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P. Kofuji, T. M. Schmidt; Morphological and Physiological Characteristics of Bistratified ipRGCs. Invest. Ophthalmol. Vis. Sci. 2010;51(13):665.
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© ARVO (1962-2015); The Authors (2016-present)
Intrinsically photosensitive retinal ganglion cells (ipRGCs) express melanopsin and form a specific subpopulation of retinal ganglion cell. At least three morphological subpopulations have been identified: those monostratifying in the outermost (M1) or innermost (M2) inner plexiform layer (IPL) and those that bistratify in both the inner and outer IPL. Though the diversity of M1 and M2 cells has now been described, the morphological and physiological characteristics of bistratified ipRGCs have not been studied. The goal of the current study was to analyze the morphology, intrinsic properties, and intrinsic and extrinsic light responses of bistratified ipRGCs.
We have utilized a transgenic mouse line in which ipRGCs are labeled in vivo with EGFP to target ipRGCs for whole cell recording and dye-filling.
Bistratified ipRGCs are morphologically heterogeneous, with some cells stratifying primarily in the On or Off sublamina and some cells stratifying in both sublaminas in relatively equal proportions. Physiologically, bistratified ipRGCs were found to have a significantly smaller soma than M2 cells, significantly larger dendritic arbor than M1 cells, significantly more hyperpolarized resting membrane potential than M1 cells, and a significantly different input resistance than both M1 and M2 cells. Additionally, bistratified cells demonstrate a significantly smaller intrinsic light response than M1 cells and a more sensitive intrinsic light response than M2 cells. Bistratified ipRGCs are also modulated by the ON pathway in response to light stimulation and at rest, similar to that observed in M2 cells.
Though bistratified cells are rare relative to the other two subtypes, the distinct physiological characteristics of this subpopulation argues for its classification as a distinct ipRGC population. Though physiologically similar to M2 cells, the dendritic arborization in the outermost IPL could expose the bistratified ipRGCs to dopaminergic modulation as well as modulation by the Off pathway indicating that this subpopulation of ipRGC could serve a role distinct to M2 ipRGCs.
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