Retina Of Different Species Research Articles

Stem cell-based retina models.

From the early days of cell biological research, the eye-especially the retina-has evoked broad interest among scientists. The retina has since been thoroughly investigated and numerous models have been exploited to shed light on its development, morphology, and function. Apart from various animal models and human clinical and anatomical research, stem cell-based models of animal and human cells of origin have entered the field, especially during the last decade. Despite the observation that the retina of different species comprises endogenous stem cells, most stem cell-related research in the human retina is now based on pluripotent stem cell models. Herein, systems of two-dimensional (2D) cultures and co-cultures of distinctly differentiated retinal subtypes revealed a variety of cellular aspects but have in many aspects been replaced by three-dimensional (3D) structures-the so-called retinal organoids. These organoids not only contain all major retinal cell subtypes compared to the physiological situation, but also show a distinct layering in close proximity to the in vivo morphology. Nevertheless, all these models have inherent advantages and disadvantages, which are expounded and summarized in this review. Finally, we discuss current application aspects of stem cell-based retina models and the specific promises they hold for the future.

Bipolar cell pathways for color vision in non-primate dichromats

Color vision in mammals is based on the expression of at least two cone opsins that are sensitive to different wavelengths of light. Furthermore, retinal pathways conveying color-opponent signals are required for color discrimination. Most of the primates are trichromats, and "color-coded channels" of their retinas are unveiled to a large extent. In contrast, knowledge of cone-selective pathways in nonprimate dichromats is only slowly emerging, although retinas of dichromats like mice or rats are extensively studied as model systems for retinal information processing. Here, we review recent progress of research on color-coded pathways in nonprimate dichromats to identify differences or similarities between di- and trichromatic mammals. In addition, we applied immunohistochemical methods and confocal microscopy to retinas of different species and present data on their neuronal properties, which are expected to contribute to color vision. Basic neuronal features such as the "blue cone bipolar cell" exist in every species investigated so far. Moreover, there is increasing evidence for chromatic OFF channels in dichromats and retinal ganglion cells that relay color-opponent signals to the brain. In conclusion, di- and trichromats share similar retinal pathways for color transmission and processing.

Canonical Wnt Signaling Controls Proliferation of Retinal Stem/Progenitor Cells in Postembryonic Xenopus Eyes

Vertebrate retinal stem cells, which reside quiescently within the ciliary margin, may offer a possibility for treatment of degenerative retinopathies. The highly proliferative retinal precursor cells in Xenopus eyes are confined to the most peripheral region, called the ciliary marginal zone (CMZ). Although the canonical Wnt pathway has been implicated in the developing retina of different species, little is known about its involvement in postembryonic retinas. Using a green fluorescent protein-based Wnt-responsive reporter, we show that in transgenic Xenopus tadpoles, the canonical Wnt signaling is activated in the postembryonic CMZ. To further investigate the functional implications of this, we generated transgenic, hormone-inducible canonical Wnt pathway activating and repressing systems, which are directed to specifically intersect at the nuclear endpoint of transcriptional Wnt target gene activation. We found that postembryonic induction of the canonical Wnt pathway in transgenic retinas resulted in increased proliferation in the CMZ compartment. This is most likely due to delayed cell cycle exit, as inferred from a pulse-chase experiment on 5-bromo-2'-deoxyuridine-labeled retinal precursors. Conversely, repression of the canonical Wnt pathway inhibited proliferation of CMZ cells. Neither activation nor repression of the Wnt pathway affected the differentiated cells in the central retina. We conclude that even at postembryonic stages, the canonical Wnt signaling pathway continues to have a major function in promoting proliferation and maintaining retinal stem cells. These findings may contribute to the eventual design of vertebrate, stem cell-based retinal therapies. Disclosure of potential conflicts of interest is found at the end of this article.

NPY in rat retina is present in neurons, in endothelial cells and also in microglial and Müller cells

NPY is present in the retina of different species but its role is not elucidated yet. In this work, using different rat retina in vitro models (whole retina, retinal cells in culture, microglial cell cultures, rat Müller cell line and retina endothelial cell line), we demonstrated that NPY staining is present in the retina in different cell types: neurons, macroglial, microglial and endothelial cells. Retinal cells in culture express NPY Y 1, Y 2, Y 4 and Y 5 receptors. Retina endothelial cells express all NPY receptors except NPY Y 5 receptor. Moreover, NPY is released from retinal cells in culture upon depolarization. In this study we showed for the first time that NPY is present in rat retina microglial cells and also in rat Müller cells. These in vitro models may open new perspectives to study the physiology and the potential pathophysiological role of NPY in the retina.

Distribution of caveolin isoforms in the lemur retina

The distribution of caveolin isoforms was previously evaluated in the retinas of different species, but has not yet been described in the primate retina. In this study, the distribution of caveolins was assessed via immunochemistry using isoform-specific antibodies in the retina of the black-and-white ruffed lemur. Here, we report the presence of a variety of caveolin isoforms in many layers of the lemur retina. As normal human retinas were not available for research and the retinas of primates are fairly similar to those of humans, the lemur retina can be utilized as a model for caveolin distribution in normal humans.

Eye defects in receptor protein-tyrosine phosphatase alpha knock-down zebrafish.

Receptor protein-tyrosine phosphatase alpha (RPTP alpha) is highly expressed in the developing retina of different species, but little is known about its function there. Here, we report that injection of antisense morpholinos in zebrafish embryos reduced RPTP alpha expression to almost nondetectable levels up to 3 days postfertilization (dpf). RPTP alpha was detectable again from 4 dpf onward. RPTP alpha knock-down resulted in smaller eyes. Examination of sections of the retina at different developmental stages demonstrated that already at 28 hours postfertilization (hpf) fewer cells were present in the retina of RPTP alpha-morpholino-injected embryos. At 3 dpf, the layered organization of the retina was absent. In addition, the morphology and labeling with an axon specific antibody, acetylated tubulin, demonstrated that most cells appeared to be undifferentiated. Strikingly, at 5 dpf the lamination of the retina was partially restored, concomitant with re-expression of RPTP alpha protein. Although cells in the retina were now differentiated, the layering of the retina remained disrupted and significant gaps were observed in the amacrine cell layer. Therefore, knock-down of RPTP alpha protein provides evidence that RPTP alpha is essential for normal retinal development.

The occurrence of three calcium-independent protein kinase C subspecies (δ, ε and ζ) in retina of different species

The localisation and immunochemical identification of three different forms of calcium-independent protein kinase C (PKC-ε, PKC-δ and PKC-ζ) in retinas of different species were analysed by immunohistochemistry and SDS-PAGE/Western blotting, respectively. More than one component of different molecular weights reacted with the polyclonal antibodies in all retinal samples though in all instances a component of molecular weight corresponding to the individual PKCs was recognised and could be eliminated or reduced by preincubating the primary antibodies with the peptides used to generate the antibodies. PKC-ζ immunoreactivity was exclusively associated with the inner segments of the photoreceptors in both mammalian (guinea-pig, rabbit, rat) and non-mammalian (goldfish, chick) retinas. PKC-ε immunoreactivity is present in bipolar cells, particularly in their terminals of mammalian and goldfish retinas. In the chick retina immunoreactivity for this enzyme and for PKC-δ was with the inner segments of the photoreceptors. The Müller cells in mammalian retinas and a sub-population of ganglion cells in the goldfish retina exhibited positive immunoreactivity for PKC-δ. The immunoreactivities for all the PKC isoenzymes were eliminated or drastically reduced when the primary antibodies were first princubated with the peptides used to generate the antibodies.

The occurrence of three isoenzymes of protein kinase C (α, β and γ) in retinas of different species

The localisation and immunochemical identification of 3 different forms of protein kinase C (PKC-α, PKC-β and PKC-γ) in retinas of different species were analysed by immunohistochemistry and SDS-PAGE-Western blotting, respectively. Only in some cases was there a correlation between the findings from each procedure. One reason for the lack of correlation could be the small amounts of PKC present in some retinas, which made detection possible only by first concentrating the antigen by SDS-PAGE and then carrying out Western blotting. Another possible reason is that an antibody recognises unknown antigens immunohistochemically, but, because of their specific characteristics, they are denatured when subjected to SDS-PAGE and Western blotting and therefore remain undetected. PKC-β immunoreactivity is present in rabbit, frog and goldfish retinas but absent from the rat retina. However, SDS-PAGE and Western blotting experiments showed that the PKC-β isoenzyme is absent from the fish retina but present in the rat retina. PKC-β immunoreactivity in rabbit retina is present in ganglion and/or amacrine cells; in the frog retina the enzyme is associated with some bipolar cells. In the goldfish retina, PKC-β is associated with a large population of cells in the ganglion cell layer as well as with some amacrine cell bodies. PKC-α is present primarily in bipolar cells of rat, fish and rabbit retinas and was not detected by immunohistochemistry or blotting experiments in the frog retina. SDS-PAGE and Western blotting of retinal extracts from different species showed that PKC-γ occurs in the rabbit where it was associated with ganglion and/or amacrine cells. While PKC-γ could be detected by blotting experiments in brain extracts from frog, rat and rabbit it was absent from both retina and brain extracts of the goldfish and frog and rat retinal extracts. However, PKC-γ immunoreactivity was associated with many amacrine cells in the frog retina as well as ganglion-like cells in the fish retina.

Possible neurotransmitter role of noradrenaline in the teleost retina

The role of dopamine as a neurotransmitter in the retina of different species has been clearly established; however, there is still some controversy as to whether noradrenaline (NA) is present as a neurotransmitter in this tissue. In this study, we show that, under controlled conditions, NA is present in the retina of goldfish at a concentration of 0.15 +/- 0.03 ng/mg protein and its biosynthetic enzyme, dopamine beta-hydroxylase shows an activity of 2.5 +/- 0.2 pmol NA/hr/mg protein. The amount of NA increases to 1.88 +/- 0.24 ng/mg protein in light adapted animals and decreases to undetectable levels in dark adapted ones. By contrast, dopamine-beta-hydroxylase levels are not affected by changes in light conditions. This finding provides further evidence in favor of a neurotransmitter role for NA in vertebrate retina.

Immunolocalization of cellular retinoic acid binding protein to müller cells and/or a subpopulation of GABA‐positive amacrine cells in retinas of different species

Retinoic acid (RA) and its specific binding protein, cellular RA binding protein (CRABP), are found in relative abundance in bovine and rat retinas. Since RA does not participate in the visual cycle, the presence of RA and its binding protein in retina suggests that they may be involved in other aspects of retinoid action. As an initial step in identifying the role of RA and its binding protein in retina, monoclonal antibodies were prepared against CRABP purified from bovine retina and used to localize this antigen by immunocytochemistry in retinas of different species. Human and monkey retinas showed specific cytoplasmic labeling of Müller cells. Cat, bovine, rabbit, rat, turtle, and chick retinas showed specific cytoplasmic labeling of some somata in the inner nuclear and ganglion cell layers and characteristic strata in the inner plexiform layer. Cat and bovine retinas also showed cytoplasmic labeling of Müller cells. Immunoreactivity in these species was absent with nonimmune serum or abolished when the antibodies were preabsorbed with purified antigen. Chameleon, goldfish, and frog retinas were nonreactive. We used double-labeling immunofluorescence experiments to determine if the CRABP-positive cells were also positive for known neurotransmitters or associated enzymes. CRABP-positive amacrine cells of cat, cow, rabbit, rat, and chick represented a subset of the more numerous gamma-aminobutyric acid (GABA)-positive amacrine cells. However, turtle CRABP-positive amacrine cells were negative for GABA despite the fact that turtle retina contains many GABA positive cells. CRABP-positive amacrine cells in rat retinas were not immunoreactive for glycine, choline acetyltransferase, somatostatin, or tyrosine hydroxylase.(ABSTRACT TRUNCATED AT 250 WORDS)

Cholinergic systems and multiple cholinergic receptors in ocular tissues.

Acetylcholine (ACh), choline acetyltransferases and cholinesterases occur in cornea, iris-ciliary body complex and retina of several vertebrates. In cornea, ACh may serve as a sensory transmitter as well as a local hormone, the function of which is not delineated. The function of ACh as the parasympathetic neurotransmitter at the iris and ciliary body is well established. The muscarinic receptors on the iris smooth muscle are similar to the muscarinic receptors (M2 type in two way classification) at other smooth muscles towards their interaction with agonists and antagonists. Binding studies using radiolabeled antagonists and their displacement by agonists indicate that muscarinic receptors in membranes of iris-ciliary body complex are heterogeneous indicating more than one subtype of muscarinic receptors. A subtype other than M2 receptors may occur at the presynaptic sites of parasympathetic nerves, which have yet to be investigated using specific agonists and antagonists. Cholinergic markers, choline acetyltransferase and acetylcholinesterase, differ quantitatively and qualitatively in retinas of different species. However, amacrine cells are cholinergic in all vertebrate species. Although they make up 1% of retinal neurons, they influence the activity of a majority of ganglion cells. Cholinergic effects in ganglia are mediated through nicotinic and muscarinic receptors. Both of these types of cholinergic receptors are heterogeneous. They have yet to be investigated for their subtypes using specific agonists and antagonists. Although the role of cholinergic retinal neurons in the processing of visual information is not known, their input to ganglion cells generally increases the rate of spontaneous activity or the number of action potentials in light-evoked responses. Thus, the cholinergic input seems to modify the overall neuronal input to the ganglion cells from the receptive fields. Endothelial cells of blood vessels contain muscarinic receptors, which are activated by ACh to cause relaxation. Although retinal blood vessels provide recognizable characteristic signs in diabetes mellitus and hypertensive disease, no information is available on the muscarinic receptors of these vessels.

The cone oil droplets of avian retinas

The cone oil droplets of 19 species of birds from 11 families were examined by microspectrophotometry. Individual droplets were expanded with mineral oil, suspended in aqueous glycerol, and absorbance spectra measured between 700 and 320 nm. A classification of oil droplets is proposed, in which objective measurements of their carotenoids are related to the size, position and visual appearance of the droplets under the microscope. Some droplets contain no carotenoid and are transparent at wavelengths longer than 320 nm. Other droplets appear colorless but contain carotenoids absorbing at 385 or 402 nm. The pale droplets that have traditionally been described as greenish contain a mixture of two carotenoids. All of these types are distinct from yellow and red droplets. Red droplets contain astaxanthin esters, and yellow droplets contain a carotenoid with a spectrum similar to zeaxanthin. The 402 nm chromophore is galloxanthin, a C 27 apo-carotenoid with 8 double bonds. The in vivo optical densities are 1–4 in the paler droplets, range up to about 8 in the yellow droplets, and can exceed 20 in the red droplets. All droplets that contain carotenoid can exhibit substantial absorption in the near u.v. The frequencies of the several droplet types in the retinas of different species suggests that these organelles respond readily to natural selection and may be involved in more than one function.

Glucagon immunoreactive neurons in the retina of different species.

Neurons displaying glucagon immunoreactivity were detected among the amacrine cells in the retina of goldfish, frog and pigeon. Nerve cell bodies were located in the inner nuclear layer with their processes ramifying in 2-3 more or less well-defined sublayers in the inner plexiform layer. The distribution of cell bodies and processes varied with the species. In pigeon retina two separate populations of glucagon immunoreactive neurons were found among the amacrine cells. In frog retina glucagon immunoreactivity was also discerned in cell bodies in the ganglion cell layer. These cell bodies sent processes outwards to the inner plexiform layer. No glucagon immunoreactive neurons were detected in the retina of the rat, rabbit, cat, pig or cow.

Somatostatin and VIP neurons in the retina of different species.

Neurons displaying somatostatin or vasoactive intestinal polypeptide (VIP) immunoreactivity were detected among the amacrine cells in the retina of baboon, cynomolgus monkey, squirrel monkey, cow, pig, cat, rabbit, guinea-pig, rat, mouse, frog and goldfish. Generally, immunoreactive cell bodies were located in the inner nuclear layer with processes ramifying in three more or less well-defined sublayers in the inner plexiform layer. The density of the sublayers and their location varied with the peptide and species investigated. In most cases there was a sublayer in the outermost part (Ramon y Cajal's sublamina 1) of the inner plexiform layer and this sublayer was usually the best developed. In some species a few somatostatin fibres were also detected in the outer plexiform layer, suggesting that some interplexiform cells contain somatostatin. In the baboon VIP was found exclusively in interstitial amacrine cells which have their cell bodies and processes entirely within the inner plexiform layer.

Modelling and simulation of vertebrate retina: extended network.

In a recent work (Oğuztöreli, 1980) a mathematical model for studying the neutral activities in a vertebrate retina has been investigated, where the basic retinal network involves interconnected five neurons of different kind. This model is general enough to cover a great variety of neurons in the same retina as well as in the retinas of different species. In the present work we deal with an extension of the basic network considered in (Oğuztöreli, 1980). This extended model contains interconnected twelve neurons: three receptor cells, two horizontal cells, two bipolar cells, two amacrine cells and three ganglion cells. The performance of the model under different conditions, and, the experimental determination of the system parameters are discussed. The background of the modelling and simulations can be found in (Oğuztöreli, 1979, 1980).

On the synaptogenic sequence in the chick retina.

AbstractStudy of the developing chick retina with the electron microscope revealed that dyad ribbon synapses begin to form in the inner plexiform layer before synaptic ribbons begin to appear in photoreceptor terminals of the outer plexiform layer. This centrifugal (inner to outer) sequence of synaptogenesis in the predominantly cone retina of the chick differs from the centripetal sequence that has been reported for the predominantly rod retinas of the mouse and rat. This difference does not favor the hypothesis, suggested by others, that the photo‐receptor may influence the maturation of inner retinal elements. The different patterns of synaptogenesis are discussed briefly with reference to anatomical differences between the retinas of different species.

Changes during Maturation and Metamorphosis in the Synaptic Organization of the Tadpole Retina Inner Plexiform Layer

ELECTROPHYSIOLOGICAL studies have shown that there is considerable variation in the degree of processing of visual information carried out by the retinas of different species, apparently correlated with anatomical difference between species. In amphibian and avian retinas with complex receptive fields there seem to be more conventional (amacrine cell) synapses than in mammalian retinas with simple organization. Moreover, the greater density of serial-conventional synapses, in which a presynaptic amacrine process is also postsynaptic to another amacrine process, is particularly striking in complex retinas. The density of ribbon (bipolar cell) synapses remains fairly constant from species to species1. The fact that tadpoles apparently make little use of visual cues, whereas adult frogs depend on them for survival, suggests that electrophysiological and anatomical retinal reorganization occurs during metamorphosis. There is some evidence for this2,3. Here I report changes in retinal synaptic organization found in Rana pipiens both during maturation and metamorphosis and as a result of a hormone pellet implantation.