Purchase this article with an account.
Matthew Alan Smith, Christina Z Xia, Kelly M Fening, Kyle T Nakamoto, Christine Dengler-Crish, Brett R Schofield, Samuel D Crish; Three-Dimensional Ultrastructure of Retinal Ganglion Cell Synapses in the DBA/2J Mouse Model of Glaucoma. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2450.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Axonal transport defects are an early pathology occurring within the retinofugal projection of the DBA/2J mouse model of glaucoma. Retinal ganglion cell (RGC) axons and terminals appear to persist after transport is affected, yet little is known about the condition of these synapses. We sought to examine the ultrastructure of the neuropil of aged DBA/2J mouse superior collicului (SC) to determine the density and morphology of RGC synapses.
DBA/2J (9-14 mo) and DBA/2J-Gpnmb+ (control) mice received bilateral intravitreal injections of cholera toxin B conjugated to Alexa Fluor 488. Seventy-two hours later animals were perfused and SC were microdissected. Tissue was prepared and imaged with serial block face electron microscopy. A 125 μm3 block was randomly selected in the SC neuropil. All synaptic boutons and associated mitochondria within the block were traced with Reconstruct software and characterized based on mitochondrial and vesicular characteristics previously described: RLP (Round, Large, Pale) - RGC boutons; non RLP -extra-retinal excitatory and inhibitory synapses; Dendritic - boutons associated the dendrites of collicular neurons; X (uncharacterized) - boutons that we were unable to classify. We determined the density of different classes of boutons within the block, volumes of each bouton and associated mitochondria, and number and surface area of active zones.
Supporting previous conclusions, the retinal projection was still intact after transport failure - RLP density did not change between strains of mice or between neural areas with different transport integrity. Even though axonal transport was compromised, we did not see obvious indicators of overt neurodegeneration in most of our samples. Morphologically, DBA/2J RLPs were remarkably normal, varying slightly in total volume, but they exhibited lower mitochondrial volume (especially in the areas with deficient anterograde transport) and increased active zone surface area. This finding suggests that oxidative capacity may be reduced as disease progresses, but before overt signs of pathology occur.
These findings support the idea that RGC axons retain connectivity but lose some function early in the disease process. This indicates a longer therapeutic window where interventions targeting nonfunctional axons can be developed to protect or restore vision in glaucoma.
This PDF is available to Subscribers Only