Retinal development of West Australian dhufish, Glaucosoma hebraicum

2001 ◽  
Vol 18 (5) ◽  
pp. 711-724 ◽  
Author(s):  
JULIA SHAND ◽  
MICHAEL A. ARCHER ◽  
NICOLE THOMAS ◽  
JENNIFER CLEARY
Keyword(s):  
Ganglion Cell ◽  
Ganglion Cell Layer ◽  
Light And Electron Microscopy ◽  
Low Light ◽  
Exogenous Feeding ◽  
Rod Photoreceptors ◽  
Outer Segments ◽  
Light Levels ◽  
Single Cone ◽  
Area Centralis

An investigation of retinal specializations was carried out in larval and juvenile dhufish, Glaucosoma hebraicum (Glaucosomidae, Teleostei). The development of photoreceptors and formation of the retinal mosaic was followed by light and electron microscopy. At hatching the eye was undifferentiated. Cone photoreceptors were present by day 3 posthatch (dph), when exogenous feeding began. Single and multiple cones were present in a row arrangement from 3 dph to 20 dph, when the first rod nuclei were observed. Between 20 dph and approximately 3 months posthatch (mph), the row arrangement was replaced by a square mosaic of four double cones surrounding a single cone, and the cones increased in size, with the outer segments reaching up to 30 μm in length. During the period of spatial rearrangement, triple cones were often observed. From their first appearance, rod photoreceptors were added rapidly. Investigation of ganglion cell topography in 3-mph fish that had attained the adult-like square photoreceptor mosaic was carried out using retinal wholemounts. The highest densities of neurones in the ganglion cell layer were in temporal retina but no well-defined area centralis was observed. Microspectrophotometric measurements of the visual pigments within the outer segments of the photoreceptors of 3-mph fish revealed double cones with identical absorption spectra in each member of the outer segment, and the wavelength of maximum absorption (λmax) located at 522 nm. Single cones were found to possess a visual pigment with λmax at 460 nm and rods with a λmax of 498 nm. The results imply that the larvae and juveniles are adapted for survival in coastal waters and may be active in relatively low light levels from early stages of development.

scholarly journals A novel cellular structure in the photoreceptors of insectivorous birds

2019 ◽  
Author(s):  
Luke P. Tyrrell ◽  
Leandro B.C. Teixeira ◽  
Richard R. Dubielzig ◽  
Diana Pita ◽  
Patrice Baumhardt ◽  
...  
Keyword(s):  
Cellular Structure ◽  
Bird Species ◽  
Cone Photoreceptor ◽  
Visual Channel ◽  
Low Light ◽  
Oil Droplets ◽  
Unusual Structure ◽  
Rod Photoreceptors ◽  
Light Levels ◽  
Ecological Differences

The keen visual systems of birds have been relatively well-studied. The foundations of avian vision rest on their cone and rod photoreceptors. Most birds use four cone photoreceptor types for color vision, a fifth cone for achromatic tasks, and a rod for low-light levels. The cones, along with their oil droplets, and rods are conserved across birds – with the exception of a few shifts in spectral sensitivity – despite taxonomic, behavioral and ecological differences. Here, however, we describe a novel photoreceptor in a group of New World flycatchers (Empidonax spp.) in which the traditional oil droplet is replaced with a complex of electron-dense megamitochondria surrounded by hundreds of small, orange oil droplets. These photoreceptors were unevenly distributed across the retina, being present in the central region (including in the fovea), but absent from the retinal periphery and the area temporalis. Many bird species have had their oil droplets and photoreceptors characterized, but only the two flycatchers described here (E. virescens and E. minimus) possess this unusual structure. We discuss the potential functional significance of the unique sub-cellular structure in these photoreceptors providing an additional visual channel for these small predatory songbirds.

The formation of the area centralis of the retinal ganglion cell layer in the chick

Development ◽  
1987 ◽  
Vol 100 (3) ◽  
pp. 411-420
Author(s):  
C. Straznicky ◽  
M. Chehade
Keyword(s):  
Ganglion Cell ◽  
Retinal Ganglion Cell ◽  
Ganglion Cell Layer ◽  
Cell Layer ◽  
Cell Loss ◽  
Retinal Ganglion ◽  
Retinal Periphery ◽  
Central Retina ◽  
Retinal Ganglion Cell Layer ◽  
Area Centralis

In adult domestic chickens, the neurones in the retinal ganglion cell layer are very unevenly disposed such that there is a sixfold increase in neurone density from the retinal edge to the retinal centre. The formation of the high ganglion-cell-density area centralis was studied on chick retinal wholemounts from the 8th day of incubation (E8) to 4 weeks after hatching (4WAH). The density of viable neurones and the number and the distribution of pyknotic neurones in the ganglion cell layer were estimated across the whole retina. Between E8 and E10, the distribution of neurones in the ganglion cell layer was anisodensitic with 53,000 mm-2 in the centre compared to 34,000 mm-2 in the periphery of the retina. Thereafter, a progressively steeper gradient of neurone density developed, which decreased from 24,000 mm-2 in the retinal centre to 6000 mm-2 at the retinal periphery by 4WAH. Neuronal pyknosis in the ganglion cell layer was observed between E9 and E17. From E11 onwards, consistently more pyknotic neurones were found in the peripheral than in the central retina. It was estimated that over the period of cell death approximately twice as many neurones died per unit area in the retinal periphery than in the centre. Retinal area measurements and estimation of neurone densities in the ganglion cell layer after the period of neurone generation and neurone death indicated differential retinal expansion, with more expansion in the peripheral than in the central retina. These observations allow us to conclude that the formation of the area centralis of the chick retina involves (1) slightly higher cell generation in the retinal centre, (2) higher rate of cell loss in the retinal periphery and (3) differential retinal expansion.

Changing patterns of vasculature in the developing amphibian retina.

1997 ◽  
Vol 200 (18) ◽  
pp. 2479-2492
Author(s):  
S A Dunlop ◽  
S R Moore ◽  
L D Beazley
Keyword(s):  
Ganglion Cell ◽  
Ganglion Cell Layer ◽  
Cell Layer ◽  
Retinal Vasculature ◽  
Tree Frog ◽  
Retinal Area ◽  
Branch Points ◽  
The Face ◽  
Area Centralis ◽  
Cell Densities

Patterns of vascularisation were examined in whole-mounted retinae from tadpole stages to adulthood in the tree frog Litoria moorei using perfusion with Indian ink. Changing cell densities in the underlying ganglion cell layer were studied in a parallel Cresyl-stained series. Throughout development, the vasculature was pan-retinal and the hyaloid vessel was prominent. In early tadpole stages, capillaries were arranged as a honeycomb, and their number increased at a rate sufficient to maintain high densities in the face of increasing retinal area; major arteries and veins condensed within the capillary network. By early post-metamorphic life, the retinal vasculature was remodelled by the loss of four-fifths of the capillaries; the reduction in their density was far greater than could be accounted for by continuing retinal growth. This loss resulted in a change from the honeycomb appearance to one with largely parallel vessels linked by fewer connecting ones, an arrangement that became increasingly pronounced. In post-metamorphic life, the number of branch points increased such that their density decreased only slightly in the face of considerable increases in retinal area. The density of branch points varied across the retina and changed with age. Initially, the vasculature was most dense centrally, but by mid-larval life densities were highest in two patches located in the mid-temporal and mid-nasal retina. Thereafter, the vasculature increasingly assumed gradients resembling an area centralis and visual streak, a profile that survived the vascular remodelling. The development of density gradients in the vasculature preceded that of cells in the ganglion cell layer, the latter appearing only following metamorphosis. However, in post-metamorphic life, the topographies of the retinal vasculature and cells in the ganglion cell layer were closely related.

Photoreceptors in a primitive mammal, the South American opossum, Didelphis marsupialis aurita: Characterization with anti-opsin immunolabeling

1995 ◽  
Vol 12 (5) ◽  
pp. 793-804 ◽  
Author(s):  
Peter K. Ahnelt ◽  
Jan Nora Hokoç ◽  
Pal Röhlich
Keyword(s):  
Morphological Diversity ◽  
South American ◽  
Oil Droplets ◽  
Oil Droplet ◽  
Photoreceptor Layer ◽  
Outer Segments ◽  
Single Cone ◽  
Area Centralis ◽  
American Opossum ◽  
Temporal Quadrant

AbstractThe retinas of placental mammals appear to lack the large number and morphological diversity of cone subtypes found in diurnal reptiles. We have now studied the photoreceptor layer of a South American marsupial (Didelphis marsupialis aurita) by peanut agglutinin labeling of the cone sheath and by labeling of cone outer segments with monoclonal anti-visual pigment antibodies that have been proven to consistently label middle-to-long wavelength (COS-1) and short-wavelength (OS-2) cone subpopulations in placental mammals. Besides a dominant rod population (max. = 400,000/mm2) four subtypes of cones (max. = 3000/mm2) were identified. The outer segments of three cone subtypes were labeled by COS-1: a double cone with a principal cone containing a colorless oil droplet, a single cone with oil droplet, and another single cone. A second group of single cones lacking oil droplets was labeled by OS-2 antibody. The topography of these cone subtypes showed striking anisotropies. The COS-1 labeled single cones without oil droplets were found all over the retina and constituted the dominant population in the area centralis located in the temporal quadrant of the upper, tapetal hemisphere. The population of OS-2 labeled cones was also ubiquitous although slightly higher in the upper hemisphere (200/mm2). The COS-1 labeled cones bearing an oil droplet, including the principal member of double cones, were concentrated (800/mm2) in the inferior, non-tapetal half of the retina. The two spectral types of single cones resemble those of dichromatic photopic systems in most placental mammals. The additional set of COS-1 labeled cones is a distinct marsupial feature. The presence of oil droplets in this cone subpopulation, its absence in the area centralis, and the correlation with the non-tapetal inferior hemisphere suggest a functional specialization, possibly for mesopic conditions. Thus, sauropsid features have been retained but probably with a modified function.

scholarly journals The Optimal Synapse for Sparse, Binary Signals in the Rod Pathway

2006 ◽  
Vol 18 (1) ◽  
pp. 26-44 ◽  
Author(s):  
Paul T. Clark ◽  
Mark C. W. van Rossum
Keyword(s):  
Transfer Function ◽  
Signal To Noise Ratio ◽  
Bipolar Cells ◽  
Signal To Noise ◽  
Low Light ◽  
Rod Photoreceptors ◽  
Light Levels ◽  
Noise Ratio ◽  
Simulated Images ◽  
Rod Bipolar Cells

The sparsity of photons at very low light levels necessitates a nonlinear synaptic transfer function between the rod photoreceptors and the rod-bipolar cells. We examine different ways to characterize the performance of the pathway: the error rate, two variants of the mutual information, and the signal-to-noise ratio. Simulation of the pathway shows that these approaches yield substantially different performance at very low light levels and that maximizing the signal-to-noise ratio yields the best performance when judged from simulated images. The results are compared to recent data.

Growth ofPseudotsuga menziesiiandTsuga heterophyllaseedlings along a light gradient: resource allocation and morphological acclimation

1997 ◽  
Vol 75 (9) ◽  
pp. 1424-1435 ◽  
Author(s):  
D. Mailly ◽  
J. P. Kimmins
Keyword(s):  
Leaf Morphology ◽  
Biomass Accumulation ◽  
Tsuga Heterophylla ◽  
Douglas Fir ◽  
Western Hemlock ◽  
Low Light ◽  
Growing Seasons ◽  
Light Levels ◽  
Light Gradient ◽  
Relative Light Intensity

Silvicultural alternatives that differ in the degree of overstory removal may create shady environments that will be problematic for the regeneration of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Gradients of light in the field were used to compare mortality, growth, and leaf morphological acclimation of two conifer species of contrasting shade tolerances: Douglas-fir and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Results after two growing seasons indicated that Douglas-fir mortality occurred mainly at relative light intensity (RLI) below 20%, while western hemlock mortality was evenly distributed along the light gradient. Height, diameter, and biomass of the planted seedlings increased with increasing light for both species but at different rates, and maximum biomass accumulation always occurred in the open. Douglas-fir allocated more resources to stem biomass than western hemlock, which accumulated more foliage biomass. Increases in specific leaf area for Douglas-fir seedlings occurred at RLI ≤ 0.4 and red/far red (R/FR) ratio ≤ 0.6, which appear to be the minimal optimum light levels for growth. Conversely, western hemlock seedlings adjusted their leaf morphology in a more regular pattern, and changes were less pronounced at low light levels. These results, along with early mortality results for Douglas-fir, suggest that the most successful way to artificially regenerate this species may be by allowing at least 20% of RLI for ensuring survival and at least 40% RLI for optimum growth. Key words: light, light quality, leaf morphology, acclimation.

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