Dorsotemporal Retina Research Articles

The organization of tyrosine hydroxylase-immunopositive cells in the sparrow retina

The purpose of this study was to identify tyrosine hydroxylase-immunopositive (TH+) cells in the sparrow retina using immunocytochemistry and quantitative analysis. All TH+ cells were conventional amacrine cells. Based on dendritic morphology, at least two types were observed. The first type had a single thick primary process that descended from the cell body and many densely beaded processes in substrata (s) 1, less beaded processes in s3, and spiny processes in s4/5 of the inner plexiform layer. The dendrites of the second type appeared similar in each layer, but it displayed several primary processes that spread laterally away from the soma before descending to the inner plexiform layer. The average density of TH+ cells was 37.48 ± 1.97 cells/mm2 (mean ± standard deviation; n = 4), and the estimated total number of TH+ cells was 3,061.25 ± 192.79. The highest and lowest densities of TH+ cells were located in the central dorsotemporal retina and periphery of the ventronasal retina, respectively. TH+ cells did not express calbindin-D28 K, calretinin, or parvalbumin. These results suggest that all TH+ cells in specific amacrine cell subpopulations are involved in retinal information processing in both the ON and OFF sublaminae in sparrow retina.

The two-step development of a duplex retina involves distinct events of cone and rod neurogenesis and differentiation

Unlike in mammals, persistent postembryonic retinal growth is a characteristic feature of fish, which includes major remodeling events that affect all cell types including photoreceptors. Consequently, visual capabilities change during development, where retinal sensitivity to different wavelengths of light (photopic vision), -and to limited photons (scotopic vision) are central capabilities for survival. Differently from well-established model fish, Atlantic cod has a prolonged larval stage where only cone photoreceptors are present. Rods do not appear until juvenile transition (metamorphosis), a hallmark of indirect developing species. Previously we showed that whole gene families of lws (red-sensitive) and sws1 (UV-sensitive) opsins have been lost in cod, while rh2a (green-sensitive) and sws2 (blue-sensitive) genes have tandem duplicated. Here, we provide a comprehensive characterization of a two-step developing duplex retina in Atlantic cod. The study focuses on cone subtype dynamics and delayed rod neurogenesis and differentiation in all cod life stages. Using transcriptomic and histological approaches we show that different opsins disappear in a topographic manner during development where central to peripheral retina is a key axis of expressional change. Early cone differentiation was initiated in dorso-temporal retina different from previously described in fish. Rods first appeared during initiation of metamorphosis and expression of the nuclear receptor transcription factor nr2e3-1, suggest involvement in rod specification. The indirect developmental strategy thus allows for separate studies of cones and rods development, which in nature correlates with visual changes linked to habitat shifts. The clustering of key retinal genes according to life stage, suggests that Atlantic cod with its sequenced genome may be an important resource for identification of underlying factors required for development and function of photopic and scotopic vision.

Functional segregation of retinal ganglion cell projections to the optic tectum of rainbow trout.

The interpretation of visual information relies on precise maps of retinal representation in the brain coupled with local circuitry that encodes specific features of the visual scenery. In nonmammalian vertebrates, the main target of ganglion cell projections is the optic tectum. Although the topography of retinotectal projections has been documented for several species, the spatiotemporal patterns of activity and how these depend on background adaptation have not been explored. In this study, we used a combination of electrical and optical recordings to reveal a retinotectal map of ganglion cell projections to the optic tectum of rainbow trout and characterized the spatial and chromatic distribution of ganglion cell fibers coding for increments (ON) and decrements (OFF) of light. Recordings of optic nerve activity under various adapting light backgrounds, which isolated the input of different cone mechanisms, yielded dynamic patterns of ON and OFF input characterized by segregation of these two fiber types. Chromatic adaptation decreased the sensitivity and response latency of affected cone mechanisms, revealing their variable contributions to the ON and OFF responses. Our experiments further demonstrated restricted input from a UV cone mechanism to the anterolateral optic tectum, in accordance with the limited presence of UV cones in the dorsotemporal retina of juvenile rainbow trout. Together, our findings show that retinal inputs to the optic tectum of this species are not homogeneous, exhibit highly dynamic activity patterns, and are likely determined by a combination of biased projections and specific retinal cell distributions and their activity states.

Topography of ganglion cells and photoreceptors in the sheep retina

Retinal topographies of some cell types and distribution of the tapetum lucidum in the sheep's eye were investigated in this study. The tapetum was observed macroscopically in the fundus. The topographical distributions of retinal ganglion cells (RGCs), cones, and rods were simultaneously analyzed in retinal whole mounts stained with cresyl violet. Short-wavelength-sensitive (S) cones were immunocytochemically identified in retinal whole mounts. The tapetum was located dorsal to the optic disc, with the nasal part elongated horizontally and the temporal part expanded dorsally. RGCs were distributed densely in the area centralis, horizontal visual streak, and anakatabatic area. The highest density in the area centralis was approximately 18,000 RGCs/mm(2). Cones showed high density in the horizontal area crossing the optic disc and dorsotemporal area, whereas rods showed high density in the horizontal area, which was greater in height than the horizontal area of high cone density. S cones showed high density in the dorsotemporal retina. The rod/cone ratios were high horizontally in the dorsal retina to the optic disc, with a mean value of 11:1. The cone/RGC and rod/RGC ratios were lower in the horizontal and dorsotemporal retina, and the rod/cone/RGC ratio was lowest in the area centralis (9:1:1). The retinal topographies and distribution of the tapetum were specialized in the horizontal and dorsotemporal fundus. This suggests that sheep have better visual acuity in horizontal and anteroinferior visual fields and that this specialization is related to the visual ecology of sheep.

Changes in thyroid hormone reception precede SWS1 opsin downregulation in trout retina

Rainbow trout undergo natural cone degeneration and thus are interesting models for examining mechanisms of neural degeneration. They have ultraviolet-sensitive (UVS) cones that are lost over most of the retina during development; only a small functional population remains in the dorsal retina. How this spatial distribution of UVS cones is maintained is unclear. Thyroxine (T4) induces UVS cone loss, and local thyroid hormone regulation was hypothesized to control UVS cone distribution. Thyroid hormone receptor alpha (TRalpha), thyroid hormone receptor beta (TRbeta) and Type 2 deiodinase (D2) regulate thyroid hormone exposure to target cells. Regional retinal expression of these genes was investigated during exogenous T4 treatment and natural smoltification of rainbow trout. Each retina from dark-adapted parr, T4-treated parr and natural smolts was divided into four quadrants, and total RNA was isolated. Quantitative real-time RT-PCR analysis demonstrated that all retinal quadrants had increased accumulation of TRbeta transcripts 2 days post-T4 treatment, corresponding to initiation of SWS1 opsin downregulation. Smolts exhibited decreased accumulation of TRalpha and TRbeta transcripts in all quadrants, but this effect was most pronounced in the dorso-temporal (DT) retinal quadrant where UVS cones persist. By contrast, in 2 day T4-treated parr, the DT quadrant showed increased expression of TRalpha and TRbeta. Furthermore, D2 transcripts decreased in the DT quadrant of T4-treated parr but increased in the DT quadrant of smolts. These results suggest that T4 upregulates TRbeta expression to initiate SWS1 opsin downregulation, while TRalpha and TRbeta downregulation occurs to prevent natural loss of UVS cones from the DT retina.

Retinal ganglion cells in the eastern newt Notophthalmus viridescens: Topography, morphology, and diversity

The topography and morphology of retinal ganglion cells (RGCs) in the eastern newt were studied. Cells were retrogradely labeled with tetramethylrhodamine-conjugated dextran amines or horseradish peroxidase and examined in retinal wholemounts. Their total number was 18,025 +/- 3,602 (mean +/- SEM). The spatial density of RGCs varied from 2,100 cells/mm(2) in the retinal periphery to 4,500 cells/mm(2) in the dorsotemporal retina. No prominent retinal specializations were found. The spatial resolution estimated from the spatial density of RGCs varied from 1.4 cycles per degree in the periphery to 1.95 cycles per degree in the region of the peak RGC density. A sample of 68 cells was camera lucida drawn and subjected to quantitative analysis. A total of 21 parameters related to RGC morphology and stratification in the retina were estimated. Partitionings obtained by using different clustering algorithms combined with automatic variable weighting and dimensionality reduction techniques were compared, and an effective solution was found by using silhouette analysis. A total of seven clusters were identified and associated with potential cell types. Kruskal-Wallis ANOVA-on-Ranks with post hoc Mann-Whitney U tests showed significant pairwise between-cluster differences in one or more of the clustering variables. The average silhouette values of the clusters were reasonably high, ranging from 0.52 to 0.79. Cells assigned to the same cluster displayed similar morphology and stratification in the retina. The advantages and limitations of the methodology adopted are discussed. The present classification is compared with known morphological and physiological RGC classifications in other salamanders.

Number and distribution of neurons in the retinal ganglion cell layer in relation to foraging behaviors of tyrant flycatchers

The tyrant flycatchers represent a monophyletic radiation of predominantly insectivorous passerine birds that exhibit a plethora of stereotyped prey capture techniques. However, little is known about their retinal organization. Using retinal wholemounts, we estimated the total number and topography of neurons in the ganglion cell layer in the generalist yellow-bellied elaenia (Elaenia flavogaster) and the up-hover-gleaner mouse-colored tyrannulet (Phaeomyias murina) with the optical fractionator method. The mean estimated total number of neurons in the ganglion cell layer was 4,152,416 +/- 189,310 in E. flavogaster and 2,965,132 +/- 354,359 in P. murina. Topographic maps of isocounting lines revealed a similar distribution for both species: a central fovea and a temporal area surrounded by a poorly defined horizontal streak. In addition, both species had increased numbers of giant ganglion cells in the dorsotemporal retina forming an area giganto cellularis. In E. flavogaster, these giant ganglion cells were also distributed across the nasal and ventral retinal peripheries, which is in agreement with the generalist habits of this species. However, in P. murina these cells were rarely seen along the nasal and ventral peripheries, possibly reflecting a lesser need to perceive movement because this species captures stationary insects resting on foliage. Thus, we suggest that the retinas of the tyrant flycatchers in the present study show a general common pattern of neuron distribution in the ganglion cell layer irrespective of their foraging habits. We also suggest that the distribution of giant ganglion cells is indicative of the visual requirements of the species.

Retinal topography of ganglion cells in immature ocean sunfish, Mola mola

The ocean sunfish, Mola mola, is the largest known bony fish. Based on prior studies of diet composition, it is considered to be a pelagic zooplanktivore. However, a recent study using acoustic telemetry revealed that they repeatedly dive to depths of >50 m during the day. We examined the distribution of cells within the retinal ganglion cell layer in the immature ocean sunfish (c.a. 50 cm total length) and estimated their visual acuity with respect to the main visual axis and visual fields. Visual acuity was between 3.37 and 4.41 cycles/degree. The region of highest cell density was located in the dorso-temporal retina, indicating that the main visual axis of ocean sunfish is directed towards the lower frontal portion of the visual field. This axis is considered beneficial for detecting prey items when the sunfish are migrating vertically through the water column, and in foraging behavior near the sea bottom.

Cone topography and spectral sensitivity in two potentially trichromatic marsupials, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus)

The potential for trichromacy in mammals, thought to be unique to primates, was recently discovered in two Australian marsupials. Whether the presence of three cone types, sensitive to short- (SWS), medium- (MWS) and long- (LWS) wavelengths, occurs across all marsupials remains unknown. Here, we have investigated the presence, distribution and spectral sensitivity of cone types in two further species, the quokka (Setonix brachyurus) and quenda (Isoodon obesulus). Immunohistochemistry revealed that SWS cones in the quokka are concentrated in dorso-temporal retina, while in the quenda, two peaks were identified in naso-ventral and dorso-temporal retina. In both species, MWS/LWS cone spatial distributions matched those of retinal ganglion cells. Microspectrophotometry (MSP) confirmed that MWS and LWS cones are spectrally distinct, with mean wavelengths of maximum absorbance at 502 and 538 nm in the quokka, and at 509 and 551 nm, in the quenda. Although small SWS cone outer segments precluded MSP measurements, molecular analysis identified substitutions at key sites, accounting for a spectral shift from ultraviolet in the quenda to violet in the quokka. The presence of three cone types, along with previous findings in the fat-tailed dunnart and honey possum, suggests that three spectrally distinct cone types are a feature spanning the marsupials.

Topographies of retinal cone photoreceptors in two Australian marsupials.

Microspectrophotometry indicates the presence of at least three cone visual pigments in two Australian marsupials, the fat-tailed dunnart (Sminthopsis crassicaudata) and honey possum (Tarsipes rostratus). Here we have examined the distribution of cone types using antisera, JH455 and JH492, that recognize short-wavelength-sensitive (SWS) and medium-to-long-wavelength-sensitive (M/LWS) cone opsins, respectively. SWS cones were concentrated in dorso-temporal retina in the dunnart with a shallow decreasing gradient extending to the periphery (2300-1500/mm2). In the honey possum, SWS cones showed a uniform distribution (2700/mm2), except for a slight increase in a narrow peripheral band (3100/mm2). In both species, M/LWS cones dominated and their distributions were similar to those of retinal ganglion cells: a horizontal streak in the dunnart (31,000-21,000/mm2) and a shallow mid-ventral to peripheral gradient in the honey possum (37,000-26,000/mm2). A low number of cones remained unlabeled when the antisera were combined revealing further minority cone population(s). We discuss cone distributions in relation to visual capabilities and requirements of the species.

Sensory organ development in cultured striped trumpeter larvae Latris lineata: implications for feeding behaviour

Teleost larvae are reliant on sensory organs for feeding, in particular for the detection and subsequent capture of prey. The present study describes the development of sensory organs in cultured striped trumpeter larvae, Latris lineata. In addition, a short-term feeding trial was conducted to examine the feeding response of larvae with different senses available; streptomycin sulfate was used to ablate the superficial neuromasts, and testing larvae in the dark prevented visually mediated feeding. Some non-visual senses are available to striped trumpeter larvae from an early age, as indicated by the presence of superficial neuromasts at hatching, and innervated olfactory organs and a developed inner ear from Day 3 post hatching. The neuromasts proliferated on the head and body with increasing larval age, and formation of the lateral line canal had commenced by Day 26 post hatching. Oral taste buds were not present in any of the larvae examined, up to Day 26 post hatching. At hatching, the retina was at an early stage in development, but differentiated rapidly and was presumed functional coincident with the onset of feeding on Day 7 post hatching. The ventro-temporal retina was the last to differentiate, and was distorted by the embryonic fissure, such that larval vision in the forward and upward visual field would be compromised. In contrast, the dorso-temporal retina was the first area to differentiate, and presumptive rod and double-cone development occurred in this area from Days 11 and 16, respectively, indicating that the forward and downward directed visual field is most suited for acute image formation. Larvae on Day 18 post hatching demonstrated increased feeding with an increase in the senses available, with 8 ± 3% of streptomycin-treated larvae feeding in the dark (chemoreception and inner ear mechanoreception only) and 27 ± 5% of untreated larvae feeding in the light (all senses available). It remains to be demonstrated whether there is an advantage to larval growth and survival by providing live feed during the dark phase in culture, facilitating feeding 24 hours per day.

Functional mapping of ultraviolet photosensitivity during metamorphic transitions in a salmonid fish, Oncorhynchus mykiss.

Ultraviolet visual sensitivity appears to be reduced and, possibly, lost during smoltification in anadromous populations of salmonid fishes. Similar changes occur in non-anadromous salmonids over a mass range that is associated with smoltification in their anadromous conspecifics. However, in sexually mature adult salmonids, ultraviolet-sensitive cones are present in the dorso-temporal retina, suggesting that ultraviolet sensitivity (i) may be regained with sexual maturity or (ii) might never be completely lost. Both smoltification and the transition to sexual maturity are regulated, in part, by the hormone thyroxine. Thyroxine treatment of juvenile Oncorhynchus mykiss results in precocial developmental changes that mimic smoltification, including a reduction of ultraviolet sensitivity. However, whether loss of ultraviolet sensitivity in O. mykiss or in other species of salmonids is complete during normal development (or in response to thyroxine treatment) is unclear. In the present study, we have 'mapped' topographically ultraviolet photosensitivity during natural and hormone-induced smoltification. Thyroxine-treated O. mykiss juveniles and anadromous steelhead O. mykiss smolts were examined for ultraviolet visual sensitivity by recording compound action potentials from the optic nerve. By selectively illuminating either the dorsal or the ventral retina, we have shown that the reduction of ultraviolet sensitivity occurs primarily in the ventral retina in both groups of fish. Ultraviolet sensitivity remains intact in the dorsal retina.

Developmental patterning of rod and cone photoreceptors in embryonic zebrafish.

Cone photoreceptors in the zebrafish retina are arranged in a crystalline lattice, with each spectral subtype at a specific position in the array; rod photoreceptors are inserted around the cones. Patterning events and developmental mechanisms that lead to the formation of the cone mosaic are not known. To begin investigating this issue, we examined the initial stages of opsin expression in zebrafish embryos by in situ hybridization with goldfish opsin cRNA probes to determine how and when the cone mosaic pattern arises. We found both differences and similarities in the spatiotemporal patterns of rod and cone development, which suggest the following: 1) Expression of opsin message (including rod opsin, blue and red cone opsins) was found in a ventral patch of retina located nasal to the choroid fissure. 2) The cone mosaic pattern was generated by a crystallization-like process initiated in the precocial ventral patch and secondarily in nasal retina, which then swept like a wave into dorsotemporal retina. 3) The remainder of the retina, suggesting that these precocial rods might differ from typical rods. 4) Developmental maturation of rods in zebrafish, as reflected by expression of opsin, may be accelerated compared to cones, which are thought to become postmitotic before rods. These data are consistent with a model in which lateral inductive interactions among differentiating photoreceptors lead to patterning of the array.

Retinal afferents to the tectum opticum and the nucleus opticus principalis thalami in the pigeon

The retinal afferents of the tectum opticum and the n. opticus principalis thalami (OPT) were studied with fluorescent tracers in pigeons. Injections into the tectum opticum revealed topographically related areas of high density labelling in the contralateral retina. In these areas up to 15,000 cells/mm2 were labelled. After tectal injections the soma sizes of labelled retinal ganglion cells in the area centralis ranged from 5 to 23 microns with a mean of 7.5 microns. Afferents from the ipsilateral retina could not be demonstrated. Injections into the OPT labelled neurons throughout the retina without a clear topographical relation to the locus of injection. The density never exceeded 150 cells per mm2. The soma size range was 8 to 35 microns with a mean of 14.6 microns. Independently of the injection area within the OPT, the red field in the dorsotemporal retina was always extremely sparsely labelled. The number of labelled ganglion cells in this area never exceeded 25 neurons/mm2. After OPT injections the average density of labelling per unit area was six times higher in the yellow than in the red field. The results confirm previous reports of a massive and topographically organized retinal projection onto the optic tectum. The projection onto the OPT was clearly smaller and with the retrograde tracing techniques in use, an orderly topography has not been demonstrated. The paucity of red field projections onto the OPT suggests that the role of the thalamofugal pathway in binocular integration is very limited.

Novel Area Serving Binocular Vision in the Retinae of Procellariiform Seabirds

Procellariiforms are pelagic seabirds which fly close to the sea surface and feed either by taking items from the surface or by shallow diving. The retinal ganglion cells in five species (Manx shearwater, Puffinus puffinus, Kerguelen petrel, Pterodroma brevirostris, great shearwater, Puffinus gravis, broad-billed prion, Pachyptila vittata, and common diving petrel, Pelecanoides urinatrix) were examined by Nissl staining and also by silver staining in the case of the common diving petrel. In all five species, a well-defined region in the dorsotemporal retina, close to the ora, was identified. This region is characterized by the presence of ganglion cells which are both regularly arrayed and larger than those found in the rest of the retina. These cells also have a large dendritic field of sparsely branched dendrites with much dendritic overlap between cells, thick axons, and dendrites confined to the proximal inner plexiform layer. Morphologically, they appear similar to the alpha cells of the retina in cats. It is suggested that the region containing these cells should be regarded as a retinal area, and the name area giganto cellularis is proposed. In the Manx shearwater, it is found that this novel area projects visually into the binocular field below the bill. Unlike previously described areas in avian retinae, it seems that this novel area is not concerned with high spatial resolution. It may function in the detection of objects on the sea surface and/or be concerned with the detection of the actual sea surface as a bird flies low over it.

Pathfinding and target selection of goldfish retinal axons regenerating under TTX-induced impulse blockade.

To define the extent to which impulse blockade interferes with the morphological changes of regenerating retinal axons during their growth through the tectum, axons were deprived of activity by repeated intraocular injections of TTX. At intervals between 24 and 189 days after optic nerve section (ONS), a defined group of TTX-silenced axons and of axons with normal activity (controls) were labeled by applications of HRP to the ventro- or dorsotemporal retina. The trajectories of these labeled axons were traced in DAB processed tectal wholemounts. As in controls, TTX-blocked axons went through a phase of exploratory growth at early regeneration stages (24 to 80 days after ONS). Coursing in abnormal routes, the axons initially distributed their growing endings widely over the tectum. Axons with and without activity extended side branches with growth cones and filopodia over all regions of the tectum. These ramifications were of similar dimensions for the TTX-blocked and control axons. Despite abnormal routes and branching over inappropriate territories, axons showed a preference for the rostral tectum. At late regeneration stages (120-189 days after ONS), axons had lost their side branches and their growth cones. Their preterminal segments exhibited striking bends, suggesting that they had undergone course corrections to achieve access to the retinotopic target. Axonal processes had disappeared from the caudal tectum, and the preferential accumulation of axons over the rostral tectum had increased. The majority of the TTX-blocked and control axons ended in terminal arbors at retinotopic regions. The labeled arbors of the TTX-group were no larger than those of the control group. The arbors of each group lay close together in a continuous cluster in the TTX-group as well as in two-thirds of the control group. In the other one-third of the control group, however, terminal arbors were aggregated into separate patches. The clusters of the TTX-blocked axons covered between 2.2 and 3.9% (mean 2.95%) of the tectal surface and the clusters and/or patches of active axons between 1.9 and 3.4% (mean 2.7%). Thus the terminal arbor clusters of the TTX-silenced axons were not significantly larger than those of the active axons. These data show that retinal ganglion cell impulse activity is required for neither the extension of side branches in the early exploratory phase of regeneration nor for the withdrawal of these branches nor for the establishment of target-directed routes and the deployment of normal-size terminal arbors at retinotopic loci.(ABSTRACT TRUNCATED AT 400 WORDS)

Asymmetric distribution of cells in the inner nuclear and cone mosaic layers of the goldfish retina

Cell counts in hematoxylin-stained, flat-mounted retinae revealed that the inner nuclear (INL) and cone mosaic layers (CML) of the goldfish retina contained a high density of cells along the temporal boundary between dorsal and ventral retina. Our findings indicate that the goldfish contains a region situated in the temporal retina in which the density of a wide variety of cell types, that span several retinal layers, is elevated. This study indicates that the dorsotemporal retina, which is the first retinal region to develop, contains the highest density of cells.

Dorsotemporal retinal ganglion cell axons of goldfish are located in the dorsal rather than ventral optic tract

Cobaltous-lysine was injected into the eyes of goldfish after a slit was made in the temporal retina. Cobalt-filled optic fibers were found in the dorsal optic tract and tracing them to their destinations revealed that they terminated rostrally in the peripheral edges of both the dorsal and ventral aspects of the optic tectum. Hence, axons from ganglion cells in the dorsotemporal retina are in the dorsal optic brachium rather than in the ventral optic brachium as was previously assumed.