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Michaela Fuchs, Anna Sendelbeck, Johann H. Brandstätter; Examining the Molecular Basis of Light Adaptation at the Photoreceptor Ribbon Synapse. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1177.
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Photoreceptor ribbon synapses transmit light signals over a wide dynamic range and continuously adjust their synaptic output to changes in stimulus intensity. Such a high level of performance requires a specialized presynapse and complex adaptive mechanisms. From the literature it is well known that the synaptic ribbon is a highly dynamic organelle, which changes its size and shape depending on illumination and thus activity. However, the molecular basis of these adaptational changes remains to be elucidated. The aim of this study is to identify the molecules at the photoreceptor ribbon synapse which are involved in the light-dependent, adaptational processes.
Using immunocytochemistry, high resolution light and electron microscopy, and laser microdissection in combination with quantitative real-time PCR, we have started to study the expression and localization of presynaptic proteins during the regular 24 h cycle and under various light and dark regimes in the pigmented retina of the C57BL/6 mouse.
Comparing the structure of the ribbon during the regular diurnal cycle - 12/12 light/dark with an average illumination of 200 lux - we found no obvious differences in ribbon length and shape. Even more surprising was the finding that neither a dark nor a light stimulus (200 lux) following a 3 h period of light or dark adaptation, respectively, triggered any significant structural ribbon changes. Only when the retina was exposed to bright light (1000 lux), the outer plexiform layer (OPL) appeared disorganized and the photoreceptor ribbon structure less compact. Electron microscopy confirmed the formation of club-shaped ribbons and spherical ribbon material.
Most of our knowledge about the dynamic changes of the ribbon structure, following different light and dark regimes, originates from studies of the albinotic retina. To trigger comparable structural changes at the photoreceptor ribbon synapse of the pigmented C57BL/6 mouse retina, much higher light intensities are required. Thus, it remains to be shown whether the structural changes are indeed physiologically relevant or whether other mechanisms contribute to light adaptation at the photoreceptor ribbon synapse.
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