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D.C. Tu, D. Zhang, J. Demas, R.N. Van Gelder; Functional Development of Intrinsically Photosensitive Retinal Ganglion Cells . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2239.
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Purpose: Intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the putative photopigment melanopsin have recently been described in mammals. Via projections to nonvisual brain regions including the suprachiasmatic nucleus and olivary pretectal nucleus, ipRGCs contribute to circadian photoentrainment and the pupillary light reflex. Here we isolate retinae from postnatal mice and employ multi–electrode array (MEA) recordings to characterize the developmental progression of ipRGC photo–excitability. Methods: A postnatal mouse retina (c57/BL6) is positioned with the inner–retinal face in contact with a planar array of sixty electrodes (Multi Channel Systems). The tissue is perfused with bicarbonate–buffered physiologic solution oxygenated with 95% O2 / 5% CO2 while the temperature of both perfusate and tissue chamber are maintained at 31oC. After dark–adaptation, the retina is stimulated via light from a calibrated xenon light source and the resulting electrical activity recorded. Results: Postnatal mouse ipRGCs assessed by MEA recordings ex vivo show a spectral sensitivity peak near 480nm, similar to melanopsin–dependent photoresponses described in adult animals. At postnatal day 5 (P5), ipRGC light responses are relatively insensitive with a half maximal response to 480nm light at approximately 1013 photons/sec/cm2. In contrast, P7 ipRGCs are at least 10 fold more sensitive to light. While P5 ipRGCs are unable to maintain persistent light responsive activity during a one minute light pulse, P7 ipRGCs are capable of continuously firing action potentials throughout a prolonged light stimulus. Conclusions: The required elements for ipRGC phototransduction are present and functional early in mouse development. Significant changes in ipRGC photo–excitability occur over a short developmental period. As postnatal mice progress from P5 to P7, their ipRGCs attain increased photosensitivity and the capacity for persistent light responsive activity.
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