Wide-field ganglion cells in macaque retinas

Functional diversity in the output of the primate retina

The visual image transmitted by the retina to the brain has long been understood in terms of spatial filtering by the center-surround receptive fields of retinal ganglion cells (RGCs). Recently, this textbook view has been challenged by the stunning functional diversity and specificity observed in ∼40 distinct RGC types in the mouse retina. However, it is unclear whether the ∼20 morphologically and molecularly identified RGC types in primates exhibit similar functional diversity, or instead exhibit center-surround organization at different spatial scales. Here, we reveal striking and surprising functional diversity in macaque and human RGC types using large-scale multi-electrode recordings from isolated macaque and human retinas. In addition to the five well-known primate RGC types, 18-27 types were distinguished by their functional properties, likely revealing several previously unknown types. Surprisingly, many of these cell types exhibited striking non-classical receptive field structure, including irregular spatial and chromatic properties not previously reported in any species. Qualitatively similar results were observed in recordings from the human retina. The receptive fields of less-understood RGC types formed uniform mosaics covering visual space, confirming their classification, and the morphological counterparts of two types were established using single-cell recording. The striking receptive field diversity was paralleled by distinctive responses to natural movies and complexity of visual computation. These findings suggest that diverse RGC types, rather than merely filtering the scene at different spatial scales, instead play specialized roles in human vision.

Thorny and Tufted Retinal Ganglion Cells Express the Transcription Factor Forkhead Proteins Foxp1 and Foxp2 in Marmoset (Callithrix jacchus)

The transcription factor forkhead/winged-helix domain proteins Foxp1 and Foxp2 have previously been studied in mouse retina, where they are expressed in retinal ganglion cells named F-mini and F-midi. Here we show that both transcription factors are expressed by small subpopulations (on average less than 10%) of retinal ganglion cells in the retina of the marmoset monkey (Callithrix jacchus). The morphology of Foxp1- and Foxp2-expressing cells was revealed by intracellular DiI injections of immunofluorescent cells. Foxp1- and Foxp2-expressing cells comprised multiple types of wide-field ganglion cells, including broad thorny cells, narrow thorny cells, and tufted cells. The large majority of Foxp2-expressing cells were identified as tufted cells. Tufted cells stratify broadly in the middle of the inner plexiform layer. They resemble broad thorny cells but their proximal dendrites are bare of branches and the distal dendrites branch frequently forming dense dendritic tufts. Double labeling with calretinin, a previously established marker for broad thorny and narrow thorny cells, showed that only a small proportion of ganglion cells co-expressed calretinin and Foxp1 or Foxp2 supporting the idea that the two markers are differentially expressed in retinal ganglion cells of marmoset retina.

Neural activity of retinal ganglion cells under continuous, dynamically-modulated high frequency electrical stimulation

Objective.Current retinal prosthetics are limited in their ability to precisely control firing patterns of functionally distinct retinal ganglion cell (RGC) types. The aim of this study was to characterise RGC responses to continuous, kilohertz-frequency-varying stimulation to assess its utility in controlling RGC activity.Approach.We usedin vitropatch-clamp experiments to assess electrically-evoked ON and OFF RGC responses to frequency-varying pulse train sequences. In each sequence, the stimulation amplitude was kept constant while the stimulation frequency (0.5-10 kHz) was changed every 40 ms, in either a linearly increasing, linearly decreasing or randomised manner. The stimulation amplitude across sequences was increased from 10 to 300µA.Main results.We found that continuous stimulation without rest periods caused complex and irreproducible stimulus-response relationships, primarily due to strong stimulus-induced response adaptation and influence of the preceding stimulus frequency on the response to a subsequent stimulus. In addition, ON and OFF populations showed different sensitivities to continuous, frequency-varying pulse trains, with OFF cells generally exhibiting more dependency on frequency changes within a sequence. Finally, the ability to maintain spiking behaviour to continuous stimulation in RGCs significantly reduced over longer stimulation durations irrespective of the frequency order.Significance.This study represents an important step in advancing and understanding the utility of continuous frequency modulation in controlling functionally distinct RGCs. Our results indicate that continuous, kHz-frequency-varying stimulation sequences provide very limited control of RGC firing patterns due to inter-dependency between adjacent frequencies and generally, different RGC types do not display different frequency preferences under such stimulation conditions. For future stimulation strategies using kHz frequencies, careful consideration must be given to design appropriate pauses in stimulation, stimulation frequency order and the length of continuous stimulation duration.

Synaptic Origins of the Complex Receptive Field Structure in Primate Smooth Monostratified Retinal Ganglion Cells

Considerable progress has been made in studying the receptive fields of the most common primate retinal ganglion cell (RGC) types, such as parasol RGCs. Much less is known about the rarer primate RGC types and the circuitry that gives rise to noncanonical receptive field structures. The goal of this study was to analyze synaptic inputs to smooth monostratified RGCs to determine the origins of their complex spatial receptive fields, which contain isolated regions of high sensitivity called "hotspots." Interestingly, smooth monostratified RGCs co-stratify with the well-studied parasol RGCs and are thus constrained to receiving input from bipolar and amacrine cells with processes sharing the same layer, raising the question of how their functional differences originate. Through 3D reconstructions of circuitry and synapses onto ON smooth monostratified and ON parasol RGCs from central macaque retina, we identified four distinct sampling strategies employed by smooth and parasol RGCs to extract diverse response properties from co-stratifying bipolar and amacrine cells. The two RGC types differed in the proportion of amacrine cell input, relative contributions of co-stratifying bipolar cell types, amount of synaptic input per bipolar cell, and spatial distribution of bipolar cell synapses. Our results indicate that the smooth RGC's complex receptive field structure arises through spatial asymmetries in excitatory bipolar cell input which formed several discrete clusters comparable with physiologically measured hotspots. Taken together, our results demonstrate how the striking differences between ON parasol and ON smooth monostratified RGCs arise from distinct strategies for sampling a common set of synaptic inputs.

Artificial intelligence techniques for retinal prostheses: a comprehensive review and future direction

Objective. Retinal prostheses are promising devices to restore vision for patients with severe age-related macular degeneration or retinitis pigmentosa disease. The visual processing mechanism embodied in retinal prostheses play an important role in the restoration effect. Its performance depends on our understanding of the retina's working mechanism and the evolvement of computer vision models. Recently, remarkable progress has been made in the field of processing algorithm for retinal prostheses where the new discovery of the retina's working principle and state-of-the-arts computer vision models are combined together.Approach. We investigated the related research on artificial intelligence techniques for retinal prostheses. The processing algorithm in these studies could be attributed to three types: computer vision-related methods, biophysical models, and deep learning models.Main results. In this review, we first illustrate the structure and function of the normal and degenerated retina, then demonstrate the vision rehabilitation mechanism of three representative retinal prostheses. It is necessary to summarize the computational frameworks abstracted from the normal retina. In addition, the development and feature of three types of different processing algorithms are summarized. Finally, we analyze the bottleneck in existing algorithms and propose our prospect about the future directions to improve the restoration effect.Significance. This review systematically summarizes existing processing models for predicting the response of the retina to external stimuli. What's more, the suggestions for future direction may inspire researchers in this field to design better algorithms for retinal prostheses.

Preparation of Retinal Explant Cultures

Organotypic retinal explants are routinely used as alternatives to in vitro cell culture and to replace the use of animals in modelling retinal neurodegenerative diseases. Retinal explants fill the gap between in vivo which are expensive, time consuming, and complex due to inaccessibility of target tissues. However, organotypic retinal explants are less expensive and rapid and retinal cell types in the explant maintain their morphologic interactions with other cells in the retina. Therefore, retinal explants have high potential to be used as tools to assess the pharmacological and other therapies prior to in vivo validation, reducing the use of live animals.

Mechanisms of retinal ganglion cell injury following acute increases in intraocular pressure

The maintenance of intraocular pressure (IOP) is critical to preserving the pristine optics required for vision. Disturbances in IOP can directly impact the optic nerve and retina, and inner retinal injury can occur following acute and chronic IOP elevation. There are a variety of animal models that have been developed to study the effects of acute and chronic elevation of IOP on the retina, retinal ganglion cell (RGC) morphology, intracellular signaling, gene expression changes, and survival. Acute IOP models induce injury that allows for the study of RGC response to well characterized injury and potential recovery. This review will focus on the initial impact of acute IOP elevation on RGC injury and recovery as these early responses may be the best targets for potential therapeutic interventions to promote RGC survival in glaucoma.

Optogenetic Therapy for Visual Restoration

Optogenetics is a recent breakthrough in neuroscience, and one of the most promising applications is the treatment of retinal degenerative diseases. Multiple clinical trials are currently ongoing, less than a decade after the first attempt at visual restoration using optogenetics. Optogenetic therapy has great value in providing hope for visual restoration in late-stage retinal degeneration, regardless of the genotype. This alternative gene therapy consists of multiple elements including the choice of target retinal cells, optogenetic tools, and gene delivery systems. Currently, there are various options for each element, all of which have been developed as a product of technological success. In particular, the performance of optogenetic tools in terms of light and wavelength sensitivity have been improved by engineering microbial opsins and applying human opsins. To provide better post-treatment vision, the optimal choice of optogenetic tools and effective gene delivery to retinal cells is necessary. In this review, we provide an overview of the advancements in optogenetic therapy for visual restoration, focusing on available options for optogenetic tools and gene delivery methods.

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.

Origins of direction selectivity in the primate retina

From mouse to primate, there is a striking discontinuity in our current understanding of the neural coding of motion direction. In non-primate mammals, directionally selective cell types and circuits are a signature feature of the retina, situated at the earliest stage of the visual process. In primates, by contrast, direction selectivity is a hallmark of motion processing areas in visual cortex, but has not been found in the retina, despite significant effort. Here we combined functional recordings of light-evoked responses and connectomic reconstruction to identify diverse direction-selective cell types in the macaque monkey retina with distinctive physiological properties and synaptic motifs. This circuitry includes an ON-OFF ganglion cell type, a spiking, ON-OFF polyaxonal amacrine cell and the starburst amacrine cell, all of which show direction selectivity. Moreover, we discovered that macaque starburst cells possess a strong, non-GABAergic, antagonistic surround mediated by input from excitatory bipolar cells that is critical for the generation of radial motion sensitivity in these cells. Our findings open a door to investigation of a precortical circuitry that computes motion direction in the primate visual system.

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.

Retinal ganglion cells projecting to superior colliculus and pulvinar in marmoset

We determined the retinal ganglion cell types projecting to the medial subdivision of inferior pulvinar (PIm) and the superior colliculus (SC) in the common marmoset monkey, Callithrix jacchus. Adult marmosets received a bidirectional tracer cocktail into the PIm (conjugated to Alexa fluor 488), and the SC (conjugated to Alexa fluor 594) using an MRI-guided approach. One SC injection included the pretectum. The large majority of retrogradely labelled cells were obtained from SC injections, with only a small proportion obtained after PIm injections. Retrogradely labelled cells were injected intracellularly in vitro using lipophilic dyes (DiI, DiO). The SC and PIm both received input from a variety of ganglion cell types. Input to the PIm was dominated by broad thorny (41%), narrow thorny (24%) and large bistratified (25%) ganglion cells. Input to the SC was dominated by parasol (37%), broad thorny (24%) and narrow thorny (17%) cells. Midget ganglion cells (which make up the large majority of primate retinal ganglion cells) and small bistratified (blue-ON/yellow OFF) cells were never observed to project to SC or PIm. Small numbers of other wide-field ganglion cell types were also encountered. Giant sparse (presumed melanopsin-expressing) cells were only seen following the tracer injection which included the pretectum. We note that despite the location of pulvinar complex in dorsal thalamus, and its increased size and functional importance in primate evolution, the retinal projections to pulvinar have more in common with SC projections than they do with projections to the dorsal lateral geniculate nucleus.

Synaptic inputs to broad thorny ganglion cells in macaque retina

In primates, broad thorny retinal ganglion cells are highly sensitive to small, moving stimuli. They have tortuous, fine dendrites with many short, spine-like branches that occupy three contiguous strata in the middle of the inner plexiform layer. The neural circuits that generate their responses to moving stimuli are not well-understood, and that was the goal of this study. A connectome from central macaque retina was generated by serial block-face scanning electron microscopy, a broad thorny cell was reconstructed, and its synaptic inputs were analyzed. It received fewer than 2% of its inputs from both ON and OFF types of bipolar cells; the vast majority of its inputs were from amacrine cells. The presynaptic amacrine cells were reconstructed, and seven types were identified based on their characteristic morphology. Two types of narrow-field cells, knotty bistratified Type 1 and wavy multistratified Type 2, were identified. Two types of medium-field amacrine cells, ON starburst and spiny, were also presynaptic to the broad thorny cell. Three types of wide-field amacrine cells, wiry Type 2, stellate wavy, and semilunar Type 2, also made synapses onto the broad thorny cell. Physiological experiments using a macaque retinal preparation in vitro confirmed that broad thorny cells received robust excitatory input from both the ON and the OFF pathways. Given the paucity of bipolar cell inputs, it is likely that amacrine cells provided much of the excitatory input, in addition to inhibitory input.

Visual properties of human retinal ganglion cells

The retinal output is the sole source of visual information for the brain. Studies in non-primate mammals estimate that this information is carried by several dozens of retinal ganglion cell types, each informing the brain about different aspects of a visual scene. Even though morphological studies of primate retina suggest a similar diversity of ganglion cell types, research has focused on the function of only a few cell types. In human retina, recordings from individual cells are anecdotal or focus on a small subset of identified types. Here, we present the first systematic ex-vivo recording of light responses from 342 ganglion cells in human retinas obtained from donors. We find a great variety in the human retinal output in terms of preferences for positive or negative contrast, spatio-temporal frequency encoding, contrast sensitivity, and speed tuning. Some human ganglion cells showed similar response behavior as known cell types in other primate retinas, while we also recorded light responses that have not been described previously. This first extensive description of the human retinal output should facilitate interpretation of primate data and comparison to other mammalian species, and it lays the basis for the use of ex-vivo human retina for in-vitro analysis of novel treatment approaches.

Retinal Ganglion Cells-Diversity of Cell Types and Clinical Relevance

Retinal ganglion cells (RGCs) are the bridging neurons that connect the retinal input to the visual processing centres within the central nervous system. There is a remarkable diversity of RGCs and the various subtypes have unique morphological features, distinct functions, and characteristic pathways linking the inner retina to the relevant brain areas. A number of psychophysical and electrophysiological tests have been refined to investigate this large and varied population of RGCs. Technological advances, such as high-resolution optical coherence tomography imaging, have provided additional tools to define the pattern of RGC involvement and the chronological sequence of events in both inherited and acquired optic neuropathies. The mechanistic insights gained from these studies, in particular the selective vulnerability and relative resilience of particular RGC subtypes, are of fundamental importance as they are directly relevant to the development of targeted therapies for these invariably progressive blinding diseases. This review provides a comprehensive description of the various types of RGCs, the developments in proposed methods of classification, and the current gaps in our knowledge of how these RGCs are differentially affected depending on the underlying aetiology. The synthesis of the current body of knowledge on the diversity of RGCs and the pathways that are potentially amenable to therapeutic modulation will hopefully lead to much needed effective treatments for patients with optic neuropathies.

Morphological identification and systematic classification of mammalian retinal ganglion cells. I. Rabbit retinal ganglion cells

Retinal ganglion cells (RGCs) convey visual signals to 50 regions of the brain. For reasons of interest and convenience, they constitute an excellent system for the study of brain structure and function. There is general agreement that, absent a complete "parts list," understanding how the nervous system processes information will remain an elusive goal. Recent studies indicate that there are 30-50 types of ganglion cell in mouse retina, whereas only a few years ago it was still written that mice and the more visually oriented lagomorphs had less than 20 types of RGC. More than 30 years ago, I estimated that rabbits have about 40 types of RGC. The present study indicates that this number is much too low. I have employed the old but powerful method of Golgi-impregnation to rabbit retina, studying the range of component neurons in this already well-studied retinal system. Close quantitative and qualitative analyses of 1,142 RGCs in 26 retinas take into account cell body and dendritic field size, level(s) of dendritic stratification in the retina's inner plexiform layer, and details of dendritic branching. Ninety-one morphologies are recognized. Of these, at least 32 can be correlated with physiologically studied RGCs, dye-injected for morphological analysis. It is unlikely that rabbits have 91 types of RGC, but is argued here that this number lies between 60 and 70. The present study provides a "yardstick" for measuring the output of future molecular studies that may be more definitive in fixing the number of RGC types in rabbit retina.

Wide-field amacrine cell inputs to ON parasol ganglion cells in macaque retina

Parasol cells are one of the major types of primate retinal ganglion cells. The goal of this study was to describe the synaptic inputs that shape the light responses of the ON type of parasol cells, which are excited by increments in light intensity. A connectome from central macaque retina was generated by serial blockface scanning electron microscopy. Six neighboring ON parasol cells were reconstructed, and their synaptic inputs were analyzed. On average, they received 21% of their input from bipolar cells, excitatory local circuit neurons receiving input from cones. The majority of their input was from amacrine cells, local circuit neurons of the inner retina that are typically inhibitory. Their contributions to the neural circuit providing input to parasol cells are not well-understood, and the focus of this study was on the presynaptic wide-field amacrine cells, which provided 17% of the input to ON parasol cells. These are GABAergic amacrine cells with long, relatively straight dendrites, and sometimes also axons, that run in a single, narrow stratum of the inner plexiform layer. The presynaptic wide-field amacrine cells were reconstructed, and two types were identified based on their characteristic morphology. One presynaptic amacrine cell was identified as semilunar type 2, a polyaxonal cell that is electrically coupled to ON parasol cells. A second amacrine was identified as wiry type 2, a type known to be sensitive to motion. These inputs likely make ON parasol cells more sensitive to stimuli that are rapidly changing outside their classical receptive fields.

'The last channel': vision at the temporal margin of the field

The human visual field, on the temporal side, extends to at least 90° from the line of sight. Using a two-alternative forced-choice procedure in which observers are asked to report the direction of motion of a Gabor patch, and taking precautions to exclude unconscious eye movements in the direction of the stimulus, we show that the limiting eccentricity of image-forming vision can be established with precision. There are large, but reliable, individual differences in the limiting eccentricity. The limiting eccentricity exhibits a dependence on log contrast; but it is not reduced when the modulation visible to the rods is attenuated, a result compatible with the histological evidence that the outermost part of the retina exhibits a high density of cones. Our working hypothesis is that only one type of neural channel is present in the far periphery of the retina, a channel that responds to temporally modulated stimuli of low spatial frequency and that is directionally selective.

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.

Synaptic inputs from identified bipolar and amacrine cells to a sparsely branched ganglion cell in rabbit retina

There are more than 30 distinct types of mammalian retinal ganglion cells, each sensitive to different features of the visual environment. In rabbit retina, they can be grouped into four classes according to their morphology and stratification of their dendrites in the inner plexiform layer (IPL). The goal of this study was to describe the synaptic inputs to one type of Class IV ganglion cell, the third member of the sparsely branched Class IV cells (SB3). One cell of this type was partially reconstructed in a retinal connectome developed using automated transmission electron microscopy (ATEM). It had slender, relatively straight dendrites that ramify in the sublamina a of the IPL. The dendrites of the SB3 cell were always postsynaptic in the IPL, supporting its identity as a ganglion cell. It received 29% of its input from bipolar cells, a value in the middle of the range for rabbit retinal ganglion cells studied previously. The SB3 cell typically received only one synapse per bipolar cell from multiple types of presumed OFF bipolar cells; reciprocal synapses from amacrine cells at the dyad synapses were infrequent. In a few instances, the bipolar cells presynaptic to the SB3 ganglion cell also provided input to an amacrine cell presynaptic to the ganglion cell. There was apparently no crossover inhibition from narrow-field ON amacrine cells. Most of the amacrine cell inputs were from axons and dendrites of GABAergic amacrine cells, likely providing inhibitory input from outside the classical receptive field.

Unusual Physiological Properties of Smooth Monostratified Ganglion Cell Types in Primate Retina

The functions of the diverse retinal ganglion cell types in primates and the parallel visual pathways they initiate remain poorly understood. Here, unusual physiological and computational properties of the ON and OFF smooth monostratified ganglion cells are explored. Large-scale multi-electrode recordings from 48 macaque retinas revealed that these cells exhibit irregular receptive field structure composed of spatially segregated hotspots, quite different from the classic center-surround model of retinal receptive fields. Surprisingly, visual stimulation of different hotspots in the same cell produced spikes with subtly different spatiotemporal voltage signatures, consistent with a dendritic contribution to hotspot structure. Targeted visual stimulation and computational inference demonstrated strong nonlinear subunit properties associated with each hotspot, supporting a model in which the hotspots apply nonlinearities at a larger spatial scale than bipolar cells. These findings reveal a previously unreported nonlinear mechanism in the output of the primate retina that contributes to signaling spatial information.

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.

Particle-Mediated Gene Transfection and Organotypic Culture of Postmortem Human Retina

Purpose

Particle-mediated gene transfer has been used in animal models to study the morphology and connectivity of retinal ganglion cells. The aim of the present study was to apply this method to transfect ganglion cells in postmortem human retina.

Methods

Postmortem human eyes from male and female donors aged 40 to 76 years old were obtained within 15 hours after death. In addition, two marmoset retinas were obtained immediately after death. Ganglion cells were transfected with an expression plasmid for the postsynaptic density 95 protein conjugated to green or yellow fluorescent protein. Retinas were cultured for 3 days, fixed and then processed with immunohistochemical markers to reveal their stratification in the inner plexiform layer.

Results

The retinas maintained their morphology and immunohistochemical properties for at least 3 days in culture. Bipolar and ganglion cell morphology was comparable to that observed in noncultured tissue. The quality of transfected cells in human retina was similar to that in freshly enucleated marmoset eyes. Based on dendritic field size and stratification, at least 11 morphological types of retinal ganglion cell were distinguished.

Conclusions

Particle-mediated gene transfer allows efficient targeting of retinal ganglion cells in cultured postmortem human retina.

Translational Relevance

The translational value of this methodology lies in the provision of an in vitro platform to study structural and connectivity changes in human eye diseases that affect the integrity and organization of cells in the retina.

Molecular Fingerprinting of On-Off Direction-Selective Retinal Ganglion Cells Across Species and Relevance to Primate Visual Circuits

The ability to detect moving objects is an ethologically salient function. Direction-selective neurons have been identified in the retina, thalamus, and cortex of many species, but their homology has remained unclear. For instance, it is unknown whether direction-selective retinal ganglion cells (DSGCs) exist in primates and, if so, whether they are the equivalent to mouse and rabbit DSGCs. Here, we used a molecular/circuit approach in both sexes to address these issues. In mice, we identify the transcription factor Satb2 (special AT-rich sequence-binding protein 2) as a selective marker for three RGC types: On-Off DSGCs encoding motion in either the anterior or posterior direction, a newly identified type of Off-DSGC, and an Off-sustained RGC type. In rabbits, we find that expression of Satb2 is conserved in On-Off DSGCs; however, it has evolved to include On-Off DSGCs encoding upward and downward motion in addition to anterior and posterior motion. Next, we show that macaque RGCs express Satb2 most likely in a single type. We used rabies virus-based circuit-mapping tools to reveal the identity of macaque Satb2-RGCs and discovered that their dendritic arbors are relatively large and monostratified. Together, these data indicate Satb2-expressing On-Off DSGCs are likely not present in the primate retina. Moreover, if DSGCs are present in the primate retina, it is unlikely that they express Satb2.SIGNIFICANCE STATEMENT The ability to detect object motion is a fundamental feature of almost all visual systems. Here, we identify a novel marker for retinal ganglion cells encoding directional motion that is evolutionarily conserved in mice and rabbits, but not in primates. We show in macaque monkeys that retinal ganglion cells (RGCs) that express this marker comprise a single type and are morphologically distinct from mouse and rabbit direction-selective RGCs. Our findings indicate that On-Off direction-selective retinal neurons may have evolutionarily diverged in primates and more generally provide novel insight into the identity and organization of primate parallel visual pathways.

Receptive Field Properties of Koniocellular On/Off Neurons in the Lateral Geniculate Nucleus of Marmoset Monkeys

The koniocellular (K) layers of the primate dorsal lateral geniculate nucleus house a variety of visual receptive field types, not all of which have been fully characterized. Here we made single-cell recordings targeted to the K layers of diurnal New World monkeys (marmosets). A subset of recorded cells was excited by both increments and decrements of light intensity (on/off-cells). Histological reconstruction of the location of these cells confirmed that they are segregated to K layers; we therefore refer to these cells as K-on/off cells. The K-on/off cells show high contrast sensitivity, strong bandpass spatial frequency tuning, and their response magnitude is strongly reduced by stimuli larger than the excitatory receptive field (silent suppressive surrounds). Stationary counterphase gratings evoke unmodulated spike rate increases or frequency-doubled responses in K-on/off cells; such responses are largely independent of grating spatial phase. The K-on/off cells are not orientation or direction selective. Some (but not all) properties of K-on/off cells are consistent with those of local-edge-detector/impressed-by-contrast cells reported in studies of cat retina and geniculate, and broad-thorny ganglion cells recorded in macaque monkey retina. The receptive field properties of K-on/off cells and their preferential location in the ventral K layers (K1 and K2) make them good candidates for the direct projection from geniculate to extrastriate cortical area MT/V5. If so, they could contribute to visual information processing in the dorsal ("where" or "action") visual stream.SIGNIFICANCE STATEMENT We characterize cells in an evolutionary ancient part of the visual pathway in primates. The cells are located in the lateral geniculate nucleus (the main visual afferent relay nucleus), in regions called koniocellular layers that are known to project to extrastriate visual areas as well as primary visual cortex. The cells show high contrast sensitivity and rapid, transient responses to light onset and offset. Their properties suggest they could contribute to visual processing in the dorsal ("where" or "action") visual stream.

Distribution and diversity of intrinsically photosensitive retinal ganglion cells in tree shrew

Intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate the pupillary light reflex, circadian entrainment, and may contribute to luminance and color perception. The diversity of ipRGCs varies from rodents to primates, suggesting differences in their contributions to retinal output. To further understand the variability in their organization and diversity across species, we used immunohistochemical methods to examine ipRGCs in tree shrew (Tupaia belangeri). Tree shrews share membership in the same clade, or evolutionary branch, as rodents and primates. They are highly visual, diurnal animals with a cone-dominated retina and a geniculo-cortical organization resembling that of primates. We identified cells with morphological similarities to M1 and M2 cells described previously in rodents and primates. M1-like cells typically had somas in the ganglion cell layer, with 23% displaced to the inner nuclear layer (INL). However, unlike M1 cells, they had bistratified dendritic fields ramifying in S1 and S5 that collectively tiled space. M2-like cells had dendritic fields restricted to S5 that were smaller and more densely branching. A novel third type of melanopsin immunopositive cell was identified. These cells had somata exclusively in the INL and monostratified dendritic fields restricted to S1 that tiled space. Surprisingly, these cells immunolabeled for tyrosine hydroxylase, a key component in dopamine synthesis. These cells immunolabeled for an RGC marker, not amacrine cell markers, suggesting that they are dopaminergic ipRGCs. We found no evidence for M4 or M5 ipRGCs, described previously in rodents. These results identify some organizational features of the ipRGC system that are canonical versus species-specific.

Diagnosing the Neural Circuitry of Reading

We summarize the current state of knowledge of the brain's reading circuits, and then we describe opportunities to use quantitative and reproducible methods for diagnosing these circuits. Neural circuit diagnostics-by which we mean identifying the locations and responses in an individual that differ significantly from measurements in good readers-can help parents and educators select the best remediation strategy. A sustained effort to develop and share diagnostic methods can support the societal goal of improving literacy.

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.

Melanopsin-expressing ganglion cells on macaque and human retinas form two morphologically distinct populations

The long-term goal of this research is to understand how retinal ganglion cells that express the photopigment melanopsin, also known as OPN4, contribute to vision in humans and other primates. Here we report the results of anatomical studies using our polyclonal antibody specifically against human melanopsin that confirm and extend previous descriptions of melanopsin cells in primates. In macaque and human retina, two distinct populations of melanopsin cells were identified based on dendritic stratification in either the inner or the outer portion of the inner plexiform layer (IPL). Variation in dendritic field size and cell density with eccentricity was confirmed, and dendritic spines, a new feature of melanopsin cells, were described. The spines were the sites of input from DB6 diffuse bipolar cell axon terminals to the inner stratifying type of melanopsin cells. The outer stratifying melanopsin type received inputs from DB6 bipolar cells via a sparse outer axonal arbor. Outer stratifying melanopsin cells also received inputs from axon terminals of dopaminergic amacrine cells. On the outer stratifying melanopsin cells, ribbon synapses from bipolar cells and conventional synapses from amacrine cells were identified in electron microscopic immunolabeling experiments. Both inner and outer stratifying melanopsin cell types were retrogradely labeled following tracer injection in the lateral geniculate nucleus (LGN). In addition, a method for targeting melanopsin cells for intracellular injection using their intrinsic fluorescence was developed. This technique was used to demonstrate that melanopsin cells were tracer coupled to amacrine cells and would be applicable to electrophysiological experiments in the future. J. Comp. Neurol. 524:2845-2872, 2016. © 2016 The Authors The Journal of Comparative Neurology Published by Wiley Periodicals, Inc.

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.

Broad thorny ganglion cells: a candidate for visual pursuit error signaling in the primate retina

Functional analyses exist only for a few of the morphologically described primate ganglion cell types, and their correlates in other mammalian species remain elusive. Here, we recorded light responses of broad thorny cells in the whole-mounted macaque retina. They showed ON-OFF-center light responses that were strongly suppressed by stimulation of the receptive field surround. Spike responses were delayed compared with parasol ganglion cells and other ON-OFF cells, including recursive bistratified ganglion cells and A1 amacrine cells. The receptive field structure was shaped by direct excitatory synaptic input and strong presynaptic and postsynaptic inhibition in both ON and OFF pathways. The cells responded strongly to dark or bright stimuli moving either in or out of the receptive field, independent of the direction of motion. However, they did not show a maintained spike response either to a uniform background or to a drifting plaid pattern. These properties could be ideally suited for guiding movements involved in visual pursuit. The functional characteristics reported here permit the first direct cross-species comparison of putative homologous ganglion cell types. Based on morphological similarities, broad thorny ganglion cells have been proposed to be homologs of rabbit local edge detector ganglion cells, but we now show that the two cells have quite distinct physiological properties. Thus, our data argue against broad thorny cells as the homologs of local edge detector cells.

Short-wavelength cone-opponent retinal ganglion cells in mammals

In all of the mammalian species studied to date, the short-wavelength-sensitive (S) cones and the S-cone bipolar cells that receive their input are very similar, but the retinal ganglion cells that receive synapses from the S-cone bipolar cells appear to be quite different. Here, we review the literature on mammalian retinal ganglion cells that respond selectively to stimulation of S-cones and respond with opposite polarity to longer wavelength stimuli. There are at least three basic mechanisms to generate these color-opponent responses, including: (1) opponency is generated in the outer plexiform layer by horizontal cells and is conveyed to the ganglion cells via S-cone bipolar cells, (2) inputs from bipolar cells with different cone inputs and opposite response polarity converge directly on the ganglion cells, and (3) inputs from S-cone bipolar cells are inverted by S-cone amacrine cells. These are not mutually exclusive; some mammalian ganglion cells that respond selectively to S-cone stimulation seem to utilize at least two of them. Based on these findings, we suggest that the small bistratified ganglion cells described in primates are not the ancestral type, as proposed previously. Instead, the known types of ganglion cells in this pathway evolved from monostratified ancestral types and became bistratified in some mammalian lineages.

Identification of a pathway from the retina to koniocellular layer K1 in the lateral geniculate nucleus of marmoset

Three well characterized pathways in primate vision (midget-parvocellular, parasol-magnocellular, bistratified-koniocellular) have been traced from the first synapse in the retina, through the visual thalamus (lateral geniculate nucleus, LGN), to the visual cortex. Here we identify a pathway from the first synapse in the retina to koniocellular layer K1 in marmoset monkeys (Callithrix jacchus). Particle-mediated gene transfer of an expression plasmid for the postsynaptic density 95-green fluorescent protein (PSD95-GFP) was used to label excitatory synapses on retinal ganglion cells and combined with immunofluorescence to identify the presynaptic bipolar cells. We found that axon terminals of one type of diffuse bipolar cell (DB6) provide dominant synaptic input to the dendrites of narrow thorny ganglion cells. Retrograde tracer injections into the LGN and photofilling of retinal ganglion cells showed that narrow thorny cells were preferentially labeled when koniocellular layer K1 was targeted. Layer K1 contains cells with high sensitivity for rapid movement, and layer K1 sends projections to association visual areas as well as to primary visual cortex. We hypothesize that the DB6-narrow thorny-koniocellular pathway contributes to residual visual functions ("blindsight") that survive injury to primary visual cortex in adult or early life.

Diversity of retinal ganglion cells identified by transient GFP transfection in organotypic tissue culture of adult marmoset monkey retina

The mammalian retina has more diversity of neurons than scientists had once believed in order to establish complicated vision processing. In the monkey retina, morphological diversity of retinal ganglion cells (RGCs) besides dominant midget and parasol cells has been suggested. However, characteristic subtypes of RGCs in other species such as bistratified direction-selective ganglion cells (DSGC) have not yet been identified. Increasing interest has been shown in the common marmoset (Callithrix jacchus) monkey as a "super-model" of neuroscientific research. Here, we established organotypic tissue culture of the adult marmoset monkey retina with particle-mediated gene transfer of GFP to survey the morphological diversity of RGCs. We successfully incubated adult marmoset monkey retinas for 2 to 4 days ex vivo for transient expression of GFP. We morphologically examined 121 RGCs out of more than 3240 GFP-transfected cells in 5 retinas. Among them, we identified monostratified or broadly stratified ganglion cells (midget, parasol, sparse, recursive, thorny, and broad thorny ganglion cells), and bistratified ganglion cells (recursive, large, and small bistratified ganglion cells [blue-ON/yellow-OFF-like]). By this survey, we also found a candidate for bistratified DSGC whose dendrites were well cofasciculated with ChAT-positive starburst dendrites, costratified with ON and OFF ChAT bands, and had honeycomb-shaped dendritic arbors morphologically similar to those in rabbits. Our genetic engineering method provides a new approach to future investigation for morphological and functional diversity of RGCs in the monkey retina.

Types of parvalbumin-containing retinotectal ganglion cells in mouse

The calcium-binding protein parvalbumin (PV) occurs in the retinal ganglion cells (RGCs) of various vertebrate species. In the present study, we aimed to identify the types of PV-containing RGCs that project to the superior colliculus (SC) in the mouse. We injected retrograde tracer dextran into the mouse SC to label RGCs. PV-containing RGCs were first identified by immunocytochemistry and then neurons double-labeled with dextran and PV were iontophoretically injected with a lipophilic dye, DiI. Subsequently, confocal microscopy was used to characterize the morphologic classification of the PV-immunoreactive (IR) retinotectal ganglion cells on the basis of dendritic field size, branching pattern, and stratification within the inner plexiform layer. Among the 8 different types of PV-containing RGCs in the mouse retina, we found all 8 types of RGCs projecting to the SC. The RGCs were heterogeneous in morphology. The combined approach of using tracer injection and a single cell injection after immunocytochemistry on a particular protein will provide valuable data to further understand the functional features of the RGCs which constitute the retinotectal pathway.

A novel type of complex ganglion cell in rabbit retina

The 15-20 physiological types of retinal ganglion cells (RGCs) can be grouped according to whether they fire to increased illumination in the receptive-field center (ON cells), decreased illumination (OFF cells), or both (ON-OFF cells). The diversity of RGCs has been best described in the rabbit retina, which has three types of ON-OFF RGCs with complex receptive-field properties: the ON-OFF direction-selective ganglion cells (DSGCs), the local edge detectors, and the uniformity detectors. Here we describe a novel type of bistratified ON-OFF RGC that has not been described in either physiological or morphological studies of rabbit RGCs. These cells stratify in the ON and OFF sublaminae of the inner plexiform layer, branching at about 30% and 60% depth, between the ON and OFF arbors of the bistratified DSGCs. Similar to the ON-OFF DSGCs, these cells respond with transient firing to both bright and dark spots flashed in the receptive field but, unlike the DSGCs, they show no directional preference for moving stimuli. We have termed these cells "transient ON-OFF" RGCs. Area-response measurements show that both the ON and the OFF spike responses have an antagonistic receptive-field organization, but with different spatial extents. Voltage-clamp recordings reveal transient excitatory inputs at light ON and light OFF; this excitation is strongly suppressed by surround stimulation, which also elicits direct inhibitory inputs to the cells at light ON and light OFF. Thus the receptive-field organization is mediated both within the presynaptic circuitry and by direct feed-forward inhibition.

Synaptic inputs to two types of koniocellular pathway ganglion cells in marmoset retina

The retinal connectivity of the diverse group of cells contributing to koniocellular visual pathways (widefield ganglion cells) is largely unexplored. Here we examined the synaptic inputs onto two koniocellular-projecting ganglion cell types named large sparse and broad thorny cells. Ganglion cells were labeled by retrograde tracer injections targeted to koniocellular layer K3 in the lateral geniculate nucleus in marmosets (Callithrix jacchus) and subsequently photofilled. Retinal preparations were processed with antibodies against the C-terminal binding protein 2, the AMPA receptor subunit GluR4, and against CD15 to identify bipolar (excitatory) and/or antibodies against gephyrin to identify amacrine (inhibitory) input. Large sparse cells are narrowly stratified close to the ganglion cell layer. Broad thorny ganglion cells are broadly stratified in the center of the inner plexiform layer. Bipolar input to large sparse cells derives from DB6 and maybe other ON bipolar types, whereas that to broad thorny cells derives from ON and OFF bipolar cell types. The total number of putative synapses on broad thorny cells is higher than the number on large sparse cells but the density of inputs (between 2 and 5 synapses per 100 μm(2) dendritic area) is similar for the two cell types, indicating that the larger number of synapses on broad thorny cells is attributable to the larger membrane surface area of this cell type. Synaptic input density is comparable to previous values for midget-parvocellular and parasol-magnocellular pathway cells. This suggests functional differences between koniocellular, parvocellular, and magnocellular pathways do not arise from variation in synaptic input densities.

Vision out of the corner of the eye

The margin of the temporal visual field lies more than 90° from the line of sight and is critical for detecting incoming threats and for balance and locomotive control. We show (i) contrast sensitivity beyond 70° is higher for moving stimuli than for stationary, and in the outermost region, only moving stimuli are visible; (ii) sensitivity is highest for motion in directions near the vertical and horizontal axes and is higher for forward than for backward directions; (iii) the former anisotropy arises early in the visual pathway; (iv) thresholds for discriminating direction are lowest for upward and downward motion.

Evaluation of AAV-mediated expression of Chop2-GFP in the marmoset retina

PURPOSE

Converting inner retinal neurons to photosensitive cells by expressing channelrhodopsin-2 (ChR2) offers a novel approach for treating blindness caused by retinal degenerative diseases. In the present study, the recombinant adeno-associated virus serotype 2 (rAAV2)-mediated expression and function of a fusion construct of channelopsin-2 (Chop2) and green fluorescent protein (GFP) (Chop2-GFP) were evaluated in the inner retinal neurons in the common marmoset Callithrix jacchus.

METHODS

rAAV2 vectors carrying ubiquitous promoters were injected into the vitreous chamber. Expression of Chop2-GFP and functional properties of ChR2 were examined by immunocytochemical and electrophysiological methods 3 months after injection.

RESULTS

The percentage of Chop2-GFP-expressing cells in the ganglion cell layer was found to be retinal region- and animal age-dependent. The highest percentage was observed in the far-peripheral region. Chop2-GFP expression was also found in the foveal and parafoveal region. In the peripheral retina in young animals with high viral concentrations, the expression of Chop2-GFP was observed in all major classes of retinal neurons, including all major types of ganglion cells. The morphologic properties of Chop2-GFP-positive cells were normal for at least 3 months, and ChR2-mediated light responses were demonstrated by electrophysiological recordings.

CONCLUSIONS

The rAAV2-mediated expression of ChR2 was observed in the inner retinal neurons in the marmoset retina through intravitreal delivery. The marmoset could be a valuable nonhuman primate model for developing ChR2-based gene therapy for treating blinding retinal degenerative diseases.

Histamine reduces flash sensitivity of on ganglion cells in the primate retina

PURPOSE. In Old World primates, the retina receives input from histaminergic neurons in the posterior hypothalamus. They are a subset of the neurons that project throughout the central nervous system and fire maximally during the day. The contribution of these neurons to vision, was examined by applying histamine to a dark-adapted, superfused baboon eye cup preparation while making extracellular recordings from peripheral retinal ganglion cells. METHODS. The stimuli were 5-ms, 560-nm, weak, full-field flashes in the low scotopic range. Ganglion cells with sustained and transient ON responses and two cell types with OFF responses were distinguished; their responses were recorded with a 16-channel microelectrode array. RESULTS. Low micromolar doses of histamine decreased the rate of maintained firing and the light sensitivity of ON ganglion cells. Both sustained and transient ON cells responded similarly to histamine. There were no statistically significant effects of histamine in a more limited study of OFF ganglion cells. The response latencies of ON cells were approximately 5 ms slower, on average, when histamine was present. Histamine also reduced the signal-to-noise ratio of ON cells, particularly in those cells with a histamine-induced increase in maintained activity. CONCLUSIONS. A major action of histamine released from retinopetal axons under dark-adapted conditions, when rod signals dominate the response, is to reduce the sensitivity of ON ganglion cells to light flashes. These findings may relate to reports that humans are less sensitive to light stimuli in the scotopic range during the day, when histamine release in the retina is expected to be at its maximum.

Synaptic inputs onto small bistratified (blue-ON/yellow-OFF) ganglion cells in marmoset retina

The inner plexiform layer of the retina contains functional subdivisions, which segregate ON and OFF type light responses. Here, we studied quantitatively the ON and OFF synaptic input to small bistratified (blue-ON/yellow-OFF) ganglion cells in marmosets (Callithrix jacchus). Small bistratified cells display an extensive inner dendritic tier that receives blue-ON input from short-wavelength-sensitive (S) cones via blue cone bipolar cells. The outer dendritic tier is sparse and is thought to receive yellow-OFF input from medium (M)- and long (L)-wavelength-sensitive cones via OFF diffuse bipolar cells. In total, 14 small bistratified cells from different eccentricities were analyzed. The cells were retrogradely labeled from the koniocellular layers of the lateral geniculate nucleus and subsequently photofilled. Retinal preparations were processed with antibodies against the C-terminal binding protein 2, the AMPA receptor subunit GluR4, and/or gephyrin to identify bipolar and/or amacrine input. The results show that the synaptic input is evenly distributed across the dendritic tree, with a density similar to that reported previously for other ganglion cell types. The population of cells showed a consistent pattern, where bipolar input to the inner tier is about fourfold greater than bipolar input to the outer tier. This structural asymmetry of bipolar input may help to balance the weight of cone signals from the sparse S cone array against inputs from the much denser M/L cone array.

Types and density of calretinin-containing retinal ganglion cells in mouse

Calcium-binding proteins are present in a number of retinal cell types. Types and density of parvalbumin-immunoreactive (IR) retinal ganglion cells (RGCs) in the mouse retina were previously reported using a newly developed single-cell injection technique following immunocytochemistry [Kim, T.J., Jeon, C.J., 2006. Morphological classification of parvalbumin-containing retinal ganglion cells in mouse: single-cell injection after immunocytochemistry. Invest. Ophthalmol. Vis. Sci. 47, 2757-2764]. The present study was aimed at describing the types and density of calretinin-containing RGCs in the mouse. Calretinin-containing RGCs were first identified by immunocytochemistry and were then iontophoretically injected with a lipophilic dye, DiI. Subsequently, confocal microscopy was used to characterize the morphologic classification of the calretinin-IR ganglion cells on the basis of the dendritic field size, branching pattern, and stratification within the inner plexiform layer (IPL). The results indicated that at least 10 morphologically different types of RGCs express calretinin in the mouse retina. They were heterogeneous in morphology: monostratified to bistratfied, small-to-large dendritic field size, and sparse-to-dense dendritic arbors. The present study showed that 86.59% (38,842/44,857) of RGCs contained calretinin. The density of calretinin-IR ganglion cell in the mouse retina was 2795cells/mm(2). The combined approach of cell morphology and the selective expression of a particular protein would provide valuable data for further knowledge on functional features of the RGCs.

Uniform signal redundancy of parasol and midget ganglion cells in primate retina

The collective representation of visual space in high resolution visual pathways was explored by simultaneously measuring the receptive fields of hundreds of ON and OFF midget and parasol ganglion cells in isolated primate retina. As expected, the receptive fields of all four cell types formed regular mosaics uniformly tiling the visual scene. Surprisingly, comparison of all four mosaics revealed that the overlap of neighboring receptive fields was nearly identical, for both the excitatory center and inhibitory surround components of the receptive field. These observations contrast sharply with the large differences in the dendritic overlap between the parasol and midget cell populations, revealing a surprising lack of correspondence between the anatomical and functional architecture in the dominant circuits of the primate retina.