Damien Broderick's right, "head transplant" is the wrong term.
It should be "body transplant."
And we're a tiny bit closer to being able to do it right, according to the
following news item.
--J. R.
A gentle tug can turn nerve cells into cables for repairing spinal cords
http://www.newscientist.com/newsletter/news.jsp?id=ns228739
STRETCHING neurons on the rack might seem like torture, but it could be the
key to repairing spinal cords.
By gradually pulling apart bunches of neurons, Douglas Smith and his
colleagues at the University of Pennsylvania in Philadelphia have persuaded
the cells' processes, or axons, to grow up to a centimetre in just 10 days.
"For an axon just a micron wide, that's an enormous distance," Smith says.
The researchers say these nerve cells could be used to bridge the gap between
damaged nerves in the spinal cords of people who are paralysed. They have
already begun trials in animals. "You can think about what we have as jumper
cables," Smith says.
While it's too early to know if the approach will work for people with spinal
cord injuries, Smith thinks it is a viable alternative to other strategies.
For example, many researchers are trying to encourage nerve cells to regrow in
the spine by, say, implanting an artificial scaffold seeded with appropriate
chemicals.
"But everything about the spinal cord is screaming 'stop growing'," Smith
says, so it's hard to get axons to grow long distances. "The difference with
growing cells outside the body is that you don't have to worry about this
inhibitory environment."
Smith's team placed groups of human neurons on adjacent membranes and grew
them for three days to allow the axons from the groups to form connections.
The membranes were then pulled apart 3.5 micrometres every 5 minutes over 10
days, until the axons connecting the two groups of cells had grown a
centimetre. Any faster and the axons were torn apart. They ended up with long
bundles containing tens of thousands of axons.
It's an interesting approach, says Paul Reier, a pioneering researcher into
spinal cord repair at the University of Florida. The big problem will be
implanting the cells in the right place and keeping them alive, he says.
"Adult neurons usually die when transplanted."
But Smith says his team is using a cell line that managed to survive when
implanted into stroke patients. He also speculates that transplanting
integrated bundles of cells will boost their survival. "Cells may be less
likely to die if they stay with their 'friends'," he says.
Reier thinks it will someday be possible to persuade cells to grow long
distances in the spinal cord, though. "Axon growth is becoming less of a
challenge than we thought."
Whatever approach is used, many questions remain. It's not even clear that
bridging a damaged part of the spinal cord will restore nerve activity. In
some injuries, some or all of the nerve fibres remain intact, yet still don't
work, Reier points out.
Smith's work may also help us understand other disorders, however. He thinks
that stretch-induced growth plays an important role in embryos and children.
Some degenerative disorders in young children may be caused by nerve fibres
that can't grow fast enough to keep up. Smith's team is now trying to
understand exactly how the process works. "Nobody's ever studied this type of
growth before," he says.
---------------------------
Stay hungry,
--J. R.
Useless hypotheses:
consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism
Everything that can happen has already happened, not just once,
but an infinite number of times, and will continue to do so forever.
(Everything that can happen = more than anyone can imagine.)
This archive was generated by hypermail 2b30 : Mon May 28 2001 - 09:59:47 MDT