Published online 12 November 1998 | Nature | doi:10.1038/news981112-4

News

Regenerating brain cells

One of the most dearly-held tenets of human biology - that the human brain cannot replace neurons - has been proved wrong with the publication in Nature Medicine of a study showing that some human brain cells can regenerate. This exciting finding will shed new light on the natural ageing of the brain and on neurodegenerative disorders such as Parkinson’s disease, Alzheimer’s disease and Huntington’s disease - all of which are characterised by a gradual loss of neurons.

Led by Fred Gage, researchers at the Salk institute for Biological Studies in La Jolla, California, found evidence of replication in cells from the dentate gyrus (an area of the brain involved in learning and memory) in five deceased cancer patients.

The patients, aged between 50 and 80, who were treated at the Sahlgrenska University Hospital, Sweden, had received intravenous injections of a substance called bromodoexyuridine (BrdU) in order to check for tumour cell proliferation. BrdU is a compound that labels dividing cells by incorporating itself into newly synthesised DNA. When the brains of these BrdU-labelled patients came to post mortem, Gage’s team took advantage of a rare opportunity to look for signs of cell division in the dentate gyrus. The researchers wished to follow up reports of the formation of new neurons -neurogenesis - in the corresponding part of the brain in rodents and monkeys.

Although most cells are constantly dividing, the mammalian brain has long been considered to be anatomically fait accompli at birth. Over the last few decades animal studies have proved otherwise, first with the discovery of neurogenesis in rats, then guinea pigs and most recently in marmosets. But nothing, it seemed, could dent the dogma that somewhere in the course of evolution the higher primates had relinquished their regenerative capacity in order to protect their neuronal hard-wiring.

“Now our study demonstrates once and for all that cell genesis does occur in human brains,” enthuses Gage, “and that the human brain retains the potential for self renewal throughout life.” But he also urges caution, “although our results indicate that some of the newly generated cells can survive and develop into cells that look like neurons, we have not yet proven that these newly generated cells are functional.”

Even so, “this is a thrilling discovery” says Professor Elizabeth Gould of Princeton University who earlier this year made a similar discovery in marmosets. “Now we can get on with finding out why these cells are regenerating, working out whether or not something similar is occurring in other brain regions and seeing how we can manipulate the process.”