Abstract
Recent studies examine the behavioral capacities of rats and mice with and without visual input, and the neuronal mechanisms underlying such capacities. These animals are assumed to be functionally blind under red light, an assumption that might originate in the fact that they are dichromats who possess ultraviolet and green cones, but not red cones. But the inability to see red as a color does not necessarily rule out form vision based on red light absorption. We measured Long-Evans rats' capacity for visual form discrimination under red light of various wavelength bands. Upon viewing a black and white grating, they had to distinguish between two categories of orientation: horizontal and vertical. Psychometric curves plotting judged orientation versus angle demonstrate the conserved visual capacity of rats under red light. Investigations aiming to explore rodent physiological and behavioral functions in the absence of visual input should not assume red-light blindness.
Highlights
Rats, like many rodents, are largely crepuscular and, even during daylight, are usually to be found in poorly illuminated environments (Macdonald et al, 1994)
Red illumination is often used in reverse light cycle conditions in animal husbandry settings with the assumption that it will not affect rodent circadian rhythms (Emmer et al, 2018)
Experiments done under red light are believed to place the animal in dark conditions while allowing the experimenter to observe the preparation directly or by video recording (Cloke et al, 2015; Englund et al, 2020; van Goethem et al, 2012; Harris and Diamond, 2000; Harris et al, 1999; Jacklin et al, 2016; Nikbakht et al, 2012; Pacchiarini et al, 2020; Reid et al, 2014; Salaberry et al, 2017; Sieben et al, 2015; Vasconcelos et al, 2011; Winters and Reid, 2010)
Summary
Like many rodents, are largely crepuscular and, even during daylight, are usually to be found in poorly illuminated environments (Macdonald et al, 1994) Their retina is rod-dominated, with cones making up as little as 1% of photoreceptors (Jacobs et al, 2001; La Vail, 1976). Electroretinogram (ERG) responses of the photopic spectral sensitivity curves of photoreceptors of rats and mice were measured throughout the UV-visible spectrum (300 to 700 nm) (Rocha et al, 2016). These measurements identified two sensitivity peaks in Wistar rats, 362 and 502 nm; no significant response to long wavelength light (above 620 nm) was detected. In the present study we challenge the notion of form vision blindness under red light and find, contrary to expectation, good performance
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