Immunotoxin-Induced Ablation of the Intrinsically Photosensitive Retinal Ganglion Cells in Rhesus Monkeys

Developmental control of rod number via a light-dependent retrograde pathway from intrinsically photosensitive retinal ganglion cells

Photoreception is essential for the development of the visual system, shaping vision's first synapse to cortical development. Here, we find that the lighting environment controls developmental rod apoptosis via Opn4-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs). Using genetics, sensory environment manipulations, and computational approaches, we establish a pathway where light-dependent glutamate released from ipRGCs is detected via a transiently expressed glutamate receptor (Grik3) on rod precursors within the inner retina. Communication between these cells is mediated by hybrid neurites on ipRGCs that sense light before eye opening. These structures span the ipRGC-rod precursor distance over development and contain the machinery for photoreception (Opn4) and neurotransmitter release (Vglut2 & Syp). Assessment of the human gestational retina identifies conserved hallmarks of an ipRGC-to-rod axis, including displaced rod precursors, transient GRIK3 expression, and ipRGCs with deep-projecting neurites. This analysis defines an adaptive retrograde pathway linking the sensory environment to rod precursors via ipRGCs prior to eye opening.

Retinal dysfunction in Parkinson's disease-results of the extended protocol for photopic negative response (PHNR) full-field electroretinogram (ERG)

BACKGROUND

We investigated whether the photopic negative response (PhNR) in the electroretinogram (ERG) was affected in Parkinson's disease (PD) patients and whether it was associated with retinal changes on optical coherence tomography (OCT).

METHODS

Thirty-two patients with PD and 31 age and sex-matched healthy controls from a single tertiary centre were included in the study. Hoehn and Yahr scale scores and the presence of REM sleep behaviour were recorded. PhNR, a-wave and b-wave responses in photopic ERG (red on blue background) and retinal layer thicknesses in OCT were obtained.

RESULTS

The mean age was 61 ± 10.4 in the PD group (female/male: 18/14) and 60.9 ± 7 in the control group (female/male: 18/13). The amplitudes of the PhNR, a- and b-waves in the ERG were significantly decreased in the PD group, but the implicit times were not significantly different. BCVA was significantly correlated with Hoehn and Yahr scores (p < 0.001, r = - 0.596). There was a significant correlation between BCVA and a-wave amplitude (p = 0.047, r = - 0.251). On OCT analysis, the thickness of the nasal INL was increased, and the temporal and inferior OPL and temporal peripapillary RNFL were decreased in the PD group compared to healthy controls (p = 0.032, p = 0.002, p = 0.016 and p = 0.012, respectively).

CONCLUSION

This study demonstrated reduced a-wave, b-wave and PhNR-wave amplitudes on ERG measurements in PD patients. These findings suggest that the whole ERG response, not just the PhNR, is attenuated in patient with PD, suggesting a possible involvement of the visual system in the disease.

Encoding of environmental illumination by primate melanopsin neurons

Light regulates physiology, mood, and behavior through signals sent to the brain by intrinsically photosensitive retinal ganglion cells (ipRGCs). How primate ipRGCs sense light is unclear, as they are rare and challenging to target for electrophysiological recording. We developed a method of acute identification within the live, ex vivo retina. Using it, we found that ipRGCs of the macaque monkey are highly specialized to encode irradiance (the overall intensity of illumination) by blurring spatial, temporal, and chromatic features of the visual scene. We describe mechanisms at the molecular, cellular, and population scales that support irradiance encoding across orders-of-magnitude changes in light intensity. These mechanisms are conserved quantitatively across the ~70 million years of evolution that separate macaques from mice.

Central retina plays a decisive role in the suppression of pupillary escape

PURPOSE

To explore the pupil redilation during persistent light exposure (pupillary escape phenomenon) at the macula and periphery with monochromatic light stimuli.

METHODS

Forty healthy subjects aged 18-64 years (24 females) were examined by chromatic pupil campimetry (CPC) using red and blue 4-s stimuli of 10° radius at the center and 20°-peripheral locations one per quadrant. One glaucoma patient and one achromatopsia patient served as disease models. For statistical analyses, linear mixed-effects models were performed followed by post hoc t-tests.

RESULTS

A distinct pupillary escape could be demonstrated peripherally (blue 0.099%*s, red 0.153%*s); at the central healthy retina, there was no relevant escape, neither for blue nor red stimulation. Comparing central versus peripheral stimulation revealed highly significant differences in the escape (difference blue 0.100 ± 0.013, red 0.144 ± 0.013, < 0.0001, respectively). In the periphery, the escape was significantly more pronounced for red compared with blue stimulation (difference 0.054 ± 0.013; p = 0.0001). Enhanced pupillary escape outside of the 95% confidence interval of the linear mixed-effects model of the healthy population could be exemplarily shown in a patient with glaucomatous ganglion cell damage. In the achromatopsia example, no relevant escape was found for blue stimulation, but for red stimulation in the periphery in a comparable range to healthy controls.

CONCLUSION

The results emphasize that an intact inner retinal network of nerve fibers arising from the central macular region is necessary for maintaining pupillary constriction during a bright 4-s light stimulus and preventing increase of pupillary escape. Increasing receptive field sizes towards the periphery on the level of retinal ganglion cells and less input from central 1:1 connections could be one of the driving mechanisms for pupillary escape.

Melanopsin photoreception differentially modulates rod-mediated and cone-mediated human temporal vision

To evaluate the nature of interactions between visual pathways transmitting the slower melanopsin and faster rod and cone signals, we implement a temporal phase summation paradigm in human observers using photoreceptor-directed stimuli. We show that melanopsin stimulation interacts with and alters both rod-mediated and cone-mediated vision regardless of whether it is perceptually visible or not. Melanopsin-rod interactions result in either inhibitory or facilitatory summation depending on the temporal frequency and photoreceptor pathway contrast sensitivity. Moreover, by isolating rod vision, we reveal a bipartite intensity response property of the rod pathway in photopic lighting that extends its operational range at lower frequencies to beyond its classic saturation limits but at the expense of attenuating sensitivity at higher frequencies. In comparison, melanopsin-cone interactions always lead to facilitation. These interactions can be described by linear or probability summations and potentially involve multiple intraretinal and visual cortical pathways to set human visual contrast sensitivity.

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Melanopsin ipRGCs support vision independent of the rod and cone signals

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Rod pathways mediate robust visual responses in daylight

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Temporal contrast sensitivity is contingent on the melanopsin excitation level

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Visual performance is collectively regulated by melanopsin, rod and cone pathways

The role of melanopsin photoreception on visual attention linked pupil responses

A decision during a visual task is marked by a task‐evoked pupil dilation (TEPD) that is linked to the global cortical arousal state. Melanopsin expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) form the afferent pathway for this pupil response. Melanopsin activation also influences mood and arousal and increases activity in decision‐making brain areas that receive direct ipRGC projections. Here, an optical photostimulation method controlled the excitations of all five photoreceptor classes in the human eye to isolate melanopsin‐mediated photoreception. We hypothesised that the TEPD can be driven by directing active visual covert attention through the ipRGC pathway. When observers are completely certain of the stimulus presence, melanopsin‐directed stimulation produces a TEPD of similar amplitude to a cone‐directed stimulation, with their combination producing larger amplitudes. This dilation is satisfactorily modelled by linear addition with a higher melanopsin weighting in ipRGCs. Visual reaction times were longest in response to melanopsin‐directed lights. Next, we asked whether the afferent photoreceptor input and decision certainty, controlled by priming the observer's a priori expectation, interact to drive the TEPD. Signal detection analysis showed that by fixing the predecision certainty (bias), the phasic arousal and TEPD amplitude vary with observer criterion (c′) and sensitivity (d′) but not with preferential activation of melanopsin. The signature feature of the melanopsin response during attention was a biphasic TEPD. We conclude that active covert attention can be modulated by visual information mediated via ipRGCs, but that phasic arousal responses marked using the TEPD are not increased by higher levels of melanopsin activation.

How lesions at different locations along the visual pathway influence pupillary reactions to chromatic stimuli

PURPOSE

To examine systematically how prechiasmal, chiasmal, and postchiasmal lesions along the visual pathway affect the respective pupillary responses to specific local monochromatic stimuli.

METHODS

Chromatic pupil campimetry (CPC) was performed in three patient groups (10 subjects with status after anterior ischemic optic neuropathy, 6 with chiasmal lesions, and 12 with optic tract or occipital lobe lesions (tumor, ischemia)) using red, low-intensity red, and blue local stimuli within the central 30° visual field. Affected areas - as determined by visual field defects revealed using conventional static perimetry - were compared with non-affected areas. Outcome parameters were the relative maximal constriction amplitude (relMCA) and the latency to constriction onset of the pupillary responses.

RESULTS

A statistically significant relMCA reduction was observed in the affected areas of postchiasmal lesions with red (p = 0.004) and low-intensity red stimulation (p = 0.001). RelMCA reduction in the affected areas seemed more pronounced for low-intensity red stimulation (46.5% mean reduction compared to non-affected areas; 36% for red stimulation), however statistically not significant. In prechiasmal lesions, a statistically significant latency prolongation could be demonstrated in the affected areas with low-intensity red stimulation (p = 0.015).

CONCLUSION

Our results indicate that the choice of stimulus characteristics is relevant in detecting defects in the pupillary pathway of impairment along the visual pathway, favoring red stimuli of low intensity over blue stimuli. Such knowledge opens the door for further fundamental research in pupillary pathways and is important for future clinical application of pupillography in neuro-ophthalmologic patients.

Long-Term Narrowband Lighting Influences Activity but Not Intrinsically Photosensitive Retinal Ganglion Cell-Driven Pupil Responses

Purpose: Light affects a variety of non-image forming processes, such as circadian rhythm entrainment and the pupillary light reflex, which are mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs). The purpose of this study was to assess the effects of long- and short-wavelength ambient lighting on activity patterns and pupil responses in rhesus monkeys. Methods: Infant rhesus monkeys were reared under either broadband "white" light (n = 14), long-wavelength "red" light (n = 20; 630 nm), or short-wavelength "blue" light (n = 21; 465 nm) on a 12-h light/dark cycle starting at 24.1 ± 2.6 days of age. Activity was measured for the first 4 months of the experimental period using a Fitbit activity tracking device and quantified as average step counts during the daytime (lights-on) and nighttime (lights-off) periods. Pupil responses to 1 s red (651 nm) and blue (456 nm) stimuli were measured after approximately 8 months. Pupil metrics included maximum constriction and the 6 s post-illumination pupil response (PIPR). Results: Activity during the lights-on period increased with age during the first 10 weeks (p < 0.001 for all) and was not significantly different for monkeys reared in white, red, or blue light (p = 0.07). Activity during the 12-h lights-off period was significantly greater for monkeys reared in blue light compared to those in white light (p = 0.02), but not compared to those in red light (p = 0.08). However, blue light reared monkeys exhibited significantly lower activity compared to both white and red light reared monkeys during the first hour of the lights-off period (p = 0.01 for both) and greater activity during the final hour of the lights-off period (p < 0.001 for both). Maximum pupil constriction and the 6 s PIPR to 1 s red and blue stimuli were not significantly different between groups (p > 0.05 for all). Conclusion: Findings suggest that long-term exposure to 12-h narrowband blue light results in greater disruption in nighttime behavioral patterns compared to narrowband red light. Normal pupil responses measured later in the rearing period suggest that ipRGCs adapt after long-term exposure to narrowband lighting.

Light adaptation characteristics of melanopsin

Following photopigment bleaching, the rhodopsin and cone-opsins show a characteristic exponential regeneration in the dark with a photocycle dependent on the retinal pigment epithelium. Melanopsin pigment regeneration in animal models requires different pathways to rods and cones. To quantify melanopsin-mediated light adaptation in humans, we first estimated its photopigment regeneration kinetics through the photo-bleach recovery of the intrinsic melanopsin pupil light response (PLR). An intense broadband light (~120,000 Td) bleached 43% of melanopsin compared to 86% of the cone-opsins. Recovery from a 43% bleach was 3.4X slower for the melanopsin than cone-opsin. Post-bleach melanopsin regeneration followed an exponential growth with a 2.5 min time-constant (τ) that required 11.2 min for complete recovery; the half-bleaching level (I_p) was ~ 4.47 log melanopic Td (16.10 log melanopsin effective photons.cm^-2.s^-1; 8.25 log photoisomerisations.photoreceptor^-1.s^-1). The effect on the cone-directed PLR of the level of the melanopsin excitation during continuous light adaptation was then determined. We observed that cone-directed pupil constriction amplitudes increased by ~ 10% when adapting lights had a higher melanopic excitation but the same mean photometric luminance. Our findings suggest that melanopsin light adaptation enhances cone signalling along the non-visual retina-brain axis. Parameters τ and I_p will allow estimation of the level of melanopsin bleaching in any light units; the data have implications for quantifying the relative contributions of putative melanopsin pathways to regulate the post-bleach photopigment regeneration and adaptation.

Pupillary light reflex circuits in the Macaque Monkey: the olivary pretectal nucleus

The olivary pretectal nucleus is the first central connection in the pupillary light reflex pathway, the circuit that adjusts the diameter of the pupil in response to ambient light levels. This study investigated aspects of the morphology and connectivity of the olivary pretectal nucleus in macaque monkeys by use of anterograde and retrograde tracers. Within the pretectum, the vast majority of neurons projecting to the preganglionic Edinger-Westphal nucleus were found within the olivary pretectal nucleus. Most of these neurons had somata located at the periphery of the nucleus and their heavily branched dendrites extended into the core of the nucleus. Retinal terminals were concentrated within the borders of the olivary pretectal nucleus. Ultrastructural examination of these terminals showed that they had clear spherical vesicles, occasional dense-core vesicles, and made asymmetric synaptic contacts. Retrogradely labeled cells projecting to the preganglionic Edinger-Westphal nucleus displayed relatively few somatic contacts. Double labeling indicated that these neurons receive direct retinal input. The concentration of retinal terminals within the nucleus and the extensive dendritic trees of the olivary projection cells provide a substrate for very large receptive fields. In some species, pretectal commissural connections are a substrate for balancing the direct and consensual pupillary responses to produce pupils of equal size. In the macaque, there was little evidence for such a commissural projection based on either anterograde or retrograde tracing. This may be due to the fact that each macaque retina provides nearly equal density projections to the ipsilateral and contralateral olivary pretectal nucleus.

Melanopsin and the Intrinsically Photosensitive Retinal Ganglion Cells: Biophysics to Behavior

The mammalian visual system encodes information over a remarkable breadth of spatiotemporal scales and light intensities. This performance originates with its complement of photoreceptors: the classic rods and cones, as well as the intrinsically photosensitive retinal ganglion cells (ipRGCs). IpRGCs capture light with a G-protein-coupled receptor called melanopsin, depolarize like photoreceptors of invertebrates such as Drosophila, discharge electrical spikes, and innervate dozens of brain areas to influence physiology, behavior, perception, and mood. Several visual responses rely on melanopsin to be sustained and maximal. Some require ipRGCs to occur at all. IpRGCs fulfill their roles using mechanisms that include an unusual conformation of the melanopsin protein, an extraordinarily slow phototransduction cascade, divisions of labor even among cells of a morphological type, and unorthodox configurations of circuitry. The study of ipRGCs has yielded insight into general topics that include photoreceptor evolution, cellular diversity, and the steps from biophysical mechanisms to behavior.

Melanopsin-Containing ipRGCs Are Resistant to Excitotoxic Injury and Maintain Functional Non-Image Forming Behaviors After Insult in a Diurnal Rodent Model

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are critical for the light signaling properties of non-image forming vision. Melanopsin-expressing ipRGCs project to retinorecipient brain regions involved in modulating circadian rhythms. Melanopsin has been shown to play an important role in how animals respond to light, including photoentrainment, masking (i.e., acute behavioral responses to light), and the pupillary light reflex (PLR). Importantly, ipRGCs are resistant to various forms of damage, including ocular hypertension, optic nerve crush, and excitotoxicity via N-methyl-D-aspartic acid (NMDA) administration. Although these cells are resistant to various forms of injury, the question still remains whether or not these cells remain functional following injury. Here we tested the hypothesis that ipRGCs would be resistant to excitotoxic damage in a diurnal rodent model, the Nile grass rat (Arvicanthis niloticus). In addition, we hypothesized that following insult, grass rats would maintain normal circadian entrainment and masking to light. In order to test these hypotheses, we injected NMDA intraocularly and examined its effect on the survivability of ipRGCs and RGCs, along with testing behavioral and functional consequences. Similar to findings in nocturnal rodents, ipRGCs were spared from significant damage but RGCs were not. Importantly, whereas image-forming vision was significantly impaired, non-image forming vision (i.e, photoentrainment, masking, and PLR) remained functional. The present study aims to characterize the resistance of ipRGCs to excitotoxicity in a diurnal rodent model.

Melanopsin and Cone Photoreceptor Inputs to the Afferent Pupil Light Response

Background: Retinal photoreceptors provide the main stage in the mammalian eye for regulating the retinal illumination through changes in pupil diameter, with a small population of melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) forming the primary afferent pathway for this response. The purpose of this study is to determine how melanopsin interacts with the three cone photoreceptor classes in the human eye to modulate the light-adapted pupil response.

Methods: We investigated the independent and combined contributions of the inner and outer retinal photoreceptor inputs to the afferent pupil pathway in participants with trichromatic color vision using a method to independently control the excitations of ipRGCs, cones and rods in the retina.

Results: We show that melanopsin-directed stimuli cause a transient pupil constriction generated by cones in the shadow of retinal blood vessels; desensitizing these penumbral cone signals uncovers a signature melanopsin pupil response that includes a longer latency (292 ms) and slower time (4.1x) and velocity (7.7x) to constriction than for cone-directed stimuli, and which remains sustained post-stimulus offset. Compared to melanopsin-mediated pupil responses, the cone photoreceptor-initiated pupil responses are more transient with faster constriction latencies, higher velocities and a secondary constriction at light offset. The combined pupil responses reveal that melanopsin signals are additive with the cone signals.

Conclusions: The visual system uses the L–, M–, and S–cone photoreceptor inputs to the afferent pupil pathway to accomplish the tonic modulations of pupil size to changes in image contrast. The inner retinal melanopsin-expressing ipRGCs mediate the longer-term, sustained pupil constriction to set the light-adapted pupil diameter during extended light exposures.