Wednesday February 23 5:21 PM ET
WASHINGTON (Reuters) - Using some of the smallest of all bird brains, scientists said on Wednesday they had coaxed brain cells to grow from elusive adult stem cells, so-called master cells that are the focus of frenzied research.
They said that by destroying certain brain cells in zebra finches, they prompted the generation of new cells. Writing in the journal Neuron, they said they believed that neural stem cells must have been the source of the new neurons.
"This is, we believe, the first example where it has been demonstrated that one can induce the birth of new neurons and that they actually contribute to a complex behavior,'' Jeffrey Macklis, a neuroscientist at Boston's Children's Hospital, said in a statement. "It is a step toward attempting the same in mammals.''
Adult stem cells are a kind of nursery or progenitor cell that exist throughout the body. They include cells that are used to regenerate bone marrow after cancer chemotherapy, and are different from the embryonic stem cells that scientists want to use for tissue transplants, to grow new organs, and for other research.
Scientists are trying to find ways to use either adult or embryonic stem cells, or both, to regenerate various forms of tissue, including brain cells of patients with disease such as Alzheimer's or Parkinson's.
The cells are hard to isolate and grow. They can be taken from aborted fetuses or from embryos left over from IVF (test-tube) fertilization efforts, but these sources can be controversial.
Working with colleagues at New York's Rockefeller University, Macklis decided to see if they could be prompted into growing in place, in the body.
They chose zebra finches because of an interesting variation in bird biology.
Canaries stop singing every autumn when a population of song-generating neurons in a part of their brains called the high vocal center dies off.
Over the winter, a whole new population of neurons grows back and in the spring the canaries learn their songs all over again.
But zebra finches -- small birds favored by bird-fanciers -- lack this seasonal cycle. Instead, their brains generate a constant, tiny trickle of new neurons.
Songbirds devote a great deal of brain space to singing, but the way the zebra finch's brain works more resembles the way the brains of mammals, including humans, operate.
Until recently scientists believed brain cells did not regenerate at all, but they now know new cells grow to a limited degree, especially in the olfactory bulb and the hippocampus.
One theory holds that when certain neurons die, they somehow signal stem cells and prompt the production of replacements.
Macklis's team selectively killed one kind of song-related neuron in their zebra finches. The birds, as predicted, partly lost their songs. But three months later they were singing as normal.
When the researchers looked at their brains, they saw that the neurons had grown back, in much the same way that canary neurons come back.
They said they were doing more experiments to see just where the new
cells came from.