The types of retinal ganglion cells: current status and implications for neuronal classification

Revealing the neurodevelopmental toxicity of face mask-derived microplastics to humans based on neural organoids

The massive use of face masks during and after the COVID-19 pandemic has raised global concerns about environmental issues. Microplastics released from face masks pose great threats to ecosystems and human health. However, the potentially hazardous effects of face mask-derived microplastics (FMMs) on humans remain poorly understood. Using neural organoid models aims to reveal the toxicity of FMMs to human early neural development. Retinal organoids derived from human embryonic stem cells were exposed to FMMs for 21 days during early retinogenesis. FMMs were internalized by retinal organoids. Exposure to FMMs disrupted the growth and development of retinal organoids in dose- and time-dependent manners, as evidenced by abnormal morphologies. Aberrant cell events, such as cell proliferation, apoptosis, and differentiation contributed to the disarrangement of the neural retina. Transcriptome data proved that the neurotoxicity of FMMs was closely related to disordered neurogenesis, anatomical structure morphogenesis, and axon guidance. Co-exposure to triphenyl phosphate (a common organophosphate flame retardant) and FMMs exhibited more pronounced neurotoxicity than FMM exposure alone. These findings are expected to uncover the potential threats of FMMs to human neurodevelopment and emphasize the importance of optimizing the management and safe disposal of used face masks.

Effect of brimonidine on retinal ganglion cell function by in vivo calcium imaging of optic nerve crush in mice

Brimonidine has shown neuroprotective effects in animal studies, but clinical trials failed to demonstrate effective endpoints. Here, we used a newly developed in vivo calcium imaging method to measure RGC function of brimonidine in mice optic nerve crush (ONC) models. To transduce RGCs in vivo, wild-type C57Bl/6j mice were treated with intravitreal AAV2-mSncg-jGCaMP7s, a live-cell Ca2+ tracer. RGCs are defined as 10 subtypes according to different responses to UV light. Mice were treated with topical brimonidine or placebo three times daily for two weeks after ONC. The calcium signals of live-cell RGCs were measured with the Heidelberg cSLO system. Ganglion cell complex (GCC) thickness and IOP were examined at different timepoints after treatment. RGCs were counted after RBPMS immunostaining. Live calcium imaging showed ONC significantly decreased RGC number at 14 days post-ONC compared to controls. The topical brimonidine administration changed calcium signal responses of RGC to UV light in ONC mice. It showed brimonidine partly prevented the decrease of survival ON-RGCs percent after ONC. Single RGC analysis showed a lower conversion percent of ON-RGCs to OFF-RGCs with brimonidine administration after ONC. However, no significant differences in RGC survival, IOP or GCC thickness were noted between eyes treated with brimonidine or placebo. In the acute ONC mice model, in vivo calcium imaging revealed that brimonidine maintained the Ca2+ activation of ON-RGCs to UV stimulation, inhibiting the conversion of survival ON-RGCs to OFF-RGCs. This indicates that ON-RGCs may be more resilient to acute optic nerve injury based on the calcium imaging method.

Visualizing sphingomyelin in the retina

Sphingomyelin (SM) is a major component of cellular membranes that is altered by retinal and optic nerve degenerations. However, our understanding of the influence of SM during degenerations is hampered by methodological limitations. Prior investigations have demonstrated the accumulation of SM to plasma membranes of cultured cells, using an enhanced green fluorescent non-toxic truncated form of lysenin (EGFP-NT-Lys), which is a protein that specifically binds to SM. Here, we used EGFP-NT-Lys and a permeabilization-free method for immunohistochemistry, which preserves membrane integrity, to demonstrate the accumulation of SM to the plasma membranes of retinal ganglion cells (RGCs) and retinal endothelial cells (RECs) of the intact mouse retina. To determine the sensitivity and selectivity of EGFP-NT-Lys for SM and SM species, we performed lipid dot blot assays. We found EGFP-NT-Lys is highly selective for SM and preferentially binds to longer-chain SMs. We confirmed that EGFP-NT-Lys labeling of SM is modifiable by treatment with the catabolic enzyme, sphingomyelinase. In addition, we verified EGFP-NT-Lys binding to SM by competition assays and EGFP. Confocal image analysis of immunofluorescence of RGC and REC markers and EGFP-NT-Lys labeling in flat mount mouse retinas revealed SM heavily accumulates within the retinal vasculature and around the perimeter of RGCs. Our data demonstrates that EGFP-NT-Lys combined with a permeabilization-free method for immunohistochemistry can be used to detect and quantify plasma membrane associated SM in defined cells of the intact retina.

On analogies in vertebrate and insect visual systems

Despite the large evolutionary distance between vertebrates and insects, the visual systems of these two taxa bear remarkable similarities that have been noted repeatedly, including by pioneering neuroanatomists such as Ramón y Cajal. Fuelled by the advent of transgenic approaches in neuroscience, studies of visual system anatomy and function in both vertebrates and insects have made dramatic progress during the past two decades, revealing even deeper analogies between their visual systems than were noted by earlier observers. Such across-taxa comparisons have tended to focus on either elementary motion detection or relatively peripheral layers of the visual systems. By contrast, the aims of this Review are to expand the scope of this comparison to pathways outside visual motion detection, as well as to deeper visual structures. To achieve these aims, we primarily discuss examples from recent work in larval zebrafish (Danio rerio) and the fruitfly (Drosophila melanogaster), a pair of genetically tractable model organisms with comparatively sized, small brains. In particular, we argue that the brains of both vertebrates and insects are equipped with third-order visual structures that specialize in shared behavioural tasks, including postural and course stabilization, approach and avoidance, and some other behaviours. These wider analogies between the two distant taxa highlight shared behavioural goals and associated evolutionary constraints and suggest that studies on vertebrate and insect vision have a lot to inspire each other.

Experience influences the refinement of feature selectivity in the mouse primary visual thalamus

Neurons exhibit selectivity for specific features: a property essential for extracting and encoding relevant information in the environment. This feature selectivity is thought to be modifiable by experience at the level of the cortex. Here, we demonstrate that selective exposure to a feature during development can alter the population representation of that feature in the primary visual thalamus. This thalamic plasticity is not due to changes in corticothalamic inputs and is blocked in mutant mice that exhibit deficits in retinogeniculate refinement, suggesting that plasticity is a direct result of changes in feedforward connectivity. Notably, experience-dependent changes in thalamic feature selectivity also occur in adult animals, although these changes are transient, unlike in juvenile animals, where they are long lasting. These results reveal an unexpected degree of plasticity in the visual thalamus and show that salient environmental features can be encoded in thalamic circuits during a discrete developmental window.

Survival and Axonal Regeneration of Retinal Ganglion Cells in a Mouse Optic Nerve Crush Model After a Cell-Based Intravitreal Co-Administration of Ciliary Neurotrophic Factor and Glial Cell Line-Derived Neurotrophic Factor at Different Post-Lesion Time Points

We recently showed, in a mouse optic nerve crush model, that a sustained cell-based intravitreal administration of ciliary neurotrophic factor (CNTF) and glial cell line-derived neurotrophic factor (GDNF) synergistically slowed the lesion-induced degeneration of retinal ganglion cells (RGCs), resulting in the presence of approximately 35% viable RGCs eight months after the lesion. However, the combinatorial neuroprotective treatment was initiated shortly after the lesion. To mimic a more clinically relevant situation, we co-administered both factors either three or five days after an intraorbital nerve crush when approximately 35% or 57% of the RGCs were degenerated, respectively. Analyses of the retinas at different time points after the lesion consistently revealed the presence of significantly more surviving RGCs in retinas co-treated with CNTF and GDNF than in retinas treated with either factor alone. For example, when the neurotrophic factors were administered five days after the nerve crush and the animals were analyzed two months after the lesion, retinas co-treated with CNTF and GDNF contained approximately 40% of the RGCs present at the start of treatment. In comparison, monotherapy with either CNTF or GDNF protected only about 15% or 10% of the RGCs present at baseline, respectively. The number of regenerating axons in the distal nerve stumps was similar in CNTF- and CNTF/GDNF-treated animals, despite the significantly higher number of rescued RGCs in the latter group. These findings have potential implications for studies aimed at developing neuroprotective treatments for optic neuropathies such as glaucoma.

Connectome-driven neural inventory of a complete visual system

Vision provides animals with detailed information about their surroundings and conveys diverse features such as colour, form and movement across the visual scene. Computing these parallel spatial features requires a large and diverse network of neurons. Consequently, from flies to humans, visual regions in the brain constitute half its volume. These visual regions often have marked structure-function relationships, with neurons organized along spatial maps and with shapes that directly relate to their roles in visual processing. More than a century of anatomical studies have catalogued in detail cell types in fly visual systems1-3, and parallel behavioural and physiological experiments have examined the visual capabilities of flies. To unravel the diversity of a complex visual system, careful mapping of the neural architecture matched to tools for targeted exploration of this circuitry is essential. Here we present a connectome of the right optic lobe from a male Drosophila melanogaster acquired using focused ion beam milling and scanning electron microscopy. We established a comprehensive inventory of the visual neurons and developed a computational framework to quantify their anatomy. Together, these data establish a basis for interpreting how the shapes of visual neurons relate to spatial vision. By integrating this analysis with connectivity information, neurotransmitter identity and expert curation, we classified the approximately 53,000 neurons into 732 types. These types are systematically described and about half are newly named. Finally, we share an extensive collection of split-GAL4 lines matched to our neuron-type catalogue. Overall, this comprehensive set of tools and data unlocks new possibilities for systematic investigations of vision in Drosophila and provides a foundation for a deeper understanding of sensory processing.

Cadherin 4 assembles a family of color-preferring retinal circuits that respond to light offset

Retinal interneurons and projection neurons (retinal ganglion cells, RGCs) connect in specific combinations in a specialized neuropil called the inner plexiform layer (IPL). The IPL is divided into multiple sublaminae, with neurites of each neuronal type confined to one or a few layers. This laminar specificity is a major determinant of circuit specificity and circuit function. Using a combination of approaches, we show that RGCs targeting IPL sublaminae 1 and 3a (s1-s3a) express the cell adhesion molecule cadherin 4 (Cdh4). Using calcium imaging and iterative immunostaining, we classified Cdh4 RGCs into nine types that each encode unique aspects of dark visual stimuli. Cdh4 loss selectively disrupted the layer targeting of these RGCs, reduced their synaptic inputs from interneurons, and severely altered their visual responses. Overexpression of Cdh4 in other retinal neurons directed their neurites to s1-s3a through homophilic interactions. Taken together, these results demonstrate that Cdh4 is a novel layer-targeting system for nearly a quarter of all RGCs.

Sustained Experimental Myopia Exacerbates the Effect of Eye Growth on Retinal Ganglion Cell Density and Function

The aim of this study is to describe the effect that sustained myopic eye growth has on the cellular distribution and function of retinal ganglion cells as myopia progresses over time. Ganglion cell density and the photopic negative response (PhNR) were assessed using immunochemistry and electroretinography (ERG), respectively, on twelve common marmoset eyes (Callithrix jacchus). Myopia was induced in six eyes using negative defocus (three eyes from 2 to 6 months of age, 6-month-old myopes; three eyes from 2 to 12 months of age, 12-month-old myopes). These six treated eyes were compared to six age-matched control eyes. Marmosets induced with myopia for four months showed a reduced pan-retinal ganglion cell density, which continued to decrease in the peripapillary area of marmosets induced with sustained myopia for ten months. Ganglion cell density decreased as a function of axial length. Full-field ERGs revealed a dampening of the PhNR in the 12-month-old, but not 6-month-old myopes. The myopic changes observed in ganglion cell density and retinal function suggest a reorganization of the ganglion cell template during myopia development and progression that increases over time with sustained myopic eye growth and translates into functional alterations at later stages of myopia development in the absence of degenerative changes. It remains unknown whether these changes positively or negatively impact retinal function and health.

Characterize neuronal responses to natural movies in the mouse superior colliculus

While artificial stimuli have been widely used in visual neuroscience and have significantly advanced our understanding of visual processing, they differ dramatically from the natural scenes that animals encounter in the wild. How natural stimuli are encoded in the superior colliculus (SC) and how neuronal responses to artificial and natural stimuli are related remain poorly understood. Here I applied two-photon calcium imaging to record neuronal activity in the mouse superficial SC in response to natural movies. An unsupervised learning algorithm grouped recorded neurons into 16 clusters based on their response patterns. Each cluster exhibited distinct temporal profiles, which arose from differences in both receptive field coverage and how neurons encode local visual features. Interestingly, I found a strong correlation between neuronal responses to natural movies and functional properties previously characterized using artificial stimuli. This suggests that the SC maintains a stable neural representation of visual information that is largely independent of the types of visual stimuli. Furthermore, neuronal responses to natural movies varied with depth within the superficial SC and across genetically defined neuronal types. These findings bridge the gap between our understanding of responses to artificial and natural stimuli, providing new insights into visual processing in the SC.

Serotonin regulates in a cell-type specific manner light-evoked response and synaptic activity in mouse retinal ganglion cells

BACKGROUND

Serotonin (5-HT) is known to be synthesized and accumulated in the vertebrate retina through the 5-HT transporter, SERT. While manipulation of the serotonergic system has been shown to impact visual processing, the role of 5-HT and SERT as modulators of retinal synaptic function remains poorly understood.

RESULTS

Using mouse retinal slices, we show that acute application of 5-HT produces a cell-type specific reduction in light-evoked excitatory responses (L-EPSC) in ON-OFF retinal ganglion cells (RGCs), but not in ON RGCs. Similarly, increasing 5-HT tone by acute application of citalopram, a selective 5-HT reuptake inhibitor, also reduces L-EPSC in ON-OFF RGCs while not affecting ON RGCs. Importantly, citalopram-mediated reduction of L-EPSC was absent in ON-OFF RGCs recorded from SERT null retina, highlighting the role of SERT in regulating light-evoked responses in RGCs. The effects of both exogenous and endogenous 5-HT on L-EPSC in ON-OFF RGCs are likely due to a presynaptic reduction in excitatory synaptic strength as 5-HT and citalopram reduced the frequency but not the amplitude of spontaneous excitatory currents (sEPSCs) in ON-OFF RGCs. Moreover, 5-HT and citalopram had no effect on currents elicited by the direct activation of postsynaptic receptors in RGCs by brief application of glutamate in the inner retina.

CONCLUSIONS

Altogether these findings indicate that 5-HT modulates excitatory inputs onto RGCs in a cell-type specific manner and highlight that in the adult mouse retina, 5-HT-mediated effects onto RGCs are tightly controlled by the 5-HT transporter SERT.

Predicting the Regenerative Potential of Retinal Ganglion Cells Based on Developmental Growth Trajectories

Retinal ganglion cells in the mammalian central nervous system fail to regenerate following injury, with the capacity to survive and regrow varying by cell type. This variability may be linked to differences in developmental programs that overlap with the genetic pathways that mediate regeneration. To explore this correlation, we compared the structural changes in mouse retinal ganglion cells during development with those occurring after axonal injury. The dendritic trees of over 1,000 ganglion cells were reconstructed at different developmental stages, revealing that each cell type follows a distinct timeline. ON-sustained (sONα) cells reach maturity by P14, whereas ON-transient (tONα) cells achieve their maximum dendritic size by P10. Modeling of the dendritic changes indicate that while sONα and tONα follow similar growth programs the onset of growth was later in sONα. After optic nerve crush, the remodeling of dendritic architecture differed between the two cell-types. sONα cells exhibited rapid dendritic shrinkage, while tONα cells shrank more gradually with changes in branching features. Following injury, sONα cells reverted to an earlier developmental state than tONα cells. In addition, after co-deletion of PTEN and SOC3, neurons appeared to regress further back in developmental time. Our results provide evidence that a ganglion cell's resilience to injury and regenerative potential is predicted by its maturation timeline. Understanding these intrinsic differences could inform targeted neuroprotective interventions.

Retinal ganglion cell vulnerability to pathogenic tau in Alzheimer's disease

Pathological tau isoforms, including hyperphosphorylated tau at serine 396 (pS396-tau) and tau oligomers (Oligo-tau), are elevated in the retinas of patients with mild cognitive impairment (MCI) due to Alzheimer's disease (AD) and AD dementia. These patients exhibit significant retinal ganglion cell (RGC) loss, however the presence of tau isoforms in RGCs and their impact on RGC integrity, particularly in early AD, have not been studied. Here, we analyzed retinal superior temporal cross-sections from 25 MCI or AD patients and 16 age- and sex-matched cognitively normal controls. Using the RGC marker ribonucleic acid binding protein with multiple splicing (RBPMS) and Nissl staining, we found a 46-56% reduction in RBPMS+ RGCs and Nissl+ neurons in the ganglion cell layer (GCL) of MCI and AD retinas (P < 0.05-0.001). RGC loss was accompanied by soma hypertrophy (10-50% enlargement, P < 0.05-0.0001), nuclear displacement, apoptosis (30-50% increase, P < 0.05-0.01), and prominent expression of granulovacuolar degeneration (GVD) bodies and GVD-necroptotic markers. Both pS396-tau and Oligo-tau were identified in RGCs, including in hypertrophic cells. PS396-tau+ and Oligo-tau+ RGC counts were significantly increased by 2.1-3.5-fold in MCI and AD retinas versus control retinas (P < 0.05-0.0001). Tauopathy-laden RGCs strongly inter-correlated (rP=0.85, P < 0.0001) and retinal tauopathy associated with RGC reduction (rP=-0.40-(-0.64), P < 0.05-0.01). Their abundance correlated with brain pathology and cognitive deficits, with higher tauopathy-laden RGCs in patients with Braak stages (V-VI), clinical dementia ratings (CDR = 3), and mini-mental state examination (MMSE ≤   26) scores. PS396-tau+ RGCs in the central and mid-periphery showed the closest associations with disease status, while Oligo-tau+ RGCs in the mid-periphery exhibited the strongest correlations with brain pathology (NFTs, Braak stages, ABC scores; rS=0.78-0.81, P < 0.001-0.0001) and cognitive decline (MMSE; rS=-0.79, P = 0.0019). Overall, these findings identify a link between pathogenic tau in RGCs and RGC degeneration in AD, involving apoptotic and GVD-necroptotic cell death pathways. Future research should validate these results in larger and more diverse cohorts and develop RGC tauopathy as a potential noninvasive biomarker for early detection and monitoring of AD progression.

Bile duct ligation impairs visual acuity in rats by ammonia- and bilirubin-induced retinal degeneration

Patients with hepatic failure are often accompanied by hepatic retinopathy, but the cellular and molecular mechanisms underlying the hepatic retinopathy remain unclear. In this study, we investigated how liver failure leads to hepatic retinopathy using bile duct ligation (BDL) rats as a cholestasis animal model. Light-dark box test was used to assess sensitivity to light, indexed as visual acuity. On D28 post-BDL, rats were subjected to light-dark box test and blood samples were collected for biochemical analyses. The rats then were euthanized. Liver, spleen and both side of eye were quickly harvested. We showed that BDL impaired rat sensitivity to light, significantly decreased the thickness of inner nuclear layer (INL), outer nuclear layer (ONL) and total retina, as well as the retinal cell numbers in ONL and ganglion cell layer (GCL). The expression of rhodopsin (RHO), brn-3a and GPX4 was significantly decreased in retina of BDL rats, whereas the expression of cleaved caspase 3, 8, 9, bax/bcl-2, RIP1, GFAP, and iba-1, as well as TUNEL-positive cells were significantly increased. In cultured retinal explant, we found that NH4Cl (0.2, 1, 5 mM) concentration-dependently impaired activity of retinal explant, decreased thickness of INL and ONL, downregulated expression of brn-3a, RHO and GFAP, increased expression of cl-caspase 3 and TUNEL-positive cell numbers, with NH4Cl (5 mM) almost completely disrupting the structure of the cultured retina; bilirubin (1 μM) significantly upregulated GFAP expression, whereas high level (10 μM) of bilirubin downregulated expression of GFAP. We further demonstrated in vivo that hyperammonemia impaired rat sensitivity to light, decreased thickness of INL and ONL, downregulated expression of RHO, brn-3a, GFAP and increased expression of cl-caspase 3; hyperbilirubinemia impaired rat sensitivity to light, upregulated expression of GFAP and iba-1. In conclusion, BDL impaired rat visual acuity due to the elevated levels of ammonia and bilirubin. Ammonia induced loss of retinal ganglion cells and rod photoreceptor cells via apoptosis-mediated cell death. Bilirubin impaired retinal function via activating microglia and Müller cells.

Cholinergic waves have a modest influence on the transcriptome of retinal ganglion cells

In the early stages of development, correlated activity known as retinal waves causes periodic depolarizations of retinal ganglion cells (RGCs). The β2KO mouse, which lacks the β2 subunit of the nicotinic acetylcholine receptor, serves as a model for understanding the role of these cholinergic waves. β2KO mice have disruptions in several developmental processes of the visual system, including reduced retinotopic and eye-specific refinement of RGC axonal projections to their primary brain targets and an impact on the retinal circuits underlying direction selectivity. However, the effects of this mutation on gene expression in individual functional RGC types remain unclear. Here, we performed single-cell RNA sequencing on RGCs isolated at the end of the first postnatal week from wild-type and β2KO mice. We found that in β2KO mice, the molecular programs governing RGC differentiation were not impacted and the magnitude of transcriptional changes was modest compared to those observed during two days of normal postnatal maturation. This contrasts with the substantial transcriptomic changes seen in downstream visual system areas under wave disruption in recent studies. However, we identified ∼238 genes whose expression was altered in a type-specific manner. We confirmed this result via in situ hybridization and whole-cell recording by focusing on one of the downregulated genes in aRGCs, Kcnk9 , which encodes the two-pore domain leak potassium channel TASK3. Our study reveals a limited transcriptomic impact of cholinergic signaling in the retina and instead of affecting all RGCs uniformly, these waves show subtle modulation of molecular programs in a type-specific manner.

SIGNIFICANCE STATEMENT

Spontaneous retinal waves are critical for the development of the mammalian visual system. However, their role in transcriptional regulation in the retina across the diverse retinal ganglion cell (RGC) types that underpin the detection and transmission of visual features is unclear. Using single-cell RNA sequencing, we analyzed RGC transcriptome from wild-type mice and mice with disrupted retinal waves. We identified several genes that show RGC-type-specific regulation in their expression, including multiple neuropeptides and ion channels. However, wave-dependent changes in the transcriptome were more subtle than developmental changes, indicating that spontaneous activity-dependent molecular changes in retinal ganglion cells are not primarily manifested at the transcriptomic level.

The unbearable slowness of being: Why do we live at 10 bits/s?

This article is about the neural conundrum behind the slowness of human behavior. The information throughput of a human being is about 10 bits/s. In comparison, our sensory systems gather data at ∼109 bits/s. The stark contrast between these numbers remains unexplained and touches on fundamental aspects of brain function: what neural substrate sets this speed limit on the pace of our existence? Why does the brain need billions of neurons to process 10 bits/s? Why can we only think about one thing at a time? The brain seems to operate in two distinct modes: the "outer" brain handles fast high-dimensional sensory and motor signals, whereas the "inner" brain processes the reduced few bits needed to control behavior. Plausible explanations exist for the large neuron numbers in the outer brain, but not for the inner brain, and we propose new research directions to remedy this.

Morphological and functional convergence of visual projection neurons from diverse neurogenic origins in Drosophila

The Drosophila visual system is a powerful model to study the development of neural circuits. Lobula columnar neurons-LCNs are visual output neurons that encode visual features relevant to natural behavior. There are ~20 classes of LCNs forming non-overlapping synaptic optic glomeruli in the brain. To address their origin, we used single-cell mRNA sequencing to define the transcriptome of LCN subtypes and identified lines that are expressed throughout their development. We show that LCNs originate from stem cells in four distinct brain regions exhibiting different modes of neurogenesis, including the ventral and dorsal tips of the outer proliferation center, the ventral superficial inner proliferation center and the central brain. We show that this convergence of similar neurons illustrates the complexity of generating neuronal diversity, and likely reflects the evolutionary origin of each subtype that detects a specific visual feature and might influence behaviors specific to each species.

Role of Elavl-like RNA-binding protein in retinal development and signal transduction

RNA-binding proteins (RBPs) play central roles in post-transcriptional gene regulation. However, the function of RBP in retinal progenitor cell differentiation and synaptic signal transmission are largely unexplored. Previously we have shown that Elavl2 regulates amacrine cell (AC) differentiation during retinogenesis, by directly binding to Nr4a2 and Barhl2. Elavl2 is expressed in early neuronal progenitors to mature neurons, and Elavl4 expression begins slightly later, during cortical neuron development as a paralog. Here, Retinal-specific Elavl2 and Elavl4 double knockout mice were made to further explore the role of Elavl2 and Elavl4 in retinal development and signal transduction. We disclose that Elavl4 binds to Satb1 to regulate Neurod1, then promoting retinal progenitor and amacrine cells differentiation. We were also surprised to find that Elavl2 interacted with GABAB receptors at the RNA and protein levels. In conclusion, Elavl2 and Elavl4 regulate amacrine cells differentiation through different pathways, leading to decreased scotopic vision. Our findings reveal the roles of Elavl2 and Elavl4 in retinal amacrine cells differentiation in modulating visual functions.

Fluorescent identification of axons, dendrites and soma of neuronal retinal ganglion cells with a genetic marker as a tool for facilitating the study of neurodegeneration

This study characterizes a fluorescent Slc17a6-tdTomato neuronal reporter mouse line with strong labeling of axons throughout the optic nerve, of retinal ganglion cell (RGC) soma in the ganglion cell layer (GCL), and of RGC dendrites in the inner plexiform layer (IPL). The model facilitated assessment of RGC loss in models of degeneration and of RGC detection in mixed neural/glial cultures. The tdTomato signal showed strong overlap with >98% cells immunolabeled with RGC markers RBPMS or BRN3A, consistent with the ubiquitous presence of the vesicular glutamate transporter 2 (VGUT2, SLC17A6) in all RGC subtypes. There was no cross-labeling of ChAT-positive displaced amacrine cells in the GCL, although some signal emanated from the outer plexiform layer, consistent with horizontal cells. The fluorescence allowed rapid screening of RGC loss following optic nerve crush and intraocular pressure (IOP) elevation. The bright fluorescence also enabled non-invasive monitoring of extensive neurite networks and neuron/astrocyte interactions in culture. Robust Ca2+ responses to P2X7R agonist BzATP were detected from fluorescent RGCs using Ca2+-indicator Fura-2. Fluorescence from axons and soma was detected in vivo with a confocal scanning laser ophthalmoscope (cSLO); automatic RGC soma counts enhanced through machine learning approached the numbers found in retinal wholemounts. Controls indicated no impact of Slc17a6-tdTomato expression on light-dependent neuronal function as measured with a microelectrode array (MEA), or on retinal structure as measured with optical coherence tomography (OCT). In summary, the bright fluorescence in axons, dendrites and soma of ~all RGCs in the Slc17a6-tdTomato reporter mouse may facilitate the study of RGCs.

miRNA changes associated with differentiation of human embryonic stem cells into human retinal ganglion cells

miRNA, short non-coding RNA, are rapidly emerging as important regulators in cell homeostasis, as well as potential players in cellular degeneration. The latter has led to interest in them as both biomarkers and as potential therapeutics. Retinal ganglion cells (RGC), whose axons connect the eye to the brain, are central nervous system cells of great interest, yet their study is largely restricted to animals due to the difficulty in obtaining healthy human RGC. Using a CRISPR/Cas9-based reporter embryonic stem cell line, human RGC were generated and their miRNA profile characterized using NanoString miRNA assays. We identified a variety of retinal specific miRNA upregulated in ESC-derived RGC, with half of the most abundant miRNA also detectable in purified rat RGC. Several miRNA were however identified to be unique to RGC from human. The findings show which miRNA are abundant in RGC and the limited congruence with animal derived RGC. These data could be used to understand miRNA's role in RGC function, as well as potential biomarkers or therapies in retinal diseases involving RGC degeneration.

Molecular and spatial analysis of ganglion cells on retinal flatmounts: diversity, topography, and perivascularity

Diverse retinal ganglion cells (RGCs) transmit distinct visual features from the eye to the brain. Recent studies have categorized RGCs into 45 types in mice based on transcriptomic profiles, showing strong alignment with morphological and electrophysiological properties. However, little is known about how these types are spatially arranged on the two-dimensional retinal surface-an organization that influences visual encoding-and how their local microenvironments impact development and neurodegenerative responses. To address this gap, we optimized a workflow combining imaging-based spatial transcriptomics (MERFISH) and immunohistochemical co-staining on thin flatmount retinal sections. We used computational methods to register en face somata distributions of all molecularly defined RGC types. More than 75% (34/45) of types exhibited non-uniform distributions, likely reflecting adaptations of the retina's anatomy to the animal's visual environment. By analyzing the local neighborhoods of each cell, we identified perivascular RGCs located near blood vessels. Seven RGC types are enriched in the perivascular niche, including members of intrinsically photosensitive RGC (ipRGC) and direction-selective RGC (DSGC) subclasses. Orthologous human RGC counterparts of perivascular types - Melanopsin-enriched ipRGCs and ON DSGCs - were also proximal to blood vessels, suggesting their perivascularity may be evolutionarily conserved. Following optic nerve crush in mice, the perivascular M1-ipRGCs and ON DSGCs showed preferential survival, suggesting that proximity to blood vessels may render cell-extrinsic neuroprotection to RGCs through an mTOR-independent mechanism. Overall, our work offers a resource characterizing the spatial profiles of RGC types, enabling future studies of retinal development, physiology, and neurodegeneration at individual neuron type resolution across the two-dimensional space.

Band Visibility in High-Resolution Optical Coherence Tomography Assessed With a Custom Review Tool and Updated, Histology-Derived Nomenclature

Purpose

For structure-function research at the transition of aging to age-related macular degeneration, we refined the current consensus optical coherence tomography (OCT) nomenclature and evaluated a novel review software for investigational high-resolution OCT imaging (HR-OCT; <3 µm axial resolution).

Method

Volume electron microscopy, immunolocalizations, histology, and investigational devices informed a refined OCT nomenclature for a custom ImageJ-based review tool to assess retinal band visibility. We examined effects on retinal band visibility of automated real-time averaging (ART) 9 and 100 (11 eyes of 10 healthy young adults), aging (10 young vs 22 healthy aged), and age-related macular degeneration (AMD; 22 healthy aged, 17 early (e)AMD, 15 intermediate (i)AMD). Intrareader reliability was assessed.

Results

Bands not included in consensus nomenclature are now visible using HR-OCT: inner plexiform layer (IPL) 1-5, outer plexiform layer (OPL) 1-2, outer segment interdigitation zone 1-2 (OSIZ, including hyporeflective outer segments), and retinal pigment epithelium (RPE) 1-5. Cohen's kappa was 0.54-0.88 for inner and 0.67-0.83 for outer retinal bands in a subset of 10 eyes. IPL-3-5 and OPL-2 visibility benefitted from increased ART. OSIZ-2 and RPE-1,2,3,5 visibility was worse in aged eyes than in young eyes. OSIZ-1-2, RPE-1, and RPE-5 visibility decreased in eAMD and iAMD compared to healthy aged eyes.

Conclusions

We reliably identified 28 retinal bands using a novel review tool for HR-OCT. Image averaging improved inner retinal band visibility. Aging and AMD development impacted outer retinal band visibility.

Translational Significance

Detailed knowledge of anatomic structures visible on OCT will enhance precision in research, including AI training and structure-function analyses.

Effects of triploidization on light sensitivity in larval stage of Pacific bluefin tuna Thunnus orientalis

Triploidization influences various biological characteristics of fish, which is associated with reductions in the number of multiple cell types in different tissues/organs. Our behavioral analyses revealed that triploid Pacific bluefin tuna (Thunnus orientalis) larvae exhibit lower sensitivity to light compared to diploids. Furthermore, histological analyses revealed a reduction in the number of ganglion cells and an increase in their size in the retinas of triploid T. orientalis larvae. Our findings provide the first evidence indicating that triploidization reduces sensory perception during the larval stage of fish.

Retinal ganglion cell circuits and glial interactions in humans and mice

Retinal ganglion cells (RGCs) are the brain's gateway for vision, and their degeneration underlies several blinding diseases. RGCs interact with other neuronal cell types, microglia, and astrocytes in the retina and in the brain. Much knowledge has been gained about RGCs and glia from mice and other model organisms, often with the assumption that certain aspects of their biology may be conserved in humans. However, RGCs vary considerably between species, which could affect how they interact with their neuronal and glial partners. This review details which RGC and glial features are conserved between mice, humans, and primates, and which differ. We also discuss experimental approaches for studying human and primate RGCs. These strategies will help to bridge the gap between rodent and human RGC studies and increase study translatability to guide future therapeutic strategies.

Retinal Ganglion Cell Replacement in Glaucoma Therapy: A Narrative Review

Glaucoma is a leading cause of irreversible blindness worldwide. It leads to the progressive degeneration of retinal ganglion cells (RGCs), the axons of which form the optic nerve. Enormous RGC apoptosis causes a lack of transfer of visual information to the brain. The RGC loss typical of the central nervous system is irreversible, and when glaucoma progresses, the total amount of RGCs in the retina enormously diminishes. The successful treatment in glaucoma patients is a direct neuroprotection by decreasing the intraocular pressure, which enables RGC protection but does not revive the lost ones. The intriguing new therapy for advanced glaucoma is the possibility of RGC replacement with new healthy cells. In this review article, the strategies regarding RGC replacement therapy are presented with the latest advances in the technique and the obstacles that it meets.

Cellular Characterization and Interspecies Evolution of the Tree Shrew Retina across Postnatal Lifespan

Tree shrews (TSs) possess a highly developed visual system. Here, we establish an age-related single-cell RNA sequencing atlas of retina cells from 15 TSs, covering 6 major retina cell classes and 3 glial cell types. An age effect is observed on the cell subset composition and gene expression pattern. We then verify the cell subtypes and identify specific markers in the TS retina including CA10 for bipolar cells, MEGF11 for H1 horizontal cells, and SLIT2, RUNX1, FOXP2, and SPP1 for retinal ganglion cell subpopulations. The cross-species analysis elucidates the cell type-specific transcriptional programs, different cell compositions, and cell communications. The comparisons also reveal that TS cones and subclasses of bipolar and amacrine cells exhibit the closest relationship with humans and macaques. Our results suggests that TS could be used as a better disease model to understand age-dependent cellular and genetic mechanisms of the retina, particularly for the retinal diseases associated with cones.

AAV dose-dependent transduction efficiency in retinal ganglion cells and functional efficacy of optogenetic vision restoration

Optogenetics is a promising approach for restoring vision to the blind after photoreceptor degeneration. The ability to restore vision through AAV-mediated delivery of light-sensitive proteins, especially channelrhodopsins, into retinal ganglion cells has been extensively demonstrated in animal models. For clinical application, knowledge of viral dose-dependent functional efficacy is desired. In this study, using a triple-knockout blind mouse model and a highly light-sensitive channelrhodopsin variant, we evaluated viral dose-dependent vision restoration through retinal ganglion cell expression by using optomotor behavioral assays. Our results show that both the restored light sensitivity and visual acuity reached peak levels at a medial viral dose of 108 vg. With increasing dose, transduction efficiency continued to increase while protein expression peaked at the dose of ~109 vg and declined at higher doses. Also, a significant increase in retinal gliosis and inflammatory responses started at the dose of ~109 vg, and a marked increase was observed at the dose of ~1010. These results provide valuable insights into viral dose design for clinical studies.

Molecular Mechanisms of Glaucoma Pathogenesis with Implications to Caveolin Adaptor Protein and Caveolin-Shp2 Axis

Glaucoma is a common retinal disorder characterized by progressive optic nerve damage, resulting in visual impairment and potential blindness. Elevated intraocular pressure (IOP) is a major risk factor, but some patients still experience disease progression despite IOP-lowering treatments. Genome-wide association studies have linked variations in the Caveolin1/2 (CAV-1/2) gene loci to glaucoma risk. Cav-1, a key protein in caveolae membrane invaginations, is involved in signaling pathways and its absence impairs retinal function. Recent research suggests that Cav-1 is implicated in modulating the BDNF/TrkB signaling pathway in retinal ganglion cells, which plays a critical role in retinal ganglion cell (RGC) health and protection against apoptosis. Understanding the interplay between these proteins could shed light on glaucoma pathogenesis and provide potential therapeutic targets.

Whole-brain annotation and multi-connectome cell typing of Drosophila

The fruit fly Drosophila melanogaster has emerged as a key model organism in neuroscience, in large part due to the concentration of collaboratively generated molecular, genetic and digital resources available for it. Here we complement the approximately 140,000 neuron FlyWire whole-brain connectome1 with a systematic and hierarchical annotation of neuronal classes, cell types and developmental units (hemilineages). Of 8,453 annotated cell types, 3,643 were previously proposed in the partial hemibrain connectome2, and 4,581 are new types, mostly from brain regions outside the hemibrain subvolume. Although nearly all hemibrain neurons could be matched morphologically in FlyWire, about one-third of cell types proposed for the hemibrain could not be reliably reidentified. We therefore propose a new definition of cell type as groups of cells that are each quantitatively more similar to cells in a different brain than to any other cell in the same brain, and we validate this definition through joint analysis of FlyWire and hemibrain connectomes. Further analysis defined simple heuristics for the reliability of connections between brains, revealed broad stereotypy and occasional variability in neuron count and connectivity, and provided evidence for functional homeostasis in the mushroom body through adjustments of the absolute amount of excitatory input while maintaining the excitation/inhibition ratio. Our work defines a consensus cell type atlas for the fly brain and provides both an intellectual framework and open-source toolchain for brain-scale comparative connectomics.

Retinal ganglion cell vulnerability to pathogenic tau in Alzheimer's disease

Accumulation of pathological tau isoforms, especially hyperphosphorylated tau at serine 396 (pS396-tau) and tau oligomers, has been demonstrated in the retinas of patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Previous studies have noted a decrease in retinal ganglion cells (RGCs) in AD patients, but the presence and impact of pathological tau isoforms in RGCs and RGC integrity, particularly in early AD stages, have not been explored. To investigate this, we examined retinal superior temporal cross-sections from 25 patients with MCI (due to AD) or AD dementia and 16 cognitively normal (CN) controls, matched for age and gender. We utilized the RGC marker ribonucleic acid binding protein with multiple splicing (RBPMS) and Nissl staining to assess neuronal density in the ganglion cell layer (GCL). Our study found that hypertrophic RGCs containing pS396-tau and T22-positive tau oligomers were more frequently observed in MCI and AD patients compared to CN subjects. Quantitative analyses indicated a decline in RGC integrity, with 46-55% and 55-56% reductions of RBPMS+ RGCs (P<0.01) and Nissl+ GCL neurons (P<0.01-0.001), respectively, in MCI and AD patients. This decrease in RGC count was accompanied by increases in necroptotic-like morphology and the cleaved caspase-3 apoptotic marker in RGCs of AD patients. Furthermore, there was a 2.1 to 3.1-fold increase (P<0.05-0.0001) in pS396-tau-laden RGCs in MCI and AD patients, with a greater abundance observed in individuals with higher Braak stages (V-VI), more severe clinical dementia ratings (CDR=3), and lower mini-mental state examination (MMSE) scores. Strong correlations were noted between the decline in RGCs and the total amount of retinal pS396-tau and pS396-tau+ RGCs, with pS396-tau+ RGC counts correlating significantly with brain neurofibrillary tangle scores (r= 0.71, P= 0.0001), Braak stage (r= 0.65, P= 0.0009), and MMSE scores (r= -0.76, P= 0.0004). These findings suggest that retinal tauopathy, characterized by pS396-tau and oligomeric tau in hypertrophic RGCs, is associated with and may contribute to RGC degeneration in AD. Future research should validate these findings in larger cohorts and explore noninvasive retinal imaging techniques that target tau pathology in RGCs to improve AD detection and monitor disease progression.

Impact of Glaucomatous Ganglion Cell Damage on Central Visual Function

Glaucoma, a leading cause of irreversible blindness, is characterized by the progressive loss of retinal ganglion cells (RGCs) and subsequent visual field defects. RGCs, as the final output neurons of the retina, perform key computations underpinning human pattern vision, such as contrast coding. Conventionally, glaucoma has been associated with peripheral vision loss, and thus, relatively little attention has been paid to deficits in central vision. However, recent advancements in retinal imaging techniques have significantly bolstered research into glaucomatous damage of the macula, revealing that it is prevalent even in the early stages of glaucoma. Thus, it is an opportune time to explore how glaucomatous damage undermines the perceptual processes associated with central visual function. This review showcases recent studies addressing central dysfunction in the early and moderate stages of glaucoma. It further emphasizes the need to characterize glaucomatous damage in both central and peripheral vision, as they jointly affect an individual's everyday activities.

Evaluation of thickness of individual macular retinal layers in diabetic eyes from optical coherence tomography

The effect of diabetes mellitus (DM) on individual retinal layers remains incompletely understood. We evaluated the intra-retinal layer thickness alterations in 71 DM eyes with no diabetic retinopathy (DR), 90 with mild DR, and 63 with moderate DR without macular edema, using spectral-domain optical coherence tomography (SD-OCT) and the Iowa Reference Algorithm for automated retinal layer segmentation. The average thickness of 10 intra-retinal layers was then corrected for ocular magnification using axial length measurements, and pairwise comparisons were made using multivariable linear regression models adjusted for gender and race. In DM no DR eyes, significant thinning was evident in the ganglion cell layer (GCL; p < 0.001), inner nuclear layer (INL; p = 0.001), and retinal pigment epithelium (RPE; p = 0.014) compared to normal eyes. Additionally, mild DR eyes exhibited a thinner inner plexiform layer (IPL; p = 0.008) than DM no DR eyes. Conversely, moderate DR eyes displayed thickening in the INL, outer nuclear layer, IPL, and retinal nerve fiber layer (all p ≤ 0.002), with notably worse vision. These findings highlight distinctive patterns: early diabetic eyes experience thinning in specific retinal layers, while moderate DR eyes exhibit thickening of certain layers and slightly compromised visual acuity, despite the absence of macular edema. Understanding these structural changes is crucial for comprehending diabetic eye complications.

The mechanical theory of glaucoma in terms of prelaminar, laminar, and postlaminar factors

The mechanical theory is one of the oldest concepts regarding the development of glaucomatous neural degeneration. However, after a prolonged period of relative monopoly among the various theories explaining the pathogenesis of glaucoma, this concept gradually faded away from discourse. Several developments in the recent past have rekindled interest in the mechanical theory of glaucoma. Now we know a lot more about the biomechanics of the eye, prelaminar changes, mechanisms of retinal ganglion cell death, biomechanical features of the optic nerve head and sclera, extracellular matrix composition and its role, astrocytic changes, axoplasmic flow, and postlaminar factors such as translaminar pressure difference. These factors and others can be categorized into prelaminar, laminar, and postlaminar elements. The objective of this review was to present a concise analysis of these recent developments. The literature search for this narrative review was performed through databases, such as PubMed, Google Scholar, and Clinical Key.

Fluorescent identification of axons, dendrites and soma of neuronal retinal ganglion cells with a genetic marker as a tool for facilitating the study of neurodegeneration

This study characterizes a fluorescent Slc17a6 -tdTomato neuronal reporter mouse line offering strong labeling in axons throughout the optic nerve, dendrites and soma in 99% of retinal ganglion cells (RGCs). The model facilitates neuronal assessment ex vivo with wholemounts quantified to show neurodegeneration following optic nerve crush or elevated IOP as related to glaucoma, in vitro with robust Ca 2+ responses to P2X7 receptor stimulation in neuronal cultures, and in vivo using a confocal scanning laser ophthalmoscope (cSLO). While the tdTomato signal showed strong overlap with RGC markers, BRN3A and RBPMS, there was no cross-labeling of displaced amacrine cells in the ganglion cell layer. Controls indicated no impact of Slc17a6 -tdTomato expression on light-dependent neuronal function, as determined with a microelectrode array (MEA), or on structure, as measured with optical coherence tomography (OCT). In summary, this novel neuronal reporter mouse model offers an effective means to increase the efficiency for real-time, specific visualization of retinal ganglion cells. It holds substantial promise for enhancing our understanding of RGC pathology in glaucoma and other diseases of the optic nerve, and could facilitate the screening of targeted therapeutic interventions for neurodegeneration.

Abstract Figure

The mechanism of human color vision and potential implanted devices for artificial color vision

Vision plays a major role in perceiving external stimuli and information in our daily lives. The neural mechanism of color vision is complicated, involving the co-ordinated functions of a variety of cells, such as retinal cells and lateral geniculate nucleus cells, as well as multiple levels of the visual cortex. In this work, we reviewed the history of experimental and theoretical studies on this issue, from the fundamental functions of the individual cells of the visual system to the coding in the transmission of neural signals and sophisticated brain processes at different levels. We discuss various hypotheses, models, and theories related to the color vision mechanism and present some suggestions for developing novel implanted devices that may help restore color vision in visually impaired people or introduce artificial color vision to those who need it.

Membrane depolarization mediates both the inhibition of neural activity and cell-type-differences in response to high-frequency stimulation

Neuromodulation using high frequency (>1 kHz) electric stimulation (HFS) enables preferential activation or inhibition of individual neural types, offering the possibility of more effective treatments across a broad spectrum of neurological diseases. To improve effectiveness, it is important to better understand the mechanisms governing activation and inhibition with HFS so that selectivity can be optimized. In this study, we measure the membrane potential (Vm) and spiking responses of ON and OFF α-sustained retinal ganglion cells (RGCs) to a wide range of stimulus frequencies (100-2500 Hz) and amplitudes (10-100 µA). Our findings indicate that HFS induces shifts in Vm, with both the strength and polarity of the shifts dependent on the stimulus conditions. Spiking responses in each cell directly correlate with the shifts in Vm, where strong depolarization leads to spiking suppression. Comparisons between the two cell types reveal that ON cells are more depolarized by a given amplitude of HFS than OFF cells-this sensitivity difference enables the selective targeting. Computational modeling indicates that ion-channel dynamics largely account for the shifts in Vm, suggesting that a better understanding of the differences in ion-channel properties across cell types may improve the selectivity and ultimately, enhance HFS-based neurostimulation strategies.

Deciphering the genetic code of neuronal type connectivity through bilinear modeling

Understanding how different neuronal types connect and communicate is critical to interpreting brain function and behavior. However, it has remained a formidable challenge to decipher the genetic underpinnings that dictate the specific connections formed between neuronal types. To address this, we propose a novel bilinear modeling approach that leverages the architecture similar to that of recommendation systems. Our model transforms the gene expressions of presynaptic and postsynaptic neuronal types, obtained from single-cell transcriptomics, into a covariance matrix. The objective is to construct this covariance matrix that closely mirrors a connectivity matrix, derived from connectomic data, reflecting the known anatomical connections between these neuronal types. When tested on a dataset of Caenorhabditis elegans, our model achieved a performance comparable to, if slightly better than, the previously proposed spatial connectome model (SCM) in reconstructing electrical synaptic connectivity based on gene expressions. Through a comparative analysis, our model not only captured all genetic interactions identified by the SCM but also inferred additional ones. Applied to a mouse retinal neuronal dataset, the bilinear model successfully recapitulated recognized connectivity motifs between bipolar cells and retinal ganglion cells, and provided interpretable insights into genetic interactions shaping the connectivity. Specifically, it identified unique genetic signatures associated with different connectivity motifs, including genes important to cell-cell adhesion and synapse formation, highlighting their role in orchestrating specific synaptic connections between these neurons. Our work establishes an innovative computational strategy for decoding the genetic programming of neuronal type connectivity. It not only sets a new benchmark for single-cell transcriptomic analysis of synaptic connections but also paves the way for mechanistic studies of neural circuit assembly and genetic manipulation of circuit wiring.

The Complement System as a Therapeutic Target in Retinal Disease

The complement cascade is a vital system in the human body's defense against pathogens. During the natural aging process, it has been observed that this system is imperative for ensuring the integrity and homeostasis of the retina. While this system is critical for proper host defense and retinal integrity, it has also been found that dysregulation of this system may lead to certain retinal pathologies, including geographic atrophy and diabetic retinopathy. Targeting components of the complement system for retinal diseases has been an area of interest, and in vivo, ex vivo, and clinical trials have been conducted in this area. Following clinical trials, medications targeting the complement system for retinal disease have also become available. In this manuscript, we discuss the pathophysiology of complement dysfunction in the retina and specific pathologies. We then describe the results of cellular, animal, and clinical studies targeting the complement system for retinal diseases. We then provide an overview of complement inhibitors that have been approved by the Food and Drug Administration (FDA) for geographic atrophy. The complement system in retinal diseases continues to serve as an emerging therapeutic target, and further research in this field will provide additional insights into the mechanisms and considerations for treatment of retinal pathologies.

VDAC in Retinal Health and Disease

The retina, a tissue of the central nervous system, is vital for vision as its photoreceptors capture light and transform it into electrical signals, which are further processed before they are sent to the brain to be interpreted as images. The retina is unique in that it is continuously exposed to light and has the highest metabolic rate and demand for energy amongst all the tissues in the body. Consequently, the retina is very susceptible to oxidative stress. VDAC, a pore in the outer membrane of mitochondria, shuttles metabolites between mitochondria and the cytosol and normally protects cells from oxidative damage, but when a cell's integrity is greatly compromised it initiates cell death. There are three isoforms of VDAC, and existing evidence indicates that all three are expressed in the retina. However, their precise localization and function in each cell type is unknown. It appears that most retinal cells express substantial amounts of VDAC2 and VDAC3, presumably to protect them from oxidative stress. Photoreceptors express VDAC2, HK2, and PKM2-key proteins in the Warburg pathway that also protect these cells. Consistent with its role in initiating cell death, VDAC is overexpressed in the retinal degenerative diseases retinitis pigmentosa, age related macular degeneration (AMD), and glaucoma. Treatment with antioxidants or inhibiting VDAC oligomerization reduced its expression and improved cell survival. Thus, VDAC may be a promising therapeutic candidate for the treatment of these diseases.

How Does the Inner Retinal Network Shape the Ganglion Cells Receptive Field? A Computational Study

We consider a model of basic inner retinal connectivity where bipolar and amacrine cells interconnect and both cell types project onto ganglion cells, modulating their response output to the brain visual areas. We derive an analytical formula for the spatiotemporal response of retinal ganglion cells to stimuli, taking into account the effects of amacrine cells inhibition. This analysis reveals two important functional parameters of the network: (1) the intensity of the interactions between bipolar and amacrine cells and (2) the characteristic timescale of these responses. Both parameters have a profound combined impact on the spatiotemporal features of retinal ganglion cells' responses to light. The validity of the model is confirmed by faithfully reproducing pharmacogenetic experimental results obtained by stimulating excitatory DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) expressed on ganglion cells and amacrine cells' subclasses, thereby modifying the inner retinal network activity to visual stimuli in a complex, entangled manner. Our mathematical model allows us to explore and decipher these complex effects in a manner that would not be feasible experimentally and provides novel insights in retinal dynamics.

POU6F2, a risk factor for glaucoma, myopia and dyslexia, labels specific populations of retinal ganglion cells

Pou6f2 is a genetic connection between central corneal thickness (CCT) in the mouse and a risk factor for developing primary open-angle glaucoma. POU6F2 is also a risk factor for several conditions in humans, including glaucoma, myopia, and dyslexia. Recent findings demonstrate that POU6F2-positive retinal ganglion cells (RGCs) comprise a number of RGC subtypes in the mouse, some of which also co-stain for Cdh6 and Hoxd10. These POU6F2-positive RGCs appear to be novel of ON-OFF directionally selective ganglion cells (ooDSGCs) that do not co-stain with CART or SATB2 (typical ooDSGCs markers). These POU6F2-positive cells are sensitive to damage caused by elevated intraocular pressure. In the DBA/2J mouse glaucoma model, heavily-labeled POU6F2 RGCs decrease by 73% at 8 months of age compared to only 22% loss of total RGCs (labeled with RBPMS). Additionally, Pou6f2-/- mice suffer a significant loss of acuity and spatial contrast sensitivity along with an 11.4% loss of total RGCs. In the rhesus macaque retina, POU6F2 labels the large parasol ganglion cells that form the magnocellular (M) pathway. The association of POU6F2 with the M-pathway may reveal in part its role in human glaucoma, myopia, and dyslexia.

Comparative In Vivo Imaging of Retinal Structures in Tree Shrews, Humans, and Mice

Rodent models, such as mice and rats, are commonly used to examine retinal ganglion cell damage in eye diseases. However, as nocturnal animals, rodent retinal structures differ from primates, imposing significant limitations in studying retinal pathology. Tree shrews (Tupaia belangeri) are small, diurnal paraprimates that exhibit superior visual acuity and color vision compared with mice. Like humans, tree shrews have a dense retinal nerve fiber layer (RNFL) and a thick ganglion cell layer (GCL), making them a valuable model for investigating optic neuropathies. In this study, we applied high-resolution visible-light optical coherence tomography to characterize the tree shrew retinal structure in vivo and compare it with that of humans and mice. We quantitatively characterize the tree shrew's retinal layer structure in vivo, specifically examining the sublayer structures within the inner plexiform layer (IPL) for the first time. Next, we conducted a comparative analysis of retinal layer structures among tree shrews, mice, and humans. We then validated our in vivo findings in the tree shrew inner retina using ex vivo confocal microscopy. The in vivo and ex vivo analyses of the shrew retina build the foundation for future work to accurately track and quantify the retinal structural changes in the IPL, GCL, and RNFL during the development and progression of human optic diseases.

Evaluation of the neuroprotective efficacy of the gramine derivative ITH12657 against NMDA-induced excitotoxicity in the rat retina

Purpose

The aim of this study was to investigate, the neuroprotective effects of a new Gramine derivative named: ITH12657, in a model of retinal excitotoxicity induced by intravitreal injection of NMDA.

Methods

Adult Sprague Dawley rats received an intravitreal injection of 100 mM NMDA in their left eye and were treated daily with subcutaneous injections of ITH12657 or vehicle. The best dose-response, therapeutic window study, and optimal treatment duration of ITH12657 were studied. Based on the best survival of Brn3a + RGCs obtained from the above-mentioned studies, the protective effects of ITH12657 were studied in vivo (retinal thickness and full-field Electroretinography), and ex vivo by quantifying the surviving population of Brn3a + RGCs, αRGCs and their subtypes α-ONsRGCs, α-ONtRGCs, and α-OFFRGCs.

Results

Administration of 10 mg/kg ITH12657, starting 12 h before NMDA injection and dispensed for 3 days, resulted in the best significant protection of Brn3a + RGCs against NMDA-induced excitotoxicity. In vivo, ITH12657-treated rats showed significant preservation of retinal thickness and functional protection against NMDA-induced retinal excitotoxicity. Ex vivo results showed that ITH12657 afforded a significant protection against NMDA-induced excitotoxicity for the populations of Brn3a + RGC, αRGC, and αONs-RGC, but not for the population of αOFF-RGC, while the population of α-ONtRGC was fully resistant to NMDA-induced excitotoxicity.

Conclusion

Subcutaneous administration of ITH12657 at 10 mg/kg, initiated 12 h before NMDA-induced retinal injury and continued for 3 days, resulted in the best protection of Brn3a + RGCs, αRGC, and αONs-RGC against excitotoxicity-induced RGC death. The population of αOFF-RGCs was extremely sensitive while α-ONtRGCs were fully resistant to NMDA-induced excitotoxicity.

The Interplay between Neurotransmitters and Calcium Dynamics in Retinal Synapses during Development, Health, and Disease

The intricate functionality of the vertebrate retina relies on the interplay between neurotransmitter activity and calcium (Ca2+) dynamics, offering important insights into developmental processes, physiological functioning, and disease progression. Neurotransmitters orchestrate cellular processes to shape the behavior of the retina under diverse circumstances. Despite research to elucidate the roles of individual neurotransmitters in the visual system, there remains a gap in our understanding of the holistic integration of their interplay with Ca2+ dynamics in the broader context of neuronal development, health, and disease. To address this gap, the present review explores the mechanisms used by the neurotransmitters glutamate, gamma-aminobutyric acid (GABA), glycine, dopamine, and acetylcholine (ACh) and their interplay with Ca2+ dynamics. This conceptual outline is intended to inform and guide future research, underpinning novel therapeutic avenues for retinal-associated disorders.

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.

rAAV-compatible human mini promoters enhance transgene expression in rat retinal ganglion cells

Recombinant adeno-associated viral vectors (rAAV) are the safest and most effective gene delivery platform to drive the treatment of many inherited eye disorders in well-characterized animal models. The use in rAAV of ubiquitous promoters derived from viral sequences such as CMV/CBA (chicken β-actin promoter with cytomegalovirus enhancer) can lead to unwanted side effects such as pro-inflammatory immune responses and retinal cytotoxicity, thus reducing therapy efficacy. Thus, an advance in gene therapy is the availability of small promoters, that potentiate and direct gene expression to the cell type of interest, with higher safety and efficacy. In this study, we used six human mini-promoters packaged in rAAV2 quadruple mutant (Y-F) to test for transduction of the rat retina after intravitreal injection. After four weeks, immunohistochemical analysis detected GFP-labeled cells in the ganglion cell layer (GCL) for all constructs tested. Among them, Ple25sh1, Ple25sh2 and Ple53 promoted a widespread reporter-transgene expression in the GCL, with an increased number of GFP-expressing retinal ganglion cells when compared with the CMV/CBA vector. Moreover, Ple53 provided the strongest levels of GFP fluorescence in both cell soma and axons of retinal ganglion cells (RGCs) without any detectable adverse effects in retina function. Remarkably, a nearly 50-fold reduction in the number of intravitreally injected vector particles containing Ple53 promoter, still attained levels of transgene expression similar to CMV/CBA. Thus, the tested MiniPs show great potential for protocols of retinal gene therapy in therapeutic applications for retinal degenerations, especially those involving RGC-related disorders such as glaucoma.

Cadherin-13 Maintains Retinotectal Synapses via Transneuronal Interactions

Maintaining precise synaptic contacts between neuronal partners is critical to ensure the proper functioning of the mammalian central nervous system (CNS). Diverse cell recognition molecules, such as classic cadherins (Cdhs), are part of the molecular machinery mediating synaptic choices during development and synaptic maintenance. Yet, the principles governing neuron-neuron wiring across diverse CNS neuron types remain largely unknown. The retinotectal synapses, connections from the retinal ganglion cells (RGCs) to the superior collicular (SC) neurons, offer an ideal experimental system to reveal molecular logic underlying synaptic choices and formation. This is due to the retina's unidirectional and laminar-restricted projections to the SC and the large databases of presynaptic RGC subtypes and postsynaptic SC neuronal types. Here, we focused on determining the role of Type II Cdhs in wiring the retinotectal synapses. We surveyed Cdhs expression patterns at neuronal resolution and revealed that Cdh13 is enriched in the wide-field neurons in the superficial SC (sSC). In either the Cdh13 null mutant or selective adult deletion within the wide-field neurons, there is a significant reduction of spine densities in the distal dendrites of these neurons in both sexes. Additionally, Cdh13 removal from presynaptic RGCs reduced dendritic spines in the postsynaptic wide-field neurons. Cdh13-expressing RGCs use differential mechanisms than αRGCs and On-Off Direction-Selective Ganglion Cells (ooDSGCs) to form specific retinotectal synapses. The results revealed a selective transneuronal interaction mediated by Cdh13 to maintain proper retinotectal synapses in vivo.

A presynaptic source drives differing levels of surround suppression in two mouse retinal ganglion cell types

In early sensory systems, cell-type diversity generally increases from the periphery into the brain, resulting in a greater heterogeneity of responses to the same stimuli. Surround suppression is a canonical visual computation that begins within the retina and is found at varying levels across retinal ganglion cell types. Our results show that heterogeneity in the level of surround suppression occurs subcellularly at bipolar cell synapses. Using single-cell electrophysiology and serial block-face scanning electron microscopy, we show that two retinal ganglion cell types exhibit very different levels of surround suppression even though they receive input from the same bipolar cell types. This divergence of the bipolar cell signal occurs through synapse-specific regulation by amacrine cells at the scale of tens of microns. These findings indicate that each synapse of a single bipolar cell can carry a unique visual signal, expanding the number of possible functional channels at the earliest stages of visual processing.

Factorized discriminant analysis for genetic signatures of neuronal phenotypes

Navigating the complex landscape of single-cell transcriptomic data presents significant challenges. Central to this challenge is the identification of a meaningful representation of high-dimensional gene expression patterns that sheds light on the structural and functional properties of cell types. Pursuing model interpretability and computational simplicity, we often look for a linear transformation of the original data that aligns with key phenotypic features of cells. In response to this need, we introduce factorized linear discriminant analysis (FLDA), a novel method for linear dimensionality reduction. The crux of FLDA lies in identifying a linear function of gene expression levels that is highly correlated with one phenotypic feature while minimizing the influence of others. To augment this method, we integrate it with a sparsity-based regularization algorithm. This integration is crucial as it selects a subset of genes pivotal to a specific phenotypic feature or a combination thereof. To illustrate the effectiveness of FLDA, we apply it to transcriptomic datasets from neurons in the Drosophila optic lobe. We demonstrate that FLDA not only captures the inherent structural patterns aligned with phenotypic features but also uncovers key genes associated with each phenotype.

Optogenetic targeting of AII amacrine cells restores retinal computations performed by the inner retina

Most inherited retinal dystrophies display progressive photoreceptor cell degeneration leading to severe visual impairment. Optogenetic reactivation of inner retinal neurons is a promising avenue to restore vision in retinas having lost their photoreceptors. Expression of optogenetic proteins in surviving ganglion cells, the retinal output, allows them to take on the lost photoreceptive function. Nonetheless, this creates an exclusively ON retina by expression of depolarizing optogenetic proteins in all classes of ganglion cells, whereas a normal retina extracts several features from the visual scene, with different ganglion cells detecting light increase (ON) and light decrease (OFF). Refinement of this therapeutic strategy should thus aim at restoring these computations. Here we used a vector that targets gene expression to a specific interneuron of the retina called the AII amacrine cell. AII amacrine cells simultaneously activate the ON pathway and inhibit the OFF pathway. We show that the optogenetic stimulation of AII amacrine cells allows restoration of both ON and OFF responses in the retina, but also mediates other types of retinal processing such as sustained and transient responses. Targeting amacrine cells with optogenetics is thus a promising avenue to restore better retinal function and visual perception in patients suffering from retinal degeneration.