Samantha Butler
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Hardwiring the Nervous SystemHow developing neurons find their way
By Eva Emerson
September 2004
Before the brain can produce thought, control limbs or make us flinch
in pain, innumerable connections must be built between the more than
one hundred billion cells that make up the central nervous system.
Figuring out exactly how this occurs drives the research of Samantha
Butler, an assistant professor of biological sciences in USC College,
who focuses on how the brain and spinal cord get wired up.
“We are just beginning to understand how these neural networks are
built,” says Butler, who arrived at USC College last winter from
Columbia University’s Center for Neurobiology and Behavior. “The idea
is to look at how these are set up to begin with, in the embryo,” she
says.
Understanding how the body builds new neural connections would be key
to any future scheme to repair damaged neural networks, such as those
found in spinal cord lesions — a leading cause of paralysis.
Butler studies how axons — the threadlike extensions of neurons that
transmit signals from a neuron — hook up with other neurons. During this
carefully orchestrated process, axons must grow thousands of times the
width of a neuron to form the stereotypical pattern encoded in the
genetic blueprint.
Work over the last 20 years has shown that, to navigate this long and
vitally important journey, axons rely on a series of molecular cues.
These molecules may attract the tip of the axon in one direction or
repel it from another direction, guiding the axon to grow toward
precise targets in the developing spinal cord and brain, Butler says.
Butler is best known for demonstrating that BMPs, members of a family
of growth factors, can repel axons. Although BMPs had been studied for
years by molecular and developmental biologists, Butler was the first
to show their important role in axon guidance — a key finding that
spawned new interest in the BMP family of proteins among
neuroscientists.
Butler continues to search for other so-called chemorepellents and
chemoattractants, as well as looking at molecular and cellular events
involved in the process. Eventually, she aims to understand how the
many guidance cues work together to direct axons on the right path in
the spinal cord.
“The practical aspect of this work, which would be dependent on
parallel advances in neural stem cell research and medicine, is to see
if we could somehow use similar compounds to help re-establish neural
pathways after injury,” she says.
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