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Regina D. Nobles, In-Beom Kim, Hideo Hoshi, Wei L. Liu, Stephen L. Mills, Stephen C. Massey; Two Morphological Types of Melanopsin Retinal Ganglion Cell Have Distinct Coupling Patterns in Rabbit Retina. Invest. Ophthalmol. Vis. Sci. 2011;52(14):3459. doi: https://doi.org/.
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A population of retinal ganglion cell photoreceptors is intrinsically photosensitive (ipRGCs) and expresses the photopigment melanopsin. Two morphologically distinct types, M1 and M2, have been more completely characterized in mouse retina (Berson et al, 2010). Also in mouse there is physiological evidence of coupling in ipRGCs (Sekaran et al, 2003; Tu et al, 2005). We investigated the morphological homologues of M1 and M2 ipRGCs and their dendritic stratification patterns in rabbit retina.
Sections of adult rabbits were removed from the sclera and placed on filter paper ganglion cell side up. To label ipRGCs, sections were incubated in primary antibody and stored overnight. Sections were incubated in secondary antibody the following day and placed in a perfusion chamber onto the stage of an epifluorescent microscope. IpRGCs were injected using glass microelectrodes and iontophoresed with 2nA current. After injection, sections were fixed in 4% PFA, incubated in streptavidin-Alexa 488 and imaged using epifluorescent microscopy.
Intracellular injections identified two distinct types of ipRGCs in rabbit retina similar to M1 and M2 ipRGCs previously described in mouse retina. The dendrites of M1 ipRGCs stratify in the OFF sublamina of the IPL and make point to point contacts with other M1 dendrites and are coupled to ACs. The dendrites of M2 ipRGCs stratify in the ON sublamina of the IPL and make point to point contacts with other M2 dendrites and are also coupled to displaced ACs (dACs).
In rabbit retina there are separate matrices of dye-coupled M1 to M1 ipRGCs and M2 to M2 ipRGCs. In addition, both M1 and M2 ipRGCs are coupled to different AC and dAC populations, respectively (Müller et al, 2010). Our results suggest that the homologous and heterologous networks of ipRGCs and ACs may be important for the integration and synchronization of visual signals in the image and non-imaging forming pathways of the retina.
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