Neurobiologists find chronic stress in early life causes anxiety, aggression in adulthood

In experiments to assess the impacts of social stress upon adolescent mice, both at the time they are experienced and during adulthood, a Cold Spring Harbor Laboratory team conducted many different kinds of stress tests and means of measuring their impacts. The research indicates that a 'hostile environment in adolescence disturbs psychoemotional state and social behaviors of animals in adult life,' the team says.

In recent years, behavioral neuroscientists have debated the meaning and significance of a plethora of independently conducted experiments seeking to establish the impact of chronic, early-life upon behavior – both at the time that stress is experienced, and upon the same individuals later in life, during adulthood.

These experiments, typically conducted in rodents, have on the one hand clearly indicated a link between certain kinds of early stress and dysfunction in the neuroendocrine system, particularly in the so-called HPA axis (hypothalamic-pituitary-adrenal), which regulates the endocrine glands and stress hormones including corticotropin and glucocorticoid.

Yet the evidence is by no means unequivocal. Stress studies in rodents have also clearly identified a native capacity, stronger in some individuals than others, and seemingly weak or absent in still others, to bounce back from chronic early-life stress. Some rodents subjected to early life stress have no apparent behavioral consequences in adulthood – they are disposed neither to anxiety nor depression, the classic pathologies understood to be induced by stress in certain individuals.

Today, a research team led by Associate Professor Grigori Enikolopov of Cold Spring Harbor Laboratory (CSHL) reports online in the journal PlOS One the results of experiments designed to assess the impacts of upon adolescent mice, both at the time they are experienced and during adulthood. Involving many different kinds of and means of measuring their impacts, the research indicates that a "hostile environment in adolescence disturbs psychoemotional state and social behaviors of animals in adult life," the team says.

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.

"The tests assessed levels of anxiety, depression, and capacity to socialize and communicate with an unfamiliar partner," explains Enikolopov. 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 exposure to a hostile environment during their adolescence had profound consequences in terms of emotional state and the ability to interact with peers," Dr. Enikolopov observes.

More information: "Extended Effect of Chronic Social Defeat Stress in Childhood on Behaviors in Adulthood" appears online in PlOS One Tuesday, March 25, 2014.

add to favorites email to friend print save as pdf

Related Stories

Recommended for you

Brains transform remote threats into anxiety

Nov 21, 2014

Modern life can feel defined by low-level anxiety swirling through society. Continual reports about terrorism and war. A struggle to stay on top of family finances and hold onto jobs. An onslaught of news ...

Mental disorders due to permanent stress

Nov 21, 2014

Activated through permanent stress, immune cells will have a damaging effect on and cause changes to the brain. This may result in mental disorders. The effects of permanent stress on the immune system are studied by the ...

Could there be a bright side to depression?

Nov 21, 2014

(Medical Xpress)—A group of researchers studying the roots of depression has developed a test that leads them closer to the idea that depression may actually be an adaptation meant to help people cope with ...

User comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.