Different Types Of Retinal Ganglion Cells Research Articles

Systemic administration of 7,8‐dihydroxyflavone (DHF) after intraorbital optic nerve section in the rat produces neuroprotection of the Brn3a+retinal ganglion cell population

AbstractObjective: To investigate the short‐ and long‐term responses of different retinal ganglion cell (RGC) populations to intraorbital optic nerve transection (IONT) and their protection with systemic administration of 7,8‐dihydroxyflavone (DHF), a potent selective agonist of the tropomyosin related kinase B (TrkB) receptor,Methods: Adult anaesthetized Sprague–Dawley rats received an IONT of their left eye and daily intraperitoneal (ip) injections of vehicle (0.9% NaCl containing 1% DMSO) or of DHF (5 mg/kg in the same vehicle). One group of animals was used to investigate long term protection of DHF and was processed 7, 10, 14, 21, 30 or 60 days (n = 8 for each survival interval) after the lesion. Another group of animals was used to investigate the responses of different RGC types to DHF treatment and was processed 7, 14 or 21 days (n = 5–8 for each survival interval) after the lesion. The retinas were prepared as wholemounts and immunolabelled for Brn3a, melanopsin (m), Osteopontin (OPN) and the T‐box transcription factor T‐brain‐2 (Tbr2) to identify the following retinal ganglion cells (RGCs) populations: Brn3a+, melanopsin+, α‐ like (OPN+), α‐OFF like (OPN+Brn3a+) and M4‐like/α‐ON sustained RGCs (OPN+Tbr2+). The labelled RGCs were quantified automatically (Brn3a) or dotted manually and quantified with a graphic software, and distribution of the different populations represented on topographical logical maps.Results: IONT resulted in the loss of 83% or 59% of the Brn3a+ or m+RGC population, respectively, 14 days after vehicle treatment. The Brn3a+RGCs further diminished an additional 9% from 14 to 60 days whereas m+RGCs did not, thus at 60 days the proportion of surviving m+RGCs was almost five times greater than Brn3a+RGCs, thus showing greater resistance to IONT. Systemic administration of DHF resulted in prevention of Brn3a+RGCs loss during 21 days and permanent protection of m+RGCs. Different RGC populations showed different losses. In vehicle treated rats, IONT resulted in the rapid and massive loss of all OPN+Brn3a+RGCS, progressive and massive loss of Brn3a+RGCs and large but not progressive loss of OPN+RGCs or OPN+Tbr2+RGCs, indicating a certain resistance of the later types to IONT. DHF treatment resulted in significant prevention of the IONT‐induced loss of Brn3a+, OPN+ and OPN+‐Tbr2+ RGCs, but not of the OPN+‐Brn3a+.Conclusions: Our in vivo studies on adult rats document that IONT and vehicle treatment results in characteristic patterns of loss of the different types of RGCs including Brn3a, melanopsin, alpha and alpha‐ON sustained RGCs, although melanopsin, alpha and alpha‐ON sustained RGCs show certain resistance to the injury. DHF treatment affords in vivo protection of axotomized RGCs that lasts 21 days for the Brn3a+, m+, alpha and alpha‐ON sustained, but not for alpha‐OFF RGCs, which were not responsive to treatment.

Contribution of intraocular pressure‐dependent and pressure‐independent glaucoma models to neuroprotection

AbstractGlaucoma is considered a heterogeneous group of degenerative optic neuropathies characterized mainly by an ongoing loss of retinal ganglion cells (RGCs) which causes progressive deterioration of the visual field and irreversible blindness. The aetiology and pathophysiology of glaucoma are not known in detail and are a matter of debate. Although the most significant risk factor in the development and progression of glaucoma correlates with elevated intraocular pressure (IOP), at present the only treatment available to prevent or delay its development is to reduce IOP by medication or surgery to slow its detrimental effects. But reducing IOP alone does not stop the progression of the disease. Therefore, IOP may not be the only motive for glaucomatous retinopathy and optic neuropathy, and there could be other hidden mechanisms contributing to the loss of RGCs.A suitable animal model of neurodegenerative disease, such as glaucoma, should be easy to induce and reproduce, feasible and predictable, and allow detection and quantification at the biochemical, morphological and functional levels of the induced pathological changes. However, no model emulates all aspects of a pathology such as glaucoma, which is likely to have more than one aetiology and manifest itself through different pathological mechanisms. Hence, the interest and need to establish and use different experimental models in rodents to improve our understanding of the pathophysiology of glaucoma and to investigate possible neuroprotective agents. In general, experimental models of glaucoma established in rodents involve a transient or chronic increase in IOP above normal values, which allows us to study the pathological changes associated with ocular hypertension. However, elevated IOP may not be the only cause of glaucomatous retinopathy and optic neuropathy, hence the need for models that do not involve an increase in intraocular pressure to deal with specific issues of the evolution of this pathology, such as optic nerve injury, retinal ischaemia/reperfusion, intravitreal injection of excitatory amino acids or endothelin‐induced optic neuropathy.Results obtained in different experimental models of glaucoma mimicking ocular hypertension or optic nerve damage have confirmed the existence of morphofunctional differences in the time course of RGC loss, both between different types of RGCs and between different lesions. As well as the effects on other retinal cell populations. In this regard, in the outer retina, there is a significant contrast between damage caused by ocular hypertension and optic nerve injury. Both axotomy and ocular hypertension induce a selective loss of RGCs, but ocular hypertension also promotes a loss of photoreceptors.Thanks to the different glaucoma models studied, the findings obtained have contributed to improving our knowledge of glaucomatous pathology and to the development of future neuroprotective therapies.

Probing Light-Stimulated Activities in the Retina via Transparent Graphene Electrodes.

Graphene has triggered tremendous research due to its superior properties. In particular, the intrinsic high light transmission illustrates the unique advantage in neural biosensing. Here, we combine perforated flexible graphene electrodes with microfluidic platforms to explore real-time extracellular electrical activities of retinal ganglion cells (RGCs). Under light stimulation, the transparent graphene electrodes have demonstrated the capability of recording the electrical activities of stimulated RGCs in direct contact. Different types of RGCs have shown three distinct light induced patterns, ON, OFF, and ON-OFF, which are primarily operated by cone photoreceptors. Moreover, the observed spiking waveforms can be divided into two groups: the biphasic waveform usually occurs at contacts with soma, while the triphasic waveform is likely related to the axon. Under high K+ stimulation, the graphene electrodes exhibit higher electrical sensitivity than gold counterparts with an average 2.5-fold enhancement in spiking amplitude. Furthermore, a strong response has been observed with the firing rate first increasing and then ceasing, which could be due to the potassium-induced neural depolarization. These results show that graphene electrodes can be a promising candidate in the electrophysiology studies of retina and offer a route to engineering future two-dimensional materials-based biosensors.

Response Profiles of Retinal Ganglion Cells to Sinusoidal Electric Stimulation vary for Low vs. High Frequencies.

Microelectronic retinal prostheses electrically stimulate retinal neurons with the goal of restoring vision in patients blinded by outer retinal degeneration. Despite some success in clinical trials, the quality of vision elicited by these devices is still limited. To improve the performance of retinal prostheses, our group studied how retinal neurons respond to electric stimulation. Our previous work showed that responses of retinal ganglion cells (RGCs) are frequency-dependent and different types of RGCs can be preferentially activated with a specific frequency and current amplitude. In the present study, we systemically examined responses of RGCs to sinusoidal electric stimulation with varying frequencies and amplitudes. We found that ON sustained alpha RGCs show distinct stimulus-response relationships to low and high frequency stimulation. For example, RGCs showed monotonic response curves to 500 Hz sinusoidal stimulation, whereas they showed non-monotonic response curves to 2000 Hz stimulation. We also described how increasing stimulus frequency gradually changed the response curves of RGCs.

The Susceptibility of Retinal Ganglion Cells to Glutamatergic Excitotoxicity Is Type-Specific.

Retinal ganglion cells (RGCs) are the only output neurons that conduct visual signals from the eyes to the brain. RGC degeneration occurs in many retinal diseases leading to blindness and increasing evidence suggests that RGCs are susceptible to various injuries in a type-specific manner. Glutamate excitotoxicity is the pathological process by which neurons are damaged and killed by excessive stimulation of glutamate receptors and it plays a central role in the death of neurons in many CNS and retinal diseases. The purpose of this study is to characterize the susceptibility of genetically identified RGC types to the excitotoxicity induced by N-methyl-D-aspartate (NMDA). We show that the susceptibility of different types of RGCs to NMDA excitotoxicity varies significantly, in which the αRGCs are the most resistant type of RGCs to NMDA excitotoxicity while the J-RGCs are the most sensitive cells to NMDA excitotoxicity. These results strongly suggest that the differences in the genetic background of RGC types might provide valuable insights for understanding the selective susceptibility of RGCs to pathological insults and the development of a strategy to protect RGCs from death in disease conditions. In addition, our results show that RGCs lose dendrites before death and the sequence of the morphological and molecular events during RGC death suggests that the initial insult of NMDA excitotoxicity might set off a cascade of events independent of the primary insults. However, the kinetics of dendritic retraction in RGCs does not directly correlate to the susceptibility of type-specific RGC death.

Single-compartment models of retinal ganglion cells with different electrophysiologies

ABSTRACTThere are more than 15 different types of retinal ganglion cells (RGCs) in the mammalian retina. To model responses of RGCs to electrical stimulation, we use single-compartment Hodgkin–Huxley-type models and run simulations in the Neuron environment. We use our recently published in vitro data of different morphological cell types to constrain the model, and study the effects of electrophysiology on the cell responses separately from the effects of morphology. We find simple models that can match the spike patterns of different types of RGCs. These models, with different input–output properties, may be used in a network to study retinal network dynamics and interactions.

Correspondence between visual and electrical input filters of ON and OFF mouse retinal ganglion cells

Objective. Over the past two decades retinal prostheses have made major strides in restoring functional vision to patients blinded by diseases such as retinitis pigmentosa. Presently, implants use single pulses to activate the retina. Though this stimulation paradigm has proved beneficial to patients, an unresolved problem is the inability to selectively stimulate the on and off visual pathways. To this end our goal was to test, using white noise, voltage-controlled, cathodic, monophasic pulse stimulation, whether different retinal ganglion cell (RGC) types in the wild type retina have different electrical input filters. This is an important precursor to addressing pathway-selective stimulation. Approach. Using full-field visual flash and electrical and visual Gaussian noise stimulation, combined with the technique of spike-triggered averaging (STA), we calculate the electrical and visual input filters for different types of RGCs (classified as on, off or on–off based on their response to the flash stimuli). Main results. Examining the STAs, we found that the spiking activity of on cells during electrical stimulation correlates with a decrease in the voltage magnitude preceding a spike, while the spiking activity of off cells correlates with an increase in the voltage preceding a spike. No electrical preference was found for on–off cells. Comparing STAs of wild type and rd10 mice revealed narrower electrical STA deflections with shorter latencies in rd10. Significance. This study is the first comparison of visual cell types and their corresponding temporal electrical input filters in the retina. The altered input filters in degenerated rd10 retinas are consistent with photoreceptor stimulation underlying visual type-specific electrical STA shapes in wild type retina. It is therefore conceivable that existing implants could target partially degenerated photoreceptors that have only lost their outer segments, but not somas, to selectively activate the on and off visual pathways.

GPGPU implementation of a synaptically optimized, anatomically accurate spiking network simulator

Simulation of biological spiking networks is becoming more relevant in understanding neuronal processes. An increasing proportion of these simulations focuses on large scale modeling efforts. Unfortunately the size of large networks is often limited by both computational power and memory. Computational power constrains both the maximum number of differential equations and the maximum number of spikes that can be processed per unit time. Memory size limits the maximum number of neurons and synapses that can be simulated. To solve for the computational bottleneck, a neuronal simulator is implemented on a CUDA-based General Purpose Graphic Processing Unit (GPGPU). CUDA provides a C-like environment to harness the computational power of specialized video cards from NVIDIA (these cards provide a computational peak power on single precision floats of 1TFLOPS, at least an order of magnitude higher than the fastest CPU). To solve for the memory bottleneck, a just-in-time synapse storing algorithm is implemented requiring only 4 bytes per synapse. Only the synaptic weight is stored, while both post-synaptic contact and delay are recomputed at run-time. This allows a resource shift from memory to computation which fits with the peculiar GPGPU architecture, where an abundance of compute nodes access the memory via a bandwidth-limited bus. Neurons are represented by a single compartment whose activity is modeled by the Izhikevich formalism. Excitatory synapses are plastic and follow both a spike-timing-dependent plasticity rule and a short term potentiation/depression rule. We are able to simulate networks with up to a million neurons and up to 100 million synapses on a single GPGPU card. Networks of this size cannot be simulated on desktop computers. For smaller networks the speedup obtained is at least of an order of magnitude compared to traditional CPU platform. As an example of possible use of the present work we present preliminary results on the simulation of early stage of the visual pathway. In the retina, Retinal Ganglion Cells (RGC) project to the Lateral Geniculate Nucleus (LGN). LGN projects to the cortical area V1. V1 projects back to LGN. The network is represented by 100,000 neurons, 10 million synapses, and 32 different morphological classes with >350 topological projections. Input to the network is provided by current injection in the RGC layer. The RGC layer models midget and parasol ganglion cells (representing 80% of the RGC in primates). Each ganglion type is then subdivided into on- and off-center cells for a total of 4 different types of RGC. Training is performed via natural stimuli while testing is done with vertical and horizontal bars. The network average spiking frequency is within biological limits. Testing performed with both vertical and horizontal bars shows each pattern propagating along the network’s anatomical projections. At each stage the pattern is progressively elaborated and modified. In conclusion we present a novel simulator that is fast, synaptically optimized and anatomically accurate. At an additional cost to an available desktop PC of few hundred dollars we think the GPGPU is an ideal platform to simulate large spiking networks.

Susceptibility to N-methyl-d-aspartate toxicity in morphological and functional types of cat retinal ganglion cells

To examine whether different types of retinal ganglion cells (RGCs) in the cat retina have different survival rates when exposed to N-methyl-D-aspartate (NMDA). NMDA injury was induced by intravitreal administration of NMDA at final concentrations of 0.2, 0.4, 0.6, and 0.8 mM. The total number of surviving RGCs and their distribution were counted by retrograde labeling with a fluorescent dye. Measurements of the proportions of the main RGC types (alpha, beta, and neither alpha nor beta cells) were obtained by using intracellular injections of Lucifer yellow. The mean percentage of surviving RGCs in the NMDA-injected retina was reduced to 59.4% (0.2 mM NMDA), 35.8% (0.4 mM), 10.8% (0.6 mM), and 14.1% (0.8 mM). At 0.2 mM, the survival rate of alpha cells was reduced to 56%, but that of beta cells remained at 81%. At 0.8 mM, the survival rate of alpha cells was 19%, while beta cells rapidly decreased to 9.9%. No difference was detected in NMDA vulnerability between ON- and OFF-center RGCs. Different RGC types display different susceptibilities to NMDA injury. A specific examination of the functions of different types of RGCs would be helpful in detecting retinal excitotoxicity such as in chronic retinal ischemia.

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 2795 cells/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.

Accurate Representation of Light-intensity Information by the Neural Activities of Independently Firing Retinal Ganglion Cells

For successful restoration of visual function by a visual neural prosthesis such as retinal implant, electrical stimulation should evoke neural responses so that the information on visual input is properly represented. A stimulation strategy, which means a method for generating stimulation waveforms based on visual input, should be developed for this purpose. We proposed to use the decoding of visual input from retinal ganglion cell (RGC) responses for the evaluation of stimulus encoding strategy. This is based on the assumption that reliable encoding of visual information in RGC responses is required to enable successful visual perception. The main purpose of this study was to determine the influence of inter-dependence among stimulated RGCs activities on decoding accuracy. Light intensity variations were decoded from multiunit RGC spike trains using an optimal linear filter. More accurate decoding was possible when different types of RGCs were used together as input. Decoding accuracy was enhanced with independently firing RGCs compared to synchronously firing RGCs. This implies that stimulation of independently-firing RGCs and RGCs of different types may be beneficial for visual function restoration by retinal prosthesis.

An in vitro model of the kitten retinogeniculate pathway.

An organotypic explant coculture method is described for the developing retinogeniculate pathway of the cat. Retinal explants and thalamic slices containing the dorsal lateral geniculate nucleus (LGN), derived from early postnatal kittens, can be grown in serum-free culture medium for several days. In such cultures, retinal ganglion cells (RGCs) and LGN neurons retained their age-specific morphological features and developed functional connections. Labeling of RGCs and their processes with DiI showed that all three major classes of RGCs (alpha/Y, beta/X, gamma/W) were present in cocultured retinal explants. Retinal axons readily regenerated into thalamic slices and, over time, developed arbors within the LGN. Retrograde labeling from the LGN traced the origin of these axons almost exclusively to alpha-cells in the retina. In vitro intracellular recordings indicated that LGN cells maintained their basic electrophysiological properties in coculture. Current injection generated action potentials, and, at hyperpolarized levels, it led to low-threshold Ca2+ spiking. Regenerated retinal axons also formed functional connections with LGN neurons. Electrical stimulation of the retinal explant elicited excitatory postsynaptic responses (EPSPs) in LGN cells. Drop application of specific glutamate antagonists indicated that EPSPs had both N-methyl-D-aspartate (NMDA) and non-NMDA receptor components. The morphology of the LGN neurons was examined after intracellular injections of biocytin during recording. Labeled cells were very similar to those of early postnatal kittens. Although, in general, they had relatively small soma and simple dendritic branching patterns, a few could be recognized as X- or Y-cells. Thus the coculture model can be used to assay the regenerative propensity of different types of RGCs during development.