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Michaela Bitzer, Frank Schaeffel; Defocus-Induced Changes in ZENK Expression in the Chicken Retina. Invest. Ophthalmol. Vis. Sci. 2002;43(1):246-252.
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purpose. To characterize the visual stimuli that control the expression of the
transcription factor ZENK in glucagon-immunoreactive amacrine
cells of the chicken retina. ZENK was previously found to change in
correlation with the sign (+ or −) of imposed defocus, making
it a potential candidate for regulation of the synthesis of growth
factors involved in emmetropization.
methods. Chicks were unilaterally treated with positive or negative lenses from
40 minutes to 2 hours. They were either kept in their cage environment
(1000 lux) or in a large hemispheric dome under more homogeneous
illumination (300 lux) in white or quasimonochromatic light (555 nm).
In another experiment they were permitted only one viewing distance.
ZENK expression was quantified in glucagon amacrine cells after the
different treatments by means of double staining and cell counting.
results. In all conditions tested, the number of ZENK-expressing cells was
increased with positive lenses and reduced with negative lenses after
only 40 minutes of exposure. If only one viewing distance was possible,
the level of ZENK still responded to the sign of imposed defocus,
although it required 80 minutes of treatment. In this experiment, the
interocular difference was largely produced by changes in the
contralateral control eyes rather than the lens-treated eyes. Finally,
changes in ZENK expression appeared to be related to lens powers with a
sigmoidal function, with saturation at approximately +7 D and −7 D of
conclusions. The results confirm that changes in ZENK expression are selective for
the sign of imposed defocus. They may be independent of illuminance and
do not require chromatic cues or variable viewing distances. The
pathways for the substantial interactions between both eyes are not
clear at present.
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