Chronic stress in early life linked to anxiety, aggression in adulthood

Researchers have suggested that chronic stress in early life causes anxiety, aggression in adulthood.

A research team led by Associate Professor Grigori Enikolopov of Cold Spring Harbor Laboratory (CSHL) conducted experiments designed to assess the impacts of social stress upon adolescent mice, both at the time they are experienced and during adulthood.

The tests began with 1-month-old male mice – the equivalent, in human terms of adolescents - each placed for 2 weeks in a cage shared with an aggressive adult male.

The animals were separated by a transparent perforated partition, but the young males were exposed daily to short attacks by the adult males. This kind of chronic activity produces what neurobiologists call social-defeat stress in the young mice. These mice were then studied in a range of behavioral tests.

These experiments showed that in young mice chronic social defeat induced high levels of anxiety helplessness, diminished social interaction, and diminished ability to communicate with other young animals. Stressed mice also had less new nerve-cell growth (neurogenesis) in a portion of the hippocampus known to be affected in depression: the subgranular zone of the dentate gyrus.

Another group of young mice was also exposed to social stress, but was then placed for several weeks in an unstressful environment. Following this "rest" period, these mice, now old enough to be considered adults, were tested in the same manner as the other cohort.

In this second, now-adult group, most of the behaviors impacted by social defeat returned to normal, as did neurogenesis, which retuned to a level seen in healthy controls. "This shows that young mice, exposed to adult aggressors, were largely resilient biologically and behaviorally," says Dr. Enikolopov.

However, in these resilient mice, the team measured two latent impacts on behavior. As adults they were abnormally anxious, and were observed to be more aggressive in their social interactions.

The study has been published online in the journal PLOS ONE.