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At least 1,333 records · Page 74Linked to original sources
PubMed1978

The tectum opticum of Pantodactylus schreiberii Wiegmann (Teiidae, Lacertilia, Reptilia).

We study the histology of the optic lobe of Pantodactylus schreiberii Wiegmann. It has 14 layers with characteristic cells in each of them. We study with emphasis the elements of the superficial layers, discussing some physiologic implications. We described four strata of optic terminals. To the strata 1 and 3 reach fibres from layer 14. To the stratum 4, from the layer 12 and to the stratum 2, fibres from both layers 14 and 12. Some optic fibres from layer 12 send collaterals which reach the stratum 4 of optic terminals.

Animals↗
PubMed1976

Central mechanisms of vision: parallel processing.

Despite repeated attempts by several laboratories to discover increasingly complex "feature detector" neurons in higher visual centers of mammals, there has been little convincing evidence for the existence of such neurons. What had been reported instead is that many neurons in higher centers show less rather than more specificity when compared with cells in areas 17, 18 and 19. Studies in mammalian retina have revealed multiple processing systems apparently operating in parallel at the level of the ganglion cells. Striate cortex receives at least two different kinds of visual input from the lateral geniculate, and sends at least two different parallel outputs to other brain regions. Within striate cortex there is some segregation of different functional cell types in separate layers. The accumulated evidence suggests the existence of parallel visual processing mechanisms beginning in mammalian retina and extending through striate cortex to higher cortical centers. The notion of separate processing systems for the detection of different features in the visual world recalls earlier work by Lettvin, Maturana, McCulloch and Pitts concerning visual processing in the frog retina and optic tectum.

Animals↗
PubMed1981

Interactions between compound and normal eye projections in dually innervated tectum: a study of optic nerve regeneration in Xenopus.

Right compound eyes were formed in Xenopus embryos at tailbud stages by the fusion of two nasal (NN), two temporal (TT) or two ventral (VV) halves. The left eye was kept intact. Two to four weeks after metamorphosis the optic nerve from the intact eye was severed to induced bilateral optic nerve regeneration. The contralateral retinotectal projections from the compound eye and the induced ipsilateral projections from the intact eye to the same (dually innervated) tectum were studied by [3H]proline autoradiography and visuotectal mapping from 3 to 6 months after the postmetamorphic surgery. The results showed that the NN, TT and VV projections, in the presence of optic fibres from the intact eye failed to spread across the whole extent of the dually innervated tectum. Unexpectedly the bulk of the regenerating projection from the intact eye was confined to the previously uninnervated parts of the dually innervated tecta, the caudomedial region in TT, the rostrolateral region in NN and the lateral region in VV eye animals. The partial segregation of the two populations of optic fibres in the dually innervated tectum has been taken as a further indication of the role of fibre-fibre and fibre-tectum interactions in retinotectal map formation.

Animals↗
PubMed2004

Beamline 10.3.2 at ALS: a hard X-ray microprobe for environmental and materials sciences.

Beamline 10.3.2 at the ALS is a bend-magnet line designed mostly for work on environmental problems involving heavy-metal speciation and location. It offers a unique combination of X-ray fluorescence mapping, X-ray microspectroscopy and micro-X-ray diffraction. The optics allow the user to trade spot size for flux in a size range of 5-17 microm in an energy range of 3-17 keV. The focusing uses a Kirkpatrick-Baez mirror pair to image a variable-size virtual source onto the sample. Thus, the user can reduce the effective size of the source, thereby reducing the spot size on the sample, at the cost of flux. This decoupling from the actual source also allows for some independence from source motion. The X-ray fluorescence mapping is performed with a continuously scanning stage which avoids the time overhead incurred by step-and-repeat mapping schemes. The special features of this beamline are described, and some scientific results shown.

Arabidopsis↗
PubMed1979

Conduction velocity distribution of the retinal input to the hamster's superior colliculus and a correlation with receptive field characteristics.

Cells driven reliably by shocks delivered to the optic nerve or optic chiasm were encountered throughout the depth of the colliculus. The incidence of such cells, however, decreased markedly in the laminae ventral to the stratum opticum. The distribution of conduction velocities for the retinal afferents to the tectum was quite broad (range: 1.7-25.5 m/sec) and clearly biomodal with peaks at about 6 and 12 m/sec. A small number of cells were innervated by rapidly (greater than 15 m/sec) conducting axons. No evidence of an indirect-fast pathway from the retina to the colliculus via the lateral geniculate nucleus and visual cortex was obtained. Afferent conduction velocity was not correlated with retinal eccentricity, collicular depth or speed selectivity. It was, however, clearly related to directional selectivity. Ninety percent of the tectal neurons receiving inputs from axons having conduction velocities of less than 5 m/sec were directionally selective while only 41% of those neurons innervated by more rapidly conducting fibers (greater than 5 m/sec) exhibited selectivity. One hundred and sixteen cells in the anterior portion of the colliculus were tested with shocks delivered to the ipsilateral optic nerve and photic stimulation of the ipsilateral eye. Of these, 11% exhibited some degree of binocularity and only 6% were responsive to optic nerve shocks. These electrophysiological findings were correalted with the limited nature of the retinal input to the ipsilateral superior colliculus.

Animals↗
PubMed1983

Topographic organization of certain tectal afferent and efferent connections can develop normally in the absence of retinal input.

To test the hypothesis that the topographic organization of the connections of the optic tectum is determined during development by the "retinotopically" ordered input that it receives from the eye, we have mapped certain of the connections of the tectum in chicken embryos and chicks in which both eye rudiments were removed before the outgrowth of optic fibers. Because several of the connections of the tectum are normally organized retinotopically, we should expect, if this hypothesis were correct, that some or all of these connectional patterns would be significantly altered in such "eyeless" chickens. In fact, we have found that the connections formed between the optic tectum and two of the isthmic nuclei, with which it is reciprocally connected, show the same topographic organization in "eyeless" animals as in control chickens raised under the same conditions. This clearly indicates that the topographic organization of the chicken optic tectum is independently specified and is not contingent upon the input that it receives from the retina.

Afferent Pathways↗
PubMed2005

Optical coherence tomography: a pilot study of a new imaging technique for noninvasive examination of cervical tissue.

OBJECTIVE: Optical coherence tomography (OCT) is a novel noninvasive technique that can map subsurface tissue structure with a resolution of 10 to 20 mum. The objective of this study was to determine whether an OCT imaging system could be used clinically in vivo to image and distinguish features of normal and abnormal cervical tissue. STUDY DESIGN: Cervical OCT images and biopsy specimens were obtained from consenting volunteers. Images were analyzed quantitatively for intensity of backscattered light from the epithelia and for rates of signal decay of signal over the depth of epithelia (slope). Patients were stratified by menopausal status, and parameters were compared in normal and abnormal cervical samples, as diagnosed by routine histopathologic techniques. RESULTS: Average epithelial intensities were significantly stronger in the abnormal tissue than in the normal tissue of premenopausal women (P<.0024), but were stronger in the normal tissue of postmenopausal women (P<.062). No significant differences in signal decay rate were detected. CONCLUSION: OCT images, which contain information about epithelial and stromal structure, can be clinically obtained. Image features of normal and abnormal cervical epithelium differ significantly.

Adult↗
PubMed1981

Isolation of 10-nm filaments from astrocytes in the mouse optic nerve.

Astroglial filaments approximately 10 nm in diameter were isolated from degenerated mouse optic nerves by Triton X-100 and DNase I treatments followed by sucrose density gradient centrifugation. 2-4 wk after bilateral enucleation, optic nerves contained virtually a single population of 10-nm filaments (astroglial filaments), free from neurofilaments. In negative-staining and thin-section electron microscopy, the isolated filaments were seen as nonbranching linear structures with smooth contour, and were morphologically identical to those in situ. Sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed the isolated filaments to be composed of two major polypeptides with molecular weights of 45,000 and 55,000, present in an approximate molar ratio of 1:1. These findings, together with the results of one-dimensional peptide mapping and solubility study, indicate that the astroglial filaments in the mouse optic nerve are primarily composed of these two polypeptides.

Animals↗
PubMed2005

[Screening for diabetic retinopathy and optic disc topography with the "retinal thickness analyzer" (RTA)].

BACKGROUND: The RTA features a fundus photography mode and optic disc topography. Those two new modes were investigated regarding their clinical use. METHODS: First, the combination of wide-field photography with a retinal thickness map was assessed for tele-screening for diabetic retinopathy in 31 eyes. Second, normal values of the optic disc were collected on 30 non-glaucomatous probands in the non-mydriatic mode and compared to the results of the mydriatic mode, for which reproducibility was also investigated. RESULTS: For diabetic retinopathy, the RTA yielded mean 93% sensitivity for proliferative diabetic retinopathy and 100% sensitivity for detecting diabetic macular edema compared to clinical examination at specificities ranging from 58 to 96%. Regarding the measurements of the optic disc, the normal values in mydriasis coincided with those in miosis in all but 4 of 12 parameters. CONCLUSIONS: The RTA is suitable for application in tele-screening for diabetic retinopathy. The topography of the optic disc is highly reproducible and may be used for glaucoma diagnostics.

Diabetic Retinopathy↗
PubMed2003

Noninvasive laser-induced photoacoustic tomography for structural and functional in vivo imaging of the brain.

Imaging techniques based on optical contrast analysis can be used to visualize dynamic and functional properties of the nervous system via optical signals resulting from changes in blood volume, oxygen consumption and cellular swelling associated with brain physiology and pathology. Here we report in vivo noninvasive transdermal and transcranial imaging of the structure and function of rat brains by means of laser-induced photoacoustic tomography (PAT). The advantage of PAT over pure optical imaging is that it retains intrinsic optical contrast characteristics while taking advantage of the diffraction-limited high spatial resolution of ultrasound. We accurately mapped rat brain structures, with and without lesions, and functional cerebral hemodynamic changes in cortical blood vessels around the whisker-barrel cortex in response to whisker stimulation. We also imaged hyperoxia- and hypoxia-induced cerebral hemodynamic changes. This neuroimaging modality holds promise for applications in neurophysiology, neuropathology and neurotherapy.

Animals↗
PubMed2006

Selective magnetization transfer ratio decrease in the visual cortex following optic neuritis.

Patients with clinically isolated syndromes suggestive of multiple sclerosis have evidence for abnormality in normal appearing grey matter detected using the magnetization transfer ratio (MTR), a quantitative MRI measure. One potential mechanism for the decreased grey matter MTR (GM MTR) observed is trans-synaptic morphological abnormality secondary to demyelinating lesions that are in an anatomically linked pathway but remote location. We investigated this potential association by studying the location of abnormalities using voxel-based analysis of GM MTR maps in a group of 80 patients studied within 6 months of presenting with isolated optic neuritis and compared the findings with those seen in 50 age- and sex-matched healthy controls. Occipital cortex and whole brain analysis comparing all optic neuritis patients and controls revealed a selective decrease of MTR bilaterally in the visual cortex in patients [Brodmann area (BA) 17]. Whole brain analysis of patients fulfilling the McDonald criteria for multiple sclerosis (n = 20) showed a lower MTR compared to controls bilaterally in the visual cortex (BA 17/18), left hippocampus, bilateral superior temporal gyrus, bilateral lenticular nuclei and the right cerebellum. There was no significant difference in the percentage of grey matter between patients and controls in the regions of abnormal MTR detected in the visual cortex. The intrinsic MTR decrease seen in patients suggests that there are structural changes in the visual cortex following an attack of optic neuritis. Potential mechanisms for this include trans-synaptic neuronal degeneration and cortical synaptic morphological changes; such abnormalities may also contribute to MTR abnormalities observed in the normal appearing grey matter in multiple sclerosis.

Adult↗
PubMed1972

Redistribution of visual projections in altered optic tecta of adult goldfish.

The retinotectal connections formed in adult goldfish after removal of the rostro-caudal strip of dorsal tectum were mapped electrophysiologically. Initial maps recorded 1 month after surgery revealed visual scotoma corresponding to the ablated tectum. Subsequent maps recorded 4-5 months after the operation showed that the entire visual field redistributed appropriately over the remaining tectum. It is suggested that, in spite of an abnormal optic tectum, the reformed projection demonstrates a tendency to retain its completeness.

Action Potentials↗
PubMed2006

Energy-dispersive absorption spectroscopy for hard-X-ray micro-XAS applications.

Originally developed for time-resolved X-ray absorption spectroscopy (XAS), energy-dispersive absorption spectroscopy offers new opportunities for applications such as fluorescence detection and microbeams for scanning probe spectroscopy, thanks to recent developments in both instrumentation and optics. In this context, this paper presents a first example of chemical mapping recorded at ID24, the energy-dispersive XAS beamline at the ESRF. Attributes of this geometry for microanalysis are addressed. Finally, present and future plans are discussed and developed in the light of the evolution of the focal spot on this instrument in the past ten years.

Image Processing, Computer-Assisted↗
PubMed2000

Odor maps in the mammalian olfactory bulb: domain organization and odorant structural features.

Psychophysical studies indicate that structural features of odorants differentially influence their perceived odor. In the olfactory bulb (OB), odorants are represented by ensembles of activated glomeruli. Here we used optical imaging of intrinsic signals to examine how these structural features are represented spatially in the sensory map of the rat OB. We found that the dorsal OB contained two topographically fixed domains; constituent glomeruli in each domain could be activated by odorants with particular functional groups. Within each domain, other structural features such as carbon chain length and branching were represented by local differences in patterns. These results suggest that structural features are categorized into two classes, primary features (functional groups) that characterize each domain, and secondary features that are represented by local positions within each domain. Such hierarchical representations of different structural features correlate well with psychophysical structure-odor relationships.

Action Potentials↗
PubMedDate not supplied

Hematocrit as an indicator of blood volume and a predictor of intradialytic morbid events.

Hematocrit (H) levels can change during hemodialysis, and these changes in H are inversely related to changes in blood volume (BV). The objectives of this study were to determine whether mean arterial pressure (MAP) decreases with decreasing BV and rising H during hemodialysis, and to determine the relationship between dialysis induced intravascular volume depletion and intradialytic morbid events (IME), defined as hypotension, cramping, or lightheadedness that led to dialysis staff intervention. We monitored H continuously using a noninvasive optical technique in 93 hemodialysis sessions in 16 patients. IME occurred in 48 sessions. MAP decreased with increasing H in 10 of 16 patients (P < 0.05), but the relationship between MAP and H varied among the patients. The rate of BV change during sessions without morbidity (5.6 +/- 3.6 [SD] %/hr) was lower (P < 0.001) than that preceding IME in the other sessions (12.2 +/- 5.5 [SD] %/hr). Twelve of 16 patients who exhibited recurrent IME during this study experienced these events when H reached a patient specific threshold. It is concluded that MAP decreases with decreasing BV and increasing H in many patients on hemodialysis, and that a high rate of BV change often indicates that IME are forthcoming. It is further hypothesized that a patient specific H threshold is indicative of a critical BV level below which certain patients experience IME.

Blood Pressure↗
PubMed2003

Wiring the olfactory bulb--activity-dependent models of axonal targeting in the developing olfactory pathway.

Two recent experimental studies /20,21/ revealed that odorant-evoked activity-dependent competition is significant in the organisation and maintenance of the olfactory system. In this paper, we investigate the generation of a chemotopic sensory map in the olfactory bulb through three models driven by high-density optical chemosensor arrays which have similar properties to olfactory receptor neurons. By exposing the sensor arrays to various odours, these models were subjected to Hebbian learning to achieve self-organisation, potentially explaining the activity-dependent competition demonstrated by these recent studies. Our final model also predicts a role for periglomerular cells in the formation of the chemotopic sensory map in the olfactory bulb.

Animals↗