Guinea pigs reared in a monochromatic environment exhibit changes in cone density and opsin expression

Short-wavelength artificial light affects visual neural pathway development in mice

Nearly all modern life depends on artificial light; however, it does cause health problems. With certain restrictions of artificial light emitting technology, the influence of the light spectrum is inevitable. The most remarkable problem is its overload in the short wavelength component. Short wavelength artificial light has a wide range of influences from ocular development to mental problems. The visual neuronal pathway, as the primary light-sensing structure, may contain the fundamental mechanism of all light-induced abnormalities. However, how the artificial light spectrum shapes the visual neuronal pathway during development in mammals is poorly understood. We placed C57BL/6 mice in three different spectrum environments (full-spectrum white light: 400-750 nm; violet light: 400 ± 20 nm; green light: 510 ± 20 nm) beginning at eye opening, with a fixed light time of 7:00-19:00. During development, we assessed the ocular axial dimension, visual function and retinal neurons. After two weeks under short wavelength conditions, the ocular axial length (AL), anterior chamber depth (ACD) and length of lens thickness, real vitreous chamber depth and retinal thickness (LLVR) were shorter, visual acuity (VA) decreased, and retinal electrical activity was impaired. The density of S-cones in the dorsal and ventral retinas both decreased after one week under short wavelength conditions. In the ventral retina, it increased after three weeks. Retinal ganglion cell (RGC) density and axon thickness were not influenced; however, the axonal terminals in the lateral geniculate nucleus (LGN) were less clustered and sparse. Amacrine cells (ACs) were significantly more activated. Green light has few effects. The KEGG and GO enrichment analyses showed that many genes related to neural circuitry, synaptic formation and neurotransmitter function were differentially expressed in the short wavelength light group. In conclusion, exposure to short wavelength artificial light in the early stage of vision-dependent development in mice delayed the development of the visual pathway. The axon terminus structure and neurotransmitter function may be the major suffering.

Contribution of M-opsin-based color vision to refractive development in mice

M-opsin, encoded by opn1mw gene, is involved in green-light perception of mice. The role of M-opsin in emmetropization of mice remains uncertain. To answer the above question, 4-week-old wild-type (WT) mice were exposed to white light or green light (460-600 nm, a peak at 510 nm) for 12 weeks. Refractive development was estimated biweekly. After treatment, retinal function was assessed using electroretinogram (ERG). Dopamine (DA) in the retina was evaluated by high-performance liquid chromatography, M-opsin and S-opsin protein levels by Western blot and ELISA, and mRNA expressions of opn1mw and opn1sw by RT-PCR. Effects of M-opsin were further verified in Opn1mw^-/- and WT mice raised in white light for 4 weeks. Refractive development was examined at 4, 6, and 8 weeks after birth. The retinal structure was estimated through hematoxylin and eosin staining (H&E) and transmission electron microscopy (TEM). Retinal wholemounts from WT and Opn1mw^-/- mice were co-immunolabeled with M-opsin and S-opsin, their distribution and quantity were then assayed by immunofluorescence staining (IF). Expression of S-opsin protein and opn1sw mRNA were determined by Western blot, ELISA, or RT-PCR. Retinal function and DA content were analyzed by ERG and liquid chromatography tandem-mass spectrometry (LC-MS/MS), respectively. Lastly, visual cliff test was used to evaluate the depth perception of the Opn1mw^-/- mice. We found that green light-treated WT mice were more myopic with increased M-opsin expression and decreased DA content than white light-treated WT mice after 12-week illumination. No electrophysiologic abnormalities were recorded in mice exposed to green light compared to those exposed to white light. A more hyperopic shift was further observed in 8-week-old Opn1mw^-/- mice in white light with lower DA level and weakened cone function than the WT mice under white light. Neither obvious structural disruption of the retina nor abnormal depth perception was found in Opn1mw^-/- mice. Together, these results suggested that the M-opsin-based color vision participated in the refractive development of mice. Overexposure to green light caused myopia, but less perception of the middle-wavelength components in white light promoted hyperopia in mice. Furthermore, possible dopaminergic signaling pathway was suggested in myopia induced by green light.

Short Wavelength (Blue) Light Is Protective for Lens-Induced Myopia in Guinea Pigs Potentially Through a Retinoic Acid-Related Mechanism

Purpose

To investigate the effect of short-wavelength light (SL) on guinea pigs with lens-induced myopia (LIM) and the possible retinoic acid (RA)–related mechanisms.

Methods

Two-week-old guinea pigs (n = 60) with monocular −5D lenses were reared under white light (WL, 580 lux) or SL (440 nm, 500 lux). The left eyes were uncovered as control. Refractive error (RE) and axial length (AL) were measured at baseline, one week, two weeks, and four weeks after intervention. Retinal RA was measured from four guinea pigs after two and four weeks of treatment with HPLC. Two-week-old guinea pigs (n = 52) with monocular −5D lens were fed with either RA or its synthesis inhibitor citral every third day in the morning, and half from each group were reared under WL or SL conditions. RE and AL were recorded at baseline and two and four weeks after intervention. Retinal RA was measured after four weeks of intervention.

Results

At the end of treatment, guinea pigs exposed to SL were less myopic than to WL (2.06 ± 1.69D vs. −1.00 ± 1.88D), accompanied with shorter AL (P = 0.01) and less retinal RA (P = 0.02). SL reduced retinal RA even after exogenous RA supplementation (P = 0.02) and decelerated LIM compared to WL (1.66 ± 1.03D vs. −3.53 ± 0.90D). Citral slowed ocular growth, leading to similar RE in W+CI and S+CI groups (3.39 ± 1.65D vs. 5.25 ± 0.80D).

Conclusions

Overall, SL reduced LIM in guinea pigs, even in those supplemented with oral RA, accompanied by reduced retinal RA levels. Oral RA accelerated eye elongation, but citral equally decelerated eye elongation under SL and WL with no significant retinal RA reduction.

Interactions of cone abundancies, opsin expression, and environmental lighting with emmetropization in chickens

We had previously found that M to L cone abundancy ratios in the chicken retina are correlated with vitreous chamber depth and refractive state in chickens eyes, when they have normal visual exposure but not when they develop deprivation myopia. The finding suggests an interaction between cone abundancies and emmetropization. In the current study, we analyzed how stable this correlation was against changes in environmental variables and strain differences. We found that the correlation was preserved in two chicken strains, as long as they were raised in the laboratory facilities and not in the animal facilities of the institute. To determine the reasons for this difference, spectral and temporal lighting parameters were better adjusted in both places, whereas temperature, humidity, food, diurnal lighting cycles and illuminance were already matched. It was also verified that both strains of chickens had the same cone opsin amino acid sequences. The correlation between M to L cone abundancy and ocular biometry is highly susceptible to changes in environmental variables. Yet undetermined differences in lighting parameters were the most likely reasons. Other striking findings were that green cone opsin mRNA expression was downregulated when deprivation myopia developed. Similarly, red opsin mRNA was downregulated when chicks wore red spectacles, which made them more hyperopic. In summary, our experiments show that photoreceptor abundancies, opsin expression, and the responses to deprivation, and therefore emmetropization, are surprisingly dependent on subtle differences in lighting parameters.

Effects of the long wavelength-filtered continuous spectrum on natural refractive development in juvenile guinea pigs

AIM

To investigate the effects of spectral composition and light intensity on natural refractive development in guinea pigs.

METHODS

A total of 124 pigmented guinea pigs (2-week-old) were randomly assigned to three groups at high (Hi; 4000 lx), medium (Me; 400 lx) and low (Lo; 50 lx) light intensities under a 12:12 light/dark cycle for 6wk. Each group was subdivided into subgroups with the following spectra: broad spectrum Solux halogen light (BS), 600 nm above-filtered continuous spectrum (600F), 530 nm above-filtered continuous spectrum (530F), and 480 nm above-filtered continuous spectrum (480F; HiBS: n=10, Hi600F: n=10, Hi530F: n=10, Hi480F: n=10, MeBS: n=10, Me600F: n=10, Me530F: n=10, Me480F: n=10, LoBS: n=11, Lo600F: n=12, Lo530F: n=10, Lo480F: n=11). Refractive error, corneal curvature radius, and axial dimensions were determined by cycloplegic retinoscopy, photokeratometry, and A-scan ultrasonography before and after 2, 4, and 6wk of treatment. Average changes from both eyes in the ocular parameters and refractive error were compared among different subgroups.

RESULTS

After 6wk of exposure, high-intensity lighting enhanced hyperopic shift; medium- and low-intensity lighting enhanced myopic shift (P<0.05). Under the same spectrum, axial increase was larger in the low light intensity group than in the medium and high light intensity groups (HiBS: 0.65±0.02 mm, MeBS: 0.67±0.01 mm, LoBS: 0.82±0.02 mm; Hi600F: 0.64±0.02 mm, Me600F: 0.67±0.01 mm, Lo600F: 0.81±0.01 mm; Hi530F: 0.64±0.02 mm, Me530F: 0.67±0.01 mm, Lo530F: 0.73±0.02 mm; Hi480F: 0.64±0.01 mm, Me480F: 0.66±0.01 mm, Lo480F: 0.72±0.02 mm; P<0.05). Under 400 lx, there was a faster axial increase in the MeBS group than in the Me480F group (P<0.05). Under 50 lx, axial length changes were significantly larger in LoBS and Lo600F than in Lo530F and Lo480F (P<0.01).

CONCLUSION

Under high-intensity lighting, high light intensity rather than spectrum distributions that inhibits axial increase. Under medium- and low-intensity lighting, filtering out the long wavelength inhibits axial growth in juvenile guinea pigs.

Colour vision of green turtle (Chelonia mydas) hatchlings: do they still prefer blue under water?

Background

Several anatomical studies provide evidence that green turtles (Chelonia mydas) possess the necessary anatomy for colour vision. Behavioural experiments have previously been conducted with newly emerged hatchlings, concluding that they are attracted to shorter wavelengths compared to longer wavelengths within a terrestrial environment, suggesting a possible attraction towards blue. This paper assessed the colour vision of hatchlings within an aquatic environment, and investigated whether the attraction for shorter wavelengths remains consistent within water, whether the colour saturation of the chromatic stimuli was an important factor, and whether rearing and testing individual animals in different coloured housing tanks has an impact on their visual choices.

Methods

Forty-one hatchling green turtles were presented with a three-choice experiment where food was attached to three different coloured plates. The plates (blue, yellow, and red) were randomly arranged in the turtle’s tank and four different colour saturations were tested (100, 75, 50, and 25%). Turtles were individually placed into their housing tanks (coloured either red, white, blue or grey) with three different colour plates in front of them, from the same saturation level. The colour of the plate with food first approached and bitten by the turtle was recorded.

Results

The colour of the tank in which an individual was reared, and where experiments were conducted, significantly influenced which food item was selected on the different coloured plates. While individual turtles preferred to select the food items associated with blue plates across the entire experiment (66.1% of the time compared to 18.2% and 15.7% for yellow and red plates respectively), the preference for blue plates was influenced by the colour of the rearing/experimental tank. Individuals raised in red, white or blue tanks appeared to consistently prefer food on blue plates, but there appeared to be no plate colour preference by turtles in grey tanks. There was no significant effect of either colour saturation or the spatial arrangement of the three colours within an experimental tank on colour choice, and no significant interaction between tank colour and colour saturation.

Discussion

Thesefindings confirm that the terrestrial preference towards shorter wavelength colours, such as blue, compared to longer wavelength colours remains consistent within an aquatic environment. This preference for blue continues even as the colour saturation reduces from 100% down to 25%, and the colours become darker. Thus, it is suggested that green turtle hatchlings have a strong attraction towards blue. This attraction, however, is influenced by the colour of the tank the turtles were raised in. While this supports the notion that environmental colour may influence individual turtle visual capabilities, it suggests that this relationship is more complicated, and requires further investigation.

Effect of Altered Retinal Cones/Opsins on Refractive Development under Monochromatic Lights in Guinea Pigs

Purpose

To analyze the changes of refraction and metabolism of the retinal cones under monochromatic lights in guinea pigs.

Methods

Sixty guinea pigs were randomly divided into a short-wavelength light (SL) group, a middle-wavelength light (ML) group, and a white light (WL) group. Refraction and axial length were measured before and after 10-week illumination. The densities of S-cones and M-cones were determined by retinal cone immunocytochemistry, and the expressions of S-opsins and M-opsins were determined by real-time PCR and Western blot.

Results

After 10-week illumination, the guinea pigs developed relative hyperopia in the SL group and relative myopia in the ML group. Compared with the WL group, the density of S-cones and S-opsins increased while M-cones and M-opsins decreased in the SL group (all, p < 0.05); conversely, the density of S-cones and S-opsins decreased while M-cones and M-opsins increased in the ML group (all, p < 0.05). Increased S-cones/opsins and decreased M-cones/opsins were induced by short-wavelength lights. Decreased S-cones/opsins and increased M-cones/opsins were induced by middle-wavelength lights.

Conclusions

Altered retinal cones/opsins induced by monochromatic lights might be involved in the refractive development in guinea pigs.

Habitat-related variation in the plasticity of a UV-sensitive photoreceptor over a small spatial scale in the palmate newt

Plastic phenotypes are expected to be favoured in heterogeneous environments compared with stable environments. Sensory systems are interesting to test this theory because they are costly to produce and support, and strong fitness costs are expected if they are not tuned to the local environment. Consistently, the visual system of several species changes with the conditions experienced during early development. However, there is little information on whether the amplitude of the change, that is the reaction norm, differs between visual environments. Given the rapid change of many ecosystems, especially eutrophication for aquatic habitats, it is crucial to determine down to which spatial scale, change in the reaction norm occurs. We addressed this issue by quantifying the between-habitat variation in the expression of a UV-sensitive opsin in a newt. In western France, this species breeds in ponds of small forest patches, where water filters out UV, and in agricultural ponds where UV transmission is variable. We raised larvae from both habitats with or without exposure to UV. Opsin expression was reduced in larvae from agricultural habitats when raised without UV, whereas it was low in larvae from forest ponds under all lighting conditions. Thus, the variation in the reaction norm of opsin expression was lower in stable filtering environments and higher in heterogeneous environments. Its variation occurred between habitats across a small spatial scale. We discuss the hypotheses for this pattern and for the maintenance of residual opsin expression in forest populations.

Evolutionary conservation of the circadian gene timeout in Metazoa

Timeless (Tim) is considered to function as an essential circadian clock gene in Drosophila. Putative homologues of the Drosophila timeless gene have been identified in both mice and humans. While Drosophila contains two paralogs, timeless and timeout, acting in clock/light entrainment and chromosome integrity/photoreception, respectively, mammals contain only one Tim homolog. In this paper, we study the phylogeny of the timeless/timeout family in 48 species [including 1 protozoan (Guillardia theta), 1 nematode (Caenorhabditis elegans), 8 arthropods and 38 chordates], for which whole genome data are available by using MEGA (Molecular Evolutionary Genetics Analysis). Phylogenetic Analysis by Maximum Likelihood (PAML) was used to analyze the selective pressure acting on metazoan timeless/timeout genes. Our phylogeny clearly separates insect timeless and timeout lineages and shows that non-insect animal Tim genes are homologs of insect timeout. In this study, we explored the relatively rapidly evolving timeless lineage that was apparently lost from most deuterostomes, including chordates, and from Caenorhabditis elegans. In contrast, we found that the timeout protein, often confusingly called “timeless” in the vertebrate literature, is present throughout the available animal genomes. Selection results showed that timeout is under weaker negative selection than timeless. Finally, our phylogeny of timeless/timeout showed an evolutionary conservation of the circadian clock gene timeout in Metazoa. This conservation is in line with its multifunctionality, being essential for embryonic development and maintenance of chromosome integrity, among others.

Pronounced heritable variation and limited phenotypic plasticity in visual pigments and opsin expression of threespine stickleback photoreceptors

Vertebrate colour vision is mediated by the differential expression of visual pigment proteins (opsins) in retinal cone photoreceptors. Many species alter opsin expression during life, either as part of development or as a result of changes in habitat. The latter, a result of phenotypic plasticity, appears common among fishes, but its cellular origin and ecological significance are unknown. Here, we used adult threespine stickleback fish from different photic regimes to investigate heritable variability and phenotypic plasticity in opsin expression. Fish from clear waters had double cones that expressed long (LWS) and middle (RH2) wavelength opsins, one per double cone member. In contrast, fish from red light-shifted lakes had double cones that were >95% LWS/LWS pairs. All fish had single cones that predominantly expressed a short wavelength (SWS2) opsin but ultraviolet cones, expressing a SWS1 opsin, were present throughout the retina. Fish from red light-shifted lakes, when transferred to clear waters, had a ∼2% increase in RH2/LWS double cones, though double cone density remained constant. Comparison of visual pigment absorbance and light transmission in the environment indicated that the opsin complements of double cones maximized sensitivity to the background light, whereas single cones had visual pigments that were spectrally offset from the dominant background wavelengths. Our results indicate that phenotypic plasticity in opsin expression is minor in sticklebacks and of questionable functional significance.