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Kimberly Gokoffski, Phillip Lam, Micalla Peng, Basheer Alas; In Vivo Application of Electric Fields Directs RGC Regeneration Two Weeks After Optic Nerve Crush Injury. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1161.
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© ARVO (1962-2015); The Authors (2016-present)
Although current molecular approaches for optic nerve regeneration have been successful at directing long distance retinal ganglion cell (RGC) axon growth, they are limited by the fact that 1) they have only been shown to be successful when applied before injury, which has limited clinical application, and 2) were associated with off target migration (e.g. towards the other eye or back on itself). Cell replacement based approaches are similarly stunted by failure to direct long distance axon growth.The approach we propose to take to overcome this critical barrier of limited axonogenesis is to use electric fields (EFs) to direct long distance axon growth. The body has naturally occurring electric currents. Recently, we have demonstrated that mouse RGC axons grow directionally when exposed to an EF, in vitro. Whether EFs can direct and sustain RGC axon growth in vivo, however, is unknown. Here, we present compelling data that suggest that EFs, applied two weeks after crush injury, is effective at directing RGC axon regeneration.
To generate an EF along the rat optic nerve, a stimulating electrode was wrapped around the optic nerve while the ground electrode was stereotactically placed behind the chiasm. Following this, the optic nerve was crushed. Two weeks later, after ~50% of RGC axons degenerated, optic nerves were exposed to a charged-balanced waveform for 5 hours daily x 10 days, 0.5% duty cycle. Regenerative response past the crush site in stimulated animals was assessed by quantifying the number of axons at various distances past the injury site and compared to controls.
In situ experiments demonstrated that our set up allows for the generation of a linear voltage gradient along the rat optic nerve, similar to that observed in vitro. Moreover, just 10 days of EF stimulation directed nearly 3.5-fold more RGC axon regeneration over controls (p < 0.001). Significantly more regenerated axons could be seen 250 and 500um past the crush site in treated animals over controls.
Our work demonstrates that EFs are able to direct RGC axon regeneration after degeneration from crush injury has set in. This has important implications for patients who are blinded by advanced optic neuropathies who may have delay between time of injury and access to therapies. EFs represent a potential therapy to augment current molecular based approachs for optic nerve regeneration.
This is a 2020 ARVO Annual Meeting abstract.
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