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Rejeana M. Stephens, Carlos A. Garcia; The Effects of Ozone on Core Circadian Clock Genes in the Light Adapted Rat Retina. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4330.
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The mammalian retina contains an intrinsic peripheral circadian clock that regulates a number of physiological retinal functions independent of the central clock in the suprachiasmatic nucleus of the hypothalamus. The core circadian clock genes identified in retinal neurons include Period1 (Per1), Per2, CLOCK, Bmal1, Cryptochrome 1 (Cry1), and Cry2. Ozone (O3), a strong oxidant gas present in air pollution, has been reported to diminish acetylcholine levels in the preoptic area in the rat brain leading to disruption of paradoxical sleep. The purpose of this study is to investigate the effects of O3 on the core circadian clock genes in the light adapted retina of Long Evans rats.
Age- and sex-matched rats were randomly separated into six groups (n=6 rats); three control (clean air) and three O3-exposed groups (0.4 ppm for 4 hours; 7 days, 14 days and 28 days). In order to differentiate from an acute exposure effect, the neural retinas of the O3-exposed and control rats were dissected for analysis one day after completion of the exposures. Per1, Per2, CLOCK, Bmal1, Cry1, and Cry2 gene expression was analyzed by extracting total RNA, the samples reverse transcribed, and subjected to real time quantitative polymerase chain reaction (qPCR) using the appropriate primers.
Decreases in core clock gene expression were recorded as a function of days of O3 exposure. For the longest exposure tested (28-days), the gene expression of Per1 decreased 81%, CLOCK decreased 80%, Cry1 decreased 75%, and Bmal1 decreased 59%. Decreases in the core clock genes were also recorded in the retinas of the 7-day and 14-day O3-exposed groups as compared to the controls.
Results of this study provide evidence that O3 disrupts the retinal circadian clock of the light adapted retina by decreasing the core circadian clock gene levels. Additional physiological functions such as photoreceptor rod outer segment disc shedding, synaptic dynamics, protein phosphorylation, and melatonin synthesis may be impacted by ozone.
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