Subcomponents of P3 in cold-blooded vertebrate retinae

Light drives the developmental progression of outer retinal function

The complex nature of rod and cone photoreceptors and the light-evoked responsivity of bipolar cells in the mature rodent retina have been well characterized. However, little is known about the emergent light-evoked response properties of the mouse retina and the role light plays in shaping these emergent responses. We have previously demonstrated that the outer retina is responsive to green light as early as postnatal day 8 (P8). Here, we characterize the progression of both photoreceptors (rods and cones) and bipolar cell responses during development and into adulthood using ex vivo electroretinogram recordings. Our data show that the majority of photoreceptor response at P8 originates from cones and that these outputs drive second-order bipolar cell responses as early as P9. We find that the magnitude of the photoresponse increases concurrently with each passing day of postnatal development and that many functional properties of these responses, as well as the relative rod/cone contributions to the total light-evoked response, are age dependent. We compare these responses at eye opening and maturity to age-matched animals raised in darkness and found that the absence of light diminishes emergent and mature cone-to-bipolar cell signaling. Furthermore, we found cone-evoked responses to be significantly slower in dark-reared retinas. Together, this work characterizes the developmental photoresponsivity of the mouse retina while highlighting the importance of properly timed sensory input for the maturation of the first visual system synapse.

Sex-Specific Retinal Anomalies Induced by Chronic Social Defeat Stress in Mice

Major depressive disorder (MDD) is one of the most common consequences of chronic stress. Still, there is currently no reliable biomarker to detect individuals at risk to develop the disease. Recently, the retina emerged as an effective way to investigate psychiatric disorders using the electroretinogram (ERG). In this study, cone and rod ERGs were performed in male and female C57BL/6 mice before and after chronic social defeat stress (CSDS). Mice were then divided as susceptible or resilient to stress. Our results suggest that CSDS reduces the amplitude of both oscillatory potentials and a-waves in the rods of resilient but not susceptible males. Similar effects were revealed following the analysis of the cone b-waves, which were faster after CSDS in resilient mice specifically. In females, rod ERGs revealed age-related changes with no change in cone ERGs. Finally, our analysis suggests that baseline ERG can predict with an efficacy up to 71% the expression of susceptibility and resilience before stress exposition in males and females. Overall, our findings suggest that retinal activity is a valid biomarker of stress response that could potentially serve as a tool to predict whether males and females will become susceptible or resilient when facing CSDS.

Ex vivo electroretinograms made easy: performing ERGs using 3D printed components

KEY POINTS

Rod and cone photoreceptors convert light into electrochemical signals that are transferred to second order cells, initiating image-forming visual processing. Electroretinograms (ERGs) can detect the associated light-induced extracellular transretinal events, allowing for physiological assessment of cellular activity from morphologically intact retinas. We outline a method for economically configuring a traditional patch-clamp rig for performing high signal-to-noise ex vivo ERGs. We accomplish this by incorporating various 3D printed components and by modifying existing light pathways in a typical patch-clamp rig. This methodology provides an additional set of tools to labs interested in studying the physiological function of neuronal populations in isolated retinal tissue.

ABSTRACT

Rod and cone photoreceptors of the retina are responsible for the initial stages in vision and convey sensory information regarding our visual world across a wide range of lighting conditions. These photoreceptors hyperpolarize in the presence of light and subsequently transmit signals to second-order bipolar and horizontal cells. The electrical components of these events are experimentally detectable, and in conjunction with pharmacological agents, can be further separated into their respective cellular contributions using electroretinograms (ERGs). Extracellular activity from populations of rods and cones generate the negative-going a-wave, while ON-bipolar cells generate positive-going b-waves. ERGs can be performed in vivo or alternatively using an ex vivo configuration, where retinas are isolated and transretinal photovoltages are recorded at high signal-to-noise ratios. However, most ERG set-ups require their own unique set of tools. We demonstrate how, at low cost, to reconfigure a typical patch-clamp rig for ERG recordings. The bulk of these modifications require implementation of various 3D printed components, which can alternatively aid in generating a stand-alone ERG set-up without a patch-rig. Further, we discuss how to configure an ERG system without a patch-clamp rig. Compared to in vivo ERGs, these are superior when measuring small responses, such as those that are cone-evoked or those from immature mouse retinae. This recording configuration provides high signal-to-noise detection of a-waves (300-600 µV) and b-waves (1-3 mV), and is ultimately capable of discerning small (1-2 µV) photovoltages from noise. These quick and economical modifications allow researchers to equip their technical arsenal with an interchangeable patch-clamp/ERG system.

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram

PURPOSE

We introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli.

METHODS

This white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.3° diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG.

RESULTS

We show that wnERG recordings are highly repeatable, with good signal-to-noise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ∼1 photopic cd.m-2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash.

CONCLUSION

The wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG.

TRANSLATIONAL RELEVANCE

The white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.

Separation and light adaptation of rod and cone signals in the retina of the goldfish

The aspartate-isolated fast P III response was used to monitor the responses of goldfish photoreceptors at varying intensities of steady background illumination. When the retina contained the normal complement of rods and cones, light adaptation consisted of response compression, a shift of the response curve to more intense stimuli (cellular adaptation), and responses to decrements as well as increments of light. Rod and cone contributions to the fast P III response were separated by taking advantage of photomechanical movements of the photoreceptors to produce "all-rod" and "all-cone" retinae. Rods employ response compression as their primary adaptation mechanism. Rods show little cellular adaptation or responses to decremental flashes. However, cones do not show response compression, but continue to respond at bright backgrounds due to cellular adaptation.

Electrophysiological analysis of taurine and glycine action on neurons of the mudpuppy retina. II. ERG, PNR and Müller cell recordings

Extracellular electrophysiological recordings of the electroretinogram (ERG) and proximal negative response (PNR) were carried out in the perfused retina-eyecup prepartation of the mudpuppy. Intracellular recordingws were obtained from Müller cells. Bath-applied taurine/glycine had identical effects on the ERG, PNR and Müller cell responses and the effects of both agents were blocked by strychnine. Taurine and glycine suppressed the d-wave of the ERG, the OFF response of Müller cells and ON and OFF responses of the PNR. These observations show that taurine/glycine sensitivity is predominantly found in the OFF channel of the ERG whose underlying neuronal basis appears to be dark evoked depolarization of OFF bipolars.

Light adaptation and temperature effects in rat PIII retinal response: analysis with a two-state model

Aspartate-isolated PIII responses from excised perfused retinas of albino rats were studied, with emphasis on background adaptation and temperature effects. When responses are measured at their peaks, it is seen that the proportion of response elicited by the background is equal to the proportion by which a test-flash response is suppressed. This supports the notion that rat PIII, although a complex response, seems to approximate a simple two-state ("compression") system and that it is therefore subject to analysis according to our recently proposed model. This model predicts that (i) responses from two-state systems should increase with decreasing temperature within limits; (ii) delta, the semisaturation constant of voltage--log intensity functions should shift to lower intensities with decreasing temperature; and (iii) the exact magnitude of the delta shift should follow the temperature dependence of the rate of rapid "neural" adaptation of the response. All of these predictions are verified for rat PIII. This suggests that rat PIII, although produced by at least two cell types, is being controlled by only two processes: a light-driven excitation and a rapid first-order "neural" dark adaptation.

A duration-dependent negative potential in the cichlid electroretinogram

A negative potential can be evoked in the local electroretinogram of the cichlid fish Cichlasoma octofasciatum by light stimuli of duration longer than 70 msec. This response superficially resembles the proximal negative response, but differs in some waveform components and dependence upon stimulus configuration and duration.

Scotopic and photopic components of the rat electroetinogram

1. Increment thresholds were measured on the albino rat retina using the e.r.g. as an indicator of visual sensitivity.2. Light adaptation produces a change in b-wave spectral sensitivity independently of whether brief or steady adapting backgrounds are used. This shows that the changed spectral sensitivity is not directly associated with the bleaching of visual pigment.3. Light adaptation does not appear to alter the spectral sensitivity of the ordinary a-wave. Consequently, after light adaptation a- and b-waves have different spectral sensitivities.4. B-wave increments determined with a blue test stimulus on a red adaptive background show rod saturation. Background levels which saturate the rods cause the a-wave mechanism to cease responding to incremental stimuli.5. A background intense enough to saturate the rods evokes a maximum a-wave response. If a light is sufficiently bright to saturate the rods then the isolated a-wave fails to signal the termination of the stimulus.6. Scotopically equated blue and orange stimuli produce equal early receptor potentials.