How regenerative is our brain really?
It has been known about rats for a long time: New nerves are constantly growing in their brains. Until now, however, it was assumed that no new neurons were formed in the brains of primates. Scientists have now discovered that new nerve cells are indeed formed there, too. In the 1960s, researchers showed that adult rats continuously produce new neurons in a certain region of the brain. This brain region is the dentate gyrus, an area responsible for acquiring new memories and is part of the hippocampus. In a series of studies beginning in 1994, neuroscientists Elizabeth Gould of Rockefeller University in New York City and her collaborators expanded this picture by demonstrating that stressed rats release adrenaline, which suppresses the production of new nerve cells in the brain. However, these studies have never been conducted in primates. It was previously assumed that the additional growth of new nerve cells was a special property of the rodent brain.
Gould, now at Princeton University, and her colleagues finally made the move to experiments on primates (Proceedings of the National Academy of Sciences 17 March 1998). The researchers injected tamarind monkeys with a chemical marker called BrdU. BrdU is integrated into the DNA of dividing cells, making newly formed cells easy to identify. Three weeks after the injection, the scientists examined the brain tissue of the monkeys and found large amounts of BrdU in the dentate gyrus. To find out whether the new cells were actually neurons, Gould and his colleagues used a different marker substance: neuron-specific enolase. It turned out that 80% of the cells labeled with BrdU also showed the enolase "tag". This was confirmation that the new cells were indeed neurons. Gould's team also noticed a specific effect of stress: monkeys that lived close to other monkeys had a third fewer cells labeled with BrdU.
The findings are "a major step forward" that "contradicts prevailing knowledge," says Gerd Kempermann, a neuroscientist at the Salk Institute in La Jolla, California. He says, "Everyone else is hoping that [the production of nerve cells] can be used to treat neurodegenerative diseases" (such as Parkinson's disease) or even trigger the aging brain to regenerate itself by stimulating the production of new nerve cells becomes. But Fred Gage, also of the Salk Institute, and others warn that it's still too early to make the transition from tamarin monkeys to humans. Previous studies have shown that the ability of adult mice to spawn new neurons in the hippocampus can be influenced by genetic background, Gage explains. He cautions that this ability can vary greatly from species to species.
