Photosensitivity to different light intensities in blind and sighted rodents

Abstract

SUMMARYPhotoperiod is an important cue regulating biological rhythms in mammals, including 'blind' subterranean and sighted fossorial rodent species. These species may respond differentially to changes in light quality according to their retinal complexity. The effects of increasing light intensity on daily rhythms of urine excretion and urinary output of 6-sulfatoxymelatonin levels were compared in 'blind' mole rats Spalax ehrenbergi and sighted social voles, Microtus socialis. Our results show that the threshold irradiance required to entrain rhythms of voles is three magnitudes greater than that for mole rats. The results suggest that mole rats have an operational photoreceptive pathway with a lower threshold irradiance than voles. Such a low threshold reflects the remarkable capability of this 'blind' species to utilize light signals even under challenging light conditions.

Effects of photophase illuminance on locomotor activity, urine production and urinary 6-sulfatoxymelatonin in nocturnal and diurnal South African rodents

“…In M. namaquensis, brighter photophase lighting actually had a slight attenuating effect on the melatonin rhythm. A similar effect has been reported in the strictly fossorial blind mole rat (S. ehrenbergi), whereby the melatonin rhythm was weakened by brighter photophase lighting conditions, presumably as a result of an increased stress response in the animals under bright lighting (Zubidat et al, 2009). Although M. namaquensis is not fossorial like S. ehrenbergi, it still sleeps and rests in protected spaces such as between rock crevices that are sheltered from intense daytime illumination.…”

“…Evidence also suggests an effect of photophase intensity on the timing of urine production, which might be species specific. In social voles (M. socialis), for instance, significant daily rhythms of urine excretion were observed at higher as opposed to lower photophase light intensities, whereas in blind mole rats (Spalax ehrenbergi), the rhythms were significant under both dim and bright photophase intensities (Zubidat et al, 2009).…”

“…Several studies suggest that species hold unique thresholds to different qualities of lighting and that these reflect the environments they are adapted to (Tast et al, 2001;Zubidat et al, 2009Zubidat et al, , 2010a. The advantage of distinguishing between light intensities within the boundaries of specific thresholds is best demonstrated in species that adjust their activity patterns according to the level of moonlight.…”

“…Furthermore, evidence suggests that species possess characteristic sensitivity thresholds in their circadian rhythms, such as the melatonin rhythm, to different light intensities and wavelengths. It is believed that these thresholds probably reflect the habitat to which the species are adapted and that it may accordingly also reflect specific visual adaptations of the species (Kumar and Rani, 1999;Peichl, 2005;Zubidat et al, 2009Zubidat et al, , 2010a.…”

Does the Modern Urbanized Sleeping Habitat Pose a Breast Cancer Risk?

“…The discovery of the non-image-forming photoreceptors (NIFPs) and the non-vision pigment melanopsin (Berson et al, 2002) enhanced chronobiological research, showing that even a subterranean rodent, such as the "blind" mole rat Spalax ehernbergi, is photosensitive to different photoperiod regimes (Haim et al, 1983), light intensities, and wavelengths (Zubidat et al, 2009(Zubidat et al, , 2010. Therefore, our vision system, which evolved from a mammalian system that entailed a subterranean stage in evolution (Vaughan, 1972), became more complex as it includes more types of functional photoreceptors whereby the NIFPs seem to play a major role in regulating circadian systems.…”