Scientists subjected mice to 10 straight days of such bullying and found that the defeated mice avoided bullies even four weeks after their initial beating.
In fact, they were so traumatized that they avoided all other mice as well—even those that were smaller and more docile.
"For both mice and men, social status is important; for mice, losing to a dominant mouse usually means that they avoid the dominant and they avoid social situations," said Thomas Insel of the National Institute of Mental Health.
When researchers gave the mice the human antidepressant drugs Prozac or Tofranil, social interaction improved. The treatment resembled that for depressed humans, said the study's senior author Eric Nestler of the University of Texas Southwestern Medical Center.