WEDNESDAY, Sept. 13 (HealthDay News) -- An injection of a natural stress hormone may help decrease post-traumatic stress, a study in mice suggests.

In the study, published in the Sept. 13 issue of the Journal of Neuroscience, researchers at the University of Texas Southwestern Medical Center at Dallas placed mice in a plastic box and subjected them to a mild electrical shock.

A couple of days later, the mice were returned to the box, and the researchers gauged their fear, based on how long they "froze" in place. After a few minutes, the researchers injected the mice with corticosterone, a natural stress hormone produced by the body.

When the mice were returned to the box again a day later, they showed significantly less fear, the researchers reported. The higher the dose of corticosterone the mice had been given, the less fear they showed.

Giving the mice the injection before returning them to the box did not reduce their fear when they were tested again a day later. But when the injections were given over four days, whether before or after their second visit to the box, their fear was reduced one day later.

The researchers believe the effect is due to a mechanism called extinction, in which the release of corticosterone causes a memory to gradually diminish.

"Corticosterone appears to enhance new memories that compete with the fearful memory thereby decreasing its negative emotional significance," study author Craig Powell, a professor of neurology and psychiatry at UT Southwestern, said in a prepared statement.

"The natural release of stress hormones during recall of a fearful memory may be a natural mechanism to decrease the negative emotional aspects of the memory," study co-author Jacqueline Blundell, a postdoctoral fellow in neurology at UT Southwestern, added in a prepared statement.

"Conversely, patients with post-traumatic stress disorder have blunted stress hormone responses and thus may not decrease fearful memories normally over time," Blundell said.

Another UT Southwestern study is in progress to see if receiving a stress hormone while reliving memories can reduce fear responses in veterans suffering from post-traumatic stress disorder.

More information

The American Academy of Family Physicians has more about post-traumatic stress disorder.