The discovery of how certain proteins prompt brain cells to grow heralds the prospect of rebuilding diseased and injured brains without surgery, says a leading European neuroscientist.

"Although such a prospect is a long way off, it is becoming realistic because of our new understanding and new techniques to make man-made proteins," said Dr. Hans Thoenen, head of the department of neurochemistry at the Max Planck Institute for Psychiatry in Martinsriedgg, West Germany.Thoenen and a panel of scientists briefed reporters on their research with growth factors at the Society for Neuroscience annual conference that attracted more than 12,000 brain researchers to a weeklong meeting in Toronto.

Although nerve growth factor, or NGF, was discovered more than 35 years ago, scientists have only recently been able to understand the meaning of that discovery.

NGF was the first substance found that is known to regulate the growth of living cells. In addditon to guiding the development of a single fertilized cell into a fully formed human being, growth-factor proteins are now known to control cell growth and repair throughout life.

"The discovery of NGF and the understanding of how these proteins work in the central nervous system has turned our theories of the brain right around," said Dr. Albert Aguayo, head of the department of neurosciences at Montreal General Hospital and McGill University.

Until that discovery, scientists and doctors had believed the human brain had a very limited capacity to grow in response to disease or injury.

"But now we have rejected that view and face exciting questions to determine how we can harness a surprising high capacity of growth," Aguayo said.

Scientists have been surprised by the great ability of brain and nerve cells to regenerate, or grow, in the presence of the proper growth factor.