WEDNESDAY, Feb. 27, 2002 (HealthDayNews) -- Not only do new nerve cells grow in the adult brain, but they also appear to develop function as well as form.
Using adult mice, scientists at the Salk Institute in California have shown that nerve cells born in a region of the brain linked to memory formation go through a gradual process of maturation and develop the functional characteristics of adult brain cells.
The finding fuels the notion that the brain can change even during adulthood, and one expert says the discovery could lead to future therapies for conditions involving brain cell degeneration, such as Alzheimer's disease.
The study appears in tomorrow's issue of Nature.
Led by genetics professor Fred H. Gage, the laboratory has previously shown cell creation occurs in all mammals, including humans, throughout adulthood -- although it's restricted to two areas of the brain. In the latest research, Gage's team focused on cell creation in the hippocampus, which plays a crucial role in the making of new memories.
The researchers parked a protein on a harmless virus that infects only cells that are dividing, and injected the virus into the brains of grown mice. The protein, which is naturally a phosphorescent green color, lit up the dividing cells when samples of brain tissue were examined under a microscope. An examination one month later showed the new nerve cells were developing functional properties.
"They don't start acting like neurons until a month after they're born in the adult brain," says Gage. "Then it takes another three or four months for them to actually fully mature into cells that are identical to the ones that have been there for a long time in the adult."
However, while this suggests the brain retains the ability to replace its own cells, it's not clear why.
Gage suspects the brain keeps this skill because younger cells may be more adaptable.
"By having this self-renewal of young cells, we maintain a better, more sensitive process for memory acquisition," says Gage. "The value of having new, recurring memories is so strong that that has some selective value in maintaining these cells."
He points out that in conditions like Alzheimer's disease, which causes early damage to this system, one of the first abilities people lose is the capacity to make new memories. "By understanding how this part of the brain can self-renew
under normal [circumstances], we might be able to utilize that information in repair."
Dr. Blair R. Leavitt, an assistant professor of medical genetics at the University of British Columbia, says the study takes another step towards laying to rest the idea that no new neurons are born in the brain.
"I'm impressed by the technical tour de force that Dr. Gage's group has accomplished here," says Leavitt.
"It really does take the characterization of these new neurons to a new level," says Leavitt. "The ability to measure the electrophysiological properties of the new neurons [is] the main and the most important finding of this paper."
"There are many people in the field now who believe that the mammalian brain is not as static as once thought, and certainly in conditions where there is ongoing brain cell death or neurodegeneration, there may be a second process by which some new neurons are being born," Leavitt says.
He adds this may suggest the process by which new neurons are formed is either slow or not very efficient, allowing cell birth to fall behind cell death.
"Understanding the process, and understanding how to intervene in that process, gives us a new therapeutic option," he says. "When we can manipulate [natural cell birth] in the brain, we can hopefully begin to develop new treatments for neurodegenerative disorders."
What To Do: Find the hippocampus in the Whole Brain Atlas, or learn the basics of neurons from How Stuff Works. You can also read about Alzheimer's disease at the Alzheimer's Association.
