NERVE growth factors may have a more complex role in the brain than
merely encouraging the growth of nerve cells. Neurobiologists say that these
chemicals perform a balancing act that may play a key role in building
memory.
A team from Duke University Medical Center in Durham, North Carolina,
measured how different nerve growth factors affected the development of cells.
They took slices of brain from two layers鈥攌nown as layers four and
six鈥攐f the visual cortex of ferrets. They then used antibodies to
selectively switch off two nerve growth factors, brain-derived neurotrophic
factor (BDNF) and neurotrophin-3 (NT-3), in the tissue.
The team reports in this month鈥檚 Neuron (vol 18, p 767) that BDNF
stimulated growth of cell dendrites鈥攍inking extensions between
cells鈥攊n layer four. But to their surprise, NT-3 inhibited the growth. The
opposite was true in layer six. The team suggests these opposing growth factors
act as signalling factors in the learning process, as the development of links
between cells is thought to play a key role in learning and memory. 鈥淭his is the
first inkling we鈥檝e had that nerve growth factors are not simply growth
promoters,鈥� says team leader Donald Lo.
Advertisement
John Rogers, a neurobiologist at the University of Cambridge, says it is
鈥渆ntirely plausible鈥� that the growth factors play a role in memory.
Lo鈥檚 colleague Lawrence Katz adds that the finding may have clinical
implications. Many researchers are testing neurotrophins to see if they
encourage nerve cell growth in people with brain damage caused by Alzheimer鈥檚,
for instance. 鈥淭hese tests have been very disappointing,鈥� says Katz. 鈥淚f you
consider the likely complexity of these chemicals, it鈥檚 not surprising. We may
need to understand better how they interact with each other.鈥�