic patients. The right hemisphere is crucial for generating internal maps used for perceptual and premotor processing of spatial information. Predominant postural imbalance with right-brain damage could thus result from a distortion of an internal postural map. Well-known manifestations of distorted internal maps due to right-hemisphere lesions, such as hemineglect, may show improvement following prism adaptation shifting the visual field to the right. We therefore investigated the effect of prism adaptation on postural imbalance in left-hemiparetic patients. Three groups of five patients were either adapted to prisms deviating the visual field to the right or left or exposed to neutral prisms while performing reaching movements of the right arm. Postural imbalance was reduced only following prism adaptation to the right. Thus, brief adaptation (i.e., 3 min) to rightward-shifting prisms can dramatically improve postural imbalance. This result shows that the effect of exposure to prisms that horizontally shift the visual field to the right in a reaching task generalizes to the postural system, and it suggests an interaction between horizontal and vertical reference frames. This also supports the theory that predominant postural imbalance in patients with right-brain damage may be partly related to a distortion of an internal postural map.

Adult↗