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G.G. Tosini, J. Aguzzi, N.M. Bullock; Light–Induced Phase–Shift of Locomotor Activity in Rcs/n–Rdy Rats Is Not Affected by Photoreceptors Degeneration . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5425.
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© ARVO (1962-2015); The Authors (2016-present)
The study of the photoreceptors and photopigments which mediate circadian photoreception in mammals is emerging as a new and exciting aspect of retinal neurobiology. A series of elegant studies in the nineties demonstrated that classical photoreceptors (rods and cones) are not necessary for the entrainment of circadian rhythms in mammals, thus indicating that an undiscovered photoreceptor (photopigment) in the mammalian retina is responsible for the photoentrainment of circadian rhythms. Recent studies have demonstrated that melanopsin is a key photopigment in the mammalian circadian system. Although Royal College of Surgeon (RCS) rats are a model to studies on retinitis pigmentosa in humans, no study has investigated circadian photoreception in these animals. The aim of this study was to examine circadian photoreception in RCS rats.
Tan–hooded RCS/N–rdy+ rats homozygous for the normal rdy allele and congenic age–matched RCS/N–rdy homozygotes with retinal dystrophy were used in this study. All animals used for these experiments were 60 +/–2 days old at the time when light–induced phase shift of locomotor activity (15 minutes of light at Circadian Time 15) was measured. At this age degeneration of the retina in RCS/N–rdy has advanced to the point where photoreceptors are both histologically and functionally undetectable and melanopsin levels are also dramatically reduced (> 90 %). Three different light intensities were used: 1x10–3, 1x10–1 and 1x101 µWcm2.
RCS/N–rdy and rdy+ did not show any significant phase–shift of the locomotor activity after a 15 minute pulse at the intensity of 1x10–3 µWcm2, whereas significant phase–shifts were observed with the other light intensities (t–test, P < 0.01). The magnitude of the light induced phase–shift of the locomotor activity was not statistically different (t–test, P > 0.05) between RCS/N–rdy and –rdy+.
The light–induced phase–shift of the locomotor activity rhythm is not affected by retinal degeneration in RCS/N–rdy rats.
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