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Yvonne Ou, Rebecca Jo, Erik M. Ullian, Rachel O Wong, Luca Della Santina; Selective vulnerability of specific retinal ganglion cell subtypes in a mouse model of ocular hypertension. Invest. Ophthalmol. Vis. Sci. 2016;57(12):3586. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Controversy exists as to whether certain retinal ganglion cell (RGC) subtypes are more vulnerable to elevated intraocular pressure (IOP). The purpose of this study is to determine the effects of laser-induced ocular hypertension on the structure and function of various subtypes of RGCs at specific time points after IOP elevation.
IOP was elevated unilaterally using laser photocoagulation of the limbal and episcleral vessels of adult CD-1 mouse eyes. Multielectrode array recordings were performed at 3, 7, 14 and 30 days. RGCs were classified into OFF-transient (OFF-T), OFF-sustained (OFF-S), ON-transient (ON-T), and ON-sustained (ON-S). Retinas were biolistically transfected with YFP-tagged PSD95 and prepared for whole-mount retina immunohistochemistry using SMI-32 to label OFF-T and ON-S RGCs and CtBP2 to label presynaptic ribbons. The Wilcoxon-Mann-Whitney rank sum test was used to calculate statistical significance.
After IOP induction, OFF-T RGCs showed the earliest decrease in spontaneous activity 14 days after IOP elevation, ON-S and OFF-S after 30 days, whereas spontaneous activity of ON-T RGCs was unchanged. A significant decrease in the receptive field size was found only in OFF-T RGCs (67±2 vs. 75±1 μm, P=0.009, N=5 mice), as early as 7 days after IOP elevation. Morphologically, OFF-T RGCs showed greater reductions in dendritic area (55779±22771 vs. 111184±35189 μm2, P=0.008, n=6) and complexity compared to the other subtypes. All alpha-like RGCs exhibited decreased PSD95 puncta density across their dendritic arbor 7 and 14 days after IOP elevation. In parallel to postsynaptic changes on RGCs, presynaptic ribbon density declined in the inner plexiform layer, with the greatest reduction observed within the OFF sublamina (0.08±0.03 vs. 0.24±0.09 ribbons/μm3, P=0.0007, N=6 mice). Finally, examination of alpha-like RGC density by SMI-32 immunostaining revealed that the proportion of OFF-T RGCs lost by 14 days after IOP elevation is greater than that of ON-S RGCs.
Taken together, these data suggest that IOP elevation differentially affects various RGC subtypes both morphologically and functionally. Neurons stratifying in the OFF sublamina undergo the highest reduction of excitatory synapses prior to cell death. OFF-T RGCs exhibit the earliest loss of function with corresponding alterations in dendritic area and complexity and rates of cell death.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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