Abstract
Purpose :
The goal of this study was to illustrate retinal axonal transport with a fluorescent nerve imaging tracer based on fast axonal transport in control and neuropathic eyes. Our hypothesis was that loss of axonal transport could be an early event in the development of neuropathy.
Methods :
Neuropathy was induced in Norway brown rats eyes by injecting N-methyl-D-aspartic acid (NMDA) into the vitreous of one eye and PBS into the contralateral eye as a control. 48 Hours after the NMDA injection, a fluorescently labeled neural imaging probe based on the non-toxic, C-fragment of Tetanus Toxin (TTc) was injected into the vitreous of both the treated and control eyes. In vivo imaging of the distribution of TTc was performed using retinal ophthalmoscopy. Retinas were harvested at 3 hours after TTc injections, followed by whole retinal flat mount microscopy and immuno-histology.
Results :
Axonal TTc co-localizes with the retinal axonal (RA) neurofilament marker (SMI32) while a selective cytoplasmic marker (RBPMS) for retinal ganglion cells (RGC), confirmed the presence TTc endovesicles in the RGC neural somas. In contrast, neuropathic eyes showed a marked reduction in the RA TTc uptake. Plotting circular transects around the optic nerve head at a radius of 500 µm demonstrated that axonal strand crossings were markedly reduced in retinopathic eyes at 365 ± 41.46 vs control eyes 479 ± 48.41 (P=0.003). There is co-localization (Pearson’s r – 0.7+/- 0.05) between TTc and the neurofilament marker in the control eye RAs. A relative loss of RA fluorescence in retinopathic eyes showed a reduction in co-localization (Pearson’s r – 0.4+/-SD) between neurofilament marker and the neural probe.
Conclusions :
The retinal uptake and transport of the neural tracer, TTc, could be observed using ophthalmoscopy, and was markedly different between the normal and neuropathic state. These findings were confirmed to be specific with specific histologic markers for RAs and RGCs. NMDA induced retinopathy decreases neuronal uptake and transport of TTc, indicating that abnormalities of neuronal uptake and transport are early events in the development of retinal neuropathy.
This is a 2021 ARVO Annual Meeting abstract.