Scarred for life: Rat nerve cells damaged by stress

By Julie Steenhuysen

CHICAGO (Reuters) - One socially crushing moment -- think schoolyard bullies -- can challenge the survival of new nerve cells in the brain and may even lead to depression, U.S. researchers said on Tuesday.

In a study of young rats threatened by aggressive, older rats, the bullied ones were able to generate new nerve cells in key memory and emotion regions of the brain but most of those cells later died.

The research suggests that stress kills young nerve cells, a finding that might lead to potential interventions.

"If we can keep these new nerve cells alive, we might be able to forestall or prevent the types of depressive symptoms that might normally occur," said Daniel Peterson, a researcher at the Rosalind Franklin University of Medicine and Science in North Chicago, Illinois, who led the study.

Peterson's team put a young rat in a cage with two older rats for 20 minutes. The older rats quickly cornered, pinned down and often bit the younger one, they reported in the Journal of Neuroscience.

The younger rats became fearful and acted depressed around the bigger animals, with their stress hormones six times higher than young rats who were spared the stressful encounter.

Based on prior research, Peterson and his colleagues had expected that elevated stress hormone levels would prevent the development of young nerve cells or kill them off immediately.

Instead, when the rats' brains were examined under a microscope, the researchers found new cells had developed but that only about a third of them had survived a week later.

"There is this time frame after you encounter this dreadful stress episode where you could probably intervene," Peterson said in a telephone interview.

He plans to examine what role antidepressants might play in rescuing nerve cells. But because most antidepressants now on the market need weeks to take effect, he believes that may not be quick enough to do any good.

"What we are seeing is the stress is changing the environment. That is what we need to understand now," Peterson said. "That will tell us what therapies could be useful to intervene."