Studies on the eyes of catfishes with special reference to the tapetum lucidum

1974 ◽  
Vol 186 (1082) ◽  
pp. 13-36 ◽  
Keyword(s):  
Ictalurus Punctatus ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Single Layer ◽  
High Refractive Index ◽  
Extensive Study ◽  
Rods And Cones ◽  
Light Yellow ◽  
Membrane Bound ◽  
Pigment Epithelial Cells

Marine catfishes (Ariidae) and freshwater catfishes (Ictaluridae) have ocular tapeta lucida. Species examined were Bagre marinus (Mitchill), Arius felis (L.), Ictalurus punctatus (Rafinesque), I. natalis (Lesueur), I. nebulosus (Lesueur) and Pylodictis olivaris (Rafinesque). The tapeta are white reflectors located in the pigment epithelium; they occupy most of the fundus except for a narrow black ventral field. A more extensive study was made of the tapetum of the hardhead catfish A. felis . In histologic sections the tapetum is yellow brown and is easily confused with retinal pigment. It can be distinguished because it stains with ferric-ferricyanide and dissolves in methanol-hydrochloric acid after Carnoy fixation. The tapetum is occluded by melanosomes which move inwards in light, and it is exposed by movement outwards of melanosomes in dim light or darkness. Electron microscopy shows that processes of the pigment epithelial cells contain many membrane-bound tapetal spheres which enclose the tapetal pigment and are responsible for reflexion of light. Spheres are 370 nm in diameter (average); there are about 5.5 spheres in 1 μm 3 , and the tapetum is about 90 μm thick. Rods and cones are equal in number; rods form a single layer, cones are single and possess an accessory outer segment. Transmission of the tapetum is minimal at short wavelengths and rises steadily above 500 nm. Reflectance is diffuse; it rises to a maximum at 500 nm, and is high at long wavelengths. The tapetum has a high refractive index, ca . 1.56, favouring light scattering. Some characteristics of the extracted tapetal pigment are pre­sented: it is light yellow, and absorbance maxima occur at 260 and 330 nm in acidic meth­anol. The pigment epithelium contains lysosome-like bodies but no myeloid bodies. The hardhead retina contains a visual pigment 527 2 . Measurements of natural light (irradiance) in coastal waters inhabited by sea catfishes are presented: the waters are turbid and transmit maximally at 575 to 580 nm. The findings, in relation to earlier work on the catfish eye, performance of the eye and habits of the fish are discussed.

Studies on the eyes of gars (Lepisosteidae) with special reference to the tapetum lucidum

1973 ◽  
Vol 51 (5) ◽  
pp. 501-508 ◽  
Author(s):  
J. A. C. Nicol ◽  
H. J. Arnott
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Visible Spectrum ◽  
Tapetum Lucidum ◽  
Tubular System ◽  
Noteworthy Feature ◽  
Membrane Bound ◽  
Dim Light ◽  
Ammoniacal Silver ◽  
Pigment Epithelial Cells

Eyes of gars (Lepisosteus) possess a yellow tapetum lucidum which is located in processes of the pigment epithelium. A yellow reflecting pigment is involved, enclosed in tapetal spheres each about 240 nm in diameter. Retinomotor movements take place: in darkness (or dim light) the black retinal pigment retracts, exposing the tapetum, and the rods shorten; in the light the pigment migrates inwards, obscuring the tapetum, and the rods elongate. The tapetal pigment is soluble in water, dilute acid, and alkali, and insoluble in organic solvents; it is rendered insoluble (to water) by heavy metals; and it stains with reagents used to visualize phenolic compounds (ferric–ferricyanide; ammoniacal silver nitrate). A method of extracting the pigment is described, and the ultraviolet/visible spectrum shown. The refractive index is high (n23 1.59) and that, in conjunction with the size and arrangement of the tapetal spheres, is conducive to backscatter. A second noteworthy feature of the pigment epithelial cells is the presence of an extensive Golgi apparatus consisting of many dictyosomes interconnected by a complicated tubular system of smooth membranes. The tubules exhibit periodic swellings or vesiculations in which the tapetal spheres individually are formed. Comparisons are made with a similar Golgi complex in Styela, and with membrane-bound vesicles, derived from Golgi and concerned with formation of ommochrome granules, in Drosophila.

Fine structure of the retinal pigment epithelium and photoreceptor cells of an Australian marsupial Setonix brachyurus

1973 ◽  
Vol 51 (10) ◽  
pp. 1093-1100 ◽  
Author(s):  
C. R. Braekevelt
Keyword(s):  
Retinal Pigment Epithelium ◽  
Smooth Endoplasmic Reticulum ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Single Layer ◽  
Photoreceptor Cells ◽  
Rods And Cones ◽  
Outer Border ◽  
Large Lipid Droplet ◽  
Australian Marsupial

The morphology of the retinal pigment epithelium and photoreceptor cells has been studied in the quokka (Setonix brachyurus), an Australian marsupial, by light and electron microscopy.The pigment epithelium is formed by a single layer of cuboidal cells which are separated from the choriocapillaris by multilayered Bruch's membrane. Each epithelial cell is rich in organelles and inclusions, including smooth endoplasmic reticulum, mitochondria, Golgi complexes, phagosomes, and pigment granules. The outer border of the epithelial cells is highly infolded while the inner surface displays numerous processes which surround both rod and cone photoreceptor outer segments.Three photoreceptor types are seen, single rods, single cones, and twin cones. The rod photoreceptors outnumber the cones about 50 to 1 and are smaller and more electron-dense than the cones. The cones possess a large lipid droplet within their inner segments. Twin cones are seen only occasionally. They are formed by two cones lying in close apposition, with each member being morphologically quite similar to the other and to the single cone.Photoreceptor synapses in both rods and cones appear to be formed by superficial and invaginated contacts with bipolar and horizontal cells.

Retinol dehydrogenases: Membrane-bound enzymes for the visual function

2014 ◽  
Vol 92 (6) ◽  
pp. 510-523 ◽  
Author(s):  
Mustapha Lhor ◽  
Christian Salesse
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Membrane Binding ◽  
Large Family ◽  
Structural Features ◽  
Visual Cycle ◽  
Retinoid Metabolism ◽  
Current State ◽  
Membrane Bound ◽  
Membrane Bound Enzymes

Retinoid metabolism is important for many physiological functions, such as differenciation, growth, and vision. In the visual context, after the absorption of light in rod photoreceptors by the visual pigment rhodopsin, 11-cis retinal is isomerized to all-trans retinal. This retinoid subsequently undergoes a series of modifications during the visual cycle through a cascade of reactions occurring in photoreceptors and in the retinal pigment epithelium. Retinol dehydrogenases (RDHs) are enzymes responsible for crucial steps of this visual cycle. They belong to a large family of proteins designated as short-chain dehydrogenases/reductases. The structure of these RDHs has been predicted using modern bioinformatics tools, which allowed to propose models with similar structures including a common Rossman fold. These enzymes undergo oxidoreduction reactions, whose direction is dictated by the preference and concentration of their individual cofactor (NAD(H)/NADP(H)). This review presents the current state of knowledge on functional and structural features of RDHs involved in the visual cycle as well as knockout models. RDHs are described as integral or peripheral enzymes. A topology model of the membrane binding of these RDHs via their N- and (or) C-terminal domain has been proposed on the basis of their individual properties. Membrane binding is a crucial issue for these enzymes because of the high hydrophobicity of their retinoid substrates.

scholarly journals Fine structure of the retinal pigment epithelium and cones of Antarctic fish Notohenia coriiceps Richardson in light and dark-conditions

2007 ◽  
Vol 24 (1) ◽  
pp. 33-40 ◽  
Author(s):  
Lucélia Donatti ◽  
Edith Fanta
Keyword(s):  
Epithelial Cells ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Antarctic Fish ◽  
Basal Region ◽  
Dense Cytoplasm ◽  
Transmission Electron ◽  
Notothenia Coriiceps ◽  
The Antarctic ◽  
Pigment Epithelial Cells

The Antarctic fish Notothenia coriiceps Richardson, 1844 lives in an environment of daily and annual photic variation and retina cells have to adjust morphologically to environmental luminosity. After seven day dark or seven day light acclimation of two groups of fish, retinas were extracted and processed for light and transmission electron microscopy. In seven day dark adapted, retina pigment epithelium melanin granules were aggregated at the basal region of cells, and macrophages were seen adjacent to the apical microvilli, between the photoreceptors. In seven day light adapted epithelium, melanin granules were inside the apical microvilli of epithelial cells and macrophages were absent. The supranuclear region of cones adapted to seven day light had less electron dense cytoplasm, and an endoplasmic reticulum with broad tubules. The mitochondria in the internal segment of cones adapted to seven day light were larger, and less electron dense. The differences in the morphology of cones and pigment epithelial cells indicate that N. coriiceps has retinal structural adjustments presumably optimizing vision in different light conditions.

Diurnal and circadian retinomotor movements in zebrafish

2005 ◽  
Vol 22 (2) ◽  
pp. 203-209 ◽  
Author(s):  
GUS J. MENGER ◽  
JOSEPH R. KOKE ◽  
GREGORY M. CAHILL
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Pigment Granule ◽  
Constant Darkness ◽  
Light Cycle ◽  
Rods And Cones ◽  
Ambient Lighting ◽  
Bright Field Microscopy ◽  
Key Indicators

Key indicators of circadian regulation include the persistence of physiological rhythmicity in the absence of environmental time cues and entrainment of this rhythmicity by the ambient light cycle. In some teleosts, the inner segments of rod and cone photoreceptors contract and elongate according to changes in ambient lighting and the circadian cycle. Pigment granules in the retinal pigment epithelium (RPE) disperse and aggregate in a similar manner. Collectively, these movements are known as retinomotor movements. We report the histological characterization of diurnal and circadian retinomotor movements in zebrafish, Danio rerio. Adult fish subjected to a 14:10 light:dark (LD) cycle, constant darkness (DD), or constant light (LL) were sacrificed at 1–13 h intervals and processed for semithin sectioning of the retina. Using bright-field microscopy, 15 measurements of pigment granule position and the inner segment lengths of 30 rods and 30–45 cones were collected from the central third of the dorso-optic retina per time point. In LD, rods and cones followed a clear diurnal rhythm in their inner segment movements. Short-single, UV-sensitive cones were found to contract significantly 1 h before light onset in LD conditions. In DD conditions, the inner segments movements of short-single and double cones displayed statistically significant rhythms. RPE pigment granule movements are rhythmically regulated in both LD and DD although fluctuations are damped in the absence of photic cues. No significant retinomotor movements were observed in LL. These findings indicate retinomotor movements in zebrafish are differentially regulated by an endogenous oscillator and by light-dependent mechanisms.

Carbonic Anhydrase Inhibitor with Topical NSAID Therapy to Manage Cystoid Macular Edema in a Case of Gyrate Atrophy

2017 ◽  
Vol 27 (6) ◽  
pp. e179-e183 ◽  
Author(s):  
Elena Piozzi ◽  
Salvatore Alessi ◽  
Silvia Santambrogio ◽  
Giovanni Cillino ◽  
Marco Mazza ◽  
...  
Keyword(s):  
Carbonic Anhydrase ◽  
Macular Edema ◽  
Cystoid Macular Edema ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Carbonic Anhydrase Inhibitor ◽  
Gyrate Atrophy ◽  
First Case ◽  
Membrane Bound ◽  
Inflammatory Drugs

Purpose Gyrate atrophy of the choroid and retina (GACR) is a rare chorioretinal dystrophy characterized by a deficiency of the enzyme ornithine aminotransferase, inherited in an autosomal recessive pattern. Case Report We report a case of a 17-year-old girl with GACR, for whom the level of serum ornithine had been reduced by an arginine-restricted diet. The patient was responsive to an association of topical nonsteroidal anti-inflammatory drugs (NSAIDs) and a carbonic anhydrase inhibitor (CAI) to reduce cystoid macular edema (CME). Conclusions The efficacy of topical NSAIDs and systemic CAI association indicates that the imbalance in the distribution of retinal pigment epithelium membrane-bound carbonic anhydrase could play a major role in CME pathogenesis in GACR. To our knowledge, this is the first case of therapy with CAI treatment for GACR-related CME.

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