The anxiety and aggression that result from social isolation have been traced to altered levels of an enzyme that controls production of a brain hormone.

"We use this animal model for human stress because social isolation in both animals and humans can be responsible for a range of psychological effects, including anxiety, aggression and memory impairment," said Dr. Erminio Costa, director of the UIC Psychiatric Institute, professor of biochemistry and one of the authors of the study.

Previous studies had suggested that the neural pathways that underlie aggression, anxiety and fear include activation of specific types of neural circuitry that leads into the amygdala, the region of the brain responsible for emotion.

The researchers suggest that the decrease of 5-alpha-reductase type I and the consequent reduction in the hormone may impair the function of circuits leading to the amygdala and explain the aggressive behavior, perhaps related to anxiety, in socially isolated mice.