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RB Barlow, D Scheraga, B Knox, G Engbretson, E Solessio; Circadian Rhythms in Xenopus Visual Sensitivity . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3755.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Investigate possible receptor mechanisms underlying circadian rhythms in Xenopus laevis visual sensitivity. Methods: We measured visual sensitivity of Xenopus tadpoles by observing their optomotor response to a rotating pattern of vertical black and white alternating bars. The tadpoles were kept in natural diurnal lighting and allowed to dark adapt more than 24h before each experiment. A tadpole was placed in a transparent, water filled, circular container located on a pedestal at the center of the rotating pattern (11 cm high) and observed with an IR video system. A computer randomly selected the direction of the movement of the pattern, and a naïve observer determined the optomotor response of the tadpole. Visual threshold was 75% correct response (15/20 trials). The tadpoles viewed patterns having either "low" (18°/bar) or "high" (3°/bar) angular frequency illuminated by short (400nm), medium (520nm), and long (650nm) wavelength light. Visual sensitivity was also measured electrophysiologically (ERG b-wave). Results: Tadpoles exhibited a pronounced circadian rhythm in visual sensitivity to a low but not high angular frequency stimulus. Sensitivity is more than 50-fold higher during the day for the low angular frequency pattern at 520nm. No significant changes were observed under 400 and 650nm illumination. Sensitivity was only 10-fold higher during the day for the high angular frequency stimulus at 520nm. Corresponding day-night changes in the ERG b-wave suggest that circadian changes in visual sensitivity originate in part in the retina. Conclusion: Xenopus tadpoles exhibit high visual sensitivity to low angular frequency stimuli (520 nm) during the day but not at night. This circadian rhythm may be mediated by rod signals.
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