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Cyril Giles Eleftheriou, Franck P Martial, Robert J Lucas; Melanopsin drives light responses across a large fraction of retinal ganglion cells.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5567.
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© ARVO (1962-2015); The Authors (2016-present)
Melanopsin expressing intrinsically-photosensitive retinal ganglion cells (ipRGCs) project to many targets of the CNS, influencing both image forming and non-image forming portions of the visual system. Recent anatomical and electrophysiological studies have brought to light intra-retinal connectivity of ipRGCs with amacrine cells raising the possibility that ipRGCs could influence the activity of multiple ganglion cell types. Here, we characterise how widely ipRGCs drive light-dependent changes in the firing of retinal ganglion cells.
Visual responses of RGCs were recorded in vitro in 5 isolated retinas of mice both lacking cone activity (Cgna3-/-) and displaying rod degeneration (rd1 mutation). Signals were acquired using a 256 channel multi-electrode array system (MEA) with electrodes spaced 200 µm apart, allowing a widespread and retinotopic sampling of the RGC population. Full field light stimuli were delivered to the ganglion cell layer (GCL) from below by a 470 nm LED. Stimulation epochs consisted of a 10 second light step followed by 120s of darkness.
We found that full field light pulses induced changes in firing across a much wider fraction of RGCs than a series of spatially restricted stimuli covering the same area. Responses to the full field stimulus fell into two populations that differed in their reproducibility over multiple repeats. Decaying responses accounted for 48% of all recorded RGCs (n=615/1283) and responded robustly only for the first two stimulus presentations in any recording epoch. Robust responses accounted for 16% (n = 211/1283) of recorded RGCs and kept responding throughout all repeats of the stimulus. No light responses were observed in melanopsin knockout models (rd1;OPN4 -/-; n = 6 retinas).
We recorded melanopsin driven responses in far more RGCs than the estimated <10% represented by ipRGCs. The extinction properties of the decaying response-type suggest that these may be indirect responses recorded in adjacent RGCs, which do not express any photopigment.
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