The Experts below are selected from a list of 12474 Experts worldwide ranked by ideXlab platform

Jacint Ventura - One of the best experts on this subject based on the ideXlab platform.

  • Cornea, Retina, and lens morphology in five Soricidae species (Soricomorpha: Mammalia)
    Anatomical Science International, 2009
    Co-Authors: Sara Lluch, María José López-fuster, Jacint Ventura
    Abstract:

    We analyzed the cornea, Retina, and lens of five species of Soricidae (pygmy shrew, Sorex minutus ; common shrew, Sorex araneus ; Millet’s shrew, Sorex coronatus ; water shrew, Neomys fodiens ; greater white-toothed shrew, Crocidura russula ) by light and electron microscopy. In all of these species, the corneal epithelium showed a dead cell layer, which may increase the refractive power of the cornea, thereby reducing the hypermetropy that would be expected in a small eye. Moreover, the anterior surface of the lens was more curved than the posterior, thus minimizing spherical aberrations. The thicker lens and its smaller radii of curvature indicated that Sorex species and N. fodiens have a higher refractive lens power than the most nocturnal species, C. russula . In addition, only in the Retina Cone inner segments of the most diurnal species (genus Sorex ) did we find megamitochondria that might act as microlenses to enhance the efficiency of Cones. In C. russula , the scarcity of Cones and the relatively small yet abundant rod nuclei were found to be consistent with its habits. The flat lens and its more anterior arrangement, together with the lack of megamitochondria in the Retina of C. russula , indicated that this species has less visual acuity than the other shrews studied here.

  • giant mitochondria in the Retina Cone inner segments of shrews of genus sorex insectivora soricidae
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2003
    Co-Authors: Sara Lluch, Maria Jose Lopezfuster, Jacint Ventura
    Abstract:

    The Retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The Cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 μm in S. araneus, 5.68 μm in S. coronatus, and 2.42 μm in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian Retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-Cone Retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the Cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the Cone outer segment optics. Anat Rec Part A 272A:484–490, 2003. © 2003 Wiley-Liss, Inc.

  • Giant mitochondria in the Retina Cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)
    The anatomical record. Part A Discoveries in molecular cellular and evolutionary biology, 2003
    Co-Authors: Sara Lluch, María José López-fuster, Jacint Ventura
    Abstract:

    The Retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The Cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 microm in S. araneus, 5.68 microm in S. coronatus, and 2.42 microm in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian Retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-Cone Retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the Cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the Cone outer segment optics.

Terrence J. Sejnowski - One of the best experts on this subject based on the ideXlab platform.

  • Spatiochromatic Receptive Field Properties Derived from Information-Theoretic Analyses of Cone Mosaic Responses to Natural Scenes
    Neural Computation, 2003
    Co-Authors: Toshio Inui, Thomas Wachtler, Terrence J. Sejnowski
    Abstract:

    Neurons in the early stages of processing in the primate visual system efficiently encode natural scenes. In previous studies of the chromatic properties of natural images, the inputs were sampled on a regular array, with complete color information at every location. However, in the Retina Cone photoreceptors with different spectral sensitivities are arranged in a mosaic. We used an unsupervised neural network model to analyze the statistical structure of Retinal Cone mosaic responses to calibrated color natural images. The second-order statistical dependencies derived from the covariance matrix of the sensory signals were removed in the first stage of processing. These decorrelating filters were similar to type I receptive fields in parvo- or konio-cellular LGN in both spatial and chromatic characteristics. In the subsequent stage, the decorrelated signals were linearly transformed to make the output as statistically independent as possible, using independent component analysis. The independent component filters showed luminance selectivity with simple-cell-like receptive fields, or had strong color selectivity with large, often double-opponent, receptive fields, both of which were found in the primary visual cortex (V1). These results show that the “form” and “color” channels of the early visual system can be derived from the statistics of sensory signals.

Sara Lluch - One of the best experts on this subject based on the ideXlab platform.

  • Cornea, Retina, and lens morphology in five Soricidae species (Soricomorpha: Mammalia)
    Anatomical Science International, 2009
    Co-Authors: Sara Lluch, María José López-fuster, Jacint Ventura
    Abstract:

    We analyzed the cornea, Retina, and lens of five species of Soricidae (pygmy shrew, Sorex minutus ; common shrew, Sorex araneus ; Millet’s shrew, Sorex coronatus ; water shrew, Neomys fodiens ; greater white-toothed shrew, Crocidura russula ) by light and electron microscopy. In all of these species, the corneal epithelium showed a dead cell layer, which may increase the refractive power of the cornea, thereby reducing the hypermetropy that would be expected in a small eye. Moreover, the anterior surface of the lens was more curved than the posterior, thus minimizing spherical aberrations. The thicker lens and its smaller radii of curvature indicated that Sorex species and N. fodiens have a higher refractive lens power than the most nocturnal species, C. russula . In addition, only in the Retina Cone inner segments of the most diurnal species (genus Sorex ) did we find megamitochondria that might act as microlenses to enhance the efficiency of Cones. In C. russula , the scarcity of Cones and the relatively small yet abundant rod nuclei were found to be consistent with its habits. The flat lens and its more anterior arrangement, together with the lack of megamitochondria in the Retina of C. russula , indicated that this species has less visual acuity than the other shrews studied here.

  • giant mitochondria in the Retina Cone inner segments of shrews of genus sorex insectivora soricidae
    Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2003
    Co-Authors: Sara Lluch, Maria Jose Lopezfuster, Jacint Ventura
    Abstract:

    The Retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The Cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 μm in S. araneus, 5.68 μm in S. coronatus, and 2.42 μm in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian Retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-Cone Retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the Cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the Cone outer segment optics. Anat Rec Part A 272A:484–490, 2003. © 2003 Wiley-Liss, Inc.

  • Giant mitochondria in the Retina Cone inner segments of shrews of genus Sorex (Insectivora, Soricidae)
    The anatomical record. Part A Discoveries in molecular cellular and evolutionary biology, 2003
    Co-Authors: Sara Lluch, María José López-fuster, Jacint Ventura
    Abstract:

    The Retinas of three species of shrews (Sorex araneus, S. coronatus, and S. minutus) were analyzed. Two kinds of photoreceptors were identified according to (among other characteristics) the traits of the mitochondria of their inner segments. The rod inner segments contained several round or oval mitochondria distributed longitudinally inside the ellipsoid. The Cone inner segment showed a few mitochondria, which we classified as megamitochondria (maximum length = 4.22 microm in S. araneus, 5.68 microm in S. coronatus, and 2.42 microm in S. minutus). An analysis of serial thin sections in S. coronatus showed that these large organelles occurred in the apical and central portions of the ellipsoid. In the peripheral and basal regions of the ellipsoid, megamitochondria were frequently accompanied by smaller mitochondria. The giant mitochondria were irregular in form and densely packed, and a reduced cytosol was observed between each mitochondria. In general, they exhibited an electron-dense matrix and a complex system of cristae, which varied in length and array. In mammalian Retina, megamitochondria have only been described in the ellipsoid of the tree shrews Tupaia glis and T. belangeri, two diurnal Scandentia with a rich-Cone Retina. In general terms, Sorex megamitochondria are morphologically very similar to those reported for Tupaia, especially in their arrangement in the Cone ellipsoid. However, they differ in the orientation of the cristae. We propose that the ellipsoid of Sorex may serve two functions: as a source of energy for receptor cells, and as a device for improving the Cone outer segment optics.

Toshio Inui - One of the best experts on this subject based on the ideXlab platform.

  • Spatiochromatic Receptive Field Properties Derived from Information-Theoretic Analyses of Cone Mosaic Responses to Natural Scenes
    Neural Computation, 2003
    Co-Authors: Toshio Inui, Thomas Wachtler, Terrence J. Sejnowski
    Abstract:

    Neurons in the early stages of processing in the primate visual system efficiently encode natural scenes. In previous studies of the chromatic properties of natural images, the inputs were sampled on a regular array, with complete color information at every location. However, in the Retina Cone photoreceptors with different spectral sensitivities are arranged in a mosaic. We used an unsupervised neural network model to analyze the statistical structure of Retinal Cone mosaic responses to calibrated color natural images. The second-order statistical dependencies derived from the covariance matrix of the sensory signals were removed in the first stage of processing. These decorrelating filters were similar to type I receptive fields in parvo- or konio-cellular LGN in both spatial and chromatic characteristics. In the subsequent stage, the decorrelated signals were linearly transformed to make the output as statistically independent as possible, using independent component analysis. The independent component filters showed luminance selectivity with simple-cell-like receptive fields, or had strong color selectivity with large, often double-opponent, receptive fields, both of which were found in the primary visual cortex (V1). These results show that the “form” and “color” channels of the early visual system can be derived from the statistics of sensory signals.

David Hicks - One of the best experts on this subject based on the ideXlab platform.

  • Photoreceptor organization and rhythmic phagocytosis in the nile rat Arvicanthis ansorgei: a novel diurnal rodent model for the study of Cone pathophysiology.
    Investigative Ophthalmology & Visual Science, 2006
    Co-Authors: Corina Bobu, Cheryl Craft, Mireille Masson-pevet, David Hicks
    Abstract:

    PURPOSE: To characterize rod and Cone distribution, organization, and phagocytosis in the diurnal mouse-like rodent Arvicanthis ansorgei. METHODS: Retinas of adult A. ansorgei were processed for histology, electron microscopy and immunohistochemistry using rod- and mouse Cone-specific antibodies. For phagocytosis studies, Retinas were sampled every 3 hours under a 12-hour light-dark cycle and processed for double-label immunohistochemistry. The number of phagosomes in the Retinal pigmented epithelium were quantified with a morphometric system. RESULTS: A. ansorgei Retinas were composed of 33% Cones and 67% rods, approximately 10 times more Cones than mice and rats. Cones were arranged in two cell layers at the scleral surface, distributed uniformly across the entire Retina. Cone arrestin was distributed throughout the dark-adapted Cones, from outer segments to synapses, whereas short- and mid-wavelength Cone opsins were restricted to outer segments. Short-wavelength Cone density was mapped in wholemounted Retinas, in a significantly higher number in the central region. Rhodopsin immunopositive (rod) phagosomes showed a small peak late in the dark phase, then a large burst 1 to 2 hours after light onset, after decreasing to low baseline levels by 12 AM. Mid-wavelength Cone opsin immunopositive (Cone) phagosomes were 10 times less numerous than rods, and demonstrated a broad peak 1 to 2 hours after light onset. CONCLUSIONS: The diurnal rodent A. ansorgei possesses a large number of Cones, organized in a strict anatomic array. Rod and Cone outer segment phagocytosis and shedding can be monitored simultaneously and show similar profiles but different amplitudes. This species may constitute a valuable novel animal model for investigating Cone pathophysiology.