Partial re-incorporation of corner cones in the retina of the Atlantic salmon (Salmo salar)

The distribution of corner (putative ultraviolet-sensitive) cones in the retina of Atlantic salmon was examined from the small juvenile (parr) stage to the adult stage (approaching sexual maturation). Small parr weighing approximately 5 g lacked corner cones everywhere except, mainly, near the dorsal periphery. Large fish ( approximately 5 kg) approaching sexual maturation showed corner cones in other areas of the dorsal retina besides the periphery. These areas, characterized by low resolving power, had similar corner cone densities to analogous areas in the smolt retina, suggesting that corner cones are formed in the periphery and incorporated into the dorsal retina of the Atlantic salmon sometime during the smolt stage. This incorporation is partial both in numbers of cones and in location (only the dorsal retina is affected). These findings contrast with the situation in rainbow trout where corner cones from existing mosaics are only partially lost from the ventral retina, if at all, and where production and incorporation of these cones into the dorsal retina occurs throughout life. Thus, in salmonids, there are at least two different strategies that determine retinal corner cone distributions.     

The topographical distribution of rods and cones in the adult chicken retina

The relative proportion of rods and cones (single and double) in the chicken retina was determined by counting these elements in each of nine pre-determined segments prepared as periodic acid-Schiff serial sections for rod (hyperboloid glycogen) and double cone (accessory cone paraboloid glycogen) identifications and as unfixed, flat preparations for cone determinations (colored oil droplets). Periodic acid-Schiff preparations revealed that rods and accessory cones were equal in number in all retinal segments except those located directly posterior to the posterior extremity of the pecten where the double cones out-numbered the rods in a ratio of 14 : 10. On the basis of oil-droplet pigmentation, double cones housing a golden-yellow droplet in their chief component and a small yellowish-green droplet in their accessory members were constantly observed to be twice as numerous as single cones (red droplet) in all retinal segments. These data reveal that the proportion of rods to double and single cones is 2 : 2 : 1, respectively, in all areas of the chicken retina except a posterior (lateral) segment where the ratio is 10 : 14 : 7. This area of greater cone concentration corresponds to the site of the temporal fovea of some birds and may represent the area of most acute vision in the fovea-free chicken retina.     

Spectral properties of short-wavelength (blue) cones in the turtle retina.

Long- and medium-wavelength cones in the turtle retina participate in complex neural interactions. They are coupled via excitatory pathways to other cones and receive negative feedback inputs from luminosity-type horizontal cells. Little information has been collected on the S- (short-wavelength or blue) cones because they are scarce in the turtle retina and of smaller dimensions compared to the other cone types. In this paper, flash sensitivity action spectra and photoresponses of seven turtle S-cones were measured in the dark-adapted state and during chromatic background illuminations. The desensitizing action of monochromatic background lights was not uniform across the visible spectrum. A red background was most effective in desensitizing the S-cones to long-wavelength stimuli while a blue background light produced its strongest action on the photoresponses elicited by short-wavelength stimuli. The effects of chromatic adaptation on the S-cone action spectrum and on the kinetics of the small-amplitude photoresponses suggested that the S-cones in the turtle retina were involved in complex neural interactions. These included excitatory inputs probably originating in neighboring L-cones and inhibitory long-wavelength inputs probably mediated by L-type horizontal cells.     

Signals from blue cones in "red-green" opponent-colour ganglion cells of the macaque retina.

Many opponent-colour ganglion cells of the macaque retina overt input from green and red-sensitive cones but often appear to lack input from blue-sensitive cones under usual test conditions. Comparisons of field and test action spectra of the responses of a selected group of such “red-green” ganglion cells, located in the perifovea and lacking rod input, indicate the presence of blue-sensitive cone signals having a suppressive influence upon the more direct and opponent signals from green- and red-sensitive cones to a fraction of these neurones, which seems to take place at a level distal to that of the ganglion cell. No cell excitation of inhibition mediated by blue-sensitive cone signals could be observed on intense yellow-adapting lights desensitizing the other two cone types. These neurones are characterized by a sharp fall-off in their short-wavelength test sensitivity and by a secondary shoulder in their short-wavelength field sensitivity. In addition, when cell responses overtly mediated by input from green-sensitive cones are depressed by the geometry of the stimuli, the suppressive signals from blue-sensitive cones also result in a large displacement towards the short wavelengths of the test peak sensitivity of such responses. This displacement can be described with acceptable accuracy by a two-stage model based on subtractive interactions between A₁-photopigments with λ_max at 445, 535 and 570 nm, which is qualitatively consistent with other spectral properties of these ganglion cells.     

Photoreceptor cell-specific localization of S-antigen in retina

Retinal S-antigen has been found to be localized in a specific photoreceptor cell population of squirrel (Tamias striatus) and rhesus monkey retina. In these cone-rich retinas S-antigen seems only to be present in the rods. Differential immunofluorescent staining of the photoreceptor cells was accomplished by using monospecific rabbit-anti bovine S-antigen antiserum, which exhibits very limited species specificity. In view of its co-localization with rhodopsin in rods and considering data from literature, we suggest that S-antigen is a major component of the phototransduction system in these cells.     

Peroxiredoxin 3 (PDRX3) is highly expressed in the primate retina especially in blue cones

Oxidative stress and loss of mitochondrial function have been implicated in age-related ocular diseases and thus studying enzymes involved in these processes may be of particular importance in these diseases. Peroxiredoxin III (PRDX3) is one of a family of six known peroxiredoxins which are known to protect cells against oxidative damage. PRDX3 is localized to the mitochondria and has been reported to be induced by hydrogen peroxide in aortic endothelial and lens epithelial cells. Using a highly specific commercially available antibody, PRDX3 was readily detected by immunoblot in monkey neural retina. Immunohistochemical analysis of human and monkey retina localized PRDX3 mainly to the photoreceptor inner segments, the outer and inner plexiform layers, and the ganglion cells. These are areas of known high mitochondrial content. In the monkey retina some of the cone inner segments were much more strongly labeled than others. Dual labeling experiments using specific anti-cone opsin antibodies determined that the high expressing cones were of the blue subtype. By contrast, in the human retina all of the cone inner segments were immunoreactive. This difference may be due to a postmortem induction of PRDX3 in the human sample. These results suggest that PRDX3 may be important in protecting photoreceptor mitochondria especially in blue cones.     

Pattern electroretinogram of the blue cones

In man the electroretinogram to pattern reversal stimuli (P-ERG) represents a cone response of the proximal retina, dominated by the cone mechanisms sensitive to red (R) and green (G). Additionally there is a cone mechanism sensitive to blue (B) which can be studied with and without steady exposure to yellow light. During exposure to a super-imposed uniform yellow background (576 nm) the transient P-ERG of the B cones is represented by potentials of small amplitude (< 1 V). The latency (peak time) of the response is about 30 ms longer than that of the midspectral (R and G) cones. Furthermore, the P-ERG of the B cones saturates at low luminances and exhibits a maximum amplitude at about 460 nm. Without yellow adaptation, the P-ERG of the B cones can be studied only with low-intensity stimuli of short wavelengths. Near threshold, both the long-latency response of the B cones and the short-latency response of the R and G cones are recorded simultaneously, forming a double-peaked wave shape. At suprathreshold luminances, even of short wavelength (435 nm) the P-ERG of the B cones is concealed by the larger short latency response of the midspectral cone mechanism.     

The ultrastructure of cones in the walleye retina

The ultrastructure of single and twin cone photoreceptors in the retina of the walleye was analyzed by scanning and transmission electronmicroscopy. The outer segment disks resemble those of other vertebrates. An accessory outer segment arises from the inner segment, makes frequent contacts with the outer segment proper, and may thus provide a bridge for signal transmission from outer to inner segment. A palisade of some 30 calycal processes surrounds and may provide structural support for the outer segment. The region of apposition between the inner segments of twin cones consists of a space of some 28 nm with no indication of gap junctions. The proximal quarter of the inner segment displays a profusion of some 50 lateral fins which increase the inner segment surface by 3-4 X and do not contact fins of neighboring cones. The fins surround a profusion of Müller cell microvilli and probably promote metabolic exchange between cones and Müller cells. Apart from differences in size and the presence of apposed inner segments, twin and single cones appear to be morphologically similar.     

The ratio of L cones to M cones in the human parafoveal retina.

We present psychophysically-based estimates of the relative numbers of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in the parafovea of three color-normal trichromats. Using methods previously applied to the fovea centralis, we obtained estimates of the relative numbers of L and M cones at retinal eccentricities of 1.0, 1.5, 2.0, 3.0, and 4.0 deg along the horizontal meridian of the temporal retina. Results for three observers indicate that the L to M cone ratio remains approximately invariant from the fovea to 4.0 deg eccentricity, with a mean ratio near 2:1.     

Photoreceptor topography of the retina in the New World monkey Cebus apella

The number and topographical distribution of photoreceptors was studied in whole-mounted retinas of Cebus apella. It was estimated a total of 48 million rods and 3.8 million cones. The average peak foveal cone density and the Nyquist Limit at the foveola were estimated as 169, 127 cells/mm(2) and 46.77+/-7.98 cyc/deg, respectively. A cone-enriched rim was found near the ora serrata, more noticeable in the nasal retina. Rod distribution was asymmetrical along horizontal and vertical meridians with a higher density in the dorsal retina. The rod/cone ratio was variable and asymmetrical along both meridians.     

Sensitivity of the blue-sensitive cones across the central retina

We measured increment thresholds up to 5° eccentricity using a 10′ dia flash viewed against 10⁴ td of 572-nm background. We found two distinct sensitivity profiles, one with flash wavelengths 410–470 nm and another with 520–580 nm. Spectral sensitivity plots indicate blue-sensitive cones and green-sensitive cones for the two profiles, respectively. Sensitivity of blue-sensitive cones is maximum at 1° eccentricity. Measurements at greater eccentricities are susceptible to adaptation to test field. The light-collecting area of blue-sensitive cones raised to a power follows the sensitivity profile of blue sensitive cones.     

Photoreceptor autophagy: effects of light history on number and opsin content of degradative vacuoles.

PURPOSE: To investigate whether regulation of rhodopsin levels as a response to changed lighting environment is performed by autophagic degradation of opsin in rod inner segments (RISs). METHODS: Groups of albino rats were kept in 3 lux or 200 lux. At 10 weeks of age, one group was transferred from 3 lux to 200 lux, another group was switched from 200 lux to 3 lux, and two groups remained in their native lighting (baselines). Rats were killed at days 1, 2, and 3 after switching. Another group was switched from 3 lux to 200 lux, and rats were killed at short intervals after the switch. Numbers of autophagic vacuoles (AVs) in RISs were counted, and immunogold labeling was performed for opsin and ubiquitin in electron microscopic sections. RESULTS: The number of AVs increased significantly after switching from 3 lux to 200 lux at days 1 and 2 and declined at day 3, whereas the reverse intensity change did not cause any increase. Early time points after change from 3 lux to 200 lux showed a significant increase of AVs 2 and 3 hours after switching. Distinct opsin label was observed in AVs of rats switched to 200 lux. Ubiquitin label was present in all investigated specimens and was also seen in AVs especially in 200-lux immigrants. CONCLUSIONS: Earlier studies had shown that an adjustment to new lighting environment is performed by changes in rhodopsin levels in ROSs. Autophagic degradation of opsin or rhodopsin may subserve, at least in part, the adaptation to abruptly increased habitat illuminance by removing surplus visual pigment.     

高原缺氧对兔视网膜Nogo表达的影响

目的:观察在高原环境下Nogo在北京青紫蓝兔视网膜中的表达和分布。方法:北京青紫蓝兔24只随机分为实验组20只,对照组4只,分别喂养于高原环境和亚高原环境中1,3,7,10,14d取出兔眼球,制成蜡片,应用免疫组化的方法检测视网膜中Nogo的表达及分布。结果:在高原环境下Nogo在兔视网膜中的表达增多,7d达到高峰,持续到10,14d下降,与对照组比较,差异有统计学意义。结论:在高原环境下,Nogo在视网膜急性缺血缺氧损伤可能发挥了重要作用。     

Development and degeneration of retina in rds mutant mice: ultraimmunohistochemical localization of opsin

In normal retina the developing photoreceptor cells first show presence of opsin over the distal ends of the ciliary protrusions. In a fully differentiated cell intense activity is seen over the rod outer-segment discs; some activity is also seen over the Golgi zone and near the distal ends of the inner segments but the other parts of the receptor cell appear negative. In the pigment epithelium opsin is seen only over phagosomes containing rod outer segment debris. In the homozygous rds mutant retina, developing receptor cells show opsin activity over the ciliary protrusions as in the normal. These ciliary protrusions grow in size and show increased opsin activity and presumably constitute the site of phototransduction in the mutant retina. Although typical disc structures remain lacking, variable amounts of immunopositive, irregular, membranous structures are occasionally observed. The inner segments in the mutant cells show very little immunoreactivity but the perikarya and the spherule terminals show increased immunoreactivity in comparison with the normal. At the onset of degeneration, some of the receptor cells in the mutant retina show extrusion of small, membrane-bound vesicles which are immunopositive for opsin. Some receptor cells undergoing lysis disintegrate and also add to the opsin-positive vesicular structures in the interphotoreceptor space. The vesicles are phagocytized by pigment epithelial cells. In older mutant mice at an advanced stage of degeneration, the receptor cells show reduced opsin activity. In heterozygous mutant mice the outer segments are reduced in length and the discs are abnormal in form. However, the intensity and the pattern of opsin localization in the outer segments and at other sites are similar to normal.     

Exon-skipping variant of RGR opsin in human retina and pigment epithelium

An extraneous exon-skipping mRNA encodes an altered form of a light-absorbing opsin in human retina and pigment epithelium (RPE). The predicted protein variant differs from full-length RPE-retinal G protein-coupled receptor (RGR) by having an in-frame deletion of exon 6, which contains the entire sixth transmembrane domain. To verify that the exon 6-deleted RGR protein (RGR-d) exists in human retinas, we have produced RGR-d antibody probes. In Western blot assays, the RGR-d protein was detected in retinas of a large proportion ( approximately 53%) of individual donors, including patients with age-related macular degeneration (AMD). The relative abundance of RGR-d varied significantly between individuals. The altered protein is expressed in RPE cells and has a more basal subcellular localization that is remarkably different from that of normal RGR opsin. The presence of this exon-skipping variant of RGR in humans may contribute to the progressive derangement of the RPE.     

Photoreceptor degeneration and loss of immunoreactive GABA in the Abyssinian cat retina.

GABA (gamma-amino butyric acid) and its synthesizing enzyme, GAD (glutamate decarboxylase; EC 4.1.1.15) were localized in the retina of Abyssinian cats homozygous for a recessively inherited retinal degenerative disorder which in several respects is similar to the human disease, retinitis pigmentosa. Clinically normal mongrel cats and heterozygous Abyssinian cats were studied for comparison. The GABA and GAD immunoreactive neurons of the heterozygous or young homozygous (clinically unaffected animals) had the same distribution and morphology as normal mongrel European type cats. The neuronal GABA immunoreactivity in both the inner and outer parts of the retina gradually disappeared in the course of the disease, with little or no loss of GAD immunoreactive neurons. Early in the disease, the changes were most severe in patches in the mid periphery of the eye and then spread both centrally and peripherally. Loss of photoreceptors was a prerequisite for the loss of GABA immunoreactivity. The observations show that retinal changes are not limited to the photoreceptors. The GABA loss is not likely to be due to a loss of neurons, because of the persistence of GAD immunoreactive neurons.