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First published online November 13, 2009
Journal of Experimental Biology 212, 3857-3864 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.033969
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Photosensitivity to different light intensities in blind and sighted rodents

A. E. Zubidat1,*, R. J. Nelson2 and A. Haim1,3

1 Department of Evolution and Environmental Biology, University of Haifa, Haifa 31905, Israel
2 Departments of Psychology and Neuroscience, Ohio State University, Columbus, OH 43210, USA
3 Department of Biology, University of Haifa—Oranim, Kiryat Tivon 36006, Israel

* Author for correspondence (zubidat3{at}013.net.il)

Accepted 8 September 2009

Photoperiod 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.

Key words: cosinor analysis, daily variation, melanopsin, photophase irradiance, retinal photoreceptors, ultradian rhythm, urinary melatonin


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