Challenging a Myth and Misconception: Red-Light Vision in Rats

Abstract

Simple Summary: Light substantially influences animal physiology and behavior. Thus, it is a prerequisite to house laboratory animals under optimal light conditions. Different species possess different sets of photoreceptors, resulting in differential perception of the visible-light spectrum. While humans are trichromats with red-, green-and blue-sensitive cones, rats and mice are dichromats possessing ultraviolet-and green-sensitive cones. This led to the common assumption that red light is invisible to rodents and therefore red lights are commonly used in husbandry and experiments to observe animals during their dark phase. The retinal sensitivity of rats to red light though has never been assessed under scotopic conditions (dark-adapted) even though this mimics the setting red observation lights are being used. We examined the sensitivity to far-red light of the dark-and light-adapted rat retina. Our study demonstrates that the rat retina responds to far-red light under both conditions with great sensitivity, indicating that rats are not red-light blind. This should be taken into consideration when using red light to keep the effects of light on the retina and physiology to a minimum and will improve animal well-being and lead to better quality data by decreasing the variable light.Abstract: Due to the lack of L-cones in the rodent retina, it is generally assumed that red light is invisible to rodents. Thus, red lights and red filter foils are widely used in rodent husbandry and experimentation allowing researchers to observe animals in an environment that is thought to appear dark to the animals. To better understand red-light vision in rodents, we assessed retinal sensitivity of pigmented and albino rats to far-red light by electroretinogram. We examined the sensitivity to red light not only on the light-but also dark-adapted retina, as red observation lights in husbandry are used during the dark phase of the light cycle. Intriguingly, both rods and cones of pigmented as well as albino rats show a retinal response to red light, with a high sensitivity of the dark-adapted retina and large electroretinogram responses in the mesopic range. Our results challenge the misconception of rodents being red-light blind. Researchers and housing facilities should rethink the use of red observation lights at night.Animals 2020, 10, 422 2 of 14 impact of light on organisms, it is essential to ensure optimal illumination in laboratory animal facilities to maximize animal well-being.Vision is rendered in the retina. Photoreceptors convert the physical light stimulus into an electrical stimulus, which, via retinal interneurons, is further transmitted to the brain. Rats and mice are the most frequently used laboratory mammals, hence understanding exact species-and strain-specific differences in visual processing, including the range of spectral sensitivity, is key not only for ophthalmic studies but also to ensure appropriate environmental lighting conditions for husbandry. Rats and mice, being nocturnal animals, possess a rod...

Conserved visual capacity of rats under red light

“…This study reinforced the already existing notion that red light is experienced as a total absence of usable light. In contrast, another study (Niklaus et al, 2020) showed significant scotopic and photopic ERG responses to red light even at low intensities. In the present study we challenge the notion of form vision blindness under red light and find, contrary to expectation, good behavioral performance.…”

“…Rodents lack red cones ( Deegan and Jacobs, 1993 ; Jacobs et al, 1991 ; Szél and Röhlich, 1992 ), but from the inability to see red as a color, it does not necessarily follow that they cannot absorb red light through their rod-dominated retina to support form vision. A recent study ( Niklaus et al, 2020 ) examined the retinal responses mediated by rods and cones of pigmented (Brown Norway) and albino (Wistar) rats in response to monochromatic far-red light of 656 ± 10 nm in both photopic (light-adapted) and scotopic (dark-adapted) settings. Both rat strains showed significant scotopic and photopic ERG responses to red light even at low intensities.…”

Reproducible and fully automated testing of nocifensive behavior in mice

“…1D; Video 1). Rodents are typically assumed not to see red light (De Farias Rocha et al, 2016); though some evidence contradicts this (Nikbakht & Diamond, 2021;Niklaus et al, 2020), we never observed any behavioral response to red light (little of which likely reaches the eyes when applied to the hind paw), suggesting that the aiming phase does not provide mice any visual cue about the forthcoming photostimulus. Reflectance of red light off the paw is measured by the adjacent photodetector (red trace).…”

Conserved visual capacity of rats under red light

“…But from the inability to see red as a color, it does not necessarily follow that rodents cannot absorb red light through their rod-dominated retina to support form vision. A recent study (Niklaus et al, 2020) examined the retinal responses mediated by rods and cones of pigmented (Brown Norway) and albino (Wistar) rats in response to monochromatic far red light of 656 ± 10 nm in both photopic (light-adapted) and dark-adapted (scotopic) settings. Both rat strains showed significant scotopic and photopic ERG responses to red light even at low intensities.…”