Los peces regeneran sus nervios

A Fishy Recipe for Healing Nerves

Unlike people, fish can regrow damaged nerve fibers in their central
nervous systems. Now a study may have found the reason: The creatures lack
a protein called Nogo-A that prevents nerve regeneration in mammals.

Axons, or nerve fibers, are the transmission lines that conduct electrical
signals throughout the body. The fibers are protected by sheaths of myelin,
a fatty insulator that speeds the electrical impulses along. Damaged axons
in the brain and spinal cord of mammals don't regenerate, and spinal cord
injuries can therefore lead to permanent paralysis. Fish are luckier: They
can regrow the axons in their central nervous system, but curiously this
regeneration stops if their nerve endings come into contact with mammalian
myelin.

Because a protein in mammalian myelin called Nogo-A is known to inhibit
central nervous system axon growth in mammals, a team of researchers led by
biologist Claudia Stürmer at the University of Konstanz in Germany wondered
if fish might be missing this protein. When the researchers exposed
goldfish axons to rat Nogo-A, the nerves stopped growing. Furthermore, a
comparison of genomes between ten species of fish, including zebrafish and
pufferfish, and humans revealed that fish lack the genetic information to
make Nogo-A or a similar inhibitor. The team reports its findings in the
August issue of Molecular Biology and Evolution.

The paper's careful study of fish phylogeny supports an existing notion
that Nogo-A may be a recent evolutionary development that correlates with
more complex nervous systems and more complex functions, says Stephen
Strittmatter, a neurologist at Yale University in New Haven, Connecticut.
"It's an important addition to our growing understanding of the role these
inhibitors play," he says.

--CAROLYN GRAMLING

http://sciencenow.sciencemag.org/cgi/content/full/2005/805/1