In mammals, neural axons (nerves) fail to regenerate after injury. Therefore, you can get paralyzed after bone
marrow damage and you can lose your eyesight if the optic nerve suffers a
lesion. These are known facts, however, scientists all over the world dedicate
their lives to break these rules. Yes the topic is once
again breaking the law...and it isn’t just the favourite topic of mine, this is
how science reaches new frontiers. We don’t just admit facts and get along with
them. For example if doctors say chickenpox is an incurable disease, scientists
say ’challenge accepted’, and show the world that in fact, chickenpox is
curable.
A research group from the University of California, under the leadership of
Andrew D. Huberman, managed to induce optic nerve fibers to grow back to their
specific brain regions and therefore to restore some aspects of visual acuity after optic nerve injury in mice. But how was all this possible, if we know, nerves
cannot regenerate? Well indeed, the adult central nervous system contains some
factors that are unfavorable for axon regrowth, but fortunately, these factors are
already identified, which means we can get rid of them.
After optic nerve crush, the axons of retinal ganglion cells fail to grow
back beyond the lesion site, eventually resulting in the death of ganglion
cells, meaning blindness is irreversible for ever. Huberman and his research
group discovered, that downregulation of inhibitors of axon growth, increased
activity of intrinsic cell growth-promoting factors and visual stimulation of
retinal ganglion cells promote axonal regrowth beyond the lesion site and all
the way back to the appropriate brain regions, never missing the correct
target. Furthermore, these regenerated axons managed to establish new
connections with the appropriate neurons at the target site, meaning the visual
pathway was functional again.
These findings were then supported by behavioral tests in which mice showed
some restored visual functions (not all of them got restored, for example mice
could definitely detect moving objects, however they could not percieve depth) and
by specific molecular markers which allowed researchers to trace the regrown
axons and verify their target locations.
In summary, with proper stimulation, adult nerves can be induced for
long-distance, target specific regrowth and formation of new connections with
the appropriate neurons at the taget site thus promoting the restoration of
visual function.
By Antonia Stefanov
By Antonia Stefanov
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