The retinal projection to the cat pretectum

Retinal ganglion cells were labeled retrogradely by localized injections of HRP into different regions of the pretectum, tectum, and optic tract in 26 cats. Retinal projection zones in the pretectum were labeled anterogradely in the same cats by intravitreal injections of 3H-proline. This allowed the HRP injection sites to be located with respect to the retinal termination zones. The form of the projection zones from retina to pretectum was determined from serial reconstructions of either coronal or horizontal sections. The zones are best distinguished in horizontal sections, where they are seen as four roughly parallel strips on either side of the brain. They are more-or-less parallel to the anterior border of the tectum, and appear to traverse the entire width of the retinal projection to the tectum. Each zone is similar in form for the ipsilateral and contralateral projections, although the contralateral projection is thicker and denser. Binocular injections of 3H-proline showed that the projections from the two eyes were in register and did not interdigitate. Cells labeled by HRP injections in the anteromedial end of the pretectum were concentrated in the lower nasal quadrant of the contralateral retina, and the lower temporal quadrant of the ipsilateral retina. Posterolateral injections labeled cells in the upper quadrants. There is thus a rough retinotopic mapping along the elongated axis of the pretectum. When the distributions of ganglion cells labeled by HRP injections to different parts of the pretectum are combined, they show a concentration in both the visual streak and area centralis, and thereby reflect, at least qualitatively, the relative spatial distribution of the entire ganglion-cell population. About 85% of the retinal projection to the pretectum is contralateral. For all of the HRP injections, the spatial density of labeled cells was always low, accounting for no more than 3% of the total spatial density of ganglion cells in any retinal region. Several types of ganglion cells were labeled following injections to most regions of the pretectum; these included alpha, beta, and epsilon cells, as well as small-bodied cells showing a variety of morphologic forms. Alpha cells were labeled mainly from the anterolateral end of the pretectum, but other cell types were labeled from all injected regions. In the peripheral retina, 2% of the labeled cells were alpha cells, 32% were beta cells, 19% were epsilon cells, and the remaining 47% were small cells whose dendrites only occasionally filled to any significant extent.(ABSTRACT TRUNCATED AT 400 WORDS)     

Orientation of slit pupil and visual streak in the eye of the cat

The orientation of the visual streak of the cat's retina was compared to that of the long axis of the slit pupil in the same eye. In five paralyzed, anesthetized cats, the retinal projection to the superior colliculus was mapped with electrophysiological techniques. The orientation of the visual streak was estimated from the projection in visual space of the collicular region of high magnification which corresponds to the central projection of the streak. The angle by which the streak was tilted from absolute horizontal was always within one or two degrees of the angle by which the pupil axis was tilted from absolute vertical. This relationship was confirmed in three of the animals in which small retinal lesions were placed a known distance from the histologically determined axis of the streak. From the visual coordinated of these lesions, an independent estimate of the streak's orientation was obtained. In each case, the tilt of streak axis from horizontal differed by no more than 0.5° from the tilt of the pupil axis from vertical. The results support the hypothesis that planes containing the long axis of the cat's slit pupil are perpendicular to planes containing the long axis of the visual streak of the same eye.     

Cell death in the developing retinal ganglion cell layer of the wallaby Setonix brachyurus

The distribution and number of dying cells in the developing retinal ganglion cell layer of the wallaby Setonix brachyurus were assessed by using cresyl violet stained tissue. The density of dying cells has been expressed per 100 live cells for the entire retinal surface, data being presented as a grid of 500 micron squares. For statistical analysis, retinae were divided into 8 regions; dorsal, ventral, nasal, and temporal quadrants, each further divided into center and periphery. This method allowed comparison of the extent of cell death at different retinal locations as the high density area centralis of live cells developed temporal to the optic disk from 60 days onward. Between 30 and 70 days, dying cells were seen across the entire retina; beyond 100 days very few were seen. Initially, there was a significantly higher incidence of dying cells in the central retina compared to the periphery, whereas from 50 days this situation was reversed. Analysis of the central retina before and during area centralis formation consistently indicated a significantly lower number of dying cells per 100 live cells in temporal compared to other retinal quadrants. This differential pattern suggests that cell death lowers live cell densities less in the emerging area centralis than elsewhere, and therefore must play a part in establishing live cell density gradients. However, we cannot exclude the possibility that other factors are also instrumental. Indeed, factors such as areal growth (Beazley et al., in press) presumably operate at later stages since live cell density gradients continue to be accentuated even after cell death is complete. Numbers of dying cells peaked by 50 days, reaching approximately 1% of the live cell population. At this stage, counts were also maximal for live cells with values up to 30% above the adult range.     

The number and distribution of ganglion cells in the cat's retina

The number of ganglion cells in the cat's retina, and the pattern of their distribution over the retina, have been reinvestigated. Criteria are presented for the identification of ganglion cells in Nissl-stained whole mounts, most particularly for the distinction between small ganglion cells and neuroglial cells, by reference to retinas with no ganglion cells (obtained by nerve section) and to areas to retina containing a population of only small ganglion cells (obtained by optic tract section). Using these criteria, the number of ganglion cells was counted in four retinas (mean total 116,250). The number of large or "giant" cells (presumably the somas of Y-cells and of alpha-cells) varied from 4,200 to 7,100. Overall these cells comprised 4.0-6.3% of the total ganglion cell population. Their distribution over the retina showed a concentration around the area centralis, with a localized minimum density at the area centralis, and a concentration in the visual streak. These concentrations of large cells were quantitatively less than the concentrations of smaller cells in the area centralis and visual streak, so that the relative frequency of large cells was minimal (mean 1.6%) at the area centralis and increased steadily up to 5.5-6.9% in peripheral retina. Their relative frequency was distinctly lower along the visual streak than in peripheral retina above or below the streak.     

Heterogeneity of Synaptic Density in the Adult Pigmented Rabbit's Visual Cortex

In the adult pigmented rabbit, synaptic density in the lateral and medial part of the visual cortex was estimated along the projection area of the visual streak. A higher synaptic density distribution was observed in the lateral cortex (projection area of the nasal visual field) than in the medial cortex (projection area of the temporal visual field). This shows that there is a higher synaptic density in the region of the visual cortex receiving input from a retinal area with a high ganglion cell concentration than the area of the cortex receiving input from the retina with a low concentration of such cells. The regions of the visual cortex with higher and lower synaptic densities are the areas having a higher and lower magnification factor respectively.     

Number and distribution of retinal ganglion cells in anubis baboons (Papio anubis)

The number of retinal ganglion cells in Papio anubis was determined from light microscopic observations of wholemounted and vertically sectioned retinal tissue and electron microscopic examination of optic nerve cross sections. The total number of ganglion cells ranged from 1.41 to 1.81 million (mean 1.58 million, n = 6, SD = 169,927) per retina. The distribution of ganglion cells in cresyl violet stained wholemounts was also examined. Isodensity contours were almost circular perifoveally, but became horizontally elongated outside of the central retina, providing strong evidence for a visual streak. Ganglion cell somata within the streak were found to be significantly smaller than those outside of the streak in comparing regions of equal density. Finally, the distribution of blood vessels within the retina formed a watershed pattern with its crux centered on the ridge of this horizontally oriented high-density zone. Combined, these features indicate that anubis baboons possess a visual streak specialization as reported for lagomorphs, felines, and several primate species. Further, the visual streak appears more pronounced in anubis baboons than in any other primate species studied to date, with the possible exception of Homo sapiens, a similarly ground-dwelling/foraging and secondarily terrestrial species.     

Ganglion cell distribution in the albino rabbit's retina

The retinal ganglion cells of the albino rabbit are arranged in a nasotemporally oriented visual streak, with high concentration of ganglion cells along the lower margin of the myelinated band. Away from the visual streak the concentration of ganglion cells in isodensity zones decreases progressively. Contrary to that in the pigmented rabbit, the retina of the albino rabbit does not show an area centralis with a high proportion of large ganglion cells. The visual streak and the isodensity zones surrounding it showed a sparser population of ganglion cells than that in a pigmented rabbit's retina.     

Retinal ganglion cell layer of the Caspian seal Pusa caspica: topography and localization of the high-resolution area

Retinal topography, cell density and sizes of ganglion cells in the Caspian seal (Pusa caspica) were analyzed in retinal whole mounts stained with cresyl-violet. The topographic distribution of ganglion cells displayed an area of high cell density located in the temporal quadrant of the retina and was similar to the area centralis of terrestrial carnivores. It extended nasally, above the optic disk, as a streak of increased cell density. In different whole mounts, the peak cell density in the high-density area ranged from 1,684 to 1,844 cells/mm2 (mean 1,773 cells/mm2). The cell density data predict a retinal resolution of around 8.5 cycles/degree in water. A distinctive feature of the Caspian seal's retina is the large size of ganglion cells and the low cell density compared to terrestrial mammals. The ganglion cell diameter ranged from 10 to 58 μm. Cell size histograms featured bimodal patterns with groups of small and large ganglion cells. The large cells appeared similar to α-cells of terrestrial mammals and constituted 7% of the total ganglion cell population.     

Retinal ganglion cells in normal hamsters and hamsters with novel retinal projections. I. Number,distribution, and size

We examined the number, spatial distribution, and size of ganglion cells in the retinae of normal Syrian hamsters and hamsters with retinal projections to the auditory and somatosensory nuclei of the thalamus, induced by neonatal surgery. As revealed by retrograde filling with horseradish peroxidase, there are about 64,600 contralaterally projecting retinal ganglion cells (RGCs) and 1,700 ipsilaterally projecting RGCs in the retinae of normal adult hamsters. Contralaterally projecting RGCs are distributed throughout the retina and have two local density peaks located within a central streak of high RGC density that is oriented approximately along the nasal-temporal axis. RGC density falls above and below the central streak, with a steeper gradient towards the upper retina. Ipsilaterally projecting RGCs are diffusely distributed within a crescent at the inferotemporal retinal periphery and are most dense at the internal border of the crescent. The soma diameter of contralaterally projecting RGCs ranges from 6 to 25 μm; the diameter distribution is unimodal, with a peak in the 10–13 μm range and is skewed toward smaller values, with an elongated tail towards higher values. Contralaterally projecting RGCs tend to be smaller in regions of higher density. Ipsilaterally projecting RGCs tend to be larger than contralaterally projecting RGCs both globally and within the temporal crescent, and their size distributions tend to be less regular and less well related to local density. The retinae of neonatally operated hamsters with novel retinal projections to the auditory and somatosensory systems contain about one-fourth the normal number of contralaterally projecting RGCs, whose relative density distribution is approximately normal despite the drastic reduction of absolute RGC density. The range and distribution of RGC soma diameters are similar in normal and neonatally operated hamsters, and, in operated as in normal hamsters, contralaterally projecting RGC somata tend to be smaller in regions of higher density. Our results in normal hamsters suggest a role for intraretinal mechanisms in the determination of RGC size. Our findings in neonatally operated hamsters suggest that, despite the reduced number of RGCs in these animals, the same types of RGCs are found in the retinae of normal and neonatally operated hamsters. © 1995 Wiley-Liss, Inc.     

The retinal ganglion cell layer and visual acuity of the camel.

We examined the retinal ganglion cell layer of the dromedary camel, Camelus dromedarius. We have estimated that there are 8 million neurons in the ganglion cell layer of this large retina (mean area of 2,300 mm(-2)). However, only approximately 1 million are considered to be ganglion cells. The ganglion cells are arranged as two areas of high cell density, one in the temporal and one in the nasal retina. Densities of ganglion cells between these two high density regions is much lower, often less than 100 per mm(-2). In between these two high density regions, on the nasal side of the optic nerve head, is a unique and dense vertical streak of mostly non-ganglion cells; the function of this specialization is unknown. On the basis of ganglion cell density we estimate that the peak acuity in the dromedary camel is about 10 and 9.5 cycles per degree in the temporal and nasal high density regions respectively and falls to 2-3 cycles per degree in the central retina. Behavioral acuity was estimated for one bactrian camel and was found to be approximately 10 cyc deg(-1). The camel has a retina with a mean thickness of 104 microm, less than the 143 microm thickness that has previously been thought to be necessary for a retinal vasculature. Nevertheless, there is an extensive vitreal vasculature that does not appear to spare any retinal region.     

Starburst amacrine cells: morphological constancy and systematic variation in the anisotropic field of rabbit retinal neurons

Starburst amacrine cells of rabbit retina have been characterized previously in terms of their highly distinctive and regular dendritic geometry. They have been identified as probable cholinergic neurons of the retina and have been shown to direct output solely to ganglion cells. The objectives of this paper are to chart the variation of starburst amacrine cells across the retina, to register the morphological features which are held constant for individual cells, and to examine factors which may remain invariant for the population with change in retinal position. Starburst amacrine cells occur as two completely segregated mirror-symmetrical populations, type a and type b cells, separately serving OFF and ON pathways, respectively. They are treated here as two distinct subpopulations with very similar features. A characteristic morphological feature of both types, related to branching pattern and best seen in flat view, is the location of boutons in the distal annular zone. This is the effective zone of synaptic output, which is constant at 50 to 60% of dendritic field area, regardless of the cell's retinal location. Both type a and type b cells exhibit systematic increase in cell body size and dendritic field diameter, and systematic decrease in frequency of branching and of synaptic boutons with perpendicular distance from the visual streak. These rates of increase or decrease fall off considerably at distances greater than about 1.5 mm dorsal and ventral to the visual streak, but at this distance, the dendritic field diameters of cells in dorsal retina are about 65% larger than the diameters of cells in ventral retina. When type a and type b cells are closely compared, they are seen to differ in several respects. Branching patterns of type a and type b cells differ slightly, the latter being more highly branched, and the normalized branching frequency histograms, characteristic for each type, remain constant with changing retinal position. At the same retinal location type a cells always have larger dendritic field diameters than type b cells. This difference is significant in ventral retina, out to a distance of at least 4.5 mm from the streak. The maximum percentage difference in size occurs not at mid-visual streak, but about 1.5 mm ventral to the streak. The population statistics of dendritic field overlap and areal dendritic coverage have been calculated using published data on cell densities. It is concluded that overlap is extraordinarily high (k greater than 25), more than 10 times that calculated for retinal ganglion cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

The distributions of photoreceptors and ganglion cells in the California ground squirrel,Spermophilus beecheyi

The topographical distributions of photoreceptors and ganglion cells of the California ground squirrel (Spermophilus beecheyi) were quantified in a light microscopic study. The central retina contains broad, horizontal streaks of high photoreceptor density (40–44,000/mm²) and high ganglion cell density (20–24,000/mm²). The isodensity contours of both cell types are elliptical and oriented along the nasal-temporal axis. There are roughtly fivefold decreases in both photoreceptor and ganglion cell densities with increasing eccentricity, the lowest densities being found in the superior retina. Large transitions in cell density and retinal thickness occur across the linear optic nerve head. Rod frequency increases with increasing eccentricity, from 5 to 7% in the central retina to 15 to 20% in the periphery. Roughly 10% of the cones possess wide, dark-staining ellipsoids. These cones are uniformly distributed across the retina which suggests that they may belong to a separate cone class, possibly blue-sensitive cones. The ganglion cell soma size distribution is unimodal, with the majority of somata being 25–50 μm². Large ganglion cells (somata > 100 μm²) are rare in the central retina, but their frequency increases with increasing eccentricity. No evidence for separate size classes of ganglion cells was found. The gradual decrement of photoreceptor density across the ground squirrel retina suggests that there are only relatively small changes in acuity across much of the animal's visual space compared with species possessing either a narrow visual streak or fovea or area centralis.     

Quantitative analysis of the retinal ganglion cell layer in the ostrich,Struthio camelus

The total number, distribution and peak density of ganglion cells were evaluated in the Nissl-stained retina of the ostrich (Struthio camelus). The mean (n = 4) total number of retinal ganglion cells (RGC) was estimated at 2,274,128 (s.d. = 273, 152). The ostrich retina exhibited a prominent horizontal visual streak along which a central area located nasal to the pecten had a peak density of 9,500 cells/mm2. A high concentration of cells with a peak density of 2,646 cells/mm2 was also observed in the temporal retina, slightly dorsal to the visual streak. The results further showed that the ostrich eye has a 15-mm pupil entrance diameter, its mean axial length is 39.81 mm, the estimated retinal magnification factor is 0.4075 mm/deg and the maximum visual acuity along the well-defined visual streak was estimated to be 19.32 cycles/deg. The latter component of the retina might subserve vision along the horizon while the temporal region mediates binocular processing. The data also showed that the degree of retinal illumination in this bird could be comparable to that noted in some nocturnal species. The findings in this study suggest that the ostrich might not be restricted to diurnal activity.     

A quantitative analysis of the cat retinal ganglion cell topography.

A retinal ganglion cell distribution map has been prepared for the cresyl violet stained cat retina. It differs from previously published maps in revealing the visual streak to be more substantial and in showing a higher peak density of 9-10,000 ganglion cells/mm2 at the presumed visual pole. The map was used to obtain a minimum estimate of the retinal ganglion cell population as 217,000 cells, more than double the total previously reported. The problem of classifying the cells of the ganglion cell layer is discussed in detail and examples of criterion cells illustrated. The paper also includes an account of retinal mensuration (dimensions, area, etc.) and a discussion of the visual streak orientation.     

Distribution and coverage of beta cells in the cat retina

We have reexamined the retinal distribution and dendritic field dimensions of beta cells in the cat retina. Beta cells were labeled by retrograde transport from the A-layers of the lateral geniculate nucleus and distinguished from alpha cells on the basis of soma size. Dendritic fields of beta cells were visualized by intracellular staining in vitro. The fraction of cat ganglion cells that were beta cells varied with retinal location. Except near the area centralis, beta cells represented about half of all ganglion cells in the nasal hemiretina. They contributed as heavily as the other major ganglion cell classes to the nasal visual streak. In and near the area centralis and in the temporal retina, beta cells represented about two-thirds of all ganglion cells. The areas of beta cell dendritic fields were reciprocally related to beta cell density. For example, they were 3-fold smaller within the visual streak than at matched eccentricities outside it. For many cells, we could estimate both local beta cell density and dendritic field area. Coverage factor (dendritic field area × local density) remained constant at about 4 despite 100-fold variations in beta cell density, and was independent of eccentricity, nasotemporal location, or position relative to the visual streak. Analysis in terms of sampling theory suggests that the beta cell array is matched to X-cell spatial resolution so as to optimize acuity. The beta cell distribution and its systematic reflection in dendritic architecture predict acuity levels that apparently correlate well with actual visual performance across the cat's visual field. © 1996 Wiley-Liss, Inc.     

Asymmetry in the structure of average and large neurons of the ganglion layer of the frog retina

Morphometric analysis of the symmetry of middle and large ganglionic cells was performed on silver-impregnated retinal wholemounts of the frog. The nucleolus and the axis passing through the nucleolus in direction to optic disk were chosen as elements of symmetry characterizing the radial symmetry and bilateral one, respectively. It is demonstrated that the dendritic ramification angles of all cell types are smaller than 360 degrees and the angles of middle-type-GC are smaller than 180 degrees. In addition, their somata do not lie in the centre of the dendritic field, thus ganglionic cells have no radial symmetry. Directions of the axon and dendrites are opposite each other in the most of ganglionic cells, the terminals of dendrites being oriented from retinal centre to periphery in all quadrants of the retinal map. For estimation of bilateral symmetry the distance from the greatest remoted dendritic terminals to cell axis on the left and on the right from it was measured. Besides, the numbers of ramification knots and basal dendrites were counted. Most of ganglionic cells are asymmetrical in 2-3 mentioned structural parameters. Thus, the asymmetry in the structure of frog retinal neurons is rather norm than exception. Correlation between the asymmetry in ganglionic cell structure and functional asymmetry of their receptive fields is discussed.     

Retinal topography in the koala (Phascolarctos cinereus).

Nissl-stained retinal wholemounts were used to investigate the topographical organization of the ganglion cell layer of the koala (Phascolarctos cinereus); the visual resolution limit of this animal was subsequently estimated from retinal ganglion cell density data. Two types of cells could be differentiated on the basis of their size and staining characteristics: a subpopulation of presumed ganglion cells, consisting of medium to large cells with Nissl substance in the cytoplasm and pale uniformly staining nuclei, and a further subpopulation of small, densely staining cells. The latter group were presumed to be neuroglia and displaced amacrine cells. Iso-density contour maps were prepared from total cell counts and also counts of presumed ganglion cells; in all cases, the density of cells was greatest in the inferior retina where there was an area of peak density occurring as a poorly developed, horizontal streak that extended across the inferior retina. The inferior position of the streak in the koala contrasts with reports of the superior position of streaks in other marsupials. Peak cell densities of 2370 cells/mm2 and 1480 cells/mm2 were recorded for the total cell population and the presumed ganglion cell subpopulation, respectively. The latter value is equivalent to a visual resolution of 2.4 cycles/degree, based on sampling theory and a square packing paradigm, placing the koala close in visual performance to two other marsupials, the Australian Northern native cat and the American Virginia opossum.