Dying cells send signal to stimulate new cells in birds

Scientists have discovered new neuron growth each spring in songbirds that starts with a signal from the expiring cells from the previous fall that primes the brain to start producing stem cells.

If scientists can further tap into the process and understand how those signals work, it might lead to ways to exploit these signals and encourage replacement of cells in human brains that have lost neurons naturally because of ageing, severe depression or Alzheimer's disease.

Neuroscientists have long known that new neurons are generated in the adult brains of many animals but the birth of new neurons - or neurogenesis - appears to be limited in mammals and humans.

"Many neuro-degenerative disorders are not injury-induced so it is critical to determine if and how reactive neurogenesis occurs under non-injury-induced neuro-degenerative conditions," said Tracy Larson, a doctoral student in biology at the University of Washington.

The researchers worked with Gambel's white-crowned sparrows, a medium-sized species that breeds in Alaska, and then go to California and Mexico in winters.

Brain cells that multiply to help birds sing their best during breeding season are known to die naturally later in the year.

As the hormone levels decrease, the cells in the part of the brain controlling song no longer have the signal to stay alive.

Those cells undergo programmed cell death - or cell suicide as some call it.

As those cells die it is likely they are releasing some kind of signal that somehow gets transmitted to the stem cells that reside in the brain.

The signal then triggers those cells to divide and replace the loss of the cell that sent the signal to begin with.

"There is no reason to think what goes on in a bird brain does not also go on in human brains," added co-author Eliot Brenowitz, a professor of psychology.

"As far as we know, the molecules are the same, the pathways are the same, the hormones are the same. That's the ultimate purpose of all this, to identify these molecular mechanisms that will be of use in repairing human brains," he emphasised.

The paper appeared in the Journal of Neuroscience.