Any bully’s victim knows the experience can cause lingering fear. Now scientists watching big mice intimidate small ones have discovered the stress spurs genetic changes in the brain a finding that may help research into depression and other mental illnesses.
The experiment suggests a part of the brain linked to addiction also plays a previously unsuspected role in illnesses characterized by chronic anxiety and social withdrawal, Texas researchers reported on Thursday in the journal Science. In fact, a substance produced in the brain, called BDNF, seems to be the culprit, controlling whether the bullied mice turned into fearful hermits or not.
The Texas researchers subjected some small brown mice to intimidation more intense than they’d face in the wild: Each was placed for five minutes in the cage of a particularly aggressive, large white mouse, who battled the little one into a corner.
Then, researchers divided the cage with a perforated, plexiglass divider for 24 hours so the little mouse was in no physical danger, but saw and smelled the aggressor. For 10 days, each little mouse met a new bully.
The bullied mice emerged drastically cowed. Four weeks later, they still fearfully withdrew from even presumably friendly little mice.
