Cool under fire? It's all in your head

CHICAGO (Reuters) - A mechanism in the brain may explain why some people keep their cool and others crumble under stress, U.S. researchers said on Thursday.

"We have identified the ways in which the brain naturally copes with chronic stressful experiences," said Dr. Vaishnav Krishnan of the University of Texas Southwestern Medical Center, whose study appears in the journal, Cell.

Psychologists have long understood that some people are more vulnerable than others to stress, which can lead to depression and even post-traumatic stress disorder.

But little is known about mechanisms in the brain that explain this vulnerability.

Krishnan and colleagues set out to study this problem in mice that were exposed to stress.

What they found was mice that were most vulnerable to stress had too much of a chemical in a region of the brain that processes reward signals.

And they found a significant increase in this same chemical in humans with depression.

It turns out that resilient mice produce a kind of protective response that allows them to recover from stress. Vulnerable mice lack this defense.

"ACTIVE PROCESS"

"One of the major insights provided by this work is that resilience to stress is an active process," Dr. Eric Nestler of UT Southwestern said in a statement.

Nestler, Krishnan and colleagues placed genetically similar mice into a cage with a large, aggressive mouse -- basically a bully.

Then they recorded their ability to interact socially, especially when exposed to other, more aggressive mice.

While some behaved timidly even 30 days after the bully encounter, others had shaken it off and were able to interact normally.

The researchers then looked at two of the brain's reward centers -- the ventral tegmental area and the nucleus accumbens -- to see if there were differences there. These areas are part of the reward circuit of the brain and also known to be involved in fear conditioning.

What they found is that neurons were firing rapidly in the stressed-out mice, releasing a nerve growth factor called brain-derived neurotrophic factor or BDNF that has been linked with poor coping skills.

Vulnerable mice showed an increase of BDNF in the nucleus accumbens; resilient ones did not.

Resilient mice put the brakes on this excess neuron firing -- and increased release of BDNF -- by increasing the production of potassium channels, which govern the speed at which neurons fire.

Krishnan said the finding is important because the researchers also found high concentrations of BDNF in tissue taken from this same brain region in depressed people.

"It seems to be a signature of vulnerability to depression," Krishnan said.

The researchers think the finding might help lead to new therapies that build up resiliency in people.