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Temporal Retina (temporal + retina)

Distribution by Scientific Domains

Life Sciences	50%

Selected Abstracts

Expression of ephrin-A2 in the superior colliculus and EphA5 in the retina following optic nerve section in adult rat

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2001
J. Rodger
Abstract The vertebrate retina projects topographically to visual brain centres. In the developing visual system, gradients of ephrins and Eph receptors play a role in defining topography. At maturity, ephrins but not Ephs are downregulated. Here we show that optic nerve section in adult rat differentially regulates the expression of ephrin-A2 in the superior colliculus (SC) and of EphA5 in the retina. Expression was quantified immunohistochemically; ephrin-A2 levels were also estimated by semiquantitative reverse transcriptase polymerase chain reaction. In the normal SC, ephrin-A2 was expressed at low levels. At 1 month, levels of protein and of mRNA were upregulated across the contralateral SC giving rise to an increasing rostro-caudal gradient. At 6 months, levels had fallen but a gradient remained. In the retina of normal animals, EphA5 was expressed as an increasing naso-temporal gradient. By 1 month, expression was decreased in far temporal retina, resulting in a uniform expression across the naso-temporal axis. We suggest that denervation-induced plastic changes within the SC modify expression of these molecules. [source]

Nasal-temporal differences in cone-opponency in the near peripheral retina

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2009
A. Panorgias
Abstract The purpose of this study is to establish whether nasal-temporal differences in cone photoreceptor distributions are linked to differences in colour matching performance in the two hemi-fields. Perceived shifts in chromaticity were measured using an asymmetric matching paradigm. They were expressed in terms of hue rotations and relative saturation changes and also in terms of activation levels of L,M or S,(L+M) cone-opponent channels. Up to 19° eccentricity there was little difference in chromaticity shifts between nasal and temporal retina for either channel. For matches beyond 19° L,M activation is significantly lower in the nasal field and the S,(L+M) channel was equally activated in both fields. The data are consistent with the asymmetric distribution of L- and M-cones in the nasal and temporal retinae. [source]

The contrast sensitivity function for detection and resolution of blue-on-yellow gratings in foveal and peripheral vision

OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 5 2002
R. S. Anderson
Abstract Previous studies using polychromatic gratings have shown that the peripheral grating contrast sensitivity function is significantly different when the task is resolution rather than detection. Specifically, in the middle frequency range, while resolution acuity drops suddenly to zero, detection performance continues up to much higher frequencies, accompanied by observations of aliasing. We wanted to determine if the same holds true for blue-cone isolating gratings in either foveal or peripheral vision. Contrast sensitivity function (CSFs) were measured at the fovea and 20 degrees eccentricity in the temporal retina under conditions of short-wavelength-sensitive (SWS)-cone pathway isolation using a two-alternative forced choice paradigm. The detection and resolution CSF were identical at the low frequency end but at higher frequencies resolution sensitivity falls abruptly while contrast detection remained possible till higher frequencies [cut-off frequencies: fovea detection 6.0 cycles (degree),1, resolution 4.6 cycles (degree),1; periphery detection 1.6 cycles (degree),1, resolution 1.05 cycles (degree),1]. Aliasing was observable when spatial frequency exceeded the resolution limit. Medium/high contrast blue-cone-mediated resolution acuity is sampling limited in both the fovea and periphery. Previous studies of blue-cone contrast sensitivity which employed a detection task do not reflect the true resolution limit. [source]

Morphology, characterization, and distribution of retinal photoreceptors in the Australian lungfish Neoceratodus forsteri (Krefft, 1870)

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 3 2006
Helena J. Bailes
Abstract The Australian lungfish Neoceratodus forsteri (Dipnoi) is an ancient fish that has a unique phylogenetic relationship among the basal Sarcopterygii. Here we examine the ultrastructure, histochemistry, and distribution of the retinal photoreceptors using a combination of light and electron microscopy in order to determine the characteristics of the photoreceptor layer in this living fossil. Similar proportions of rods (53%) and cones (47%) reveal that N. forsteri optimizes both scotopic and photopic sensitivity according to its visual demands. Scotopic sensitivity is optimized by a tapetum lucidum and extremely large rods (18.62 ± 2.68 ,m ellipsoid diameter). Photopic sensitivity is optimized with a theoretical spatial resolving power of 3.28 ± 0.66 cycles degree,1, which is based on the spacing of at least three different cone types: a red cone containing a red oil droplet, a yellow cone containing a yellow ellipsoidal pigment, and a colorless cone containing multiple clear oil droplets. Topographic analysis reveals a heterogeneous distribution of all photoreceptor types, with peak cone densities predominantly found in temporal retina (6,020 rods mm,2, 4,670 red cones mm,2, 900 yellow cones mm,2, and 320 colorless cones mm,2), but ontogenetic changes in distribution are revealed. Spatial resolving power and the diameter of all photoreceptor types (except yellow cones) increases linearly with growth. The presence of at least three morphological types of cones provides the potential for color vision, which could play a role in the clearer waters of its freshwater environment. J. Comp. Neurol. 494:381,397, 2006. © 2005 Wiley-Liss, Inc. [source]