Origins of the electroretinogram oscillatory potentials in the rabbit retina

S-cone contribution to oscillatory potentials in patients with blue cone monochromacy

PURPOSE

The aim of this exploratory study is to investigate the role of S-cones in oscillatory potentials (OPs) generation by individuals with blue-cone monochromacy (BCM), retaining S-cones, and achromatopsia (ACHM), lacking cone functions.

METHODS

This retrospective study analyzed data from 39 ACHM patients, 20 BCM patients, and 26 controls. Central foveal thickness was obtained using spectral-domain optical coherence tomography, while amplitude and implicit time (IT) of a- and b-waves were extracted from the ISCEV Standard dark-adapted 3 cd.s.m-2 full-field ERG (ffERG). Time-frequency analysis of the same measurement enabled the extraction of OPs, providing insights into the dynamic characteristics of the recorded signal.

RESULTS

Both ACHM and BCM groups showed a significant reduction (p < .00001) of a- and b-wave amplitudes and ITs as well as the power of the OPs compared to the control groups. The comparison between ACHM and BCM didn't show any statistically significant differences in the electrophysiological parameters. The analysis of covariance revealed significantly reduced central foveal thickness in the BCM group compared to ACHM and controls (p < .00001), and in ACHM compared to controls (p < .00001), after age correction and Tukey post-hoc analysis.

CONCLUSIONS

S-cones do not significantly influence OPs, and the decline in OPs' power is not solely due to a reduced a-wave. This suggests a complex non-linear network influenced by photoreceptor inputs. Morphological changes don't correlate directly with functional alterations, prompting further exploration of OPs' function and physiological role.

Electroretinographic oscillatory potentials in Leber hereditary optic neuropathy

PURPOSE

Leber hereditary optic neuropathy (LHON) affects retinal ganglion cells causing severe vision loss. Pattern electroretinogram and photopic negative response (PhNR) of the light-adapted (LA) full-field electroretinogram (ERG) are typically affected in LHON. In the present study, we evaluated dark-adapted (DA) and LA oscillatory potentials (OPs) of the flash ERG in genetically characterized LHON patients to dissociate slow from fast components of the response.

METHODS

Seven adult patients (mean age = 28.4 ± 5.6) in whom genetic diagnosis confirmed LHON with mtDNA or nuclear DNAJC30 (arLHON) pathogenic variants were compared to 12 healthy volunteers (mean age = 35.0 ± 12.1). Full-field ERGs were recorded from both eyes. Offline digital filters at 50, 75 and 100 Hz low cutoff frequencies were applied to isolate high-frequency components from the original ERG signals.

RESULTS

ERG a-waves and b-waves were comparable between LHON patients and controls, while PhNR was significantly reduced (p = 0.009) in LHON patients compared to controls, as expected. OPs derived from DA signals (75 Hz low cutoff frequency) showed reduced peak amplitude for OP2 (p = 0.019). LA OP differences between LHON and controls became significant (OP2: p = 0.047, OP3: p = 0.039 and OP4: p = 0.013) when the 100 Hz low-cutoff frequency filter was applied.

CONCLUSIONS

Reduced OPs in LHON patients may represent disturbed neuronal interactions in the inner retina with preserved photoreceptoral (a-wave) to bipolar cell (b-wave) activation. Reduced DA OP2 and high-cutoff LA OP alterations may be further explored as functional measures to characterize LHON status and progression.

Nfia Is Critical for AII Amacrine Cell Production: Selective Bipolar Cell Dependencies and Diminished ERG

The nuclear factor one (NFI) transcription factor genes Nfia, Nfib, and Nfix are all enriched in late-stage retinal progenitor cells, and their loss has been shown to retain these progenitors at the expense of later-generated retinal cell types. Whether they play any role in the specification of those later-generated fates is unknown, but the expression of one of these, Nfia, in a specific amacrine cell type may intimate such a role. Here, Nfia conditional knockout (Nfia-CKO) mice (both sexes) were assessed, finding a massive and largely selective absence of AII amacrine cells. There was, however, a partial reduction in type 2 cone bipolar cells (CBCs), being richly interconnected to AII cells. Counts of dying cells showed a significant increase in Nfia-CKO retinas at postnatal day (P)7, after AII cell numbers were already reduced but in advance of the loss of type 2 CBCs detected by P10. Those results suggest a role for Nfia in the specification of the AII amacrine cell fate and a dependency of the type 2 CBCs on them. Delaying the conditional loss of Nfia to the first postnatal week did not alter AII cell number nor differentiation, further suggesting that its role in AII cells is solely associated with their production. The physiological consequences of their loss were assessed using the ERG, finding the oscillatory potentials to be profoundly diminished. A slight reduction in the b-wave was also detected, attributed to an altered distribution of the terminals of rod bipolar cells, implicating a role of the AII amacrine cells in constraining their stratification.SIGNIFICANCE STATEMENT The transcription factor NFIA is shown to play a critical role in the specification of a single type of retinal amacrine cell, the AII cell. Using an Nfia-conditional knockout mouse to eliminate this population of retinal neurons, we demonstrate two selective bipolar cell dependencies on the AII cells; the terminals of rod bipolar cells become mis-stratified in the inner plexiform layer, and one type of cone bipolar cell undergoes enhanced cell death. The physiological consequence of this loss of the AII cells was also assessed, finding the cells to be a major contributor to the oscillatory potentials in the electroretinogram.

Trophoblast glycoprotein is required for efficient synaptic vesicle exocytosis from retinal rod bipolar cells

Introduction

Rod bipolar cells (RBCs) faithfully transmit light-driven signals from rod photoreceptors in the outer retina to third order neurons in the inner retina. Recently, significant work has focused on the role of leucine-rich repeat (LRR) proteins in synaptic development and signal transduction at RBC synapses. We previously identified trophoblast glycoprotein (TPBG) as a novel transmembrane LRR protein localized to the dendrites and axon terminals of RBCs.

Methods

We examined the effects on RBC physiology and retinal processing of TPBG genetic knockout in mice using immunofluorescence and electron microscopy, electroretinogram recording, patch-clamp electrophysiology, and time-resolved membrane capacitance measurements.

Results

The scotopic electroretinogram showed a modest increase in the b-wave and a marked attenuation in oscillatory potentials in the TPBG knockout. No effect of TPBG knockout was observed on the RBC dendritic morphology, TRPM1 currents, or RBC excitability. Because scotopic oscillatory potentials primarily reflect RBC-driven rhythmic activity of the inner retina, we investigated the contribution of TPBG to downstream transmission from RBCs to third-order neurons. Using electron microscopy, we found shorter synaptic ribbons in TPBG knockout axon terminals in RBCs. Time-resolved capacitance measurements indicated that TPBG knockout reduces synaptic vesicle exocytosis and subsequent GABAergic reciprocal feedback without altering voltage-gated Ca2+ currents.

Discussion

TPBG is required for normal synaptic ribbon development and efficient neurotransmitter release from RBCs to downstream cells. Our results highlight a novel synaptic role for TPBG at RBC ribbon synapses and support further examination into the mechanisms by which TPBG regulates RBC physiology and circuit function.

Intraocular Adeno-Associated Virus-Mediated Transgene Endothelin-1 Delivery to the Rat Eye Induces Functional Changes Indicative of Retinal Ischemia-A Potential Chronic Glaucoma Model

Endothelin-1 (ET-1) overactivity has been implicated as a factor contributing to glaucomatous neuropathy, and it has been utilized in animal models of retinal ischemia. The functional effects of long-term ET-1 exposure and possible compensatory mechanisms have, however, not been investigated. This was therefore the purpose of our study. ET-1 was delivered into rat eyes via a single intravitreal injection of 500 µM or via transgene delivery using an adeno-associated viral (AAV) vector. Retinal function was assessed using electroretinography (ERG) and the retinal expression of potentially compensatory genes was evaluated by means of qRT-PCR. Acute ET-1 delivery led to vasoconstriction and a significant reduction in the ERG response. AAV-ET-1 resulted in substantial transgene expression and ERG results similar to the acute ET-1 injections and comparable to other models of retinal ischemia. Compensatory changes were observed, including an increase in calcitonin gene-related peptide (CGRP) gene expression, which may both counterbalance the vasoconstrictive effects of ET-1 and provide neuroprotection. This chronic ET-1 ischemia model might be especially relevant to glaucoma research, mimicking the mild and repeated ischemic events in patients with long-term vascular dysfunction. The compensatory mechanisms, and particularly the role of vasodilatory CGRP in mitigating the retinal damage, warrant further investigation with the aim of evaluating new therapeutic strategies.

Using Micro-Electrode-Array Recordings and Retinal Disease Models to Elucidate Visual Functions: Simultaneous Recording of Local Electroretinograms and Ganglion Cell Action Potentials Reveals the Origin of Retinal Oscillatory Potentials

BACKGROUND

The electroretinogram (ERG) is an essential diagnostic tool for visual function, both in clinical and research settings. Here, we establish an advanced in vitro approach to assess cell-type-specific ERG signal components.

METHODS

Retinal explant cultures, maintained under entirely controlled conditions, were derived from wild-type mice and rd10 rod- and cpfl1 cone-degeneration mouse models. Local micro-ERG (µERG) and simultaneous ganglion cell (GC) recordings were obtained from the retinal explants using multi-electrode arrays. Band-pass filtering was employed to distinguish photoreceptor, bipolar cell, amacrine cell (AC), and GC responses.

RESULTS

Scotopic and photopic stimulation discriminated between rod and cone responses in wild-type and mutant retina. The 25 kHz sampling rate allowed the visualization of oscillatory potentials (OPs) in extraordinary detail, revealing temporal correlations between OPs and GC responses. Pharmacological isolation of different retinal circuits found that OPs are generated by inner retinal AC electrical synapses. Importantly, this AC activity helped synchronise GC activity.

CONCLUSION

Our µERG protocol simultaneously records the light-dependent activities of the first-, second-, and third-order neurons within the native neuronal circuitry, providing unprecedented insights into retinal physiology and pathophysiology. This method now also enables complete in vitro retinal function testing of therapeutic interventions, providing critical guidance for later in vivo investigations.

OculusGraphy: Signal Analysis of the Electroretinogram in a Rabbit Model of Endophthalmitis Using Discrete and Continuous Wavelet Transforms

BACKGROUND

The electroretinogram is a clinical test used to assess the function of the photoreceptors and retinal circuits of various cells in the eye, with the recorded waveform being the result of the summated response of neural generators across the retina.

METHODS

The present investigation involved an analysis of the electroretinogram waveform in both the time and time-frequency domains through the utilization of the discrete wavelet transform and continuous wavelet transform techniques. The primary aim of this study was to monitor and evaluate the effects of treatment in a New Zealand rabbit model of endophthalmitis via electroretinogram waveform analysis and to compare these with normal human electroretinograms.

RESULTS

The wavelet scalograms were analyzed using various mother wavelets, including the Daubechies, Ricker, Wavelet Biorthogonal 3.1 (bior3.1), Morlet, Haar, and Gaussian wavelets. Distinctive variances were identified in the wavelet scalograms between rabbit and human electroretinograms. The wavelet scalograms in the rabbit model of endophthalmitis showed recovery with treatment in parallel with the time-domain features.

CONCLUSIONS

The study compared adult, child, and rabbit electroretinogram responses using DWT and CWT, finding that adult signals had higher power than child signals, and that rabbit signals showed differences in the a-wave and b-wave depending on the type of response tested, while the Haar wavelet was found to be superior in visualizing frequency components in electrophysiological signals for following the treatment of endophthalmitis and may give additional outcome measures for the management of retinal disease.

Origin of Retinal Oscillatory Potentials in the Mouse, a Tool to Specifically Locate Retinal Damage

To determine the origin of oscillatory potentials (OPs), binocular electroretinogram (ERG) recordings were performed under light and dark adaptation on adult healthy C57BL/6J mice. In the experimental group, 1 μL of PBS was injected into the left eye, while the right eye was injected with 1 μL of PBS containing different agents: APB, GABA, Bicuculline, TPMPA, Glutamate, DNQX, Glycine, Strychnine, or HEPES. The OP response depends on the type of photoreceptors involved, showing their maximum response amplitude in the ERG induced by mixed rod/cone stimulation. The oscillatory components of the OPs were affected by the injected agents, with some drugs inducing the complete abolition of oscillations (APB, GABA, Glutamate, or DNQX), whereas other drugs merely reduced the oscillatory amplitudes (Bicuculline, Glycine, Strychnine, or HEPES) or did not even affect the oscillations (TPMPA). Assuming that rod bipolar cells (RBC) express metabotropic Glutamate receptors, GABA_A, GABA_C, and Glycine receptors and that they release glutamate mainly on Glycinergic AII amacrine cells and GABAergic A17 amacrine cells, which are differently affected by the mentioned drugs, we propose that RBC-AII/A17 reciprocal synapses are responsible for the OP generation in the ERG recordings in the mice. We conclude that the reciprocal synapses between RBC and AII/A17 are the basis of the ERG OP oscillations of the light response, and this fact must be taken into consideration in any ERG test that shows a decrease in the OPs' amplitude.

The Development of Electroretinographic Oscillatory Potentials in Healthy Young Children

PURPOSE

This study aimed to summarize the electroretinographic oscillatory potential (OP) responses in healthy young children recorded by RETeval.

METHODS

By using the RETeval system, we recorded the implicit times and amplitudes of the OPs (OP1-5), in 132 healthy children aged from 0 to 11 years old. The age, gender, and data of implicit time and amplitude of each child were recorded and analyzed. Correlation analysis was performed between age and implicit time/amplitude.

RESULTS

No correlation was shown between the implicit times and amplitudes with gender. The implicit times and amplitudes of OP1-5 matured over 10 years of age, with exponential time constants of 1.9, 2.2, 1.8, 1.7, and 1.6 years and 2.1, 2.9, 2.8, 3.0, and 3.2 years, respectively. The majority of the trend occurred within the first 4.6 years.

CONCLUSIONS

In order to diagnose and evaluate vision-related disorders, the OP response is commonly used. The percentiles and age dependence of OP responses calculated and shown in this study could be regarded as reference data in age-matched pediatric patients.

Time-Frequency Analysis of ERG With Discrete Wavelet Transform and Matching Pursuits for Glaucoma

Purpose

To examine the performance of two time-frequency feature extraction techniques applied to electroretinograms (ERGs) for the prediction of glaucoma severity.

Methods

ERGs targeting the photopic negative response were obtained in 103 eyes of 55 patients with glaucoma. Features from the ERG recordings were extracted using two time-frequency extraction techniques based on the discrete wavelet transform (DWT) and the matching pursuit (MP) decomposition. Amplitude markers of the time-domain signal were also extracted. Linear and multivariate adaptive regression spline (MARS) models were fitted using combinations of these features to predict estimated retinal ganglion cell counts, a measure of glaucoma disease severity derived from standard automated perimetry and optical coherence tomography imaging.

Results

Predictive models using features from the time-frequency analyses-using both DWT and MP-combined with amplitude markers outperformed predictive models using the markers alone with linear (P = 0.001) and MARS (P ≤ 0.011) models. For example, the proportions of variance (R2) explained by the MARS model using the DWT and MP features with amplitude markers were 0.53 and 0.63, respectively, compared to 0.34 for the model using the markers alone (P = 0.011 and P = 0.001, respectively).

Conclusions

Novel time-frequency features extracted from the photopic ERG substantially added to the prediction of glaucoma severity compared to using the time-domain amplitude markers alone.

Translational Relevance

Substantial information about retinal ganglion cell dysfunction exists in the time-frequency domain of ERGs that could be useful in the management of glaucoma.

Surgical Menopause Impairs Retinal Conductivity and Worsens Prognosis in an Acute Model of Rat Optic Neuropathy

Deficiency of estradiol during the menopausal period is an important risk factor for neurodegenerative diseases, including various optic neuropathies. The aim of this study was to evaluate the impact of surgical menopause on the function and survival ratio of RGCs in the rat model of ONC (optic nerve crush). We used eight-week-old female Long Evans rats, divided into two main groups depending on the time between ovariectomy procedure (OVA) and euthanasia (two weeks vs. seven weeks), and subgroups—OVA, OVA + ONC, or ONC. Retinal function was assessed with electroretinography (ERG). RGC loss ratio was evaluated using immunolabelling and counting of RGCs. Seven weeks after OVA, the menopause morphologically affected interneurons but not RGC; however, when the ONC procedure was applied, RGCs appeared to be more susceptible to damage in case of deprivation of estrogens. In our analysis, PhNR (photopic negative responses) were severely diminished in the OVA + ONC group. A deprivation of estrogens in menopause results in accelerated retinal neurodegeneration that firstly involves retinal interneurons. The lack of estrogens increases the susceptibility of RGCs to insults.

Novel Machine-Learning Based Framework Using Electroretinography Data for the Detection of Early-Stage Glaucoma

Purpose

Early-stage glaucoma diagnosis has been a challenging problem in ophthalmology. The current state-of-the-art glaucoma diagnosis techniques do not completely leverage the functional measures' such as electroretinogram's immense potential; instead, focus is on structural measures like optical coherence tomography. The current study aims to take a foundational step toward the development of a novel and reliable predictive framework for early detection of glaucoma using machine-learning-based algorithm capable of leveraging medically relevant information that ERG signals contain.

Methods

ERG signals from 60 eyes of DBA/2 mice were grouped for binary classification based on age. The signals were also grouped based on intraocular pressure (IOP) for multiclass classification. Statistical and wavelet-based features were engineered and extracted. Important predictors (ERG tests and features) were determined, and the performance of five machine learning-based methods were evaluated.

Results

Random forest (bagged trees) ensemble classifier provided the best performance in both binary and multiclass classification of ERG signals. An accuracy of 91.7 and 80% was achieved for binary and multiclass classification, respectively, suggesting that machine-learning-based models can detect subtle changes in ERG signals if trained using advanced features such as those based on wavelet analyses.

Conclusions

The present study describes a novel, machine-learning-based method to analyze ERG signals providing additional information that may be used to detect early-stage glaucoma. Based on promising performance metrics obtained using the proposed machine-learning-based framework leveraging an established ERG data set, we conclude that the novel framework allows for detection of functional deficits of early/various stages of glaucoma in mice.

Retinal Degeneration in a Murine Model of Retinal Ischemia by Unilateral Common Carotid Artery Occlusion

Retinal degeneration is a progressive retinal damage in ocular vascular diseases. There are several reasons for this, such as occlusion of arteries or veins, diabetic retinopathy, or hereditary retinal diseases. To study pathological mechanisms of retinal degeneration, it is required to develop experimentally reproducible and clinically relevant models. In our previous studies, we developed a murine model of retinal hypoperfusion by unilateral common carotid artery occlusion (UCCAO) which mimics the pathophysiology of ocular ischemic syndrome (OIS) in humans, and described broad pathological mechanisms in the retina after UCCAO. However, there still remain missing pieces of the ocular pathologic process by UCCAO. In this study, we examined those unfound mechanisms. UCCAO was performed on adult mice. Ocular dysfunctions, histological deficits, and inflammation were examined after UCCAO, compared with sham-operated mice. Evaluation values were analyzed by electrophysiological, histological, and molecular biological methods. Eyelid drooping was permanently seen after UCCAO. Induction time point of acute reversible cataract under anesthesia was shortened. Retinal/visual dysfunctions were detected 2-4 weeks after UCCAO. Specifically, scotopic b-wave was more affected than a-wave, with the dysfunction of photopic b-wave. Impaired oscillatory potentials and visual evoked potential were constantly observed. Pathological Müller gliosis/inflammation was featured with NeuN-positive cell loss in the ganglion cell layer. Axial length, intraocular pressure, pupillary light reflex, and retinal pigment epithelium/choroidal thickness were not changed by UCCAO. A murine model of retinal ischemia by UCCAO can be useful for studying a series of degenerative process in the ischemic retina.

Oscillatory Potentials in Achromatopsia as a Tool for Understanding Cone Retinal Functions

Achromatopsia (ACHM) is an inherited autosomal recessive disease lacking cone photoreceptors functions. In this study, we characterize the time-frequency representation of the full-field electroretinogram (ffERG) component oscillatory potentials (OPs), to investigate the connections between photoreceptors and the inner retinal network using ACHM as a model. Time-frequency characterization of OPs was extracted from 52 controls and 41 achromat individuals. The stimulation via ffERG was delivered under dark-adaptation (DA, 3.0 and 10.0 cd·s·m-2) to assess mixed rod-cone responses. The ffERG signal was subsequently analyzed using a continuous complex Morlet transform. Time-frequency maps of both DA conditions show the characterization of OPs, disclosing in both groups two distinct time-frequency windows (~70-100 Hz and >100 Hz) within 50 ms. Our main result indicates a significant cluster (p < 0.05) in both conditions of reduced relative power (dB) in ACHM people compared to controls, mainly at the time-frequency window >100 Hz. These results suggest that the strongly reduced but not absent activity of OPs above 100 Hz is mostly driven by cones and only in small part by rods. Thus, the lack of cone modulation of OPs gives important insights into interactions between photoreceptors and the inner retinal network and can be used as a biomarker for monitoring cone connection to the inner retina.

Tauroursodeoxycholic Acid Protects Retinal and Visual Function in a Mouse Model of Type 1 Diabetes

PURPOSE

Previous studies demonstrated that systemic treatment with tauroursodeoxycholic acid (TUDCA) is protective in in vivo mouse models of retinal degeneration and in culture models of hyperglycemia. This study tested the hypothesis that TUDCA will preserve visual and retinal function in a mouse model of early diabetic retinopathy (DR).

METHODS

Adult C57BL/6J mice were treated with streptozotocin (STZ) and made diabetic at 8-10 weeks of age. Control and diabetic mice were treated with vehicle or TUDCA starting 1 or 3 weeks after induction of diabetes, and were assessed bimonthly for visual function via an optomotor response and monthly for retinal function via scotopic electroretinograms.

RESULTS

Diabetic mice showed significantly reduced spatial frequency and contrast sensitivity thresholds compared to control mice, while diabetic mice treated early with TUDCA showed preservation at all timepoints. A-wave, b-wave, and oscillatory potential 2 (OP2) amplitudes decreased in diabetic mice. Diabetic mice also exhibited delays in a-wave and OP2-implicit times. Early TUDCA treatment ameliorated a-wave, b-wave, and OP2 deficits. Late TUDCA treatment showed reduced preservation effects compared to early treatment.

CONCLUSIONS

Early TUDCA treatment preserved visual function in an STZ-mouse model of Type I diabetes. These data add to a growing body of preclinical research that may support testing whether TUDCA may be an effective early clinical intervention against declining visual function caused by diabetic retinopathy.

A Systematic Review of Carotenoids in the Management of Diabetic Retinopathy

Diabetic retinopathy, which was primarily regarded as a microvascular disease, is the leading cause of irreversible blindness worldwide. With obesity at epidemic proportions, diabetes-related ocular problems are exponentially increasing in the developed world. Oxidative stress due to hyperglycemic states and its associated inflammation is one of the pathological mechanisms which leads to depletion of endogenous antioxidants in retina in a diabetic patient. This contributes to a cascade of events that finally leads to retinal neurodegeneration and irreversible vision loss. The xanthophylls lutein and zeaxanthin are known to promote retinal health, improve visual function in retinal diseases such as age-related macular degeneration that has oxidative damage central in its etiopathogenesis. Thus, it can be hypothesized that dietary supplements with xanthophylls that are potent antioxidants may regenerate the compromised antioxidant capacity as a consequence of the diabetic state, therefore ultimately promoting retinal health and visual improvement. We performed a comprehensive literature review of the National Library of Medicine and Web of Science databases, resulting in 341 publications meeting search criteria, of which, 18 were found eligible for inclusion in this review. Lutein and zeaxanthin demonstrated significant protection against capillary cell degeneration and hyperglycemia-induced changes in retinal vasculature. Observational studies indicate that depletion of xanthophyll carotenoids in the macula may represent a novel feature of DR, specifically in patients with type 2 or poorly managed type 1 diabetes. Meanwhile, early interventional trials with dietary carotenoid supplementation show promise in improving their levels in serum and macular pigments concomitant with benefits in visual performance. These findings provide a strong molecular basis and a line of evidence that suggests carotenoid vitamin therapy may offer enhanced neuroprotective effects with therapeutic potential to function as an adjunct nutraceutical strategy for management of diabetic retinopathy.

Hypoxic-ischemic injury causes functional and structural neurovascular degeneration in the juvenile mouse retina

Ischemic stroke is a major cause of long-term disabilities, including vision loss. Neuronal and blood vessel maturation can affect the susceptibility of and outcome after ischemic stroke. Although we recently reported that exposure of neonatal mice to hypoxia–ischemia (HI) severely compromises the integrity of the retinal neurovasculature, it is not known whether juvenile mice are similarly impacted. Here we examined the effect of HI injury in juvenile mice on retinal structure and function, in particular the susceptibility of retinal neurons and blood vessels to HI damage. Our studies demonstrated that the retina suffered from functional and structural injuries, including reduced b-wave, thinning of the inner retinal layers, macroglial remodeling, and deterioration of the vasculature. The degeneration of the retinal vasculature associated with HI resulted in a significant decrease in the numbers of pericytes and endothelial cells as well as an increase in capillary loss. Taken together, these findings suggest a need for juveniles suffering from ischemic stroke to be monitored for changes in retinal functional and structural integrity. Thus, there is an emergent need for developing therapeutic approaches to prevent and reverse retinal neurovascular dysfunction with exposure to ischemic stroke.

Anti-angiogenic activity and safety of intraocular application of triterpenes

PURPOSE

Assessment of the anti-angiogenic activity and the safety of ophthalmic use of four pentacyclic triterpenes (friedelin, friedelinol, lupenone, and lupeol).

METHODS

Triterpenes cytotoxicity (5-640 µmol L^-1) was examined in ARPE-19 cells by sulforhodamine B colorimetric method, and the anti-angiogenic activity (50-1000 µmol L^-1) was evaluated in the chorioallantoic membrane model. Full-field electroretinography and histological analysis were performed to evaluate intraocular effects of these four triterpenes (at 100 or 500 μmol L^-1) in eyes of Wistar rats, for 15 days.

RESULTS

In the cytotoxicity assay, friedelin and friedelinol were not able to drastically reduce cell growth. A dose-dependent response was observed in groups exposed to lupeol or lupenone. During the chorioallantoic membrane assay, friedelinol at 500 μmol L^-1 reduced the vascularity in 26%; lupeol and lupenone showed promising anti-angiogenic activity, reducing three parameters: vascularized area (> 30%), number of junctions (> 20%), and vessel length (> 15%). According to the electroretinographic and histologic findings, triterpenes at 100 µmol L^-1 or lupenone at 500 µmol L^-1 did not induce any transient or permanent disturbance in retinal structure or functioning.

CONCLUSIONS

Triterpenes at 100 µmol L^-1 or lupenone at 500 µmol L^-1 were considered safe for potential ophthalmic use.

Arginyltransferase (Ate1) regulates the RGS7 protein level and the sensitivity of light-evoked ON-bipolar responses

Regulator of G-protein signaling 7 (RGS7) is predominately present in the nervous system and is essential for neuronal signaling involving G-proteins. Prior studies in cultured cells showed that RGS7 is regulated via proteasomal degradation, however no protein is known to facilitate proteasomal degradation of RGS7 and it has not been shown whether this regulation affects G-protein signaling in neurons. Here we used a knockout mouse model with conditional deletion of arginyltransferase (Ate1) in the nervous system and found that in retinal ON bipolar cells, where RGS7 modulates a G-protein to signal light increments, deletion of Ate1 raised the level of RGS7. Electroretinographs revealed that lack of Ate1 leads to increased light-evoked response sensitivities of ON-bipolar cells, as well as their downstream neurons. In cultured mouse embryonic fibroblasts (MEF), RGS7 was rapidly degraded via proteasome pathway and this degradation was abolished in Ate1 knockout MEF. Our results indicate that Ate1 regulates RGS7 protein level by facilitating proteasomal degradation of RGS7 and thus affects G-protein signaling in neurons.

Retinal ganglion cell ablation in guinea pigs

Guinea pigs are a common model of human ocular conditions; however, their visual function has not been fully characterized. The purpose of this study was to determine the contributions of retinal ganglion cells to structural and functional measures in guinea pigs. Healthy adult guinea pigs (n = 12) underwent unilateral optic nerve crush. Retinal structure was assessed with spectral domain optical coherence tomography (OCT), and thickness of the ganglion cell/nerve fiber layer (GC/NFL) was determined. Visual function was assessed with optomotor tracking of a drifting grating and light adapted electroretinograms (ERGs). From flash ERGs, a-wave, b-wave, oscillatory potentials (OPs), and photopic negative response (PhNR) were analyzed. From pattern ERGs, N1P1 and P1N2 were analyzed. Histological studies were done at various time points for ganglion cell quantification. Optomotor tracking was absent in optic nerve crush eyes following optic nerve crush. Significant thinning of the GC/NFL was evident four weeks following the crush. Flash ERGs revealed a significant reduction in the OP1 amplitude two weeks following crush (P < 0.01) and in the PhNR amplitude six weeks following crush (P < 0.01). There were no significant changes in a-wave, b-wave, or pattern ERG responses (P > 0.05 for all). In vivo OCT imaging showed progressive thinning of inner retinal layers. Ganglion cell density, quantified histologically, was significantly reduced by 75% in the optic nerve crush eye compared to the control eye at four weeks following crush. These findings indicate that retinal ganglion cells contribute to the PhNR and OP1 components of the full field flash ERG, but not significantly to the pattern ERG in guinea pigs. This study demonstrates that OCT imaging and full field flash ERGs are valuable in assessing retinal ganglion cell loss in vivo in guinea pigs and will help to further establish the guinea pig as a model of human ocular pathologies.

ERG Responses in Mice with Deletion of the Synaptic Ribbon Component RIBEYE

Purpose

To determine the influence of RIBEYE deletion and the resulting absence of synaptic ribbons on retinal light signaling by electroretinography.

Methods

Full-field flash electroretinograms (ERGs) were recorded in RIBEYE knock-out (KO) and wild-type (WT) littermate mice under photopic and scotopic conditions, with oscillatory potentials (OPs) extracted by digital filtering. Flicker ERGs and ERGs following intravitreal injection of pharmacological agents were also obtained under scotopic conditions.

Results

The a-wave amplitudes were unchanged between RIBEYE KO and WT mice; however, the b-wave amplitudes were reduced in KOs under scotopic, but not photopic, conditions. Increasing stimulation frequency led to a greater reduction in RIBEYE KO b-wave amplitudes compared with WTs. Furthermore, we observed prominent, supernormal OPs in RIBEYE KO mice in comparison with WT mice. Following intravitreal injections with l-2 amino-4-phosphonobutyric acid and cis-2,3 piperidine dicarboxylic acid to block ON and OFF responses at photoreceptor synapses, OPs were completely abolished in both mice types, indicating a synaptic origin of the prominent OPs in the KOs. Conversely, tetrodotoxin treatment to block voltage-gated Na⁺ channels/spiking neurons did not differentially affect OPs in WT and KO mice.

Conclusions

The decreased scotopic b-wave and decreased responses to increased stimulation frequencies are consistent with signaling malfunctions at photoreceptor and inner retinal ribbon synapses. Because phototransduction in the photoreceptor outer segments is unaffected in the KOs, their supernormal OPs presumably result from a dysfunction in retinal synapses. The relatively mild ERG phenotype in KO mice, particularly in the photopic range, is probably caused by compensatory mechanisms in retinal signaling pathways.

Atypical visual processing in a mouse model of autism

Human social cognition relies heavily on the processing of various visual cues, such as eye contact and facial expressions. Atypical visual perception and integration have been recognized as key phenotypes in individuals diagnosed with autism spectrum disorder (ASD), and may potentially contribute to impediments in normal social development, a hallmark of ASD. Meanwhile, increasing studies on visual function in ASD have pointed to detail-oriented perception, which has been hypothesized to result from heightened response to information of high spatial frequency. However, mixed results of human studies have led to much debate, and investigations using animal models have been limited. Here, using BTBR mice as a model of idiopathic ASD, we assessed retinal stimulus processing by full-field electroretinogram and found impaired photoreceptor function and retina-based alterations mostly in the cone pathway. Using the optokinetic reflex to evaluate visual function, we observed robustly enhanced visual response to finer spatial details and more subtle contrasts at only higher spatial frequencies in the BTBR mice, under both photopic and scotopic conditions. These behavioral results, which are similar to findings in a subset of ASD patients, indicate a bias toward processing information of high spatial frequencies. Together, these findings also suggest that, while enhancement of visual behaviors under both photopic and scotopic conditions might be due to alterations in visual processing common to both rod and cone pathways, these mechanisms are probably downstream of photoreceptor function.

Bevacizumab-Conjugated Quantum Dots: In Vitro Antiangiogenic Potential and Biosafety in Rat Retina

Purpose: Disturbances that affect the inside of the eyeball tend to be highly harmful since they compromise the homeostasis of this organ. Alongside this, the eyeball has several anatomical barriers that prevent the entry of substances. This way, diseases that affect the retina are among those that present greater difficulty in the treatment. In many cases, abnormal proliferation of blood vessels (neovascularization) occurs from the lower layers of the retina. This process damages its structure physiologically and anatomically, causing the rapid and irreversible loss of visual capacity. This work aims to develop nanosuspensions of quantum dots (QDs) conjugated to bevacizumab. Methods: Two types of QDs were produced by aqueous route, stabilized with chitosan conjugated to bevacizumab. The antiangiogenic activity was evaluated in the chorioallantoic membrane model, in which results indicated discrete activity at the doses tested. Samples were assessed for their biosafety in animals, after intravitreal administration, by means of electroretinography (ERG), intraocular pressure (IOP) measurement, histological, morphometric, and immunohistochemical evaluation. Results: No significant alterations were detected in ERG that suggests damage to retinal function by the samples. No significant changes in IOP were also detected. The histological sections did not show signs of acute inflammation, although there was evidence of late retinal damage. The immunohistochemical analysis did not detect any apoptotic bodies. Conclusion: Preliminary results suggest that QDs present potential applicability in ocular therapy, and it is necessary to better characterize their in vivo behavior and to optimize their dosage.

A review of electroretinography waveforms and models and their application in the dog

Electroretinography (ERG) is a commonly used technique to study retinal function in both clinical and research ophthalmology. ERG responses can be divided into component waveforms, analysis of which can provide insight into the health and function of different types and populations of retinal cells. In dogs, ERG has been used in the characterization of normal retinal function, as well as the diagnosis of retinal diseases and measuring effects of treatment. While many components of the recorded waveform are similar across species, dogs have several notable features that should be differentiated from the responses in humans and other animals. Additionally, modifications of standard protocols, such as changing flash frequency and stimulus color, and mathematical models of ERG waveforms have been used in studies of human retinal function but have been infrequently applied to visual electrophysiology in dogs. This review provides an overview of the origins and applications of ERG in addition to potential avenues for further characterization of responses in the dog.

Vigabatrin-Induced Retinal Functional Alterations and Second-Order Neuron Plasticity in C57BL/6J Mice

Purpose

Vigabatrin (VGB) is an effective antiepileptic that increases concentrations of inhibitory γ-aminobutyric acid (GABA) by inhibiting GABA transaminase. Reports of VGB-associated visual field loss limit its clinical usefulness, and retinal toxicity studies in laboratory animals have yielded conflicting results.

Methods

We examined the functional and morphologic effects of VGB in C57BL/6J mice that received either VGB or saline IP from 10 to 18 weeks of age. Retinal structure and function were assessed in vivo by optical coherence tomography (OCT), ERG, and optomotor response. After euthanasia, retinas were processed for immunohistochemistry, and retinal GABA, and VGB quantified by mass spectrometry.

Results

No significant differences in visual acuity or total retinal thickness were identified between groups by optomotor response or optical coherence tomography, respectively. After 4 weeks of VGB treatment, ERG b-wave amplitude was enhanced, and amplitudes of oscillatory potentials were reduced. Dramatic rod and cone bipolar and horizontal cell remodeling, with extension of dendrites into the outer nuclear layer, was observed in retinas of VGB-treated mice. VGB treatment resulted in a mean 3.3-fold increase in retinal GABA concentration relative to controls and retinal VGB concentrations that were 20-fold greater than brain.

Conclusions

No evidence of significant retinal thinning or ERG a- or b-wave deficits were apparent, although we describe significant alterations in ERG b-wave and oscillatory potentials and in retinal cell morphology in VGB-treated C57BL/6J mice. The dramatic concentration of VGB in retina relative to the target tissue (brain), with a corresponding increase in retinal GABA, offers insight into the pathophysiology of VGB-associated visual field loss.

Quantification of Changes in Visual Function During Disease Development in a Mouse Model of Pigmentary Glaucoma

PURPOSE

We investigated the relationship between visual parameters that are commonly affected during glaucomatous disease progression with functional measures of retina physiology using electroretinography and behavioral measures of visual function in a mouse model of glaucoma. Electroretinogram components measuring retinal ganglion cell (RGC) responses were determined using the non-invasive Ganzfeld flash electroretinography (fERG) to assess RGC loss in a mouse model of glaucoma.

METHODS

Intraocular pressure (IOP), behaviorally assessed measures of visual function, namely visual acuity and contrast sensitivity as well as fERG responses were recorded in 4- and 11-month-old male DBA/2 mice. Scotopic threshold response (STR) and photopic negative response components as well as oscillatory potentials (OPs) were isolated from fERG responses and correlated with IOP, optomotor reflex measurements, and RGC counts.

RESULTS

The 11-month-old DBA/2 mice had significantly elevated IOP, reduced visual performance, as assessed behaviorally, significant RGC loss, deficits in standardized fERG responses, reduced STRs, and differences in OP amplitudes and latencies, when compared with 4-month-old mice of the same strain. STRs and OPs correlated with some visual and physiological parameters. In addition, elevated IOP and RGC loss correlated positively with measures of visual function, specifically with surrogate measures of RGC function derived from fERG.

CONCLUSIONS

Our data suggest that RGC function as well as interactions of RGCs with other retinal cell types is impaired during glaucoma. In addition, a later OP wavelet denoted as OP4 in this study was identified as a very reproducible indicator of loss of visual function in the glaucoma mouse model.

A longitudinal assessment of retinal function and structure in the APP/PS1 transgenic mouse model of Alzheimer's disease

Background

A great body of evidence suggests that there are retinal functional and structural changes that occur in Alzheimer’s disease (AD). However, whether such changes are primary or secondary remains to be elucidated. We studied a range of retinal functional and structural parameters in association with AD- specific pathophysiological markers in the double transgenic APP/PS1 and control mice across age.

Methods

Electroretinogram (ERG) and optical coherence tomography (OCT) was performed in APP/PS1 and wild type (WT) control mice every 3 months from 3 to 12 months of age. For functional assessment, the a- and b-wave of the ERG, amplitude of oscillatory potentials (OP) and the positive scotopic threshold response (pSTR) were quantified at each time point. For structural assessment, the inner and outer retinal thickness was segmented and measured from OCT scans. Episodic memory was evaluated at 6, 9 and 12 months of age using the novel object recognition test. Amyloid beta (Aβ) distribution in the hippocampus and the retina were visualised at 3, 6 and 12 months of age. Inter- and intra- group analysis was performed to study rate of change for each parameter between the two groups.

Results

Inter-group analysis revealed a significant difference in b-wave and OPs of APP/PS1 compared to WT controls starting from 3 months (p < 0.001). There was also a significant difference in the amplitude of pSTR between the two groups starting from 6 months (p < 0.001). Furthermore, a significant difference in the inner retinal thickness, between the two groups, was observed starting from 9 months (p < 0.001).

Conclusions

We observed an age-related decline in retinal functional and structural parameters in both APP/PS1 and WT controls, however, inter-group analysis revealed that inner retinal functional and structural decline is exacerbated in APP/PS1 mice, and that retinal functional changes precede structural changes in this strain. Further studies are required to confirm whether such phenomenon occurs in humans and if studying retinal functional changes can aid-in early assessment of AD.

Electronic supplementary material

The online version of this article (10.1186/s40035-019-0170-z) contains supplementary material, which is available to authorized users.

A non-invasive nanoparticle mediated delivery of triamcinolone acetonide ameliorates diabetic retinopathy in rats

Diabetic retinopathy (DR) is a multifactorial manifestation associated with microvascular complications and is the fourth leading cause of visual impairment and blindness world-wide. Current day treatment of DR relies heavily on invasive techniques such as intravitreal injections of therapeutic agents. Unfortunately, intravitreal injections are associated with various complications such as intraocular bleeding, endophthalmitis, pain and discomfort resulting in poor patient compliance. To date, there has been no non-invasive drug delivery system reported for DR treatment. To address this, we developed a core-shell nanoparticle-based delivery system consisting of a hydrophobic polycaprolactone core and a hydrophilic Pluronic® F68 shell, loaded with triamcinolone acetonide and evaluated its efficacy in a DR rat model. After being administered as eye drops, the drug loaded nanoparticles significantly improved structural (retinal thickness and vascular health) and functional activity (rod and cone function) of retina as compared to DR controls that were treated with the drug alone or placebo nanoparticles. Furthermore, drug loaded nanoparticles reduced retinal inflammation as evidenced by a decrease in NF-κB, ICAM-1 and TNFα expression after 20 days of treatment. Similarly, a reduction in glial cell hyperplasia as evidenced by reduced GFAP expression, and a decrease in microvascular complications as evidenced by a decrease in VEGF secretion and microvascular tuft formation were observed in rat retinas after 40 days of treatment. The combined reduction in retinal inflammation and vascular abnormalities, both hallmarks of DR, demonstrates the potential of the nanoparticulate delivery system for use as a topical formulation for treating DR.

Dopamine Deficiency Mediates Early Rod-Driven Inner Retinal Dysfunction in Diabetic Mice

Purpose

Electroretinograms (ERGs) are abnormal in diabetic retinas before the appearance of vascular lesions, providing a possible biomarker for diabetic vision loss. Previously, we reported that decreased retinal dopamine (DA) levels in diabetic rodents contributed to early visual and retinal dysfunction. In the current study, we examined whether oscillatory potentials (OPs) could serve as a potential marker for detecting early inner retinal dysfunction due to retinal DA deficiency.

Methods

Retinal function was tested with dark-adapted ERGs, taken at 3, 4, and 5 weeks after diabetes induction with streptozotocin. Electrical responses were analyzed and correlations were made with previously reported retinal DA levels. The effect of restoring systemic DA levels or removing DA from the retina in diabetic mice on OPs was assessed using L-3,4-dihydroxyphenylalanine (L-DOPA) treatments and retina-specific tyrosine hydroxylase (Th) knockout mice (rTHKO), respectively.

Results

Diabetic animals had significantly delayed OPs compared to control animals in response to dim, but not bright, flash stimuli. L-DOPA treatment preserved OP implicit time in diabetic mice. Diabetic rTHKO mice had further delayed OPs compared to diabetic mice with normal retinal Th, with L-DOPA treatment also providing benefit. Decreasing retinal DA levels significantly correlated with increasing OP delays mediated by rod pathways.

Conclusions

Our data suggest that inner retinal dysfunction in early-stage diabetes is mediated by rod-pathway deficits and DA deficiencies. OP delays may be used to determine the earliest functional deficits in diabetic retinopathy and to establish an early treatment window for DA therapies that may prevent progressive vision loss.

Fibroblast Growth Factor 21 Protects Photoreceptor Function in Type 1 Diabetic Mice

Retinal neuronal abnormalities occur before vascular changes in diabetic retinopathy. Accumulating experimental evidence suggests that neurons control vascular pathology in diabetic and other neovascular retinal diseases. Therefore, normalizing neuronal activity in diabetes may prevent vascular pathology. We investigated whether fibroblast growth factor 21 (FGF21) prevented retinal neuronal dysfunction in insulin-deficient diabetic mice. We found that in diabetic neural retina, photoreceptor rather than inner retinal function was most affected and administration of the long-acting FGF21 analog PF-05231023 restored the retinal neuronal functional deficits detected by electroretinography. PF-05231023 administration protected against diabetes-induced disorganization of photoreceptor segments seen in retinal cross section with immunohistochemistry and attenuated the reduction in the thickness of photoreceptor segments measured by optical coherence tomography. PF-05231023, independent of its downstream metabolic modulator adiponectin, reduced inflammatory marker interleukin-1β (IL-1β) mRNA levels. PF-05231023 activated the AKT-nuclear factor erythroid 2-related factor 2 pathway and reduced IL-1β expression in stressed photoreceptors. PF-05231023 administration did not change retinal expression of vascular endothelial growth factor A, suggesting a novel therapeutic approach for the prevention of early diabetic retinopathy by protecting photoreceptor function in diabetes.

Retino-cortical stimulus frequency-dependent gamma coupling: evidence and functional implications of oscillatory potentials

Long‐range gamma band EEG oscillations mediate information transmission between distant brain regions. Gamma band‐based coupling may not be restricted to cortex‐to‐cortex communication but may include extracortical parts of the visual system. The retinogram and visual event‐related evoked potentials exhibit time‐locked, forward propagating oscillations that are candidates of gamma oscillatory coupling between the retina and the visual cortex. In this study, we tested if this gamma coupling is present as indicated by the coherence of gamma‐range (70–200 Hz) oscillatory potentials (OPs) recorded simultaneously from the retina and the primary visual cortex in freely moving, adult rats. We found significant retino‐cortical OP coherence in a wide range of stimulus duration (0.01–1000 msec), stimulus intensity (800–5000 mcd/mm²), interstimulus interval (10–400 msec), and stimulus frequency (0.25–25 Hz). However, at low stimulus frequencies, the OPs were time‐locked, flickering light at 25 Hz entrained continuous OP coherence (steady‐state response, SSR). Our results suggest that the retina and the visual cortex exhibit oscillatory coupling at high‐gamma frequency with precise time locking and synchronization of information transfer from the retina to the visual cortex, similar to cortico‐cortical gamma coupling. The temporal fusion of retino‐cortical gamma coherence at stimulus rates of theater movies may explain the mechanism of the visual illusion of continuity. How visual perception depends on early transformations of ascending sensory information is incompletely understood. By simultaneous measurement of flash‐evoked potentials in the retina and the visual cortex in awake, freely moving rats, we demonstrate for the first time that time‐locked gamma oscillatory potentials exhibit stable retino‐cortical synchrony across a wide range of stimulus parameters and that the temporal continuity of coherence changes with stimulus frequency according to the expected change in the visual illusion of continuity.

Contribution of GABAa, GABAc and glycine receptors to rat dark-adapted oscillatory potentials in the time and frequency domain

Retinal oscillatory potentials (OPs) consist of a series of relatively high-frequency rhythmic wavelets, superimposed onto the ascending phase of the b-wave of the electroretinogram (ERG). However, the origin of OPs is uncertain and methods of measurement of OPs are diverse. In this study, we first isolated OPs from the rat ERG and fitted them with Gabor functions and found that the envelope of the OP contained information about maximum amplitude and time-to-peak to enable satisfactory quantification of the later OPs. And the OP/b-wave ratio should be evaluated to exclude an effect of the b-wave on the OPs. Next, we recorded OPs after intravitreal injection of 2-amino-4-phosphonobutyric acid (APB), tetrodotoxin (TTX), γ-aminobutyric acid (GABA), strychnine (STR), SR95531 (SR), isoguvacine (ISO), (1,2,5,6-tetrahydropyridin-4-yl) methylphosphinic acid (TPMPA) and GABA+TPMPA. We showed that GABA and APB only removed the later OPs, when compared to control eyes. TTX delayed the peak time, and STR, SR and ISO reduced the amplitude of OPs. TPMPA delayed the peak time but increased the ratio of OPs to b-wave. Furthermore, administration of combined GABA and TPMPA caused the later OPs to increase in amplitude with time, compared with those after delivery of GABA alone. Finally, we observed that GABAc and glycine receptors contributed to a low-frequency component of the OPs, while GABAa contributed to both components. These results suggest that the early components of the OPs are mainly generated by the photoreceptors, whilst the later components are mainly regulated by GABAa, GABAc and glycine receptors.

Cellular origin of intrinsic optical signals in the rabbit retina

Optical imaging of retinal intrinsic signals is a relatively new method that provides spatiotemporal patterns of retinal activity through activity-dependent changes in light reflectance of the retina. The exact physiological mechanisms at the origin of retinal intrinsic signals are poorly understood and there are significant inter-species differences in their characteristics and cellular origins. In this study, we re-examined this issue through pharmacological dissection of retinal intrinsic signals in the rabbit with simultaneous ERG recordings. Retinal intrinsic signals faithfully reflected retinal activity as their amplitude was strongly associated with stimulation intensity (r²=0.85). Further, a strong linear relation was found using linear regression (r²=0.98) between retinal intrinsic signal amplitude and the ERG b wave, which suggests common cellular origins. Intravitreal injections of pharmacological agents were performed to isolate the activity of the retina's major cell types. Retinal intrinsic signals were abolished when the photoreceptors' activity was isolated with aspartate, indicative that they are not at the origin of this signal. A small but significant decrease in intrinsic response (20%) was observed when ganglion and amacrine cells' activity was inhibited by TTX injections. The remaining intrinsic responses were abolished in a dose-dependent manner through the inhibition of ON-bipolar cells by APB. Our results indicate that, in rabbits, retinal intrinsic signals reflect stimulation intensity and originate from the inner retina with a major contribution of bipolar cells and a minor one from ganglion or amacrine cells.

Contribution of Nav1.8 sodium channels to retinal function

We examined the contribution of the sodium channel isoform Na_v1.8 to retinal function using the specific blocker A803467. We found that A803467 has little influence on the electroretinogram (ERG) a- and b-waves, but significantly reduces the oscillatory potentials (OPs) to 40-60% of their original amplitude, with significant changes in implicit time in the rod-driven range. To date, only two cell types were found in mouse to express Na_v1.8; the starburst amacrine cells (SBACs), and a subtype of retinal ganglion cells (RGCs). When we recorded light responses from ganglion cells using a multielectrode array we found significant and opposing changes in two physiological groups of RGCs. ON-sustained cells showed significant decreases while transient ON-OFF cells showed significant increases. The effects on ON-OFF transient cells but not ON-sustained cells disappeared in the presence of an inhibitory cocktail. We have previously shown that RGCs have only a minor contribution to the OPs (Smith et al., 2014), therefore suggesting that SBACs might be a significant contributor to this ERG component. Targeting SBACs with the cholinergic neurotoxin ethylcholine mustard aziridinium (AF64A) caused a reduction in the amplitude of the OPs similar to A803467. Our results, both using the ERG and MEA recordings from RGCs, suggest that Na_v1.8 plays a role in modulating specific aspects of the retinal physiology and that SBACs are a fundamental cellular contributor to the OPs in mice, a clear demonstration of the dichotomy between ERG b-wave and OPs.

The Intoxication Effects of Methanol and Formic Acid on Rat Retina Function

Objective. To explore the potential effects of methanol and its metabolite, formic acid, on rat retina function. Methods. Sprague-Dawley rats were divided into 3- and 7-day groups and a control. Experimental groups were given methanol and the control group were provided saline by gavage. Retinal function of each group was assessed by electroretinogram. Concentrations of methanol and formic acid were detected by GC/HS and HPLC, respectively. Results. The a and b amplitudes of methanol treated groups decreased and latent periods delayed in scotopic and photopic ERG recordings. The summed amplitudes of oscillatory potentials (OPs) of groups B and C decreased and the elapsed time delayed. The amplitudes of OS1, OS3, OS4, and OS5 of group B and OS3, OS4, and OS5 of group C decreased compared with the control group. The IPI1 of group B and IPI1-4 of group C were broader compared with the control group and the IPI1-4 and ET of group B were broader than group C. Conclusions. Both of scotopic and photopic retinal functions were impaired by methanol poisoning, and impairment was more serious in the 7-day than in the 3-day group. OPs, especially later OPs and IPI2, were more sensitive to methanol intoxication than other eletroretinogram subcomponents.

Measurement of Electroretinograms and Visually Evoked Potentials in Awake Moving Mice

The development of new treatments for intractable retinal diseases requires reliable functional assessment tools for animal models. In vivo measurements of neural activity within visual pathways, including electroretinogram (ERG) and visually evoked potential (VEP) recordings, are commonly used for such purposes. In mice, the ERG and VEPs are usually recorded under general anesthesia, a state that may alter sensory transduction and neurotransmission, but seldom in awake freely moving mice. Therefore, it remains unknown whether the electrophysiological assessment of anesthetized mice accurately reflects the physiological function of the visual pathway. Herein, we describe a novel method to record the ERG and VEPs simultaneously in freely moving mice by immobilizing the head using a custom-built restraining device and placing a rotatable cylinder underneath to allow free running or walking during recording. Injection of the commonly used anesthetic mixture xylazine plus ketamine increased and delayed ERG oscillatory potentials by an average of 67.5% and 36.3%, respectively, compared to unanesthetized mice, while having minimal effects on the a-wave and b-wave. Similarly, components of the VEP were enhanced and delayed by up to 300.2% and 39.3%, respectively, in anesthetized mice. Our method for electrophysiological recording in conscious mice is a sensitive and robust means to assess visual function. It uses a conventional electrophysiological recording system and a simple platform that can be built in any laboratory at low cost. Measurements using this method provide objective indices of mouse visual function with high precision and stability, unaffected by anesthetics.

Intravitreal administration of multipotent mesenchymal stromal cells triggers a cytoprotective microenvironment in the retina of diabetic mice

Background

Diabetic retinopathy is a common complication of diabetes and the leading cause of irreversible vision loss in the Western world. The reduction in color/contrast sensitivity due to the loss of neural cells in the ganglion cell layer of the retina is an early event in the onset of diabetic retinopathy. Multipotent mesenchymal stromal cells (MSCs) are an attractive tool for the treatment of neurodegenerative diseases, since they could differentiate into neuronal cells, produce high levels of neurotrophic factors and reduce oxidative stress. Our aim was to determine whether the intravitreal administration of adipose-derived MSCs was able to prevent the loss of retinal ganglion cells in diabetic mice.

Methods

Diabetes was induced in C57BL6 mice by the administration of streptozotocin. When retinal pro-damage mechanisms were present, animals received a single intravitreal dose of 2 × 10⁵ adipose-derived MSCs or the vehicle. Four and 12 weeks later we evaluated: (a) retinal ganglion cell number (immunofluorescence); (b) neurotrophic factor levels (real-time quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA)); (c) retinal apoptotic rate (TUNEL); (d) retinal levels of reactive oxygen species and oxidative damage (ELISA); (e) electrical response of the retina (electroretinography); (f) pro-angiogenic and anti-angiogenic factor levels (RT-qPCR and ELISA); and (g) retinal blood vessels (angiography). Furthermore, 1, 4, 8 and 12 weeks post-MSC administration, the presence of donor cells in the retina and their differentiation into neural and perivascular-like cells were assessed (immunofluorescence and flow cytometry).

Results

MSC administration completely prevented retinal ganglion cell loss. Donor cells remained in the vitreous cavity and did not differentiate into neural or perivascular-like cells. Nevertheless, they increased the intraocular levels of several potent neurotrophic factors (nerve growth factor, basic fibroblast growth factor and glial cell line-derived neurotrophic factor) and reduced the oxidative damage in the retina. Additionally, MSC administration has a neutral effect on the electrical response of the retina and did not result in a pathological neovascularization.

Conclusions

Intravitreal administration of adipose-derived MSCs triggers an effective cytoprotective microenvironment in the retina of diabetic mice. Thus, MSCs represent an interesting tool in order to prevent diabetic retinopathy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0299-y) contains supplementary material, which is available to authorized users.

Revisiting visual dysfunctions in schizophrenia from the retina to the cortical cells: A manifestation of defective neurodevelopment

This review highlights morphological and functional anomalies found along the entire visual pathway in schizophrenia, from the retina to the cortex. Based on the evidence of widespread anatomical and functional visual abnormalities, we posited that a neurodevelopmental anomaly occurring early in life was likely to explain those. Incidentally, support to the neurodevelopmental theory of schizophrenia is strongly emerging from many neurobiological domains. In vertebrates, the first visual structures migrate toward the orbit position at the end of the fourth week of gestation. A neurodevelopmental defect around that time on these embryonic structures could account for the visual anomalies in schizophrenia. Retinol activity might be involved in the process. Future research in schizophrenia should focus on early visual testing, on trials combining multiple visual anomaly assessments and a closer look to retinol activity during the pregnancy.

APLP2 Regulates Refractive Error and Myopia Development in Mice and Humans

Myopia is the most common vision disorder and the leading cause of visual impairment worldwide. However, gene variants identified to date explain less than 10% of the variance in refractive error, leaving the majority of heritability unexplained (“missing heritability”). Previously, we reported that expression of APLP2 was strongly associated with myopia in a primate model. Here, we found that low-frequency variants near the 5’-end of APLP2 were associated with refractive error in a prospective UK birth cohort (n = 3,819 children; top SNP rs188663068, p = 5.0 × 10⁻⁴) and a CREAM consortium panel (n = 45,756 adults; top SNP rs7127037, p = 6.6 × 10⁻³). These variants showed evidence of differential effect on childhood longitudinal refractive error trajectories depending on time spent reading (gene x time spent reading x age interaction, p = 4.0 × 10⁻³). Furthermore, Aplp2 knockout mice developed high degrees of hyperopia (+11.5 ± 2.2 D, p < 1.0 × 10⁻⁴) compared to both heterozygous (-0.8 ± 2.0 D, p < 1.0 × 10⁻⁴) and wild-type (+0.3 ± 2.2 D, p < 1.0 × 10⁻⁴) littermates and exhibited a dose-dependent reduction in susceptibility to environmentally induced myopia (F(2, 33) = 191.0, p < 1.0 × 10⁻⁴). This phenotype was associated with reduced contrast sensitivity (F(12, 120) = 3.6, p = 1.5 × 10⁻⁴) and changes in the electrophysiological properties of retinal amacrine cells, which expressed Aplp2. This work identifies APLP2 as one of the “missing” myopia genes, demonstrating the importance of a low-frequency gene variant in the development of human myopia. It also demonstrates an important role for APLP2 in refractive development in mice and humans, suggesting a high level of evolutionary conservation of the signaling pathways underlying refractive eye development.

Gene variants identified by GWAS studies to date explain only a small fraction of myopia cases because myopia represents a complex disorder thought to be controlled by dozens or even hundreds of genes. The majority of genetic variants underlying myopia seems to be of small effect and/or low frequency, which makes them difficult to identify using classical genetic approaches, such as GWAS, alone. Here, we combined gene expression profiling in a monkey model of myopia, human GWAS, and a gene-targeted mouse model of myopia to identify one of the “missing” myopia genes, APLP2. We found that a low-frequency risk allele of APLP2 confers susceptibility to myopia only in children exposed to large amounts of daily reading, thus, providing an experimental example of the long-hypothesized gene-environment interaction between nearwork and genes underlying myopia. Functional analysis of APLP2 using an APLP2 knockout mouse model confirmed functional significance of APLP2 in refractive development and implicated a potential role of synaptic transmission at the level of glycinergic amacrine cells of the retina for the development of myopia. Furthermore, mouse studies revealed that lack of Aplp2 has a dose-dependent suppressive effect on susceptibility to form-deprivation myopia, providing a potential gene-specific target for therapeutic intervention to treat myopia.

Bioelectrical function and structural assessment of the retina in patients with early stages of Parkinson's disease (PD)

Purpose

To determine bioelectrical function and structural changes of the retina in patients with early stages of Parkinson’s disease (PD).

Materials and methods

Thirty-eight eyes of 20 patients with early idiopathic PD and 38 eyes of 20 healthy age- and sex-matched controls were ophthalmologically examined, including assessment of distance best-corrected visual acuity (DBCVA), slit lamp examination of the anterior and posterior segment of the eye, evaluation of the eye structures: paramacular retinal thickness (RT) and retinal nerve fiber layer (RNFL) thickness with the aid of OCT, and the bioelectrical function by full-field electroretinogram (ERG). Additionally, PD patients were interviewed as to the presence of dopamine-dependent visual functions abnormalities.

Results

In patients with early PD, statistically significant changes in comparison with the control group were observed in ERG. They contained a reduction in mean amplitudes of the scotopic a-wave (rod–cone response), the scotopic oscillatory potentials (OPs)—OP2 and OP3, the photopic b-wave, and a reduction in the overall index (OP1 + OP2 + OP3) and a prolongation of mean peak times of the scotopic OP1, OP2, OP3, OP4 (p < 0.05). A questionnaire concerning abnormalities of dopamine-dependent visual functions revealed that PD patients with abnormal peak times of OP1, OP2, and OP3 reported non-specific visual disturbances more frequently in comparison with PD patients with normal peak times of OPs. Other analyzed parameters of ERG, DBCVA, RT, and RNFL did not significantly differ between patients with PD and the control group.

Conclusion

In patients with early PD, bioelectrical dysfunction of the retina was observed in the ERG test, probably as a result of dopamine deficiency in the retina. The results of our study indicate that ERG may also be a useful tool for understanding the reason for non-specific visual disturbances occurring in PD patients.

Interaction of (12)C ions with the mouse retinal response to light

Astronauts in orbit reported phosphenes varying in shape and orientation across the visual field; incidence was correlated with the radiation flux. Patients with skull tumors treated by (12)C ions and volunteers whose posterior portion of the eye was exposed to highly ionizing particles in early studies reported comparable percepts. An origin in radiation activating the visual system is suggested. Bursts (∼ 4 ms) of (12)C ions evoked electrophysiological mass responses comparable to those to light in the retina of anesthetized wild-type mice at threshold flux intensities consistent with the incidence observed in humans. The retinal response amplitude increased in mice with ion intensity to a maximum at ∼ 2000 ions/burst, to decline at higher intensities; the inverted-U relationship suggests complex effects on retinal structures. Here, we show that bursts of (12)C ions presented simultaneously to white light stimuli reduced the presynaptic mass response to light in the mouse retina, while increasing the postsynaptic retinal and cortical responses amplitude and the phase-locking to stimulus of cortical low frequency and gamma (∼ 25-45 Hz) responses. These findings suggest (12)C ions to interfere with, rather than mimicking the light action on photoreceptors; a parallel action on other retinal structures/mechanisms resulting in cortical activation is conceivable. Electrophysiological visual testing appears applicable to monitor the radiation effects and in designing countermeasures to prevent functional visual impairment during operations in space.

Vigabatrin can enhance electroretinographic responses in pigmented and albino rats

PURPOSE

To evaluate the effects of the antiepileptic medication vigabatrin (VGB) on the retina of pigmented rats.

METHODS

Scotopic and photopic electroretinograms were recorded from dark- and light-adapted Long-Evans (pigmented) and Sprague Dawley (albino) rats administered, daily, 52-55 injections of 250 mg·kg(-1)·day(-1) VGB or 25-26 injections of 500 mg·kg(-1)·day(-1) VGB, or a corresponding number of sham injections. Sensitivity and saturated amplitude of the rod photoresponse (S, Rm(P3)) and postreceptor response (1/σ, Vm) were derived, as were sensitivity and amplitude of the cone-mediated postreceptor response (1/σ(cone), Vm(cone)). The oscillatory potentials and responses to a series of flickering lights (6.25, 12.5, 25 and 50 Hz) were studied in the time and frequency domains. A subset of rats' eyes was harvested for Western blotting or histology.

RESULTS

Of the parameters derived from dark-adapted ERG responses, in both pigmented and albino rats, VGB repeatedly and reliably enhanced electroretinographic parameters; no significant ERG deficits were noted. No significant alterations were observed in ER/oxidative stress or in the Akt cell death/survival pathway. There were migrations of photoreceptor nuclei toward the RPE and outgrowths of bipolar cell dendrites into the outer nuclear layer in VGB-treated rats; these were never observed in sham-treated animals.

CONCLUSIONS

Although VGB is associated with retinal dysfunction in patients and VGB toxicity has been demonstrated by other laboratories in the albino rat, in our pigmented and albino rats, VGB did not induce deficits in, but rather enhanced, retinal function. Nonetheless, retinal neuronal dysplasia was observed.

The response of the neuronal adaptive system to background illumination and readaptation to dark in the immature retina

PURPOSE

Developmental characteristics of the neuronal adaptive system of the retina, focusing on background light (BGL) adaptation and readaptation functions, were studied by measuring the oscillatory response (SOP) of the electroretinogram (ERG).

METHODS

Digitally filtered and conventional ERGs were simultaneously recorded. Rats aged 15 and 17 days were studied during exposure to BGLs of two mesopic intensities and during readaptation to dark.

RESULTS

Results were compared to adult rats. In 'low mesopic' BGL SOP instantly dropped significantly to about half of its dark-adapted (DA) value contrary to mature rats, in which the SOP significantly increased. In 'high mesopic' BGL SOP decreased to about 20% and 30% of DA values in immature and adult rats, respectively. The process of recovery of SOP in darkness lacked the transient enhancement immediately as BGL was turned off, characteristic of adult rats. There were no major age differences in adaptive behaviour of a-wave. In young rats, recovery of b-wave was relatively slower.

CONCLUSIONS

Properties of BGL adaptation and readaptation functions of the neuronal adaptive system in baby retina differed compared to the adult one by being less forceful and more restrained. Handling of mesopic illumination and recovery in the dark was immature. Development of these functions of the neuronal adaptive system progresses postnatally and lags behind that of the photoreceptor response and seems to be delayed also compared to that of the bipolar response.

Measurement of retinal function with flash-electroretinography in Chinese patients with hyperlipidemia

BACKGROUND

We used flash electroretinography (F-ERG) to determine if retinal function was impaired in patients with hyperlipidemia, including visual acuity and fundus morphological changes, and to identify predictors of impaired retinal function in hyperlipidemia patients.

METHODS

This was a prospective case-control study (Shanghai, China; February 2011 to January 2012) in 696 hyperlipidemia patients and 136 healthy controls. Exclusion criteria included best-corrected visual acuity <0.6, previous intraocular surgery, and chronic comorbidities. Each participant underwent a comprehensive series of ophthalmologic examinations, and standard F-ERG examination. Data were analyzed using t-tests and multivariate analysis.

RESULTS

Six hundred and twenty-six hyperlipidemia patients (57.69 ± 14.01 years; 59.58% female) and 120 healthy controls (55.13 ± 14.03 years; 60% female) were included in the final analysis. After adjustment for age and gender using multivariate covariance analysis, F-ERG result revealed significantly lower response amplitudes in the hyperlipidemia group (P < 0.05), and longer implicit times (P < 0.05) than the control group. F-ERG parameters were significantly different between the two groups. Stepwise multiple linear regression analysis showed that serum LDL levels (P < 0.001), BMI (P < 0.001), duration of hyperlipidemia (P < 0.001), and serum HDL levels (P = 0.03) were negatively correlated with ΣOps.

CONCLUSION

The present study suggests that the retinal function of hyperlipidemia patients was significantly lower than in healthy controls, even before the occurrence of pathological changes in the fundus.

Protective effects of naringenin eye drops on N-methyl-N-nitrosourea-induced photoreceptor cell death in rats

AIM

To investigate the effects of naringenin eye drops on N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell death in rats.

METHODS

Photoreceptor cell death was induced by single intraperitoneal injection of MNU (60 mg/kg) in rats. Both eyes of all animals were instilled with one drop of vehicle, 0.5% or 1.0% naringenin eye drops three times per day from 7d before to 17d after MNU injection. Effects of naringenin on MNU-induced photoreceptor cell death were evaluated by electrophysiological and histological analysis.

RESULTS

Flash electroretinography (FERG) and oscillatory potentials (OPs) recordings showed that the vehicle control group had remarkable reduction of amplitudes and prolongation of latency times. FERG and OPs responses were significantly reversed in MNU-induced rats treated with 0.5% or 1.0% naringenin eye drops compared with the vehicle control. The retinal morphological results showed that naringenin dose-dependently preserved the outer nuclear layer, outer retina and total retina.

CONCLUSION

These results indicate that topical treatment with naringenin eye drops prevented retinal neurons from MNU-induced structural and functional damages.

The hormone prolactin is a novel, endogenous trophic factor able to regulate reactive glia and to limit retinal degeneration

Retinal degeneration is characterized by the progressive destruction of retinal cells, causing the deterioration and eventual loss of vision. We explored whether the hormone prolactin provides trophic support to retinal cells, thus protecting the retina from degenerative pressure. Inducing hyperprolactinemia limited photoreceptor apoptosis, gliosis, and changes in neurotrophin expression, and it preserved the photoresponse in the phototoxicity model of retinal degeneration, in which continuous exposure of rats to bright light leads to retinal cell death and retinal dysfunction. In this model, the expression levels of prolactin receptors in the retina were upregulated. Moreover, retinas from prolactin receptor-deficient mice exhibited photoresponsive dysfunction and gliosis that correlated with decreased levels of retinal bFGF, GDNF, and BDNF. Collectively, these data unveiled prolactin as a retinal trophic factor that may regulate glial-neuronal cell interactions and is a potential therapeutic molecule against retinal degeneration.

AII amacrine cells discriminate between heterocellular and homocellular locations when assembling connexin36-containing gap junctions

Electrical synapses (gap junctions) rapidly transmit signals between neurons and are composed of connexins. In neurons, connexin36 (Cx36) is the most abundant isoform; however, the mechanisms underlying formation of Cx36-containing electrical synapses are unknown. We focus on homocellular and heterocellular gap junctions formed by an AII amacrine cell, a key interneuron found in all mammalian retinas. In mice lacking native Cx36 but expressing a variant tagged with enhanced green fluorescent protein at the C-terminus (KO-Cx36-EGFP), heterocellular gap junctions formed between AII cells and ON cone bipolar cells are fully functional, whereas homocellular gap junctions between two AII cells are not formed. A tracer injected into an AII amacrine cell spreads into ON cone bipolar cells but is excluded from other AII cells. Reconstruction of Cx36-EGFP clusters on an AII cell in the KO-Cx36-EGFP genotype confirmed that the number, but not average size, of the clusters is reduced - as expected for AII cells lacking a subset of electrical synapses. Our studies indicate that some neurons exhibit at least two discriminatory mechanisms for assembling Cx36. We suggest that employing different gap-junction-forming mechanisms could provide the means for a cell to regulate its gap junctions in a target-cell-specific manner, even if these junctions contain the same connexin.