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Charlie R. Braekevelt - One of the best experts on this subject based on the ideXlab platform.
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Fine structure of the Tapetum lucidum in the short-tailed stingray (Dasyatis brevicaudata).
Histology and histopathology, 1994Co-Authors: Charlie R. BraekeveltAbstract:The Tapetum lucidum of the short-tailed stingray (Dasatis brevicaudata) is located in the choroid of the superior fundus immediately external to the choriocapillaris. In this species the Tapetum consists of a single layer of overlapping cells oriented at an angle of about 30" to the incoming light. These tapetal cells alternate with and are separated from one another by melanocytes which extend beyond the tapetal cells to intervene between the tapetal cells and the choriocapillaris. The tapetal cells and the melanocytes are flattened plate-like cells with their widest dimension facing the retina. Internally the tapetal cells display a peripherally located vesicular nucleus with most organelles in a paranuclear location. The bulk of the cell is packed with regularly spaced crystals reported to be guanine. The size and spacing of these reflective crystals is commensurate with constructive interference. In lightadaptation, the melanosomes of the intervening melanocytes are widely dispersed and for the most part block the passage of light to the tapetal cells. Although dark-adapted specimens were not examined, it seems reasonable to assume that in dark-adaptation, the melanosomes will retreat to unmask the Tapetum and allow it to function as a reflective layer.
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Fine structure of the choroidal Tapetum lucidum in the Port Jackson shark ( Heterodontus phillipi )
Anatomy and embryology, 1994Co-Authors: Charlie R. BraekeveltAbstract:The choroidally located Tapetum lucidum of the Port Jackson shark (Heterodontus phillipi) was examined by light and electron microscopy in light-adapted specimens. In this species the Tapetum consists of a single layer of overlapping cells oriented at an angle of about 30° to the incoming light and situated immediately external to the choriocapillaris. These tapetal cells alternate with and are separated from one another by melanocytes which extend beyond the tapetal cells to intervene between the tapetal cells and the incoming light. The tapetal cells and the melanocytes are flattened plate-like cells with their widest dimension facing the retina. Internally the tapetal cells display a peripherally located vesicular nucleus with most organelles in a paranuclear location. The bulk of a tapetal cell is packed with regularly spaced crystals reported to be guanine. The size and spacing of these reflective crystals is commensurate with the principles of constructive interference. In light adaptation, the melanosomes of the intervening melanocytes are widely dispersed and for the most part block the passage of light to the tapetal cells. Although dark-adapted specimens were not available, it seems reasonable to assume that in dark adaptation these melanosomes will retreat to unmask the Tapetum and allow it to function as a known reflective layer.
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Electron microscopic study of the occlusible Tapetum lucidum of the southern fiddler ray (Trygonorhina fasciata).
Histology and histopathology, 1991Co-Authors: Charlie R. BraekeveltAbstract:The choroidally located Tapetum lucidum of the southern fiddler ray (Trygonorhina fasciata) has been examined by light and electron microscopy in both light- and dark-adaptation. In this species, the Tapetum consists of a single layer of overlapping cells oriented at an angle of about 30 degrees to the incoming light. These are situated immediately external to the choriocapillaris. These tapetal cells alternate with and are separated from one another by melanocytes which have an inner extension that curves and intervenes between the tapetal cells and the choriocapillaris. The tapetal cells and the melanocytes are flattened cells with their widest dimension facing the retina. Internally the tapetal cells display a peripherally-located, vesicular nucleus with most of the cell organelles in a paranuclear location. The bulk of the cell is packed with regularly-spaced crystals reported to be guanine. The size and spacing of these reflective crystals is commensurate with constructive interference. In light-adaptation the small melanosomes of the melanocytes are widely dispersed and fill the portion of the cell intervening between the tapetal cells and the incoming light. This effectively occludes the Tapetum as light is unable to reach the reflective material. In dark-adaptation the melanosomes withdraw from this location, exposing the Tapetum to light and allowing it to act as a reflective layer. The retinal epithelium overlying the tapetal area is totally unpigmented so as not to interfere with the passage of light.
Paul R. Manger - One of the best experts on this subject based on the ideXlab platform.
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The Retina of Ansorge's Cusimanse (Crossarchus ansorgei): Number, Topography and Convergence of Photoreceptors and Ganglion Cells in Relation to Ecology and Behavior.
Brain behavior and evolution, 2015Co-Authors: João Paulo Coimbra, Paul R. Manger, Consolate Kaswera-kyamakya, Emmanuel Gilissen, Shaun P. CollinAbstract:The family Herpestidae (cusimanses and mongooses) is a monophyletic radiation of carnivores with remarkable variation in microhabitat occupation and diel activity, but virtually nothing is known about how they use vision in the context of their behavioral ecology. In this paper, we measured the number and topographic distribution of neurons (rods, cones and retinal ganglion cells) and estimated the spatial resolving power of the eye of the diurnal, forest-dwelling Ansorge's cusimanse (Crossarchus ansorgei). Using retinal wholemounts and stereology, we found that rods are more numerous (42,500,000; 92%) than cones (3,900,000; 8%). Rod densities form a concentric and dorsotemporally asymmetric plateau that matches the location and shape of a bright yellow Tapetum lucidum located within the dorsal aspect of the eye. Maximum rod density (340,300 cells/mm(2)) occurs within an elongated plateau below the optic disc that corresponds to a transitional region between the Tapetum lucidum and the pigmented choroid. Cone densities form a temporal area with a peak density of 44,500 cells/mm(2) embedded in a weak horizontal streak that matches the topographic distribution of retinal ganglion cells. Convergence ratios of cones to retinal ganglion cells vary from 50:1 in the far periphery to 3:1 in the temporal area. With a ganglion cell peak density of 13,400 cells/mm(2) and an eye size of 11 mm in axial length, we estimated upper limits of spatial resolution of 7.5-8 cycles/degree, which is comparable to other carnivores such as hyenas. In conclusion, we suggest that the topographic retinal traits described for Ansorge's cusimanse conform to a presumed carnivore retinal blueprint but also show variations that reflect its specific ecological needs.
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Visual Acuity and Heterogeneities of Retinal Ganglion Cell Densities and the Tapetum lucidum of the African Elephant (Loxodonta africana)
Brain behavior and evolution, 2010Co-Authors: John D. Pettigrew, Adhil Bhagwandin, Mark Haagensen, Paul R. MangerAbstract:The eyes of three adult male African elephants were examined, the retinas were whole-mounted, stained and analyzed to determine visual acuity. A range of small to large ganglion cell types were observed across the retinas. We observed three regions of high ganglion cell density, one in the upper temporal quadrant, a visual or horizontal streak and a smaller region at the nasal end of the horizontal streak. The peak density of ganglion cells observed was 5,280/mm(2), and our calculations indicate that the elephant has a maximal visual acuity of between 13.16 and 14.37 cycles/degree. We observed a heterogeneous structure of a Tapetum lucidum, the cells of which were found to be most strongly aggregated behind the temporal and nasal densities of retinal ganglion cells. The strength of the Tapetum lucidum was weaker posterior to the density of ganglion cells forming the horizontal streak. The morphology of the elephant eye appears to be such that it reflects: (1) the importance of trunk-eye co-ordination for feeding; (2) the importance of 24-hour vigilance for either predators or conspecifics, and (3) the arrhythmic nature of the daily activity of this animal, being useful both diurnally and nocturnally.
Dipak K. Patel - One of the best experts on this subject based on the ideXlab platform.
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the experimental antipsychotic agent 1192u90 targets Tapetum lucidum in canine eyes
Toxicologic Pathology, 1996Co-Authors: John E. Dillberger, Robert L. Peiffer, Michael J. Dykstra, Michael Omara, Dipak K. PatelAbstract:To assess the potential adverse effects in people of the antipsychotic agent 1192U90, we dosed mice, rats, beagles, and cynomolgus monkeys for up to 3 mo. In dogs, but not the other species, 1192U9...
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The Experimental Antipsychotic Agent 1192U90 Targets Tapetum lucidum in Canine Eyes
Toxicologic pathology, 1996Co-Authors: John E. Dillberger, Robert L. Peiffer, Michael J. Dykstra, Michael O'mara, Dipak K. PatelAbstract:To assess the potential adverse effects in people of the antipsychotic agent 1192U90, we dosed mice, rats, beagles, and cynomolgus monkeys for up to 3 mo. In dogs, but not the other species, 1192U90 caused ocular changes detectable ophthalmoscopically as loss of tapetal reflectivity, altered tapetal color, and the appearance of black pigmentation on the tapetal fundus. Eyes from affected dogs had atrophic tapeta lucidum due to cell loss. Rodlets in remaining tapetal cells were separated by electron-lucent spaces or finely granular material, varied in size and shape, and often contained irregularly shaped electron-dense inclusions. Nontapetal ocular structures were unaffected. Because 1192U90 caused no ocular changes in nontapetal species, we hypothesized that it targeted only Tapetum lucidum and spared other ocular structures. We tried to test this hypothesis by dosing congenitally atapetal dogs; however, although these dogs were ophthalmoscopically "atapetal," they had scattered tapetal cells visible by ...
Joachim Plotz - One of the best experts on this subject based on the ideXlab platform.
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microscopic anatomy of the eye of the deep diving antarctic weddell seal leptonychotes weddellii
Journal of Morphology, 2001Co-Authors: Ulrich Welsch, Sven Ramdohr, Bernd Riedelsheimer, Regina Eisert, Rudolf Hebel, Joachim PlotzAbstract:The microscopic anatomy of the eye of the Weddell seal was studied with various light and electron microscopic methods with a view to correlating morphological findings with the biology of this seal which is adapted to the extremes of the Antarctic environment and to extreme diving excursions into the lightless depths of the sea. In the retina an area centralis was found but no fovea centralis. The densely packed photoreceptors consist exclusively of highly differentiated rods, which in primates detect light at low intensity but have rather poor image discrimination. The ganglion cells are relatively scarce, suggesting a high degree of convergence of the light-sensitive cells on the ganglion cells. The pigment epithelium is almost devoid of pigment granules. The extensive Tapetum lucidum is about 400–500 μm thick and is composed of about 30 layers of specialized cells. The cornea is 650 (center) to 800–900 (periphery) μm thick. Its structure and glycosaminoglycan histochemistry correspond to that of other mammals. The iridocorneal angle is unusually deep and pervaded by an elaborate trabecular meshwork, which together with a complex canal of Schlemm can be correlated with the ability to absorb large amounts of fluid. The ciliary muscle and its antagonist, the membrane of Bruch, are poorly developed, suggesting relatively poor abilities of accommodation. The combination of a well-developed Tapetum lucidum, an unpigmented pigment epithelium, well-developed rods, and a high number of rods converging on only few ganglion cells is obviously an adaptation to an extreme light sensitivity, enabling the animals to make use of the little light available in the deep sea. J. Morphol. 248:165–174, 2001. © 2001 Wiley-Liss, Inc.
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Microscopic anatomy of the eye of the deep‐diving Antarctic Weddell seal (Leptonychotes weddellii)
Journal of Morphology, 2001Co-Authors: Ulrich Welsch, Sven Ramdohr, Bernd Riedelsheimer, Regina Eisert, Rudolf Hebel, Joachim PlotzAbstract:The microscopic anatomy of the eye of the Weddell seal was studied with various light and electron microscopic methods with a view to correlating morphological findings with the biology of this seal which is adapted to the extremes of the Antarctic environment and to extreme diving excursions into the lightless depths of the sea. In the retina an area centralis was found but no fovea centralis. The densely packed photoreceptors consist exclusively of highly differentiated rods, which in primates detect light at low intensity but have rather poor image discrimination. The ganglion cells are relatively scarce, suggesting a high degree of convergence of the light-sensitive cells on the ganglion cells. The pigment epithelium is almost devoid of pigment granules. The extensive Tapetum lucidum is about 400–500 μm thick and is composed of about 30 layers of specialized cells. The cornea is 650 (center) to 800–900 (periphery) μm thick. Its structure and glycosaminoglycan histochemistry correspond to that of other mammals. The iridocorneal angle is unusually deep and pervaded by an elaborate trabecular meshwork, which together with a complex canal of Schlemm can be correlated with the ability to absorb large amounts of fluid. The ciliary muscle and its antagonist, the membrane of Bruch, are poorly developed, suggesting relatively poor abilities of accommodation. The combination of a well-developed Tapetum lucidum, an unpigmented pigment epithelium, well-developed rods, and a high number of rods converging on only few ganglion cells is obviously an adaptation to an extreme light sensitivity, enabling the animals to make use of the little light available in the deep sea. J. Morphol. 248:165–174, 2001. © 2001 Wiley-Liss, Inc.
John E. Dillberger - One of the best experts on this subject based on the ideXlab platform.
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the experimental antipsychotic agent 1192u90 targets Tapetum lucidum in canine eyes
Toxicologic Pathology, 1996Co-Authors: John E. Dillberger, Robert L. Peiffer, Michael J. Dykstra, Michael Omara, Dipak K. PatelAbstract:To assess the potential adverse effects in people of the antipsychotic agent 1192U90, we dosed mice, rats, beagles, and cynomolgus monkeys for up to 3 mo. In dogs, but not the other species, 1192U9...
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The Experimental Antipsychotic Agent 1192U90 Targets Tapetum lucidum in Canine Eyes
Toxicologic pathology, 1996Co-Authors: John E. Dillberger, Robert L. Peiffer, Michael J. Dykstra, Michael O'mara, Dipak K. PatelAbstract:To assess the potential adverse effects in people of the antipsychotic agent 1192U90, we dosed mice, rats, beagles, and cynomolgus monkeys for up to 3 mo. In dogs, but not the other species, 1192U90 caused ocular changes detectable ophthalmoscopically as loss of tapetal reflectivity, altered tapetal color, and the appearance of black pigmentation on the tapetal fundus. Eyes from affected dogs had atrophic tapeta lucidum due to cell loss. Rodlets in remaining tapetal cells were separated by electron-lucent spaces or finely granular material, varied in size and shape, and often contained irregularly shaped electron-dense inclusions. Nontapetal ocular structures were unaffected. Because 1192U90 caused no ocular changes in nontapetal species, we hypothesized that it targeted only Tapetum lucidum and spared other ocular structures. We tried to test this hypothesis by dosing congenitally atapetal dogs; however, although these dogs were ophthalmoscopically "atapetal," they had scattered tapetal cells visible by ...