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M.P. Feldkaemper, V. Choh, F. Schaeffel, C. Wildsoet; Regulation of ZENK mRNA Levels in the Chicken Retina by Duration of Light Exposure, by Image Quality and By Inter–Ocular Coupling . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1146.
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© ARVO (1962-2015); The Authors (2016-present)
The number of ZENK expressing glucagonergic amacrine cells in the chick retina is controlled by the sign and amount of imposed defocus. In other amacrine cells and in bipolar cells, ZENK varies with the light exposure. Both eyes show changes in ZENK mRNA levels even when spectacle lenses are applied only to one eye. This apparent yoking persists even when the optic nerve of the lens–treated eye is cut (ONS). To investigate whether the duration of light exposure contributes to this yoking effect, the effect of diurnal cycle on ZENK mRNA levels was studied in normal and ONS birds.
Retinal ZENK mRNA levels were measured in untreated control birds (n=21) and unilaterally ONS–sectioned birds (n=29). Tissues were harvested 3 to 7.5 hours after the light onset in the morning. In addition, another 33 chicks underwent unilateral ONS. Ten days later, –10 D spectacle lenses were attached to either the ONS–eye (n=17) or its fellow eye (n=16). Both eyes were harvested after 30 min (n=9, 8) or 2 hours (n=8, 8) of spectacle lens wear. An additional 18 chicks wore a lens over one eye and were harvested at the same times (n=9, 9). Transcriptional changes of ZENK were measured by real–time RT–PCR.
Retinal ZENK mRNA levels varied as a function of time of day (p=0.0084), with both untreated control and ONS eyes showing maximal levels in the morning (10:30 and 11:15 h) and declining to about 50% by mid–afternoon (14:15 and 15:00 h). Moreover, ZENK mRNA levels were reduced in ONS eyes (p=0.0033). Compared to fellow eyes, ZENK mRNA levels were lower in lens–treated normal (p=0.0013) and ONS–eyes (p<0.0001), after correction for the diurnal effects. ZENK levels in lens–wearing normal eyes were not different than their fellow ONS eyes.
Diurnal light exposure significantly affects retinal ZENK mRNA levels. Moreover, ONS itself decreases retinal ZENK mRNA levels. This is unexpected, given that ONS eyes showed reduced axial growth, and that reduced retinal ZENK levels are normally typical for eyes that elongate and become myopic.
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