Eriksson P et al; Nat Med 1998;4;1313-1317:
Conventional wisdom, that adult mammal brain tissue cannot
regenerate, has been crumbling for the past few years (see,
for example, CSR JUN 98) as more highly developed species have
been found to do so. Here, authors demonstrate for the first
time, neurogenesis in the adult human brain.
This exciting story has been in the news media for some time, as
it offers hope to those with heretofore irreparable injury or
with relentlessly progressive disease such as Parkinson's. But
it needs to be brutally oversimplified for the general public,
to the point where its significance is badly exaggerated or
distorted. My issue of Nature Medicine finally came today, so
I can offer at least a quasi-technical interpretation, for
those few listmembers having an interest in such things.
First of all, any animal which normally develops from one pair
of cells to an embryo, then an infant, and finally an adult,
must support furious growth of all its myriad types of cells,
including neurons of the central nervous system (brain and
spinal cord). But adults of higher species, including primates,
were thought to lack that ability in the CNS, perhaps as an
evolved protective strategy. Now recent research has found CNS
regeneration in mice, then rats, then marmosets, and now in
human adults. It's confined so far to the hippocampus, a small
formation (named for its slight resemblance to the spiral tail
of the seahorse, a small tropical fish) roughly central at the
base of the brain, thought to be involved in memory and
learning. Makes sense, because we feel that learning continues
throughout life (no snide comments please) and it must at least
require formation of new pathways as information is stored in
the brain. Also, progenitor cells (which differentiate into the
many types of cell, including neurons, of the adult) had been
found in the hippocampi of adult rats. Here, briefly, is how the
authors did it:
Cancer patients are sometimes injected, for diagnostic purposes,
with a chemical that binds only to DNA as it is being formed.
Therefore the chemical is a marker for cells that have formed
("grown") subsequent to the injection. The authors got
permission from 5 terminal cancer (not of the CNS) patients and
their families to sample brain tissue, for this research, after
they died. By means of elaborate staining techniques and
remarkable microphotographs they were then able to identify new
neurons which carried the marker chemical injected as early as
two years before. They chose to look at the hippocampus in
particular, probably for the reasons above. They conclude that
the human hippocampus retains its ability to generate neurons
throughout life.
The meaning of all this to PD patients anxiously waiting for a
cure is rather dim. First, we need to know just how neurons of
the hippocampus can reproduce (or develop from progenitor cells)
while others cannot. Then, we need to learn how to mimic and
control that process in the substantia nigra or wherever
(perhaps by some transplant surgery as with fetal transplants).
Then, we need to know how to prevent the new cells from dying
as the old ones did. And control of the whole process is important.
Keep in mind that uncontrolled cell growth is what killed the
subjects of this research. Altogether, it's a tall order.
Cheers,
Joe
--
J. R. Bruman (818) 789-3694
3527 Cody Road
Sherman Oaks, CA 91403-5013
