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Luca Della Santina, Alfred Yu, Alan Tran, Kelly Mai, Yvonne Ou; Degenerating retinal ganglion cells disconnect from bipolar cells using diverse strategies. Invest. Ophthalmol. Vis. Sci. 2018;59(9):2010.
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© ARVO (1962-2015); The Authors (2016-present)
Retinal ganglion cells (RGCs) undergo progressive loss of their glutamatergic excitatory postsynaptic sites when intraocular pressure (IOP) is elevated in animal models of experimental glaucoma (Della Santina et al. JNeurosci 2013, Ou et al. JNeurosci 2016). It is currently unknown whether this process follows a common pattern across all RGCs or multiple disconnection strategies are employed by different RGC types. To this purpose we investigated the connectivity between individual RGCs and presynaptic bipolar cells (BCs) after acute IOP elevation.
IOP was elevated unilaterally by laser photocoagulation of the limbal and episcleral veins of adult CD-1 mouse eyes, generating transient IOP elevation lasting one week. Whole-mount retinas were isolated and biolistically transfected to label RGCs and their excitatory postsynaptic sites (PSD95). Immunostaining with CtBP2 labeled presynaptic ribbons while immunostaining with Synaptotagmin-2 labeled axon terminals of Type-2 and Type-6 bipolar cells. RGC connectivity was measured by colocalization analysis in three dimensions on confocal imaging stacks of individual RGC dendrites at 7, 14, and 30 days after IOP elevation. Alpha RGC types (ON-Sustained, αON-S; OFF sustained, αOFF-S; OFF transient, αOFF-T) were investigated in this study.
Colocalization between ribbons and PSD95 was significantly lower than control as early as 7 days after IOP elevation (Control vs Laser, αON-S: 90±2% vs 62±4% p=0.001, αOFF-S: 74±3% vs 48±3% p=0.0007, αOFF-T: 78±3% vs 55±4% p=0.002). αON-S and αOFF-S RGCs establish preferential connectivity with type-6 and type-2 bipolars in control conditions, respectively. This preferential connectivity is lost as early as 7 days after IOP elevation for sustained alpha RGC types (Control vs Laser; αON-S: 64±2% vs 37±4% p=0.001; αOFF-S: 68±2% vs 38±4% p=0.003), while αOFF-T RGCs only undergo a slight reduction of their connectivity to type-2 bipolars (Control vs Laser: 38±3% vs 23±5% p=0.052).
Alterations to synaptic connectivity at the BC-RGC synapse are among the earliest pathologic events affecting the inner retina in mouse models of experimental glaucoma. At this synapse, ribbons are disassembled before PSD95 across all RGCs examined, indicating that presynaptic component is also affected at early disease stages. The specificity of this disconnection pattern is specific to the individual RGC type.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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