BEIJING, June 29 (Xinhuanet) -- A new study of wheel-running rats reveals exercise not only fights depression, it also helps the brain grow new cells.

Astrid Bjornebekk of the Karolinska Institute in Sweden and her colleagues studied rats that had been genetically altered to exhibit depressive behaviors, plus a second group of control rats. Some of the rats had free access to running wheels for 30 days and others did not.

Then the scientists used a standard "swim test" to find out if running turned depressed rats into cheerful rodents. They measured the amount of time the rats spent immobile in the water and the time they spent swimming around in active mode. When depressed, rats spend most of the time not moving.

"In the depressed rats, running had an antidepressant-like effect after running for 30 days," Bjornebekk told LiveScience.

The researchers also examined the hippocampus region of the brain, involved in learning and memory. Neurons there increased dramatically in the depressed rats after wheel-running.

Past studies have found the human brain's hippocampus shrinks in depressed individuals, a phenomenon thought to cause some of the mental problems often linked with depression.

"The hippocampus formation is one of the regions they have actually seen structural changes in depressed patients," Bjornebekk said.

Running had a similar effect as common antidepressants called selective serotonin reuptake inhibitors (SSRIs) on lifting depression.

The research is published in the International Journal of Neuropsychopharmacology.

(Agencies)