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P. De la Villa, N. Forns, R. Barhoum, F. Germain; Melanopsin Containing Ganglion Cells In Rd Mouse Retina: ¿Do They Make Functional Sinaptic Contacts With Other Retinal Cells? . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2060.
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© ARVO (1962-2015); The Authors (2016-present)
To study if intrinsically photosensitive retinal ganglion cells (ipRGC) make functional synaptic contacts with other retinal cells after photoreceptor degeneration. It has been shown that ipRGC receive synaptic input form bipolar cells and amacrine cells on their dendrites, which allow ipRGC to follow the rod/cone mediated light input in wild type animals. In Rd mice, after photoreceptor degeneration, ipRGC are the only photodetector for photoentrained circadian activity but no synaptic input from ipRGC to other retinal cells has been shown to date.
Electroretinography and phase shifting of circadian activity rhythms were evaluated in rd1 and rd10 mice ≥ 180 days of age. Animals were housed individually in cages equipped with activity wheels at a photoschedule of 12/12 hr light/dark cycle (light intensity 50 Cd·m–2) and dark/dark cycles. Electroretinographic responses were performed following the ISCEV protocols. Eyes enucleated from visual tested animals were fixed in 4% paraformaldehyde, cryoprotected in PBS 20% sucrose, and sectioned (10–20 µm thickness) at cryostat. Double labelling immunohistochemistry for cell–type specific markers (melanopsin, tyrosine hydroxylase, glycine, αPKC) were performed on retinal sections of rd1 and rd10 mice. All Results were compared with those obtained in age–matched C57/bl6 mice, used as controls.
Rd1 and Rd10 mice older than six months of age did not show any ERG response. Although dystrophic animals showed photoentrained circadian activity, the phase shifting of Rd mice under dark/dark cycles showed significant differences when compared to wild type animals of the same ages. Immunocytochemical experiments showed that ipRGC in control animals make synaptic contacts with dopaminergic and glycinergic amacrine cells. The extent of ipRGC synaptic contacts in Rd mice older that six months of age show apparently significant differences with age matched controls.
We demonstrate that circadian activity in dystrophic animals show significant differences with control mice. Changes in synaptic circuitry involving ipRGC might explain the functional changes.
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