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Simon Pan, Samer Hattar, Tiffany Schmidt; Dendritic Stratification of Intrinsically Photosensitive Retinal Ganglion Cells During Postnatal Retinal Development. Invest. Ophthalmol. Vis. Sci. 2013;54(15):305.
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© ARVO (1962-2015); The Authors (2016-present)
A cardinal feature of retinal ganglion cell (RGC) circuitry is the precise arborization of their dendrites within specific sublaminae in the inner plexiform layer. This arborization occurs through a postnatal maturational process during which the arbors of many immature retinal ganglion cells become monostratified. This laminar refinement has been shown to be dependent on visual activity for conventional retinal ganglion cells. The dendritic maturation of intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the photopigment melanopsin, has yet to be characterized. These unique ganglion cell photoreceptors are diverse in both physiology and morphology, including their arborization within the inner plexiform layer, and it is not known if visual activity plays a role in their stratification.
We performed immunohistochemical analysis on retinas from several genetic mouse lines that were raised in either a normal light/dark cycle or constant darkness, harvested at various times through postnatal development.
Unlike many conventional retinal ganglion cells, ipRGCs appear to show adult-like dendritic stratification in early postnatal development, before eye opening and the formation of rod/cone synaptic connections. Immunostaining of all ipRGCs reveals that the dendrites of ipRGCs are organized in two distinct ON and OFF strata immediately after the formation of the inner plexiform layer by postnatal day 4. When we analyzed the stratification of specific subtypes, we found, consistent with the total ipRGC population, that M1 and M4 ipRGC subtypes show monostratification at early developmental stages. Surprisingly, M4 ipRGCs remain monostratified even after rearing in constant darkness.
The dendritic stratification of ipRGCs occurs very early in postnatal development, and ipRGCs show adult-like dendritic morphology well before eye opening. Furthermore, this early maturation does not appear to depend on visual activity.
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