Harvard scientists have manipulated stem cells already present in the brains of mice to induce the birth of new neurons, an advance once considered impossible by most scientists.

They induced the birth of new cells by killing nearby neurons in mice, which set off a cascade of events that led to stem cells, also called precursor cells, producing new neurons in the cerebral cortex. If scientists can turn this into a therapy for humans, it would mean that patients could literally heal themselves with stem cells already present in their brains.

The researchers’ goal is not to create a therapy that would kill neurons in order to activate the birth of new ones. Rather, they hope experiments like this one, which appeared in the Proceedings of the National Academy of Sciences online, will lead to new ways to grow neurons. Researchers could eventually identify key molecules involved with neuron birth and translate them into drugs, said Jeffrey Macklis, a researcher at Harvard Medical School who led the study.

“(The neurons) developed into mature neurons that not only took up proper locations within the brain, but reconnected to the spinal cord,” Macklis said.

The newborn neurons took the place of many damaged neurons in the mice. The work could be a model for neuron replacement in spinal cord injury or diseases including Alzheimer’s, Parkinson’s and Lou Gehrig’s. And such a therapy would avoid any immune or other complications that might result from stem-cell transplantation.

Researchers long thought the adult central nervous system had little or no ability to regenerate. But recent studies have shown some regeneration, mainly in the hippocampus and olfactory regions. In 2000, Macklis and his colleagues showed for the first time they could induce neurogenesis (the birth of new cells) in complex brain regions such as the cerebral cortex. Other experiments showed that surrounding brain cells turn on molecular signals when certain types of neurons die.

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