The investigators used two groups of mice whose precursor cells had been labeled to mark those that were dividing, allowing identification of newly generated, adult-born neurons. These mice were then exposed either to a panel of unusual odors or to a normal environment. Several weeks later, the response of the adult-born neurons was evaluated by measuring the activity of genes known to be expressed when olfactory neurons respond to odors.
They found that the adult-born olfactory neurons of mice exposed to the panel of odors subsequently responded more strongly to those odors than did adult-born neurons of mice that had no experience with the odors. The findings suggest that the new cells specialize in detecting previously unencountered odors and in subsequently responding to those smells.
"These contrasting responses suggest that adult-born olfactory neurons have a unique role in the brain, becoming linked to new smells while the older neurons essentially step out of the way. And since adult-born neurons are continually being generated, there is always a group of new cells waiting to link up with new stimuli," Macklis says. "We're also seeing how the environment can alter adult-born neurons and how experience and activity are important for making sure new cells integrate properly."
An associate professor of Surgery at Harvard Medical School, Macklis also notes, "These results can contribute to our efforts, and those of others in the field, to repair diseased brain and spinal cord by directed development of specific neurons from precursor/stem cells. Our experiments show that new neurons can join brain circuits and function in complex ways ?contributing to learning, memory and potentially to motor function ?and that we may need to retrain the brain to use the new neurons effectively."