Analysis of bipolar and amacrine populations in marmoset retina

Quantitative and Qualitative Assessments of Retinal Structure with Variable A-Scan Rate Spectralis OCT: Insights into IPL Multilaminarity

The aim of this study was to evaluate the qualitative and quantitative differences between 20 and 85 kHz A-scan rate optical coherence tomography (OCT) images acquired by spectral domain OCT. The study included 60 healthy subjects analyzed with horizontal linear scans with a variable A-scan rate (SHIFT technology, Heidelberg Engineering, Heidelberg, Germany). The retinal thickness measurement of each retinal layer was performed in three different positions (subfoveal, nasal, and temporal). The qualitative assessment was performed by two independent observers who rated every image with a score ranging from 1 (“sufficient”) to 3 (“excellent”) on the basis of three parameters: visualization of the vitreo-retinal interface, characterization of the retinal layers, and visualization of the sclero-choroidal interface. No statistically significant differences in terms of retinal layer thickness between the two A-scan rate scans were observed (p > 0.05). The coefficient of variation of the retinal thickness values was lower in the 20 kHz group (25.8% versus 30.1% with the 85 kHz). The 20 kHz images showed a higher quality index for both observers. An inner plexiform layer (IPL) multilaminarity was detected in 78.3% of patients from the 20 kHz group and in 40% of patients from the 85 kHz group (p < 0.05).

Contribution of parasol-magnocellular pathway ganglion cells to foveal retina in macaque monkey

Parasol-magnocellular pathway ganglion cells form an important output stream of the primate retina and make a major contribution to visual motion detection. They are known to comprise ON and OFF type response polarities but the relative numbers of ON and OFF parasol cells, and the overall contribution of parasol cells to high-acuity foveal vision are not well understood. Here we use antibodies against carbonic anhydrase 8 (CA8) and intracellular injections of the liphilic dye DiI to show that CA8 selectively labels OFF parasol cells in macaque retina. By combined labeling with CA8 antibodies and a previously-described marker for parasol cells (GABA_A receptor antibodies), we show that ON and OFF parasol cells each comprise ∼ 6% of all ganglion cells in central retina (each peak density ∼ 3000 cells/mm² at 5 deg.), and each population comprises ∼ 10% of all ganglion cells in peripheral temporal retina. Thus, the spatial density of parasol cells in central retina is greater than reported by previous anatomical studies, and the central-peripheral gradient in parasol cell density is shallower than previously reported. The data nevertheless predict decline in spatial acuity with visual field eccentricity for both midget-parvocellular pathway and parasol-magnocellular pathway mediated visual functions. The spatial resolving power of the OFF parasol array (peak ∼ 7 cpd) falls short of macaque behavioral grating acuity by at least a factor of three throughout the retina.

Developmental errors in the common marmoset retina

Although retinal organization is remarkably conserved, morphological anomalies can be found to different extents and varieties across animal species with each presenting unique characteristics and patterns of displaced and misplaced neurons. One of the most widely used non-human primates in research, the common marmoset (Callithrix jaccus) could potentially also be of interest for visual research, but is unfortunately not well characterized in this regard. Therefore, the aim of our study was to provide a first time description of structural retinal layering including morphological differences and distinctive features in this species. Retinas from animals (n = 26) of both sexes and different ages were immunostained with cell specific antibodies to label a variety of bipolar, amacrine and ganglion cells. Misplaced ganglion cells with somata in the outermost part of the inner nuclear layer and rod bipolar cells with axon terminals projecting into the outer plexiform layer instead of the inner plexiform layer independent of age or sex of the animals were the most obvious findings, whereas misplaced amacrine cells and misplaced cone bipolar axon terminals occurred to a lesser extent. With this first time description of developmental retinal errors over a wide age range, we provide a basic characterization of the retinal system of the common marmosets, which can be taken into account for future studies in this and other animal species. The finding of misplaced ganglion cells and misplaced bipolar cell axon terminals was not reported before and displays an anatomic variation worthwhile for future analyzes of their physiological and functional impact.

No evidence for age-related alterations in the marmoset retina

The physiological aging process of the retina is accompanied by various and sometimes extensive changes: Macular degeneration, retinopathies and glaucoma are the most common findings in the elderly and can potentially lead to irreversible visual disablements up to blindness. To study the aging process and to identify possible therapeutic targets to counteract these diseases, the use of appropriate animal models is mandatory. Besides the most commonly used rodent species, a non-human primate, the common marmoset (Callithrix jacchus) emerged as a promising animal model of human aging over the last years. However, the visual aging process in this species is only partially characterized, especially with regard to retinal aberrations. Therefore, we assessed here for the first time potential changes in retinal morphology of the common marmoset of different age groups. By cell type specific immunolabeling, we analyzed different cell types and distributions, potential photoreceptor and ganglion cell loss, and structural reorganization. We detected no signs of age-related differences in staining patterns or densities of various cell populations. For example, there were no signs of photoreceptor degeneration, and there was only minimal sprouting of rod bipolar cells in aged retinas. Altogether, we describe here the maintenance of a stable neuronal architecture, distribution and number of different cell populations with only mild aberrations during the aging process in the common marmoset retina. These findings are in stark contrast to previously reported findings in rodent species and humans and deserve further investigations to identify the underlying mechanisms and possible therapeutic targets.

Retinal ganglion cells expressing CaM kinase II in human and nonhuman primates

Immunoreactivity for calcium-/calmodulin-dependent protein kinase II (CaMKII) in the primate dorsal lateral geniculate nucleus (dLGN) has been attributed to geniculocortical relay neurons and has also been suggested to arise from terminals of retinal ganglion cells. Here, we combined immunostaining with single-cell injections to investigate the expression of CaMKII in retinal ganglion cells of three primate species: macaque (Macaca fascicularis, M. nemestrina), human, and marmoset (Callithrix jacchus). We found that in all species, about 2%-10% of the total ganglion cell population expressed CaMKII. In all species, CaMKII was expressed by multiple types of wide-field ganglion cell including large sparse, giant sparse (melanopsin-expressing), broad thorny, and narrow thorny cells. Three other ganglion cells types, namely, inner and outer stratifying maze cells in macaque and tufted cells in marmoset were also found. Double labeling experiments showed that CaMKII-expressing cells included inner and outer stratifying melanopsin cells. Nearly all CaMKII-expressing ganglion cell types identified here are known to project to the koniocellular layers of the dLGN as well as to the superior colliculus. The best characterized koniocellular projecting cell type-the small bistratified (blue ON/yellow OFF) cell-was, however, not CaMKII-positive in any species. Our results indicate that the pattern of CaMKII expression in retinal ganglion cells is largely conserved across different species of primate suggesting a common functional role. But the results also show that CaMKII is not a marker for all koniocellular projecting retinal ganglion cells.

Satb1 expression in retinal ganglion cells of marmosets, macaques, and humans

Recent advances in single-cell RNA sequencing have enabled the molecular distinction of ganglion cell populations in mammalian retinas. Here we used antibodies against the transcription factor special AT-rich binding protein 1 (Satb1, a protein which is expressed by on-off direction-selective ganglion cells in mouse retina) to study Satb1 expression in the retina of marmosets (Callithrix jacchus), macaques (Macaca fascicularis), and humans. In all species, Satb1 was exclusively expressed in retinal ganglion cells. The Satb1 cells made up ∼2% of the ganglion cell population in the central retina of all species, rising to a maximum ∼7% in peripheral marmoset retina. Intracellular injections in marmoset and macaque retinas revealed that most Satb1 expressing ganglion cells are widefield ganglion cells. In marmoset, Satb1 cells have a densely branching dendritic tree and include broad and narrow thorny, recursive bistratified, and parasol cells, all of which show some costratification with the outer or inner cholinergic amacrine cells. The recursive bistratified cells showed the strongest costratification but did not show extensive cofasciculation as reported for on-off direction-selective ganglion cells in rabbit and rodent retinas. In macaque, Satb1 was not expressed in recursive bistratified cells, but in large sparsely branching cells. Our findings further support the idea that the expression of transcription factors in retinal ganglion cells is not conserved across Old World (human and macaque) and New World (marmoset) primates and provides a further step to link a molecular marker with specific cell types.

Morphology, Molecular Characterization, and Connections of Ganglion Cells in Primate Retina

The eye sends information about the visual world to the brain on over 20 parallel signal pathways, each specialized to signal features such as spectral reflection (color), edges, and motion of objects in the environment. Each pathway is formed by the axons of a separate type of retinal output neuron (retinal ganglion cell). In this review, we summarize what is known about the excitatory retinal inputs, brain targets, and gene expression patterns of ganglion cells in humans and nonhuman primates. We describe how most ganglion cell types receive their input from only one or two of the 11 types of cone bipolar cell and project selectively to only one or two target regions in the brain. We also highlight how genetic methods are providing tools to characterize ganglion cells and establish cross-species homologies.

Expression of cell markers and transcription factors in the avian retina compared with that in the marmoset retina

In the vertebrate retina, amacrine and ganglion cells represent the most diverse cell classes. They can be classified into different cell types by several features, such as morphology, light responses, and gene expression profile. Although birds possess high visual acuity (similar to primates that we used here for comparison) and tetrachromatic color vision, data on the expression of transcription factors in retinal ganglion cells of birds are largely missing. In this study, we tested various transcription factors, known to label subpopulations of cells in mammalian retinae, in two avian species: the common buzzard (Buteo buteo), a raptor with exceptional acuity, and the domestic pigeon (Columba livia domestica), a good navigator and widely used model for visual cognition. Staining for the transcription factors Foxp2, Satb1 and Satb2 labeled most ganglion cells in the avian ganglion cell layer. CtBP2 was established as marker for displaced amacrine cells, which allowed us to reliably distinguish ganglion cells from displaced amacrine cells and assess their densities in buzzard and pigeon. When we additionally compared the temporal and central fovea of the buzzard with the fovea of primates, we found that the cellular organization in the pits was different in primates and raptors. In summary, we demonstrate that the expression of transcription factors is a defining feature of cell types not only in the retina of mammals but also in the retina of birds. The markers, which we have established, may provide useful tools for more detailed studies on the retinal circuitry of these highly visual animals.

In vivo Morphometry of Inner Plexiform Layer (IPL) Stratification in the Human Retina With Visible Light Optical Coherence Tomography

From the bipolar cells to higher brain visual centers, signals in the vertebrate visual system are transmitted along parallel on and off pathways. These two pathways are spatially segregated along the depth axis of the retina. Yet, to our knowledge, there is no way to directly assess this anatomical stratification in vivo. Here, employing ultrahigh resolution visible light Optical Coherence Tomography (OCT) imaging in humans, we report a stereotyped reflectivity pattern of the inner plexiform layer (IPL) that parallels IPL stratification. We characterize the topography of this reflectivity pattern non-invasively in a cohort of normal, young adult human subjects. This proposed correlate of IPL stratification is accessible through non-invasive ocular imaging in living humans. Topographic variations should be carefully considered when designing studies in development or diseases of the visual system.

Identification of retinal ganglion cell types expressing the transcription factor Satb2 in three primate species

In primates, the retinal ganglion cells contributing to high acuity spatial vision (midget cells and parasol cells), and blue-yellow color vision (small bistratified cells) are well understood. Many other ganglion cell types with large dendritic fields (named wide-field ganglion cells) have been identified, but their spatial density and distribution are largely unknown. Here we took advantage of the recently established molecular diversity of ganglion cells to study wide-field ganglion cell populations in three primate species. We used antibodies against the transcription factor Special AT-rich binding protein 2 (Satb2) to explore its expression in macaque (Macaca fascicularis, M. nemestrina), human and marmoset (Callithrix jacchus) retinas. In all three species, Satb2 cells make up a low proportion (1.5-4%) of the ganglion cell population, with a slight increase from central to peripheral retina. Intracellular dye injections revealed that in macaque and human retinas, the large majority (over 80%) of Satb2 cells are inner and outer stratifying large sparse cells. By contrast, in marmoset retina the majority (over 60%) of Satb2 expressing cells were broad thorny cells, with smaller proportions of recursive bistratified (putative direction-selective), large bistratified, and outer stratifying narrow thorny cells. Our findings imply that Satb2 expression has undergone rapid species specific adaptations during primate evolution, because expression is not conserved across Old World (macaque, human) and New World (marmoset) suborders.

Analysis of Parvocellular and Magnocellular Visual Pathways in Human Retina

Two main subcortical pathways serving conscious visual perception are the midget-parvocellular (P), and the parasol-magnocellular (M) pathways. It is generally accepted that the P pathway serves red-green color vision, but the relative contribution of P and M pathways to spatial vision is a long-standing and unresolved issue. Here, we mapped the spatial sampling properties of P and M pathways across the human retina. Data were obtained from immunolabeled vertical sections of six postmortem male and female human donor retinas and imaged using high-resolution microscopy. Cone photoreceptors, OFF-midget bipolar cells (P pathway), OFF-diffuse bipolar (DB) types DB3a and DB3b (M pathway), and ganglion cells were counted along the temporal horizontal meridian, taking foveal spatial distortions (postreceptoral displacements) into account. We found that the density of OFF-midget bipolar and OFF-midget ganglion cells can support one-to-one connections to 1.05-mm (3.6°) eccentricity. One-to-one connections of cones to OFF-midget bipolar cells are present to at least 10-mm (35°) eccentricity. The OFF-midget ganglion cell array acuity is well-matched to photopic spatial acuity measures throughout the central 35°, but the OFF-parasol array acuity is well below photopic spatial acuity, supporting the view that the P pathway underlies high-acuity spatial vision. Outside the fovea, array acuity of both OFF-midget and OFF-DB cells exceeds psychophysical measures of photopic spatial acuity. We conclude that parasol and midget pathway bipolar cells deliver high-acuity spatial signals to the inner plexiform layer, but outside the fovea, this spatial resolution is lost at the level of ganglion cells.SIGNIFICANCE STATEMENT We make accurate maps of the spatial density and distribution of neurons in the human retina to aid in understanding human spatial vision, interpretation of diagnostic tests, and the implementation of therapies for retinal diseases. Here, we map neurons involved with the midget-parvocellular (P pathway) and parasol-magnocellular (M pathway) through human retina. We find that P-type bipolar cells outnumber M-type bipolar cells at all eccentricities. We show that cone photoreceptors and P-type pathway bipolar cells are tightly connected throughout the retina, but that spatial resolution is lost at the level of the ganglion cells. Overall, the results support the view that the P pathway is specialized to serve both high acuity vision and red-green color vision.

Cell types and cell circuits in human and non-human primate retina

This review summarizes our current knowledge of primate including human retina focusing on bipolar, amacrine and ganglion cells and their connectivity. We have two main motivations in writing. Firstly, recent progress in non-invasive imaging methods to study retinal diseases mean that better understanding of the primate retina is becoming an important goal both for basic and for clinical sciences. Secondly, genetically modified mice are increasingly used as animal models for human retinal diseases. Thus, it is important to understand to which extent the retinas of primates and rodents are comparable. We first compare cell populations in primate and rodent retinas, with emphasis on how the fovea (despite its small size) dominates the neural landscape of primate retina. We next summarise what is known, and what is not known, about the postreceptoral neurone populations in primate retina. The inventories of bipolar and ganglion cells in primates are now nearing completion, comprising ~12 types of bipolar cell and at least 17 types of ganglion cell. Primate ganglion cells show clear differences in dendritic field size across the retina, and their morphology differs clearly from that of mouse retinal ganglion cells. Compared to bipolar and ganglion cells, amacrine cells show even higher morphological diversity: they could comprise over 40 types. Many amacrine types appear conserved between primates and mice, but functions of only a few types are understood in any primate or non-primate retina. Amacrine cells appear as the final frontier for retinal research in monkeys and mice alike.

Topography of Neurons in the Rod Pathway of Human Retina

Purpose

The objective of this study was to map the distribution and density of the three major components of the classical scotopic "night vision" pathway (rods, rod bipolar, and AII amacrine cells) in postmortem human retinas.

Methods

Four postmortem donor eyes (male and female, aged 44-56 years) were used to cut vertical sections through the temporal horizontal meridian. The sections were processed for immunohistochemistry and imaged using high-resolution multichannel confocal microscopy. Rods, rod bipolar, and AII amacrine cells were counted along the temporal horizontal meridian. Two additional retinas were used for intracellular injections.

Results

Rod peak density is close to 150,000 cells/mm2 at 4 to 5 mm (15° to 20°) eccentricity, declining to below 70,000 cells/mm2 in peripheral retina. Rod bipolar density is lower but follows a similar distribution with peak density near 10,000 cells/mm2 between 2 and 4 mm (7° to 15°) eccentricity declining to below 4000 cells/mm2 in peripheral retina. The peak density of AII amacrine cells (near 4000 cells/mm2) is located close to the fovea, at 0.5- to 2 mm-eccentricity (2° to 7°) and declines to below 1000 cells/mm2 in the periphery. Thus, convergence between rods and AII cells increases from central to peripheral retina.

Conclusions

Comparison with human psychophysics and ganglion cell density indicates that the spatial resolution of scotopic vision is limited by the AII mosaic at eccentricities below 15° and by the midget ganglion cell mosaic at eccentricities above 15°.

Melanopsin and calbindin immunoreactivity in the inner retina of humans and marmosets

In primate retina, the calcium-binding protein calbindin is expressed by a variety of neurons including cones, bipolar cells, and amacrine cells but it is not known which type(s) of cell express calbindin in the ganglion cell layer. The present study aimed to identify calbindin-positive cell type(s) in the amacrine and ganglion cell layer of human and marmoset retina using immunohistochemical markers for ganglion cells (RBPMS and melanopsin) and cholinergic amacrine (ChAT) cells. Intracellular injections following immunolabeling was used to reveal the morphology of calbindin-positive cells. In human retina, calbindin-labeled cells in the ganglion cell layer were identified as inner and outer stratifying melanopsin-expressing ganglion cells, and ON ChAT (starburst amacrine) cells. In marmoset, calbindin immunoreactivity in the ganglion cell layer was absent from ganglion cells but present in ON ChAT cells. In the inner nuclear layer of human retina, calbindin was found in melanopsin-expressing displaced ganglion cells and in at least two populations of amacrine cells including about a quarter of the OFF ChAT cells. In marmoset, a very low proportion of OFF ChAT cells was calbindin-positive. These results suggest that in both species there may be two types of OFF ChAT cells. Consistent with previous studies, the ratio of ON to OFF ChAT cells was about 70 to 30 in human and 30 to 70 in marmoset. Our results show that there are species-related differences between different primates with respect to the expression of calbindin.

Expression of Ca2+-Binding Buffer Proteins in the Human and Mouse Retinal Neurons

Ca2+-binding buffer proteins (CaBPs) are widely expressed by various neurons throughout the central nervous system (CNS), including the retina. While the expression of CaBPs by photoreceptors, retinal interneurons and the output ganglion cells in the mammalian retina has been extensively studied, a general description is still missing due to the differences between species, developmental expression patterns and study-to-study discrepancies. Furthermore, CaBPs are occasionally located in a compartment-specific manner and two or more CaBPs can be expressed by the same neuron, thereby sharing the labor of Ca2+ buffering in the intracellular milieu. This article reviews this topic by providing a framework on CaBP functional expression by neurons of the mammalian retina with an emphasis on human and mouse retinas and the three most abundant and extensively studied buffer proteins: parvalbumin, calretinin and calbindin.

Morphology of Inner Retina in Rhesus Monkeys of Various Ages: A Comparative Study

Purpose

To investigate the changes of thickness in each layer, the morphology and density of inner neurons in rhesus monkeys' retina at various growth stages, thus contribute useful data for further biological studies.

Methods

The thickness of nerve fiber layer (NFL), the whole retina, inner plexiform layer (IPL), and outer plexiform layer (OPL) of rhesus monkeys at different ages were observed with hematoxylin and eosin (H&E) staining. The morphology and the density of inner neurons of rhesus monkey retina were detected by immunofluorescence.

Results

The retina showed the well-known ten layers, the thickness of each retinal layer in rhesus monkeys at various ages increased rapidly after infant, and the retina was the thickest in adulthood, but the retinal thickness stop growing in senescent. Quantitative analysis showed that the maximum density of inner neurons was reached in adolescent, and then, the density of inner neurons decreased in adults and senescent retinas. And some changes in the morphology of rod bipolar cells have occurred in senescent.

Conclusions

The structure of retina in rhesus monkeys is relatively immature at infant, and the inner retina of rhesus monkeys is mature in adolescent, while the thickness of each retinal layer was the most developed in the adult group. There was no significant change in senescence for the thickness of each retinal layer, but the number of the neurons in our study has a decreasing trend and the morphological structure has changed.

Thorny ganglion cells in marmoset retina: Morphological and neurochemical characterization with antibodies against calretinin

In primates, over 17 morphological types of retinal ganglion cell have been distinguished by their dendritic morphology and stratification, but reliable markers for specific ganglion cell populations are still rare. The calcium binding protein calretinin is known to be expressed in the inner nuclear and the ganglion cell layer of marmoset retina, however, the specific cell type(s) expressing calretinin in the ganglion cell layer are yet to be determined. Here, we identified calretinin positive retinal ganglion cells in the common marmoset Callithrix jacchus. Double labeling with the ganglion cell marker RBPMS demonstrated that the large majority (80%) of the calretinin positive cells in the ganglion cell layer are ganglion cells, and 20% are displaced amacrine cells. The calretinin positive ganglion cells made up on average 12% of the total ganglion cell population outside of the foveal region and their proportion increased with eccentricity. Prelabeling with antibodies against calretinin and subsequent intracellular injection with DiI revealed that the large majority of the injected cells (n = 74) were either narrow thorny or broad thorny ganglion cells, 14 cells were displaced amacrine cells. Narrow thorny cells were further distinguished into outer and inner stratifying cells. In addition, weakly labeled cells with a large soma were identified as parasol ganglion cells. Our results show that three types of thorny ganglion cells in marmoset retina can be identified with antibodies against calretinin. Our findings are also consistent with the idea that the proportion of wide-field ganglion cell types increases in peripheral retina.

Survey of retinal ganglion cell morphology in marmoset

In primate retina, the midget, parasol, and small bistratified cell populations form the large majority of ganglion cells. In addition, there is a variety of low-density wide-field ganglion cell types that are less well characterized. Here we studied retinal ganglion cells in the common marmoset, Callithrix jacchus, using particle-mediated gene transfer. Ganglion cells were transfected with an expression plasmid for the postsynaptic density 95-green fluorescent protein. The retinas were processed with established immunohistochemical markers for bipolar and/or amacrine cells to determine ganglion cell dendritic stratification. In total over 500 ganglion cells were classified based on their dendritic field size, morphology, and stratification in the inner plexiform layer. Over 17 types were distinguished, including midget, parasol, broad thorny, small bistratified, large bistratified, recursive bistratified, recursive monostratified, narrow thorny, smooth monostratified, large sparse, giant sparse (melanopsin) ganglion cells, and a group that may contain several as yet uncharacterized types. Assuming each characterized type forms a hexagonal mosaic, the midget and parasol cells account for over 80% of all ganglion cells in the central retina but only ∼50% of cells in the peripheral (>2 mm) retina. We conclude that the fovea is dominated by midget and parasol cells, but outside the fovea the ganglion cell diversity in marmoset is likely as great as that reported for nonprimate retinas. Taken together, the ganglion cell types in marmoset retina resemble those described previously in macaque retina with respect to morphology, stratification, and change in proportion across the retina.

AAV-mediated transduction and targeting of retinal bipolar cells with improved mGluR6 promoters in rodents and primates

Adeno-associated virus (AAV) vectors have been a powerful gene delivery vehicle to the retina for basic research and gene therapy. For many of these applications, achieving cell type-specific targeting and high transduction efficiency is desired. Recently, there has been increasing interest in AAV-mediated gene targeting to specific retinal bipolar cell types. A 200-bp enhancer in combination with a basal SV40 promoter has been commonly used to target transgenes into ON-type bipolar cells. In the current study, we searched for additional cis-regulatory elements in the mGluR6 gene for improving AAV-mediated transduction efficiency into retinal bipolar cells. Our results showed that the combination of the endogenous mGluR6 promoter with additional enhancers in the introns of the mGluR6 gene markedly enhanced AAV transduction efficiency as well as made the targeting more selective for rod bipolar cells in mice. Furthermore, the AAV vectors with the improved promoter could target to ON bipolar cells with robust transduction efficiency in the parafovea and the far peripheral retina of marmoset monkeys. The improved mGluR6 promoter constructs could provide a valuable tool for genetic manipulation in rod bipolar cells in mice and facilitate clinical applications for ON bipolar cell-based gene therapies.

Calcium buffer proteins are specific markers of human retinal neurons

Ca(2+)-buffer proteins (CaBPs) modulate the temporal and spatial characteristics of transient intracellular Ca(2+)-concentration changes in neurons in order to fine-tune the strength and duration of the output signal. CaBPs have been used as neurochemical markers to identify and trace neurons of several brain loci including the mammalian retina. The CaBP content of retinal neurons, however, varies between species and, thus, the results inferred from animal models cannot be utilised directly by clinical ophthalmologists. Moreover, the shortage of well-preserved human samples greatly impedes human retina studies at the cellular and network level. Our purpose has therefore been to examine the distribution of major CaBPs, including calretinin, calbindin-D28, parvalbumin and the recently discovered secretagogin in exceptionally well-preserved human retinal samples. Based on a combination of immunohistochemistry, Neurolucida tracing and Lucifer yellow injections, we have established a database in which the CaBP marker composition can be defined for morphologically identified cell types of the human retina. Hence, we describe the full CaBP make-up for a number of human retinal neurons, including HII horizontal cells, AII amacrine cells, type-1 tyrosine-hydroxylase-expressing amacrine cells and other lesser known neurons. We have also found a number of unidentified cells whose morphology remains to be characterised. We present several examples of the colocalisation of two or three CaBPs with slightly different subcellular distributions in the same cell strongly suggesting a compartment-specific division of labour of Ca(2+)-buffering by CaBPs. Our work thus provides a neurochemical framework for future ophthalmological studies and renders new information concerning the cellular and subcellular distribution of CaBPs for experimental neuroscience.

Connectivity between the OFF bipolar type DB3a and six types of ganglion cell in the marmoset retina

Parallel visual pathways originate at the first synapse in the retina, where cones make connections with cone bipolar cells that in turn contact ganglion cells. There are more ganglion cell types than bipolar types, suggesting that there must be divergence from bipolar to ganglion cells. Here we analyze the contacts between an OFF bipolar type (DB3a) and six ganglion cell types in the retina of the marmoset monkey (Callithrix jacchus). Ganglion cells were transfected via particle-mediated gene transfer of an expression plasmid for the postsynaptic density 95-green fluorescent protein (PSD95-GFP), and DB3a cells were labeled via immunohistochemistry. Ganglion cell types that fully or partially costratified with DB3a cells included OFF parasol, OFF midget, broad thorny, recursive bistratified, small bistratified, and large bistratified cells. On average, the number of DB3a contacts to parasol cells (18 contacts per axon terminal) is higher than that to other ganglion cell types (between four and seven contacts). We estimate that the DB3a output to OFF parasol cells accounts for at least 30% of the total DB3a output. Furthermore, we found that OFF parasol cells receive approximately 20% of their total bipolar input from DB3a cells, suggesting that other diffuse bipolar types also provide input to OFF parasol cells. We conclude that DB3a cells preferentially contact OFF parasol cells but also provide input to other ganglion cell types.

Expression and distribution of peroxiredoxins in the retina and optic nerve

Oxidative stress is implicated in various pathological conditions of the retina and optic nerve. Peroxiredoxins (Prdxs) comprise a recently characterized family of antioxidant enzymes. To date, little information exists regarding the distribution of Prdxs in the eye. Herein, we employed a combination of qRT-PCR, immunohistochemistry and Western blotting to determine the level of expression and distribution of the six Prdx isoforms in the retina and optic nerve of the rat. In addition, we performed some parallel analyses on the common marmoset (Callithrix Jacchus). In the rat, all of the Prdx transcripts were expressed in relatively high amounts in both retina and optic nerve, with abundances ranging from approximately 3–50 % of the level of the housekeeping gene cyclophilin. With regard to protein expression, each isoform was detected in the retina and optic nerve by either Western blotting and/or immunohistochemistry. Excepting Prdx4, there was a good correspondence between the rodent and primate results. In the retina, Prdx1 and Prdx2 were principally localized to neurons in the inner nuclear layer and cone photoreceptors, Prdx3 and Prdx5 displayed characteristic mitochondrial immunolabeling, while Prdx6 was associated with astrocytes and Müller cells. In the optic nerve, Prdx1 was robustly expressed by oligodendrocytes, Prdx3 and Prdx5 were observed in axons, and Prdx6 was restricted to astrocytes. The present findings augment our understanding of the distribution and expression of the Prdxs in the retina and optic nerve of rodents and primates and lay the foundation for subsequent analysis of their involvement in relevant blinding diseases.

Identification of AⅡ amacrine, displaced amacrine, and bistratified ganglion cell types in human retina with antibodies against calretinin

Antibodies against calretinin are markers for one type of rod pathway interneuron (AⅡ amacrine cell) in the retina of some but not all mammalian species. The AⅡ cells play a crucial role in night-time (scotopic) vision and have been proposed as a target for optogenetic restoration of vision in retinal disease. In the present study we aimed to characterize the AⅡ cells in human retina. Postmortem human donor eyes were obtained with ethical approval and processed for calretinin immunofluorescence. Calretinin-positive somas in the inner nuclear and the ganglion cell layer were filled with the lipophilic dye DiI. The large majority (over 80%) of calretinin-immunoreactive cells is located in the inner nuclear layer, is immunopositive for glycine transporter 1, and shows the typical morphology of AⅡ amacrine cells. In addition, a small proportion of calretinin-positive cells in the inner nuclear layer and in the ganglion cell layer is glutamic acid decarboxylase-positive and shows the morphology of widefield amacrine cells (stellate, semilunar, and thorny amacrine cells). About half of the calretinin cells in the ganglion cell layer are bistratified ganglion cells resembling the small bistratified (presumed blue-ON/yellow-OFF) and the G17 ganglion cell previously described in primates. We conclude that in human retina, antibodies against calretinin can be used to identify AⅡ amacrine cells in the inner nuclear layer as well as widefield amacrine and small bistratified ganglion cells in the ganglion cell layer.