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Y. Zhang, M. Meister, B. S. Pawlyk, O. V. Bulgakov, T. Li, M. A. Sandberg; Responses of Intrinsically-Photosensitive Retinal Ganglion Cells After Melanopsin-Gene Transfection. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4604.
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To determine if transfection of melanopsin into the adult rd/rd mouse retina will increase the sensitivity and/or number of intrinsically-photosensitive retinal ganglion cells (ipRGCs).
An AAV-vector carrying a melanopsin and GFP reporter gene (pAAV-OPN4-IZsGreen) driven by a CMV promoter was generated and injected into the vitreous of one eye of adult rd/rd mice. A control GFP-only vector (pAAV-MCS6-IZsGreen) was injected into fellow eyes. Spike responses of retinal ganglion cells to flashing bars of varying intensity and width were recorded with a multi-electrode array.
AAV-mediated melanopsin expression was detected in up to 30% of RGCs, whereas only ~1% of RGCs express melanopsin endogenously. The distribution of transgenic melanopsin showed the normal association with the plasma membrane. More than 90% of the RGCs were light sensitive in the melanopsin-transfected eyes. Responses were detected at a threshold intensity of ~1012 photons/sec/cm2 and saturated at ~3 x 1014 photons/sec/cm2. The receptive field diameter (FWHM) averaged 97 µm. In control eyes, ~30% of RGCs were light sensitive, with a similar dynamic range and receptive field diameter as in transfected eyes.
In the retina of adult rd/rd mice, ipRGCs are more numerous than expected based on melanopsin immunocytochemistry. The receptive fields of ipRGCs are smaller than previously-reported dendritic fields, suggesting that melanopsin transduction is restricted to a region close to the soma. Melanopsin transfection may render nearly the entire RGC population photosensitive.
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