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T. M. Schmidt, P. Kofuji; Heterogeneity of Form and Function of Intrinsically Photosensitive Retinal Ganglion Cells. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5026.
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© ARVO (1962-2015); The Authors (2016-present)
A subset of ganglion cells in the mammalian retina express the photopigment melanopsin and are intrinsically photosensitive (ipRGCs). These cells are implicated in non-image forming visual responses to environmental light such as the pupillary light reflex, seasonal adaptations in physiology, photic inhibition of nocturnal melatonin release, and modulation of sleep, alertness and activity. Morphological studies have confirmed the existence of at least three distinct subpopulations of ipRGCs, those with monostratified dendritic arbors in either the outer (M1) or inner (M2) inner plexiform layer (IPL), and those with dendritic arbors bistratifying in both the inner and outer IPL. Research has also indicated that these subtypes may differentially and specifically project to various visual centers in the brain. The goal of the current study was to analyze and compare the morphology, dendritic field overlap, and functional properties of the various morphological subpopulations of ipRGC within the retina.
We utilized a transgenic mouse line in which ipRGCs are labeled in vivo with EGFP to target EGFP positive ganglion cells for whole cell recording and dye-filling with Lucifer Yellow or Neurobiotin.
M2 cells display more complex dendritic arbors and more overall total dendritic length than M1 cells. Additionally, we observed extensive overlap of the dendritic fields of neighboring ipRGCs of different subtypes. We also observed functional differences between morphological ipRGC subpopulations, with M1 cells displaying larger intrinsic light responses, higher sensitivity to light, and higher input resistance compared to M2 cells.
These data indicate morphological and functional diversity across these ipRGC subpopulations that goes beyond dendritic stratification in the IPL, and implies functionally distinct roles for these ipRGC subtypes in signaling light information to the brain.
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