Photoreceptor topography in the duplex retina of the paddlefish (Polyodon spathula)

Retinal whole-mount preparations from the eyes of the North American paddlefish, Polyodon spathula, were examined with a combination of bright field and differential interference contrast microscopy. The entire retina was mapped and population counts of rod and cone photoreceptors were made at regular intervals throughout the retina. The retina is dominated by rods, but a significant percentage (ca. 38%) of the photoreceptors are cones. Mean cone packing density for the entire retina is 6,402+/-1,216 cones/mm2. There is a small (16%) but statistically significant difference between cone packing density in the dorsal retina (6,674+/-1,168 cones/mm2) and the ventral retina (5,745+/-1,076 cones/mm2). There is no region of unusually high cone concentration that might be construed as a fovea or a visual streak. Mean rod packing density for the entire retina is 10,271+/-1,205 rods/mm2. Except in the far periphery, where rods are less numerous, the density of rods is fairly uniform throughout the retina. The data are discussed with regard to paddlefish habitat and behavior.     

Immunohistochemical localization of iodopsin in the retina of the chicken and Japanese quail

Summary Localization of iodopsin in the retina of the chicken and Japanese quail was investigated immunohistochemically with the use of monoclonal antibodies (R1-R4) highly specific for R-photopsin (protein moiety of iodopsin). In paraffin sections of the retina, the outer segments of double cones (principal and accessory cones) and of one particular type of single cones were labeled with the antibodies. In addition, reticular cytoplasmic structures, probably representing the Golgi apparatus in a position close to the vitreous pole of the paraboloid and to the outer limiting membrane were intensely stained in the cone cells bearing an immunoreactive outer segment. In whole-mount preparations, 5 types of cone cells were identified according to the color of oil droplets, i.e., red, yellow, pale-green (principal member of double cones), pale-blue and clear, in addition to a sixth type devoid of an oil droplet (accessory member of double cones). The immunohistochemical analysis of the preparations revealed that R-photopsin (suggesting the presence of iodopsin) is localized in the outer segments of both the principal and accessory members of double cones, and the population of single cones displaying a red oil droplet. Other cones endowed with a yellow, blue or clear oil droplet were not labeled with the antibodies used. Similar results were obtained in the retina of the Japanese quail.     

Fine structure and development of the retina of the grenadier anchovy Coilia nasus (Engraulididae, Clupeiformes)

A study of the morphogenesis of the grenadier anchovy retina was undertaken using light and electron microscopy. Five developmental stages from prelarvae 3 days after fertilization to adult fish were studied. In addition to the general morphology of the eye and retina, special emphasis was given to the development of the photoreceptors and pigment epithelium (PE). The earliest retinae showing structural features indicative of a functioning eye are pure cone retinae composed of rows of alternating long and short cones forming a transient, tesselated pattern. At this stage there is a conventional PE containing melanin. In older stages cone rows are separated by the newly formed rods and by PE wedges filled with diffusely reflecting guanine crystallites. The findings are compared with the retinae of other engraulidids and with the development of teleost retinae in general. Moreover, the observed structural changes are discussed with respect to the photic habitat conditions of these anadromous fish that move between coastal waters, estuary, and river.     

The cone photoreceptors and visual pigments of chameleons

Visual pigments, oil droplets and photoreceptor types in the retinas of four species of true chameleons have been examined by microspectrophotometry. The species occupy different photic environments: two species of Chamaeleo are from Madagascar and two species of Furcifer are from Africa and the Arabian Peninsula. In addition to double cones, four spectrally distinct classes of single cone were identified. No rod photoreceptors were observed. The visual pigments appear to be mixtures of rhodopsins and porphyropsins. Double cones contained a pale oil droplet in the principle member and both outer segments contained a long-wave-sensitive visual pigment with a spectral maximum between about 555 nm and 610 nm, depending on the rhodopsin/porphyropsin mixture. Long-wave-sensitive single cones contained a visual pigment spectrally identical to the double cones, but combined with a yellow oil droplet. The other three classes of single cone contained visual pigments with maxima at about 480–505, 440–450 and 375–385 nm, combined with yellow, clear and transparent oil droplets respectively. The latter two classes were sparsely distributed. The transmission of the lens and cornea of C. dilepis was measured and found to be transparent throughout the visible and near ultraviolet, with a cut off at about 350 nm.     

Photoreceptors and visual pigments in the retina of the fully anadromous green sturgeon (<Emphasis Type="Italic">Acipenser medirostrus</Emphasis>) and the potamodromous pallid sturgeon (<Emphasis Type="Italic">Scaphirhynchus albus</Emphasis>)

Green sturgeon and pallid sturgeon photoreceptors were studied with scanning electron microscopy (SEM), microspectrophotometry and, in the case of the green sturgeon, retinal whole-mounts. The retinas of both species contain both rods and cones: cones comprise between 23% (whole-mount) and 36% (SEM) of the photoreceptors. The cone population of both species is dominated by large single cones, but a rare small single cone is also present. In both species, most rods have long outer segments of large diameter. A rod with a relatively thin outer segment is present in the pallid sturgeon retina. Mean cone packing density for the entire green sturgeon retina is 4,690±891 cones/mm², with the dorsal retina 14% more dense than the ventral. There is evidence for a horizontal visual streak just above and including the optic disc. Mean rod packing density is 16,006±1,668 rods/mm² for the entire retina, and fairly uniform throughout. Both species have rods with peak absorbance near 540 nm, as well as short-wavelength-sensitive cones (green: 464.5±0.7 nm; pallid: 439.7±3.5 nm); middle-wavelength-sensitive cones (green: 538.0±1.4 nm; pallid: 537.0±1.7 nm); and long-wavelength-sensitive cones (green: 613.9±3.0 nm; pallid: 617.8±7.6 nm).     

Bat Eyes Have Ultraviolet-Sensitive Cone Photoreceptors

Mammalian retinae have rod photoreceptors for night vision and cone photoreceptors for daylight and colour vision. For colour discrimination, most mammals possess two cone populations with two visual pigments (opsins) that have absorption maxima at short wavelengths (blue or ultraviolet light) and long wavelengths (green or red light). Microchiropteran bats, which use echolocation to navigate and forage in complete darkness, have long been considered to have pure rod retinae. Here we use opsin immunohistochemistry to show that two phyllostomid microbats, Glossophaga soricina and Carollia perspicillata, possess a significant population of cones and express two cone opsins, a shortwave-sensitive (S) opsin and a longwave-sensitive (L) opsin. A substantial population of cones expresses S opsin exclusively, whereas the other cones mostly coexpress L and S opsin. S opsin gene analysis suggests ultraviolet (UV, wavelengths <400 nm) sensitivity, and corneal electroretinogram recordings reveal an elevated sensitivity to UV light which is mediated by an S cone visual pigment. Therefore bats have retained the ancestral UV tuning of the S cone pigment. We conclude that bats have the prerequisite for daylight vision, dichromatic colour vision, and UV vision. For bats, the UV-sensitive cones may be advantageous for visual orientation at twilight, predator avoidance, and detection of UV-reflecting flowers for those that feed on nectar.     

Phosphorylation-independent Suppression of Light-activated Visual Pigment by Arrestin in Carp Rods and Cones

Visual pigment in photoreceptors is activated by light. Activated visual pigment (R*) is believed to be inactivated by phosphorylation of R* with subsequent binding of arrestin. There are two types of photoreceptors, rods and cones, in the vertebrate retina, and they express different subtypes of arrestin, rod and cone type. To understand the difference in the function between rod- and cone-type arrestin, we first identified the subtype of arrestins expressed in rods and cones in carp retina. We found that two rod-type arrestins, rArr1 and rArr2, are co-expressed in a rod and that a cone-type arrestin, cArr1, is expressed in blue- and UV-sensitive cones; the other cone-type arrestin, cArr2, is expressed in red- and green-sensitive cones. We quantified each arrestin subtype and estimated its concentration in the outer segment of a rod or a cone in the dark; they were ∼0.25 mm (rArr1 plus rArr2) in a rod and 0.6–0.8 mm (cArr1 or cArr2) in a cone. The effect of each arrestin was examined. In contrast to previous studies, both rod and cone arrestins suppressed the activation of transducin in the absence of visual pigment phosphorylation, and all of the arrestins examined (rArr1, rArr2, and cArr2) bound transiently to most probably nonphosphorylated R*. One rod arrestin, rArr2, bound firmly to phosphorylated pigment, and the other two, rArr1 and cArr2, once bound to phosphorylated R* but dissociated from it during incubation. Our results suggested a novel mechanism of arrestin effect on the suppression of the R* activity in both rods and cones.     

Outer retinal fine structure of the garfish Belone belone (L.) (Belonidae, Teleostei) during light and dark adaptation – photoreceptors, cone patterns and densities

In the present EM study, we investigate the retina of Belone belone , a visually-orientated marine predator living close to the water surface. In the duplex retina, four morphologically different cone types are observed: unequal and equal double cones, long single cones and triple cones. In the light-adapted state, five different cone patterns occur: row, twisted row, square, pentagonal and hexagonal patterns. High double cone densities are found ventro-nasally, ventro-temporally and dorso-temporally. Throughout the retina the double cone/single cone ratio is 2 : 1, in the ventral part, however, a 1 : 1 ratio occurs. In the vitreous body we found a curtain-like intraocular septum dividing the retina into two morphologically different regions. In most areas of the dark-adapted retina the cone patterns are absent at the ellipsoid level, with long single cones standing more vitreally in the light path than double cones. The mosaics are retained, however, in the outer nuclear layer. Typical dark adaptation, i.e. the retinomotor movements of the retinal pigment epithelium and photoreceptors in response to the dark adaptation (light change) is not present in the peripheral ventral and parts of the central ventral area. In both regions we found a twisted row pattern of cones having a vitreal position. The findings are discussed with respect to the photic habitat and feeding habits of this species.     

Oil Droplet Distribution and Colour Discrimination in the Pigeon

THE retina of the pigeon has at least four kinds of cones, which can be distinguished by the oil droplets which they contain. The colours of three of these are in the visible part of the spectrum; the fourth appears colourless or slightly green^1,2. These oil droplets are found in the paraboloid of the cones and can act as sharp cut-off filters that absorb practically all visible light below 600 (red), 550 (orange), 480 (yellow) and 430 (greenish) nm respectively. The four kinds of cones are not uniformly distributed across the retina and appear in different proportions in the four retinal zones (Table 1). Different pigeons have different proportions in the different quadrants, but their relative distribution is similar to the one shown here.     

Photoreceptor cell death, proliferation and formation of hybrid rod/S-cone photoreceptors in the degenerating STK38L mutant retina

A homozygous mutation in STK38L in dogs impairs the late phase of photoreceptor development, and is followed by photoreceptor cell death (TUNEL) and proliferation (PCNA, PHH3) events that occur independently in different cells between 7-14 weeks of age. During this period, the outer nuclear layer (ONL) cell number is unchanged. The dividing cells are of photoreceptor origin, have rod opsin labeling, and do not label with markers specific for macrophages/microglia (CD18) or Müller cells (glutamine synthetase, PAX6). Nestin labeling is absent from the ONL although it labels the peripheral retina and ciliary marginal zone equally in normals and mutants. Cell proliferation is associated with increased cyclin A1 and LATS1 mRNA expression, but CRX protein expression is unchanged. Coincident with photoreceptor proliferation is a change in the photoreceptor population. Prior to cell death the photoreceptor mosaic is composed of L/M- and S-cones, and rods. After proliferation, both cone types remain, but the majority of rods are now hybrid photoreceptors that express rod opsin and, to a lesser extent, cone S-opsin, and lack NR2E3 expression. The hybrid photoreceptors renew their outer segments diffusely, a characteristic of cones. The results indicate the capacity for terminally differentiated, albeit mutant, photoreceptors to divide with mutations in this novel retinal degeneration gene.     

Visual pigments, cone oil droplets and ocular media in four species of estrildid finch

A microspectrophotometric study was conducted on the retinal photoreceptors of four species of bird: cut-throat finches (Amadina fasciata), gouldian finches (Erythrura gouldiae), white-headed munias (Lonchura maja) and plum-headed finches (Neochmia modesta). Spectral characteristics of the photoreceptors in all four species were very similar. Rods contained a medium-wavelength-sensitive visual pigment with a wavelength of maximum absorbance at 502-504 nm. Four spectrally distinct types of single cone contained a visual pigment with wavelength of maximum absorbance at either 370-373 nm (ultraviolet-sensitive), 440-447 nm (short-wavelength-sensitive); 500 nm (medium-wavelength-sensitive) or 562-565 nm (long-wavelength-sensitive). Oil droplets in the ultraviolet-sensitive single cones showed no detectable absorption between 330 nm and 800 nm. Oil droplets in the short-, medium-, and long-wavelength-sensitive single cones had cut-off wavelengths at 415-423 nm, 510-520 nm and 567-575 nm, respectively. Double cones contained the visual pigment with wavelength of maximum absorbance at 562-565 nm observed in long-wavelength-sensitive single cones. Only the principal member of the double cone pair contained an oil droplet (P-type, cut-off wavelength at 414-489 nm depending on species and retinal location). Spectral transmittance of the intact ocular media of each species was measured along the optic axis. Wavelengths of 0.5 transmittance for all species were very similar (316-318 nm).     

Retinal Cone Photoreceptors of the Deer Mouse Peromyscus maniculatus: Development,Topography, Opsin Expression and Spectral Tuning

A quantitative analysis of photoreceptor properties was performed in the retina of the nocturnal deer mouse, Peromyscus maniculatus, using pigmented (wildtype) and albino animals. The aim was to establish whether the deer mouse is a more suitable model species than the house mouse for photoreceptor studies, and whether oculocutaneous albinism affects its photoreceptor properties. In retinal flatmounts, cone photoreceptors were identified by opsin immunostaining, and their numbers, spectral types, and distributions across the retina were determined. Rod photoreceptors were counted using differential interference contrast microscopy. Pigmented P. maniculatus have a rod-dominated retina with rod densities of about 450.000/mm² and cone densities of 3000 - 6500/mm². Two cone opsins, shortwave sensitive (S) and middle-to-longwave sensitive (M), are present and expressed in distinct cone types. Partial sequencing of the S opsin gene strongly supports UV sensitivity of the S cone visual pigment. The S cones constitute a 5-15% minority of the cones. Different from house mouse, S and M cone distributions do not have dorsoventral gradients, and coexpression of both opsins in single cones is exceptional (<2% of the cones). In albino P. maniculatus, rod densities are reduced by approximately 40% (270.000/mm²). Overall, cone density and the density of cones exclusively expressing S opsin are not significantly different from pigmented P. maniculatus. However, in albino retinas S opsin is coexpressed with M opsin in 60-90% of the cones and therefore the population of cones expressing only M opsin is significantly reduced to 5-25%. In conclusion, deer mouse cone properties largely conform to the general mammalian pattern, hence the deer mouse may be better suited than the house mouse for the study of certain basic cone properties, including the effects of albinism on cone opsin expression.     

Localization of visual pigment antigens to photoreceptor cells with different oil droplets in the chicken retina

Frozen semithin sections and unembedded retinal pieces were investigated by immunocytochemistry using two antibodies produced against visual pigments in our laboratory. One was a polyclonal serum (AO) raised against bovine rhodopsin, while the other one was a monoclonal antibody (COS-1) produced against an epitope present in a cone visual pigment. AO stained, as expected, rod outer segments; in addition it also recognized a single cone characterized by a deep yellow oil droplet as well as another single cone with a yellowish green oil droplet. In contrast, COS-1 labelled both members of the double cones; the principal member having a yellowish-green oil droplet and the accessory member. COS-1 also stained a single cone type exhibiting a large red oil droplet.     

Heterogeneous Maturation of Retina of the Pied Flycatcher Ficedula hypoleuca

A method is developed to determine the moment of establishment of functional maturity of cones by the appearance of their lipid droplet. Using this method, the process of differentiation of photoreceptor layer cells is traced and general regularities are elucidated of growth and maturation of the bifoveal retina of chicks of the pied flycatcher Ficedula hypoleuca. Development of retina occurs heterochronously; the first colored lipid droplets determining mature photoreceptors are photooptically revealed locally in the temporal retina area at the 5th day; at the 7th day, the lipid droplets appear within the limits of the central fovea; then the maturation wave moves from the temporal and central fovea towards periphery of retina. By the 14th day the entire area of retina turns out to be filled with mature photoreceptors. It is suggested that the predominant early maturation of photoreceptor cells of the temporal area is due to a necessity of the forestalling development of the retina parts providing the short-focus binocular vision that is the most important for establishment of chick alimentary behavior and start of hunting on their own after flight from the nest.     

Visual pigments, oil droplets, ocular media and cone photoreceptor distribution in two species of passerine bird: the blue tit (Parus caeruleus L.) and the blackbird (Turdus merula L.)

The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the visual pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (λ_max) of long-wavelength-sensitive single and double cone visual pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitivesingle cones of both species cut off wavelengths below 570–573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise λ_max of the long-wavelength-sensitive visual pigment is optimised for the visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their visual ecology. Accepted: 8 January 2000     

Transretinal ERG Recordings from Mouse Retina: Rod and Cone Photoresponses

There are two distinct classes of image-forming photoreceptors in the vertebrate retina: rods and cones. Rods are able to detect single photons of light whereas cones operate continuously under rapidly changing bright light conditions. Absorption of light by rod- and cone-specific visual pigments in the outer segments of photoreceptors triggers a phototransduction cascade that eventually leads to closure of cyclic nucleotide-gated channels on the plasma membrane and cell hyperpolarization. This light-induced change in membrane current and potential can be registered as a photoresponse, by either classical suction electrode recording technique^1,2 or by transretinal electroretinogram recordings (ERG) from isolated retinas with pharmacologically blocked postsynaptic response components^3-5. The latter method allows drug-accessible long-lasting recordings from mouse photoreceptors and is particularly useful for obtaining stable photoresponses from the scarce and fragile mouse cones. In the case of cones, such experiments can be performed both in dark-adapted conditions and following intense illumination that bleaches essentially all visual pigment, to monitor the process of cone photosensitivity recovery during dark adaptation^6,7. In this video, we will show how to perform rod- and M/L-cone-driven transretinal recordings from dark-adapted mouse retina. Rod recordings will be carried out using retina of wild type (C57Bl/6) mice. For simplicity, cone recordings will be obtained from genetically modified rod transducin α-subunit knockout (Tα^-/-) mice which lack rod signaling⁸.     

Genetic dissection reveals two separate pathways for rod and cone regeneration in the teleost retina

Development of therapies to treat visual system dystrophies resulting from the degeneration of rod and cone photoreceptors may directly benefit from studies of animal models, such as the zebrafish, that display continuous retinal neurogenesis and the capacity for injury-induced regeneration. Previous studies of retinal regeneration in fish have been conducted on adult animals and have relied on methods that cause acute damage to both rods and cones, as well as other retinal cell types. We report here the use of a genetic approach to study progenitor cell responses to photoreceptor degeneration in the larval and adult zebrafish retina. We have compared the responses to selective rod or cone degeneration using, respectively, the XOPS-mCFP transgenic line and zebrafish with a null mutation in the pde6c gene. Notably, rod degeneration induces increased proliferation of progenitors in the outer nuclear layer (ONL) and is not associated with proliferation or reactive gliosis in the inner nuclear layer (INL). Molecular characterization of the rod progenitor cells demonstrated that they are committed to the rod photoreceptor fate while they are still mitotic. In contrast, cone degeneration induces both Müller cell proliferation and reactive gliosis, with little change in proliferation in the ONL. We found that in both lines, proliferative responses to photoreceptor degeneration can be observed as 7 days post fertilization (dpf). These two genetic models therefore offer new opportunities for investigating the molecular mechanisms of selective degeneration and regeneration of rods and cones.     

Tetrachromatic colour vision in the duck (Anas platyrhynchos L.):microspectrophotometry of visual pigments and oil droplets

Summary Microspectrophotometric examination of the visual receptors of the duck,Anas platyrhynchos, revealed four types of single cone containing visual pigments absorbing maximally at about 420 nm, 452 nm, 502 nm and 570 nm. A single population of double cones contained the P570 in both members. Rods absorbed maximally at 505 nm.Within the single cones, three types of oil droplet, acting as cut-off filters, were identified by the wavelength at which 50% transmission occurred, approximately 580, 515 and 450 nm. A further droplet, transparent throughout the visible spectrum, was also found in a small population of single cones. A fifth droplet type with a variable cutoff between 475–500 nm was located in the principal member of the double cones.The optical density of the anterior half of the eye, established by spectrophotometry, was used, in conjunction with the visual pigment and oil droplet combinations found within intact cones, to estimate the relative spectral sensitivities of the major cone types within the retina.     

Morphology and density distribution of cone photoreceptor in the retina of the atlantic stingray,Dasyatis sabina

Light miscroscopy of the retina in the Atlantic stingray, Dasyatis sabina, reveal two distinct photoreceptor types. Histological criteria establish the two cell types as morphological rods and cones. The retina was studied through a sequential series of vertical sections in a protocol designed to evaluate the entire retina. By performing differential counts in multiple regions and expressing cones as a percent of the total photoreceptors in a domain, it was possible to determine relative cone density and distribution. Cone distribution varies throughout the retina in two patterns. First, relative cone density gradually decreases peripherally. Second, a cone-rich band occurs along the horizontal axis of the eye, extending from ora serrata to ora serrata. This structure appears to be a visual streak. Both distribution patterns are statistically significant and are consistent among animals regardless of age. © 1994 Wiley-Liss, Inc.     

Expression of cone-like properties by chick embryo neural retina cells in glial-free monolayer cultures

We report here that cells present in embryonic chick retinal monolayer cultures express differentiated properties characteristic of chick cones developing in vivo. Cell suspensions from 8-d chick embryo retina (a stage when photoreceptor differentiation has not yet started) were cultured for up to 7 d in low density, glial-free monolayers. Under these conditions, monopolar cells represent approximately 40% of the total number of process-bearing neurons. After 6 d in vitro, most of these monopolar cells showed morphological features reminiscent of developing chick cones. These features could be detected with phase-contrast microscopy, lectin cytochemistry, and transmission and scanning electron microscopy. Characteristic cone traits expressed by cultured monopolar cells included the following: (a) a highly polarized organization; (b) a single, short, usually unbranched neurite; (c) the polarized position of the nucleus close to the origin of the neurite; (d) characteristic cone inner segment features such as abundant free ribosomes, a polarized Golgi apparatus, a cluster of mitochondria distal to the nucleus, a big, membrane-bound, pigment-containing vacuole reminiscent of the "lipid droplet" characteristic of chick cones, and at least in some cases, a well-developed paraboloid; (e) the presence of a complex of apical differentiations including abundant microvilli and in some cases also a cilium-like process; and (f) the staining of the apical region of the cell with peanut lectin, which has been shown to be selective for chick embryo cones (Blanks, J.C., and L.V. Johnson, 1983, J. Comp. Neurol., 221:31-41; and Blanks, J.C., and L.V. Johnson, 1984, Invest. Ophthalmol. Visual Sci., 25:546-557). This pattern of differentiation achieved by 8-d chick retina cells after 6 d in vitro is similar to that shown by 14-d-old chick embryo cones in vivo. Outer segments are not present at this stage of development either in vivo or in vitro. This experimental system is now being used to search for cellular and molecular signals controlling survival and differentiation of cone cells.