Stress is a killer—at least for brain cells. A new animal study shows that a single socially stressful situation can destroy newly created neurons in the hippocampus, the brain region involved in memory and emotion.

Although most of the brain stops growing by adulthood, new nerve cells are continually generated in the hippocampus, where they are essential for learning. Scientists have long known that chronic stress can inhibit this neurogenesis and lead to depression. Daniel Peterson and his colleagues at the Rosalind Franklin University of Medicine and Science wanted to find out how the brain reacted to just a single stressful episode.

The team placed a young adult rat into a cage with two older rats that quickly began to
attack the newcomer. When they removed the younger animal 20 minutes later, the researchers found that its stress hormone levels were six times as high as those of other rats that had not experienced the terrifying encounter. Examining the young rat’s brain, they saw that it had produced as many new neurons as its unstressed counterparts. Yet when they repeated the experiment with different rats and examined their brains after a week, only a third of newly generated cells had survived.

The finding that a single stressful event can have an impact on the survival of newborn neurons could lead to new depression treatments for humans, Peterson says. “It may
become possible to prevent that loss because we have found that little window of time to intervene.”