Abstract
Abstract: :
Purpose:The transcription factor ZENK in the chick retina is expressed in correlation with the sign of imposed defocus (SOD) in vivo and can be used as activity marker. Because the image processing algorithms underlying SOD detection are not understood, we have studied ZENK expression both in vivo and in vitro following removal of cues that are available with normal visual experience. Methods:Experiment 1: Digitally generated videos clips were projected on the retinas of isolated eyecups with defined defocus which was controlled by infrared photoretinoscopy. Either a defocus gradient (–3 to +3 D, induced by tilting the sample by 9°, n = 16) was imposed, or a diffuser was placed in the projection beam (n = 6). Experiment 2: Anesthetized chicks were placed in the lab environment in a holder for 30 min and monocularly treated with either +7 or –7 D lenses (n = 6 each). Contralateral eyes remained uncovered. Percentages of ZENK–positive glucagon amacrine cells were determined in double–labeled transversal cryostat sections. Results:Experiment 1: Defocus gradients did not produce consistent gradients in ZENK expression. Video stimulation caused merely a significantly higher variability in ZENK expression compared to controls (p<0.001, Bartlett test). A diffuser did also not lower ZENK expression as expected from in vivo experiments. Experiment 2: Also in anesthetized chicks, ZENK expression was no longer controlled by the sign of imposed defocus. A tendency was detected in the positive lens treated group (+7 D: 62.1±16.7% ZENK–positive glucagon cells, contralateral control 48.0±21.0%) but not in the –7 D lens treated group (–7 D: 55.9±19.2%, contralateral control 55.0±17.6%; untreated chicks for comparison: 52.1±7.8%). Again, the variability of ZENK expression was significantly higher than in awake chicks treated with lenses. Conclusions:In vitro, ZENK in the retina is no longer controlled by SOD. Lack of efferent input, loss of regular photoreceptor alignment in the flattened tissue, absense of eye movements and aberrations are possible explanations. Surprisingly, SOD dependent ZENK expression was also not found in anesthetized animals. Either the optical quality had declined too much due to lid retractors, or alertness is, in fact, a requirement for sign of defocus detection.
Keywords: myopia • retina: proximal (bipolar, amacrine, and ganglion cells) • immunohistochemistry