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Chad Jackson, Megan Capozzi, Douglas McMahon; Retinal function: Assessing seasonal lighting environment on physiology. Invest. Ophthalmol. Vis. Sci. 2013;54(15):406.
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Retinal adaptation is required for visual function over a wide range of light intensities. Retinal dopamine and the circadian clock have been shown to play active parts in light adaptation; both of which are directly influenced by light stimulation. However, it is unclear if changes in lighting environment (developmental or immediate) have enduring effects on retinal dopaminergic or circadian systems. Therefore, we tested whether mice reared on short or long photoperiods display altered retinal physiology as compared to mice reared on equinox light cycles.
Retinal function: Dark- and light-adapted electroretinogram (ERG) responses, from C57/BL/6 mice reared on a short (8:16 hr), long (16:8hr) or equinox (12:12 hr) photoperiod were recorded following overnight dark-adaption. Subsequently, the photoperiods were switched to an opposing photoperiod for 3 weeks and tested again. Mice were handled under dim red-filtered light, anesthetized with ketamine/xylazine, and placed in a LKC UTAS BigShot ganzfeld. Dopamine levels: Retinal dopamine was measured by HPLC from crude retinal extracts. Retinal circadian rhythms: In Per2Luc knock-in mice, reared on the previously stated photoperiods, we observed whole tissue rhythms by monitoring bioluminescence from the retinal explant cultures measured with a LumiCycle (Actimetrics).
Dark- and light-adapted ERG responses in the short group were significantly affected by photoperiod, as compared to long and equinox groups. When the short day group is switched to the long day lighting cycle there is recovery of the dark-adapted ERG response; however, the deficit in the light-adapted ERG persist. Dopamine content was shown to be decreased in the retinas of short photoperiod mice compared to long photoperiod. Direct dopamine receptor stimulation by injection of dopamine receptor agonists rescued the light-adapted ERG. Lastly, there seems to be overt changes in retinal circadian rhythms as measured by bioluminescent measurements.
We found that prior photoperiod significantly affects dark- and light-adapted retinal function. Also, mice reared on short photoperiods have decreased levels of retinal dopamine and retinal light responses compared to mice reared on long or equinox photoperiods. The persistence of light-adapted ERG deficits following photoperiod reversal suggests enduring effects of developmental photoperiod on retinal function.
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