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Mapping photoreceptor and postreceptoral labelling patterns using a channel permeable probe (agmatine) during development in the normal and RCS rat retina.

The aim of this study was to determine whether agmatine, a channel permeable probe, can identify photoreceptor dysfunction in the Royal College of Surgeons (RCS) retina at an earlier stage to that shown by apoptosis or anatomical markers, and also characterize the neurochemical development of the inner retina in the normal and degenerating rat. We used isolated retinas at different ages incubated in physiological media containing agmatine. Subsequently, postembedding immunocytochemistry was used to determine the number of labelled photoreceptors and the labelling pattern within postreceptoral neurons. Agmatine labelling patterns revealed a sequential development of retinal neurons beginning at postnatal day (PND) 11/12 with most horizontal cells, a few ganglion and amacrine cells, showing a strong signal. The neurochemical development progressed rapidly, and reflects to a large part the known distribution of glutamate receptors, with inner nuclear labelling being evident by PND14, continuing with the same pattern of labelling in adulthood for the control retina. The RCS retina showed markedly reduced agmatine labelling in the inner retina at PND20. A rapid increase in photoreceptor AGB labelling was evident during the degeneration phase. Multiple samples at PND14 and PND16 confirmed a significant increase of labelled photoreceptors in the RCS retina.

Agmatine↗

Distribution of muscarinic acetylcholine receptors on processes of isolated retinal cells.

Binding of propylbenzilylcholine mustard, a muscarinic acetylcholine receptor antagonist, to isolated retinal cells was examined with light microscopic autoradiography. Dissociation of the adult tiger salamander retina yielded identifiable rod, cone, horizontal, bipolar, amacrine/ganglion, and Müller cells. Preservation of fine structure was assessed with conventional electron microscopy. For all cell types, the plasmalemma was intact and free of adhering debris; in addition, presynaptic ribbon complexes were present in photoreceptor and bipolar axon terminals indicating that synaptic structures were retained. Specific binding to cell bodies and processes was analyzed separately by using morphometric and statistical techniques. The highest grain densities occurred on processes of amacrine/ganglion cells and axons and 2 degrees and 3 degrees dendrites of bipolar neurons. Bipolar cells, however, seemed to be a heterogeneous population because there was great variation in the density of binding sites on both their axons and distal dendrites. Intermediate levels of binding were found on bipolar 1 degree dendrites and horizontal cells. No specific binding was detected on Müller cells and most parts of photoreceptors. Comparisons between cells showed that grain densities were similar for bipolar axons and amacrine/ganglion cell processes but bipolar dendrites were richer in binding sites than horizontal cell dendrites. Thus, muscarinic receptors in the salamander retina are located on amacrine/ganglion, bipolar, and horizontal cells and primarily confined to the processes which compose the two synaptic layers. In the inner plexiform layer, muscarinic receptors reside on processes from all three inner retinal neurons: in the outer synaptic layer, receptors are only on second-order cells and are more numerous along bipolar than horizontal cell dendrites.

Animals↗

Protein gene product 9.5-immunoreactive neurons in the retina of striped dolphin (Stenella coeruleoalba) and Fraser dolphin (Lagenodelphis hosei).

This study demonstrates immunocytochemically that protein gene product 9.5 (PGP 9.5), a neuronal marker, is expressed by various populations of retinal cells in Stenella coeruleoalba (striped dolphin) and Lagenodelphis hosei (Fraser dolphin): one in the retinal ganglion cells and the other in the inner nuclear layer, resembling horizontal and amacrine cells. The specific distribution of PGP 9.5 in a dolphin closely resembles that in rodents and carnivores; however, some differences arise among these animals. In a dolphin's retina, for example, only a few of giant ganglion cells are immunoreacted while almost all the small ganglion cells are stained strongly. The processes of horizontal cells, identified according to their localization, appear not to connect entirely in a dolphin. Instead, PGP 9.5 positive cells are widely distributed in the small to moderate ganglion cells and have distinct processes which are ramified extensively in the outer plexiform layer in rodents and carnivores. The high levels of PGP 9.5 expressing in the inner part of dolphin retina, including ganglion cells and their axons as well as distinct sublamination in the inner plexiform layer, indicate that this molecule markedly influences the retinal system, possibly in visual connection. Although mammals have various visual behavior, i.e., living marine vs. terrestrial environment, and active during daytime vs. in the night, the retina is a common model to characterize the neurochemical properties.

Adaptation, Ocular↗

Morphology of horizontal cells in the retina of the capuchin monkey, Cebus apella: how many horizontal cell classes are found in dichromatic primates?

The morphology of horizontal cells was studied in the retina of dichromatic capuchin monkeys, Cebus apella. The cells were labeled with the carbocyanine dye, 1,1',dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), and the labeling was then photoconverted to a stable product by using a diaminobenzidine reaction. The sizes of cell body, dendritic field, and axon terminal, as well as the number of dendritic clusters and cone convergence, were measured at increasing distance from the fovea. Three distinct morphological classes of horizontal cells were identified. Their dendritic and axonal morphology resembles those of H1, H2, and H3 cells described in trichromatic primates. The size of the cell bodies, dendritic fields, and axon terminals of all cell classes increases towards retinal periphery. H3 cells have larger dendritic fields and more dendritic clusters than H1 cells. All labeled horizontal cells located in selected patches of retina were further analyzed to quantify the differences between H1 and H3 cells. H1 cells have smaller dendritic field area, smaller total length of primary dendrites, more dendritic branching points, and larger fractal dimension than H3 cells. We have distinguished H1 and H3 cells based solely in morphological criteria. Their physiology should be further analyzed with detail, but their presence in both dichromatic and trichromatic primates suggests that neither of them have a specialized role in the red-green color opponent channel of color vision.

Animals↗

Independent influences of rod adaptation on cone-mediated responses to light onset and offset in distal retinal neurons.

1. The influence of rod adaptation on cone-mediated intracellular responses of distal retinal neurons was examined in the larval tiger salamander. Rods were selectively stimulated by the use of 450-520 nm adapting stimuli too dim to appreciably influence cones. Cones were primarily stimulated with the use of deep-red stimuli (maximally sensitive to wavelengths greater than 650 nm). The qualitative properties of rod-cone interaction were assessed with the use of several different photic-stimulus paradigms. 2. Confirming results of prior studies, we showed that rod adaptation changed the time course of cone-mediated responses to the onset of square-wave light flashes in horizontal cells (HCs); rod adaptation had no similar influence in other distal retinal neurons. Rod adaptation also enhanced cone-mediated responses to rapid flicker in cones, hyperpolarizing (HPBCs) and depolarizing (DPBCs) bipolar cells, as well as HCs. 3. We also examined the influence of rod-stimulating background fields on cone-mediated responses to slow (approximately 1-Hz) flicker composed of sawteeth with a rapid onset (ramp offset) or with a rapid offset (ramp onset). Such stimulation maintained a constant state of long-term adaptation while providing cones with transient-ON or transient-OFF stimulation. 4. Rod adaptation speeds up the response of HCs to rapid onset and increases response amplitude. Rod adaptation had no reliable influence on response to rapid onset in cones or bipolar cells. 5. Rod adaptation enhanced the amplitude of responses of HCs to rapid offset without altering response time course. 6. Rod adaptation greatly enhanced the amplitude of DPBC responses to rapid offset having no reliable influence on the time course of the response. 7. Rod adaptation caused responses of HPBCs to rapid offset to become much more transient. Rod backgrounds had a similar but smaller and less reliable influence on the response of cones to rapid offset. 8. The foregoing results indicate that rod adaptation exerts a minimum of two separate influences on cone-mediated responses in distal amphibian retina. Changes at light onset must reflect the operation of a mechanism that alters response kinetics of the HC membrane. Changes at light offset reflect the operation of a separate mechanism or set of mechanisms that must act in part presynaptically to the HCs.

Adaptation, Physiological↗

Microtubule-associated proteins characteristic of embryonic brain are found in the adult mammalian retina.

We have used monoclonal antibodies against each of the major mammalian brain microtubule-associated proteins (MAPs), MAP1, MAP2, MAP3, MAP5, and tau, to study the timing of appearance and the cytological distribution of these proteins during the development of the rat retina. Western blots of adult rat retina reveal MAPs that are characteristic of embryonic brain, i.e., MAP5 and the low-molecular-weight forms of MAP2 (MAP2c) and tau (juvenile tau). At the onset of neuronal differentiation within the embryonic retina, MAP5, MAP3, MAP2c, and tau are found in the perikarya or extending axons of ganglion cells. High-molecular-weight MAP2, a dendrite marker, does not appear in the retina until the second day of postnatal development, when ganglion cell dendrites ramify within the inner plexiform layer. MAP1, which is characteristic of adult brain, does not appear in the retina until 1 week after birth, and is limited to ganglion cells and their processes. In the adult retina, MAP5 and MAP2c are concentrated within the inner segments and cell bodies of photosensitive cells, whereas tau is found in horizontal cells and more internal cell layers. Since photosensitive cells are unique among retinal neurons in their constant regeneration of their primary processes, the photoreceptive outer segments, both MAP5 and MAP2c appear not only to be involved in events associated with the embryonic differentiation and growth of neurites, but also in process regeneration in adult neurons that maintain some embryonic characteristics.

Age Factors↗

Three-dimensional model of angiogenesis: coculture of human retinal cells with bovine aortic endothelial cells in the NASA bioreactor.

Ocular angiogenesis is the leading cause of blindness and is associated with diabetic retinopathy and age-related macular degeneration. We describe, in this report, our preliminary studies using a horizontally rotating bioreactor (HRB), developed by the National Aeronautics and Space Administration (NASA), to explore growth and differentiation-associated events in the early phase of ocular angiogenesis. Human retinal (HRet) cells and bovine endothelial cells (ECs) were cocultured on laminin-coated Cytodex-3 microcarrier beads in an HRB for 1-36 days. Endothelial cells grown alone in the HRB remained cuboidal and were well differentiated. However, when HRet cells were cocultured with ECs, cordlike structures formed as early as 18-36 h and were positive for von Willebrand factor. In addition to the formation of cords and capillary-like structures, ECs showed the beginning of sprouts. The HRB seems not only to promote accelerated capillary formation, but also to enhance differentiation of retinal precursor cells. This leads to the formation of rosette-like structures (which may be aggregates of photoreceptors that were positive for rhodopsin). Upregulation of vascular endothelial growth factor and basic fibroblast growth factor was seen in retinal cells grown in the HRB as compared with monolayers and could be one of the factors responsible for accelerated capillary formation. Hence, the HRB promotes three-dimensional assembly and differentiation, possibly through promoting cell-to-cell interaction and/or secretion of growth and differentiation factors.

Animals↗

Specification of the retinal fate of mouse embryonic stem cells by ectopic expression of Rx/rax, a homeobox gene.

With the goal of generating retinal cells from mouse embryonic stem (ES) cells by exogenous gene transfer, we introduced the Rx/rax transcription factor, which is expressed in immature retinal cells, into feeder-free mouse ES cells (CCE). CCE cells expressing Rx/rax as well as enhanced green fluorescent protein (CCE-RX/E cells) proliferated and remained in the undifferentiated state in the presence of leukemia inhibitory factor, as did parental ES cells. We made use of mouse embryo retinal explant cultures to address the differentiation ability of grafted ES cells. Dissociated embryoid bodies were treated with retinoic acid for use as donor cells and cocultured with retina explants for 2 weeks. In contrast to the parental CCE cells, which could not migrate into host retinal cultures, CCE-RX/E cells migrated into the host retina and extended their process-like structures between the host retinal cells. Most of the grafted CCE-RX/E cells became located in the ganglion cell and inner plexiform layers and expressed ganglion and horizontal cell markers. Furthermore, these grafted cells had the electrophysiological properties expected of ganglion cells. Our data thus suggest that subpopulations of retinal neurons can be generated in retinal explant cultures from grafted mouse ES cells ectopically expressing the transcription factor Rx/rax.

Animals↗

GABAA and GABAC receptors in adult porcine cones: evidence from a photoreceptor-glia co-culture model.

1. Edge contrast enhancement is an integrated visual function based on the complex centre-surround organization of the cone photoreceptor light response. While centre responses result from direct light activation, surround responses are thought to result from lateral inhibition mediated by horizontal cells. This feedback signal has been attributed to GABAA receptors which have been found in lower vertebrate cones. 2. In order to study the GABA response of adult mammalian photoreceptors, we designed a culture system consisting of isolated photoreceptors seeded on a layer of retinal glial cells. Mature rods and cones required the presence of Muller glial cells to survive and develop neurites; they degenerated in the absence of glial cells. 3. Cone photoreceptors generated large GABA responses whereas rod photoreceptors did not respond to GABA applications. 4. Cone GABA responses consisted of two distinct components, one suppressed by the GABAA receptor blockers bicuculline and SR95531, and the second by the GABAC receptor antagonists TPMPA and imidazole-4-acetic acid (I4AA). Pentobarbital greatly increased the GABAA receptor component whereas it did not affect, or even reduced, the GABAC receptor component. During long GABA applications, GABAA receptor currents desensitized by 78%, contrasting with the sustained GABAC response. 5. Expression of GABAC receptors in cone photoreceptors was confirmed by anti-rho-subunit immunolabelling of porcine retinal sections. 6. These results indicate that both GABAA and GABAC receptors may participate in the feedback synapse from horizontal cells to cone photoreceptors in the mammalian retina.

Animals↗

Radial asymmetry in the topography of retinoblastoma. Clues to the cell of origin.

Retinoblastoma is a malignancy of the human developing retina. In situ as well as in vitro studies have attributed tumoral histogenesis either to a primitive retinoblast with neuronal and glial differentiation potentials, or to a photosensory progenitor cell. Here it is shown in vivo that the retinal topography of 457 retinoblastoma and retinoma foci is radially asymmetrical. Tumor density appears to mimic the horizontal visual streak characteristic of red/green cone cell distribution. Such a non-random distribution seems to invalidate the hypothesis of a primitive multipotential neuroblast as the unique source of retinoblastoma and may support the view that retinoblastoma evolves along the cone cell lineage.

Eye Neoplasms↗

Kainic acid induces sprouting of retinal neurons.

The neurotoxin kainic acid caused dose-dependent morphological changes in horizontal cells of the retinas of adult cats and rabbits. High concentrations of kainic acid killed the cells, but when exposed to sublethal doses they contracted their dendritic fields and sent sprouting processes into the inner retina. It appears that kainic acid can induce neuronal growth as well as degeneration and that the potential for morphological plasticity is still present in neurons of the adult mammalian retina.

Animals↗

Functional-anatomical studies on the terminal nerve projection to the retina of bony fishes.

We have explored the structure and actions of terminal nerve (TN) fibers in the teleostean retina, the most accessible of TN projections. Using immunocytochemistry we have shown that the goldfish TN contains neuropeptides related to the molluscan cardioexcitatory peptide (FMRFamide) as well as luteinizing hormone-releasing hormone (LHRH). Retinal TN terminals were found upon major dendrites in the distal inner plexiform layer and neuronal cell bodies in the amacrine cell layer. Electron-microscopic double-labeling revealed TN terminals applied to the surface of [3H]-dopamine-, glycine-, and gamma-aminobutyric acid (GABA)-accumulating cells. Synthetic LHRH and FMRFamide at less than 1 microM modified spontaneous and light-evoked activity of ganglion cells in isolated superfused goldfish retina, especially during the active breeding season. Salmon(I)-LHRH was 10-30 times as potent as mammalian LHRH and caused rapid, prolonged desensitization. We conclude that LHRH- and FMRFamide-like peptides may be released by retinal TN endings, probably in concert with reproductive activity, and that they act independently through horizontal and/or amacrine cell pathways to modify visual information processing in the retina.

Animals↗

Development of the outer retina in the mouse.

Mice represent a valuable species for studies of development and disease. With the availability of transgenic models for retinal degeneration in this species, information regarding development and structure of mouse retina has become increasingly important. Of special interest is the differentiation and synaptogenesis of photoreceptors since these cells are predominantly involved in hereditary retinal degenerations. Thus, some of the keys to future clinical management of these retinal diseases may lie in understanding the molecular mechanisms of outer retinal development. In this study, we describe the expression of markers for photoreceptors (recoverin), horizontal cells (calbindin), bipolar cells (protein kinase C; PKC) and cytoskeletal elements pivotal to axonogenesis (beta-tubulin and actin) during perinatal development of mouse retina. Immunocytochemical localization of recoverin, calbindin, PKC and beta-tubulin was monitored in developing mouse retina (embryonic day (E) 18.5 to postnatal day (PN) 14), whereas f-actin was localized by Phalloidin binding. Recoverin immunoreactive cells, presumably the photoreceptors, were observed embryonically (E 18.5) and their number increased until PN 14. Neurite projections from the immunoreactive cells towards the outer plexiform layer (OPL) were noted at PN 0 and these processes reached the OPL at PN 7 coincident with histological evidence for the differentiation of the OPL. Outer segments, all the cell bodies in the ONL, as well as the OPL were immunoreactive to recoverin at PN 14. Calbindin immunoreactive horizontal cells were also present in E 18.5 retinas. These cells became progressively displaced proximally as the ONL developed. A calbindin immunoreactive plexus was seen in the OPL at PN 7. PKC immunoreactive bipolar cells developed postnatally, becoming distinguished at PN 7. Both beta-tubulin and actin immunoreactive cells were present in the IPL as early as E 18.5; however, appearance of processes labeled with these markers in the OPL was delayed until PN 7, concurrent with the first appearance of photoreceptor neurites, development of the horizontal cell plexus, and development of synaptophysin immunoreactivity at this location. These results provide a developmental timeframe for the expression of recoverin, calbindin, synaptophysin, beta-tubulin and actin. Our findings suggest that the time between PN 3 and PN 7 represents a critical period during which elements of the OPL are assembled.

Aging↗

Angiopoietin 2 expression in the retina: upregulation during physiologic and pathologic neovascularization.

Vascular development in the embryo requires coordinated signaling through several endothelial cell-specific receptors; however, it is not known whether this is also required later during retinal vascular development or as part of retinal neovascularization in adults. The Tie2 receptor has been implicated in stabilization and maturation of vessels through action of an agonist ligand, angiopoietin 1 (Ang1) and an antagonistic ligand, Ang2. In this study, we have demonstrated that ang2 mRNA levels are increased in the retina during development of the deep retinal capillaries by angiogenesis and during pathologic angiogenesis in a model of ischemic retinopathy. Mice with hemizygous disruption of the ang2 gene by insertion of a promoterless beta-galactosidase (beta gal) gene behind the ang2 promoter, show constitutive beta gal staining primarily in cells along the outer border of the inner nuclear layer identified as horizontal cells by colocalization of calbindin. During development of the deep capillary bed or retinal neovascularization, other cells in the inner nuclear layer and ganglion cell layer, in regions of neovascularization, stain for beta gal. Thus, there is temporal and spatial correlation of Ang2 expression with developmental and pathologic angiogenesis in the retina, suggesting that it may play a role.

Angiopoietin-1↗

Pharmacological properties and localization of dopamine-sensitive adenylate cyclase in the carp retina.

There is a specific dopamine (DA)-sensitive adenylate cyclase (EC 4.6.1.1) in the carp retina that can be stimulated by DA, DA agonists, and potassium. Experiments with the presynaptic blocker cobalt and the neurotoxin 6-hydroxydopamine strongly indicate that this adenylate cyclase is located postsynaptically. By separating retinal neurons with velocity sedimentation at unit gravity it was determined that horizontal cells possessed a DA-sensitive adenylate cyclase. The sensitivity of these cells to DA antagonists was found to be in the nanomolar range, but could be changed to the micromolar range by altering calcium concentrations within the cell. These results are discussed with respect to the multiple DA receptor theory.

1-Methyl-3-isobutylxanthine↗

Roles of aspartate and glutamate in synaptic transmission in rabbit retina. I. Outer plexiform layer.

Intracellular recordings were obtained from horizontal and bipolar cells of the superfused, isolated retina-eyecup of the rabbit. The putative neurotransmitters aspartate, glutamate, and several analogues were added to the superfusate while the membrane potential and light-responsiveness of the retinal neurons were monitored. Both L-aspartate and L-glutamate mimicked the actions of the endogenous photoreceptor transmitter on horizontal cells, on-bipolar cells, and off-bipolar cells. At applied concentrations of 2.5-20 mM, the actions of L-aspartate and L-glutamate were indistinguishable. D-aspartate potentiated the effects of both L-aspartate and L-glutamate on horizontal cells. This suggests that active uptake systems for these amino acids exist in the outer plexiform layer (OPL) of the rabbit retina. The glutamate analogue kainate produced effects similar to those of aspartate and glutamate on second-order neurons, but at concentrations lower by over two orders of magnitude. The glutamate analogue quisqualate had effects similar to kainate but with much less potency. The aspartate analogue n-methyl DL-aspartate (NMDLA) antagonized the effects of the photoreceptor transmitter on horizontal and off-bipolar cells. This action of NMDLA was only observed at low concentrations (50 microM). In addition, NMDLA could block the effects of exogenously applied kainate. The NMDLA had no clear effects on on-bipolar cells. The glutamate analogue 2-amino-4-phosphonobutyrate reversibly blocked the responses of on-bipolar cells but had no effect on either horizontal or off-bipolar cell responses. This suggests that on-bipolar cells possess a unique synaptic receptor. The aspartate analogue 2-amino-3-phosphonoproprionate did not show this selectivity, suggesting that this unique receptor is a glutamate-preferring receptor. The antagonists alpha-methyl glutamate, alpha-amino adipate, and glutamate diethyl ester all showed only a weak ability to antagonize the actions of the photoreceptor transmitter on second-order neurons. The results of this study indicate that glutamate or a glutamate-like substance is the likely transmitter of rods and cones in the rabbit retina. A comparison of the present findings with those previously obtained in lower vertebrate retinas suggests that the basic pharmacological design of the OPL of all vertebrate retinas is very similar.

Animals↗

Specific expression of the LIM/homeodomain protein Lim-1 in horizontal cells during retinogenesis.

The LIM/homeodomain transcription factor Lim-1 has been shown to play an essential role in early embryonic patterning during vertebrate development. Here we report the spatial and temporal expression patterns of Lim-1 during retinal development as detected by immunohistochemistry using a specific anti-Lim-1 antibody. By double-immunostaining, we have demonstrated for the first time that Lim-1 is exclusively expressed within the horizontal cell type in the adult retina. In the developing mouse retina, Lim-1 commences its expression in migratory horizontal cell precursors streaming toward the future horizontal cell layer in the ventricular zone. Moreover, its expression during retinogenesis is spatially and temporally coincident with that of the calcium-binding protein calbindin D-28k in horizontal cells. These data together suggest a possible role for Lim-1 in terminal differentiation and maintenance of horizontal cells, and that Lim-1 can serve as a specific molecular marker for the study of horizontal cell specification.

Animals↗

Inner retinal function in hereditary retinal dystrophies.

Hereditary retinal dystrophies are most often disorders of photoreceptors and/or the retinal pigment epithelium. Structures secondary to the photoreceptor layer such as bipolar, horizontal, amacrine and ganglion cells are secondarily involved. In later stages of the disease a mild to moderate loss of inner retina occurs, but the second and third neurons remain surprisingly viable even in late and severe stages of retinal dystrophies. The function of the inner retina in patients suffering from hereditary retinal dystrophies is not easy to determine because it depends on the input of photoreceptors. The electroretinogram (ERG) offers several possibilities in this respect: b-wave, off-response (off-ERG), oscillatory potentials, scotopic threshold response of the flash ERG and the pattern ERG (PERG). We looked at two ERG tests: the PERG and the off-ERG. The PERG is an indicator of ganglion cell function. Its amplitude is related to the photoreceptor input determined by the flash ERG and visual field testing. But in cases of an undetectable flash ERG response the PERG can be recorded in some patients, but not in others. This may be an indication of a different effect on inner retinal function in different groups of patients. On- and off-responses are related to the function of depolarizing and hyperpolarizing bipolar cells. Evaluation of 301 patients with various retinal dystrophies revealed that most hereditary disorders primarily affect the photoreceptors or the pigment epithelium. In some patients, alterations of the on- and off-response amplitudes or implicit times were indicative of inner retinal disorders and different pathophysiologic mechanisms. However, interpretation has to be made carefully, as on- and off-responses may be influenced by dysfunction of photoreceptor synapses to bipolar cells, bipolar cells, Müller cells and intercellular matrix.

Adolescent↗