Short-wavelength Sensitive Cones Research Articles

Poster Session: Eliciting Color Percepts over Extended Fields through Cone-by-Cone Stimulation.

Purpose Human color vision is informed by the relative activations of the long-, medium-, and short-wavelength sensitive cones. We have developed a display that can produce a variety of color sensations using only a single wavelength of light, by programming the activity levels of the three cone types at population scales. Methods With an Adaptive Optics Scanning Laser Ophthalmoscope, we image the retina at 840 nm over a 0.9° x 0.9° field and track the eye's fixational motion in order to deliver discrete microdoses of 543 nm light to ~2500 individual cones per frame. Using each cone type's spectral sensitivity to 543 nm, we can recapitulate the relative activations consistent with colors that are distinct from the stimulating laser, resulting in percepts of uniform colored squares that appear stable in the world. Results Using stimulation from only 543 nm light, we can elicit color percepts ranging from green to red-orange in 2 subjects who have cone spectral types classified in a region of their retina. Additionally, we find through color matching data that the distinct color percepts are lost for intentional misdeliveries that exceed 30% of the cone diameter in both subjects. Conclusions These results demonstrate our system's ability to track the retina at high speed, stimulate with cone-level precision, and generate color percepts by directly programming the activity of the human cone mosaic. These technical capabilities provide a novel platform for studying color vision.

Heterogeneity in quiescent Müller glia in the uninjured zebrafish retina drive differential responses following photoreceptor ablation.

Loss of neurons in the neural retina is a leading cause of vision loss. While humans do not possess the capacity for retinal regeneration, zebrafish can achieve this through activation of resident Müller glia. Remarkably, despite the presence of Müller glia in humans and other mammalian vertebrates, these cells lack an intrinsic ability to contribute to regeneration. Upon activation, zebrafish Müller glia can adopt a stem cell-like state, undergo proliferation and generate new neurons. However, the underlying molecular mechanisms of this activation subsequent retinal regeneration remains unclear. To address this, we performed single-cell RNA sequencing (scRNA-seq) and report remarkable heterogeneity in gene expression within quiescent Müller glia across distinct dorsal, central and ventral retina pools of such cells. Next, we utilized a genetically driven, chemically inducible nitroreductase approach to study Müller glia activation following selective ablation of three distinct photoreceptor subtypes: long wavelength sensitive cones, short wavelength sensitive cones, and rods. There, our data revealed that a region-specific bias in activation of Müller glia exists in the zebrafish retina, and this is independent of the distribution of the ablated cell type across retinal regions. Notably, gene ontology analysis revealed that injury-responsive dorsal and central Müller glia express genes related to dorsal/ventral pattern formation, growth factor activity, and regulation of developmental process. Through scRNA-seq analysis, we identify a shared genetic program underlying initial Müller glia activation and cell cycle entry, followed by differences that drive the fate of regenerating neurons. We observed an initial expression of AP-1 and injury-responsive transcription factors, followed by genes involved in Notch signaling, ribosome biogenesis and gliogenesis, and finally expression of cell cycle, chromatin remodeling and microtubule-associated genes. Taken together, our findings document the regional specificity of gene expression within quiescent Müller glia and demonstrate unique Müller glia activation and regeneration features following neural ablation. These findings will improve our understanding of the molecular pathways relevant to neural regeneration in the retina.

Effects of blue-enriched white light with same correlated colour temperature on visual fatigue

Visual fatigue has become a public health issue, while the relevant retinal mechanism and characteristics of blue light that induce visual fatigue have been rarely studied. In the retina, both short wavelength-sensitive (S) cones and melanopsin-containing intrinsically photoreceptive retinal ganglion cells (ipRGCs) are sensitive to blue light, and their responses are opposite in pupil mediation. Thus, effects of blue-enriched white light with different S-cone-opic Equivalent Daylight Illuminance (EDI) on visual fatigue was investigated, maintaining the same melanopic EDI to avoid interferences of melanopsin-containing ipRGCs. Two white illuminants (one with low S-cone-opic EDI, the other with high S-cone-opic EDI) were characterized based on α-opic EDI with the same correlated colour temperature and illuminance. Melanopic EDI was lower than S-cone-opic EDI of these two illuminants. Psychological, visual, physiological and cognitive performances were measured to investigate visual fatigue. Results showed that blue-enriched white light with high S-cone-opic EDI can induce visual fatigue. Participants felt more discomfort in their eyes under high S-cone-opic EDI along with the decline of tear film stability and changes of heart rhythm. Furthermore, the reaction time in a memory task increased significantly under high S-cone-opic EDI. The findings provide new insights into the optimization of indoor lighting environments for human health.

How chromatic cues can guide human eye growth to achieve good focus.

The postnatal growing eye uses visual cues to actively control its own axial elongation to achieve and maintain sharp focus, a process termed emmetropization. The primary visual cue may be the difference in image sharpness as sensed by the arrays of short- and long-wavelength sensitive cone photoreceptors caused by longitudinal chromatic aberration: Shorter wavelengths focus in front of longer wavelengths. However, the sparse distribution of short-wavelength sensitive cones across the retina suggests that they do not have sufficient spatial sampling resolution for this task. Here, we show that the spacing of the short-wavelength sensitive cones in humans is sufficient for them, in conjunction with the longer wavelength cones, to use chromatic signals to detect defocus and guide emmetropization. We hypothesize that the retinal spacing of the short-wavelength sensitive cones in many mammalian species is an evolutionarily ancient adaption that allows the efficient use of chromatic cues in emmetropization.

An opponent dual-detector spectral drive model of emmetropization

In post-natal developing eyes a feedback mechanism uses optical cues to regulate axial growth so as to achieve good focus, a process termed emmetropization. However, the optical cues that the feedback mechanism uses have remained unclear. Here we present evidence that a primary visual cue may be the detection of different image statistics by the short-wavelength sensitive (SWS) and long-wavelength sensitive (LWS) cone photoreceptors, caused by longitudinal chromatic aberration (LCA). We use as a model system the northern tree shrew Tupaia belangeri, diurnal cone-dominated dichromatic mammals closely related to primates. We present an optical model in which the SWS and LWS photoreceptors each represent an image at different levels of defocus. The model posits that an imbalance between SWS and LWS image statistics directs eye growth towards the point at which these image statistics are in balance. Under spectrally broadband (“white”) lighting, the focus of the eye is driven to a target point approximately in the middle of the visible spectrum, which is emmetropia. Calculations suggest that the SWS cone array, despite the sparse number of SWS cones, can plausibly detect the wavelength-dependent differences in defocus and guide refractive development. The model is consistent with the effects of various narrow-band illuminants on emmetropization in tree shrews. Simulations suggest that common artificial light spectra do not interfere with emmetropization. Simulations also suggest that multi-spectral multi-focal lenses, where the different optical zones of a multifocal lens have different spectral filtering properties, could be an anti-myopia intervention.

Analysis of zebrafish cryptochrome2 and 4 expression in UV cone photoreceptors

Cryptochromes (Cry) are ancient flavoproteins known to regulate circadian rhythms. In plants and some animals, Cry is sensitive to blue light due to its ability to bind the chromophore flavin adenine dinucleotide (FAD). Cry is also suggested to function in magnetoreception, since it can create light-dependent radical pairs with FAD that are sensitive to magnetic fields (Ritz2000; Liedvogel et al., 2007; Solov'yov et al., 2014). Cry is expressed in the visual system of various animals and specifically co-localizes with both short– and long–wavelength cone photoreceptors in birds (Bischof et al., 2011; Günther et al., 2018). However, magnetoreception is not limited to birds and the expression of cry genes in the photoreceptors of other vertebrates is unknown. Here, we use zebrafish to examine the retinal expression pattern of cry family genes. Zebrafish have seven cry genes and while most are known regulators of the circadian clock, relatively little is known about cry2 and cry4 (Haug et al., 2015; Liu et al., 2015). Therefore, we explored cry2 and cry4 expression in the larval and adult zebrafish retina. We demonstrate that cry4 is predominantly expressed in the short-wavelength ultraviolet (UV)-sensitive cone photoreceptors, while cry2 is expressed in UV cones and additional retinal photoreceptors during the day. Using Nitroreductase (NTZ)-mediated cell ablation and qRT-PCR, we find that cry4 expression significantly decreases when UV cones are ablated, but not when the neighboring short-wavelength sensitive blue cones are ablated. cry2 expression decreases after UV cone ablation but is still significantly detectable, while blue cone ablation does not alter cry2 expression. This study provides a more detailed annotation of cry2 and cry4 expression in the zebrafish retina and highlights the feasibility of a well-established ablation paradigm to test if photoreceptors are required for magnetoreception in fish. Although evidence of magnetoreception in adult zebrafish has gained considerable evidence over the last decade (Shcherbakov et al., 2005; Takebe et al., 2012; Krylov et al., 2016; Myklatun et al., 2018) the mediating mechanism(s) remain unknown. Additionally, despite limited evidence that larval zebrafish are magnetoreceptive, many other larval fish have a characterized magnetic sense; sockeye salmon fry, larval coral reef fish, larval medaka and larval Atlantic haddock have been shown to be responsive to magnetic fields (Quinn; 1980; Bottesch et al., 2016; O'Connor and Muheim. 2017; Myklatun et al., 2018; Cresci, et al. 2019). If cry-cone interactions are conserved within fish, our findings may suggest one potential mechanism, such that UV cones appear poised for light-dependent magnetoreception via photoreceptor subtype-specific expression of cry.

Short-Wavelength Sensitive Cone (S-cone) Testing as an Outcome Measure for NR2E3 Clinical Treatment Trials.

Recessively-inherited NR2E3 gene mutations cause an unusual retinopathy with abnormally-increased short-wavelength sensitive cone (S-cone) function, in addition to reduced rod and long/middle-wavelength sensitive cone (L/M-cone) function. Progress toward clinical trials to treat patients with this otherwise incurable retinal degeneration prompted the need to determine efficacy outcome measures. Comparisons were made between three computerized perimeters available in the clinic. These perimeters could deliver short-wavelength stimuli on longer-wavelength adapting backgrounds to measure whether S-cone vision can be quantified. Results from a cohort of normal subjects were compared across the three perimeters to determine S-cone isolation and test-retest variability. S-cone perimetry data from NR2E3-ESCS (enhanced S-cone syndrome) patients were examined and determined to have five stages of disease severity. Using these stages, strategies were proposed for monitoring efficacy of either a focal or retina-wide intervention. This work sets the stage for clinical trials.

Photoreceptors and eyes of pikeperch Sander lucioperca, pike Esox lucius, perch Perca fluviatilis and roach Rutilus rutilus from a clear and a brown lake

The photoreceptors and eyes of four fish species commonly cohabiting Fennoscandian lakes with different light transmission properties were compared: pikeperch Sander lucioperca, pike Esox lucius, perch Perca fluviatilis and roach Rutilus rutilus. Each species was represented by individuals from a clear (greenish) and a humic (dark brown) lake in southern Finland: Lake Vesijärvi (LV; peak transmission around 570 nm) and Lake Tuusulanjärvi (LT; peak transmission around 630 nm). In the autumn, all species had almost purely A2-based visual pigments. Rod absorption spectra peaked at c.526 nm (S. lucioperca), c. 533 nm (E. lucius) and c. 540 nm (P. fluviatilis and R. rutilus), with no differences between the lakes. Esox lucius rods had remarkably long outer segments, 1.5-2.8-fold longer than those of the other species. All species possessed middle-wavelength-sensitive (MWS) and long-wavelength-sensitive (LWS) cone pigments in single, twin or double cones. Rutilus rutilus also had two types of short-wavelength sensitive (SWS) cones: UV-sensitive [SWS1] and blue-sensitive (SWS2) cones, although in the samples from LT no UV cones were found. No other within-species differences in photoreceptor cell complements, absorption spectra or morphologies were found between the lakes. However, E. lucius eyes had a significantly lower focal ratio in LT compared with LV, enhancing sensitivity at the expense of acuity in the dark-brown lake. Comparing species, S. lucioperca was estimated to have the highest visual sensitivity, at least two times higher than similar-sized E. lucius, thanks to the large relative size of the eye (pupil) and the presence of a reflecting tapetum behind the retina. High absolute sensitivity will give a competitive edge also in terms of short reaction times and long visual range.

Juvenile Tree Shrews Do Not Maintain Emmetropia in Narrow-band Blue Light.

In spectrally broad-band light, an emmetropization mechanism in post-natal eyes uses visual cues to modulate the growth of the eye to achieve and maintain near emmetropia. When we restricted available wavelengths to narrow-band blue light, juvenile tree shrews (diurnal dichromatic mammals closely related to primates) developed substantial refractive errors, suggesting that feedback from defocus-related changes in the relative activation of long- and short-wavelength-sensitive cones is essential to maintain emmetropia. The purpose of this study was to examine the effects of narrow-band ambient blue light on refractive state in juvenile tree shrews that had completed initial emmetropization (decrease from hyperopia toward emmetropia). Animals were raised in fluorescent colony lighting until they began blue-light treatment at 24 days of visual experience, at which age they had achieved age-normal low hyperopia (mean ± SEM refractive error, 1.2 ± 0.5 diopters). Arrays of light-emitting diodes placed atop the cage produced wavelengths of 457 (five animals) or 464 nm (five animals), flickered in a pseudo-random pattern (temporally broad band). A third group of five animals was exposed to steady 464-nm blue light. Illuminance on the floor of the cage was 300 to 500 human lux. Noncycloplegic autorefractor measures were made daily for a minimum of 11 days and up to 32 days. Seven age-matched animals were raised in colony light. The refractive state of all blue-treated animals moved outside the 95% confidence limits of the colony-light animals' refractions. Most refractions first moved toward hyperopia. Then the refractive state decreased monotonically and, in some animals, passed through emmetropia, becoming myopic. From the tree shrew cone absorbance spectra, the narrow-band blue light stimulated both long-wavelength-sensitive and short-wavelength-sensitive cones, but the relative activation would not change with the refractive state. This removed feedback from longitudinal chromatic aberration that may be essential to maintain emmetropia.

Knockdown of the thyroid hormone transporter MCT8 in chicken retinal precursor cells hampers early retinal development and results in a shift towards more UV/blue cones at the expense of green/red cones

Thyroid hormones (THs) play a crucial role in coordinating brain development in vertebrates. They fine-tune processes like cell proliferation, migration, and differentiation mainly by regulating the transcriptional activity of many essential genes. Regulators of TH availability thereby define the cellular concentration of the bioactive 3,5,3′-triiodothyronine, which binds to nuclear TH receptors. One important regulator, the monocarboxylate transporter 8 (MCT8), facilitates cellular TH uptake and is known to be necessary for correct brain development, but data on its potential role during retinal development is lacking. The retinal cyto-architecture has been conserved throughout vertebrate evolution, and we used the chicken embryo to study the need for MCT8 during retinal development. Its external development allows easy manipulation, and MCT8 is abundantly expressed in the retina from early stages onwards. We induced MCT8 knockdown by electroporating a pRFP-MCT8-RNAi vector into the retinal precursor cells (RPCs) at embryonic day 4 (E4), and studied the consequences for early (E6) and late (E18) retinal development. The empty pRFP-RNAi vector was used as a control. RPC proliferation was reduced at E6. This resulted in cellular hypoplasia and a thinner retina at E18 where mainly photoreceptors and horizontal cells were lost, the two predominant cell types that are born around the stage of electroporation. At E6, differentiation into retinal ganglion cells and amacrine cells was delayed. However, since the proportion of a given cell type within the transfected cell population at E18 was similar in knockdown and controls, the partial loss of some cell types was most-likely due to reduced RPC proliferation and not impaired cell differentiation. Photoreceptors displayed delayed migration at first, but had successfully reached the outer nuclear layer at E18. However, they increasingly differentiated into short wavelength-sensitive cones at the expense of medium/long wavelength-sensitive cones, while the proportion of rods was unaltered. Improperly formed sublaminae in the inner plexiform layer additionally suggested defects in synaptogenesis. Altogether, our data echoes effects of hypothyroidism and the loss of some other regulators of TH availability in the developing zebrafish and rodent retina. Therefore, the expression of MCT8 in RPCs is crucial for adequate TH uptake during cell type-specific events in retinal development.

Isolation of photoreceptors from mature, developing, and regenerated zebrafish retinas, and of microglia/macrophages from regenerating zebrafish retinas

This paper describes experimental procedures for the dissociation of retinal cells of the zebrafish (Danio rerio) for subsequent fluorescence-activated cell sorting (FACS) and gene expression studies. Methods for dissociation of zebrafish retinas followed by FACS and RNA isolation were optimized. This methodology was applied to isolate pure sorted samples of rods, long wavelength-sensitive (LWS) cones, medium wavelength-sensitive (MWS; RH2-2) cones, short wavelength-sensitive (SWS2) cones, and UV-sensitive (SWS1) cones from retinas obtained at selective life-history stages of the zebrafish, and for some of these photoreceptors, following retinal regeneration. We also successfully separated lws1-expressing and lws2-expressing LWS cones from fish of a transgenic line in which lws1 is reported with green fluorescence protein (GFP) and lws2 is reported with red fluorescence protein (RFP). Microglia/macrophages were successfully sorted from regenerating retinas (7 days after a cytotoxic lesion) of a transgenic line in which these immune cells express GFP. Electropherograms verified downstream isolation of high-quality RNA from sorted samples. Examples of post-sorting analysis, as well as results of qRT-PCR studies, validated the purity of sorted populations. For example, qRT-PCR samples derived from isolated Rh2-2 cones contained detectable rh2-2 (opn1mw2) opsin transcripts, but lws opsin transcripts (lws1/opn1lw1, lws2/opn1lw2) were not detected, suggesting that the procedure likely separated double cone pairs. Through this method, pure, sorted cell samples can provide RNA that is reliable for downstream gene expression analyses, such as qRT-PCR and RNA-seq, which may reveal molecular signatures of photoreceptors and microglia for comparative transcriptomics studies.

Immunohistochemical profile of long-standing traumatic retinal detachment in atrophic globe in a young patient.

Photoreceptor cell death is the ultimate cause of irreversible vision loss in retinal detachment (RD). The present study aimed to investigate the retinal changes in a case of long-standing traumatic RD in a young patient. The RD-induced atrophic globe was examined following enucleation. A control eye acquired from a deceased donor (normal histology; age- and sex-matched) was evaluated correspondingly. Frozen sections of retina tissue were assessed by immunofluorescence staining. The atrophic retina demonstrated structural disruption along with reduction in the retinal outer nuclear layer/inner nuclear layer thickness ratio. Photoreceptor degeneration was noted with complete loss of the outer segment of short-wavelength sensitive (S) cones. In addition, Müller cell hypertrophy was observed across the retinal nuclear layers. These results indicate that RD without successful medical treatment may lead to retinal atrophy associated with disruption of retinal integrity, dramatic S cones loss and subretinal gliosis. Further clarifications of the mechanisms underlying photoreceptor cell death and glial cell reprogramming may facilitate the design of novel therapeutic strategies for RD.

Stereotyped Synaptic Connectivity Is Restored during Circuit Repair in the Adult Mammalian Retina

Proper function of the central nervous system (CNS) depends on the specificity of synaptic connections between cells of various types. Cellular and molecular mechanisms responsible for the establishment and refinement of these connections during development are the subject of an active area of research [1-6]. However, it is unknown if the adult mammalian CNS can form new type-selective synapses following neural injury or disease. Here, we assess whether selective synaptic connections can be reestablished after circuit disruption in the adult mammalian retina. The stereotyped circuitry at the first synapse in the retina, as well as the relatively short distances new neurites must travel compared to other areas of the CNS, make the retina well suited to probing for synaptic specificity during circuit reassembly. Selective connections between short-wavelength sensitive cone photoreceptors (S-cones) and S-cone bipolar cells provides the foundation of the primordial blue-yellowvision, common to all mammals [7-18]. Wetake advantage of the ground squirrel retina, which has a one-to-one S-cone-to-S-cone-bipolar-cellconnection, to test if this connectivity can bereestablished following local photoreceptor loss [8, 19]. We find that after invivo selective photoreceptor ablation, deafferented S-cone bipolar cells expand their dendritic trees. The new dendrites randomly explore the proper synaptic layer, bypass medium-wavelength sensitive cone photoreceptors (M-cones), and selectively synapse with S-cones. However, non-connected dendrites are not pruned back to resemble unperturbed S-cone bipolar cells. We show, for the first time, that circuit repair in the adult mammalian retina can recreate stereotypic selective wiring.

Links between global and local shape perception, coloured backgrounds, colour discrimination, and non-verbal IQ

This study explored associations between local and global shape perception on coloured backgrounds, colour discrimination, and non-verbal IQ (NVIQ). Five background colours were chosen for the local and global shape tasks that were tailored for the cone-opponent pathways early in the visual system (cardinal colour directions: L-M, loosely, reddish-greenish; and S-(L + M), or tritan colours, loosely, blueish-yellowish; where L, M and S refer to the long, middle and short wavelength sensitive cones). Participants also completed the Farnsworth-Munsell 100-hue test (FM100) to determine whether performance on the local and global shape tasks correlated with colour discrimination overall, or with performance on the L-M and tritan subsets of the FM100 test. Overall performance on the local and global shape tasks did correlate with scores on the FM100 tests, despite the colour of the background being irrelevant to the shape tasks. There were also significantly larger associations between scores for the L-M subset of the FM100 test, compared to the tritan subset, and accuracy on some of the shape tasks on the reddish, greenish and neutral backgrounds. Participants also completed the non-verbal components of the WAIS and the SPM+ version of Raven’s progressive matrices, to determine whether performance on the FM100 test, and on the local and global shape tasks, correlated with NVIQ. FM100 scores correlated significantly with both WAIS and SPM+ scores. These results extend previous work that has indicated FM100 performance is not purely a measure of colour discrimination, but also involves aspects of each participant’s NVIQ, such as the ability to attend to local and global aspects of the test, part-whole relationships, perceptual organisation and good visuomotor skills. Overall performance on the local and global shape tasks correlated only with the WAIS scores, not the SPM+. These results indicate that those aspects of NVIQ that engage spatial comprehension of local-global relationships and manual manipulation (WAIS), rather than more abstract reasoning (SPM+), are related to performance on the local and global shape tasks. Links are presented between various measures of NVIQ and performance on visual tasks, but they are currently seldom addressed in studies of either shape or colour perception. Further studies to explore these issues are recommended.

Chromatic summation and receptive field properties of blue-on and blue-off cells in marmoset lateral geniculate nucleus

The “blue-on” and “blue-off” receptive fields in retina and dorsal lateral geniculate nucleus (LGN) of diurnal primates combine signals from short-wavelength sensitive (S) cone photoreceptors with signals from medium/long wavelength sensitive (ML) photoreceptors. Three questions about this combination remain unresolved. Firstly, is the combination of S and ML signals in these cells linear or non-linear? Secondly, how does the timing of S and ML inputs to these cells influence their responses? Thirdly, is there spatial antagonism within S and ML subunits of the receptive field of these cells? We measured contrast sensitivity and spatial frequency tuning for four types of drifting sine gratings: S cone isolating, ML cone isolating, achromatic (S + ML), and counterphase chromatic (S − ML), in extracellular recordings from LGN of marmoset monkeys. We found that responses to stimuli which modulate both S and ML cones are well predicted by a linear sum of S and ML signals, followed by a saturating contrast-response relation. Differences in sensitivity and timing (i.e. vector combination) between S and ML inputs are needed to explain the amplitude and phase of responses to achromatic (S + ML) and counterphase chromatic (S − ML) stimuli. Best-fit spatial receptive fields for S and/or ML subunits in most cells (>80%) required antagonistic surrounds, usually in the S subunit. The surrounds were however generally weak and had little influence on spatial tuning. The sensitivity and size of S and ML subunits were correlated on a cell-by-cell basis, adding to evidence that blue-on and blue-off receptive fields are specialised to signal chromatic but not spatial contrast.

Concerted Shifts in Absorption Maxima of Yellow and Red Plumage Carotenoids Support Specialized Tuning of Chromatic Signals to Different Visual Systems in Near-Passerine Birds

Recent evidence that absorption maxima (λRmin) expressed by colorful plumage pigments align to diagnostic cone sensitivities of affiliated visual systems suggests that birds employ specialized signals in relation to their color vision. However, these studies compared different pigments and clades for the violet (porphyrins in non-passerines) and ultraviolet (carotenoids in passerines) sensitive system, which confounds chemistry and phylogeny with tuning patterns. To test whether signal alignments to violet (VS) and ultraviolet (UVS) systems transcend confounding factors, parallel analyses were conducted for a diversity of near-passerines, a group in which plumage carotenoids occur in taxa with either visual system. Conventional and phylogenetically informed analyses confirmed earlier findings: short wavelength absorbing (yellow carotenoid) pigments aligned λRmin with the violet-sensitive (V) cone of VS species but with the short wavelength-sensitive (S) cone of UVS species, whereas long wavelength-absorbing (red carotenoid) pigments aligned only with the S cone of VS species. More extensive variation among VS yellow carotenoids produced λRmin alignments to cone sensitivities that differed at shorter (peaks) versus longer (overlaps) wavelengths. Ancestral trait reconstructions indicated that signals evolved to match pre-existing VS systems, but did not resolve scenarios for UVS systems. Regardless of historical details, alignments expressed a higher-level pattern in which λRmin values were blue-shifted for yellow and red carotenoids in VS compared to UVS species, a pattern opposite that expressed by receptor sensitivities between systems. Thus, generalized functional designs attributed to avian color vision allow for specialized visual communication through the development of chromatic signals suited to each perceptual system.

Degeneration of short-wavelength cone cells in rd12 mice

Background Retinitis pigmentosa (RP) is one of the causes of congenital blindness.It is well known that the degeneration process of rod cells is difficult to detect in RP.Retinal degeneration 12 (rd12) mice is a new, spontaneously arising mouse model for human Leber congenital amaurosis (LCA), and it is helpful for us to explore the pathogenesis and determine the treating target of RP. Objective This study was to investigate the natural disease process of short-length sensitive cone cells in rd12 mice, a LCA Rpe65rd12 (B6[A]-Rpe65rd12/J) mouse. Methods The rd12 mice at postnatal (P) 14, P21, P35 and P90 were selected (5 mice for each), and the wild-type C57BL/6J (B6) mice with matched ages were included as controls.Photopic full-field electroretinogram (ERG) was recorded with Roland Q450SC UV visual physiology instrument.Cone response was recorded using single white light-emitting diode (LED) stimulation with the flash intensity of 1.00 cds/m2 and 1.96 cds/m2, and short wave-length sensitive cone response was recorded using ultraviolet light ([363±6]nm) stimulation with the flash intensity of 2.0 mWs/m2 and 3.0 mW/m2.The mice were sacrificed and retinal whole-mounts were prepared.The distribution and number of cone cells and UV-sensitive cone cells were detected by FITC-peanut agglutinin (FITC-PNA) and Cy3 immunofluorescence stainning, respectively. Results In P14 rd12 mice, the ERG responses of overall cone cells presented the negative waveform and the latency was delayed, and UV-sensitive cone response was unrecordable.The b-wave amplitude of overall cone cells reduced by 75% in P21 rd12 mice compared with wild-type B6 mice, and the mean latency of b-wave in the P21 rd12 mice was significantly longer than that in the wild-type B6 mice ([102.80±11.39]ms vs.[43.40±5.60]ms) (t=-8.106, P=0.001). The mean b-wave amplitudes of UV-sensitive cone cells were (59.60±36.00), (82.40±12.22) and (68.43±17.63)μV in the wild-type B6 mice, and those in the rd12 mice were unrecordable.Immunofluorescence showed that a lager number of cone cells with green fluorescence were seen, and the expression of opsin with red fluorescence was displayed in the UV-sensitive cone cells of nasal lateral on retinal ventral side in P14 wild-type B6 mice; while only a few opsin positive-response cells were seen in P14, P21 and P35 rd12 mice. Conclusions In rd12 mice, the functional abnormality and quantitative reduction of cone cells appear in the early postnatal days, and the loss of UV-sensitive cone cells is earlier and more obvious. Key words: Retinal degeneration/congenital; Eye proteins/metabolism; Photoreceptor/pathology; Electroretinography; Fluorescent antibody technique; Leber congenital amaurosis; Mice, inbred C57BL; Disease models, animal

Wavy multistratified amacrine cells in the monkey retina contain immunoreactive secretoneurin

The goals of this study were to describe the morphology, neurotransmitter content and synaptic connections of neurons in primate retinas that contain the neuropeptide secretoneurin. Amacrine cells were labeled with antibodies to secretoneurin in macaque and baboon retinas. Their processes formed three distinct plexuses in the inner plexiform layer: one in the outermost stratum, one in the center and one in the innermost stratum. In light microscopic double immunolabeling experiments, GABA was colocalized with secretoneurin in these cells, but glycine transporter 1 and Substance P were not. ON bipolar cell axon terminals labeled with antibody to the cholecystokinin precursor, G6-gly, have ON responses to stimulation of short wavelength sensitive (S) cones. Axons of these bipolar cells made contacts with amacrine cell dendrites containing secretoneurin. Secretoneurin-IR amacrine cells also made contacts with retinal ganglion cell dendrites labeled with antibody to the photopigment melanopsin, which have OFF responses to stimulation of S cones. Using electron microscopic immunolabeling, 436 synapses from macaque retina were analyzed. Axons from bipolar cells were identified by their characteristic synaptic ribbons; their synaptic densities were asymmetric like those of excitatory synapses in the brain. Amacrine cells made and received conventional synapses with symmetric synaptic densities, like those of inhibitory synapses in the brain. Ganglion cell dendrites were identified by their absence of presynaptic specializations; they received inputs from both amacrine cells and bipolar cells. The majority of inputs to the secretoneurin-IR amacrine cells were from other amacrine cells, but they also received 21% of their input from bipolar cells. They directed most of their output, 54%, to amacrine cells, but there were many synapses onto bipolar cell axons and ganglion cell dendrites, as well. The synaptic connections were very similar in the three plexuses with one notable exception; output synapses to bipolar cells were significantly less common in the innermost one, where the S-ON bipolar cells terminate. Taken together, these findings suggest that the secretoneurin-IR amacrine cells in primates receive excitatory input from S-ON bipolar cells and, in turn, inhibit intrinsically photosensitive retinal ganglion cells.

No evidence for loss of short-wavelength sensitive cone photoreceptors in normal ageing of the primate retina

In old world primates including humans, cone photoreceptors are classified according to their maximal sensitivity at either short (S, blue), middle (M, green) or long (L, red) wavelengths. Colour discrimination studies show that the S-cone pathway is selectively affected by age and disease, and psychophysical models implicate their loss. Photoreceptors have high metabolic demand and are susceptible to age or disease-related losses in oxygen and nutrient supply. Hence 30% of rods are lost over life. While comparable losses are not seen in cones, S-cones comprise less than 10% of the cone population, so significant loss would be undetected in total counts. Here we examine young and aged primate retinae stained to distinguish S from M/L-cones. We show there is no age-related cone loss in either cone type and that S-cones are as regularly distributed in old as young primates. We propose that S-cone metabolism is less flexible than in their M/L counterparts, making them more susceptible to deficits in normal cellular function. Hypoxia is a feature of the ageing retina as extracellular debris accumulates between photoreceptors and their blood supply which likely impacts S-cone function. However, that these cells remain in the ageing retina suggests the potential for functional restoration.

Vision, Color Vision, and Visually Guided Behavior: The Novel Toxicological Targets of 2,2′,4,4′-Tetrabromodiphenyl Ether (BDE-47)

Our published studies have revealed that 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) could disrupt retina morphologies and related gene expressions of zebrafish larvae. Its possible effects on fish vision needed to be uncovered since sensory systems, especially eyes, are vital to wildlife. In this paper, two tests for vision development (opsin gene expression and photoreceptor immunostaining) and two tests for visually guided behaviors (optokinetic response and looming-evoked escape) were designed to investigate the potential visual impairments and subsequent ecological consequences caused by BDE-47 exposure in 6 dpf zebrafish larvae. The short wavelength sensitive cone opsins and rhodopsin were significantly inhibited by BDE-47 exposure. Meanwhile, BDE-47 exposure significantly reduced larval optokinetic responses with blue light stimuli and induced less larvae to exhibit escape response with looming stimuli, which confirmed the adverse consequences of visual impairments in zebrafish. Our results indicat...