CHICAGO » Rats genetically bred to be depressed improved greatly after spending a month in a stimulating “playground” with toys and hiding places, Northwestern University researchers reported.

The study, published this week in the Translational Psychiatry journal, set out to determine whether a fun environment would decrease depression or a stressful environment would increase depression, said lead study investigator Eva Redei, professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine.

The study found that rats genetically bred to be depressed saw a “dramatic” reduction in depressionlike behavior after undergoing rat psychotherapy: spending one month in a “playground” — large cages where they could play with toys, climb and hide, Redei said.

“I thought that yes, maybe they would show some reduction, but not as dramatic as what we showed,” Redei said. If the rats were human, she said they would no longer be considered clinically depressed.

After spending time in the playful environment, the rats were put into a tank of water for a swim test that measures depression. The rats swam, trying to escape, a signal of hope, not depression.

Depression in humans may be caused by factors including genetics, biology and environment, according to the National Institute of Mental Health, part of the National Institutes of Health.

The study could be reassuring to humans — particularly families with a history of depression and fear they will pass it on to their children, Redei said. “It showed in this very well-controlled environment, nurture can — I wouldn’t say override nature — but it can modify nature so genes are not the overall destiny,” Redei said.

The finding makes sense from several perspectives and is consistent with what’s seen in humans, said Dr. Eric Nestler, professor of neuroscience at Mount Sinai School of Medicine in New York City and member of the Hope for Depression Research Foundation’s depression task force.

“We know that people with more mild cases of depression can do very well with different forms of behavioral treatment,” he said. “There’s more and more evidence that a routine of exercise can also be very helpful for people who are depressed.”

The combined use of cognitive behavioral therapy and medication is better at treating depression than either one separately, he said.

Although the same experiment is not done in humans — unless they hang out in a jungle gym for a month — there’s something to be said about the emphasis on adult play time and workplaces infused with game rooms. Being genetically vulnerable to depression, socially isolated and too stressed at work and working at a place that doesn’t allow for enough social time or interaction with people can increase the risk of a person getting a “depression syndrome,” he said.

“There is good evidence to suggest that people who are less isolated and more engaged in social networks, family, friends, religious groups and other social groups do better, and that can help people who have more of a mild case of depression, that can help them lift from the depression,” Nestler said.

Another part of the study explored whether a stressful environment could trigger depression in rats not bred to be depressed. Those rats were put under psychological stress and restrained for two hours a day for two weeks so they could breathe but not move, Redei said. The rats then were subjected to the swim test in a tank of water. They floated, which was a sign they gave up hope on escaping and showed depressionlike behavior, according to the researchers.

The results were not particularly surprising because stress is known to precipitate depression in humans, she said.

Redei previously published research about how she developed blood tests to diagnose depression in adults and adolescents. She tested the blood of the rats in the study exposed to the stressful environment and the playground’s nurturing environment. There were different blood markers that changed their levels indicating whether the depression was genetic versus induced, a finding that could lead to a way of distinguishing in humans whether their depression is primarily because they have a genetic predisposition or due to a stressful environment, she said.

Differentiating between genetic and environmental influences on depression could lead to a more personalized treatment, whether it is antidepressant medication or psychotherapy, Redei said.

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