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.
The study, done in mice by researchers at the University of Illinois at Chicago College of Medicine, is reported in this week's online addition of the Proceedings of the National Academy of Sciences.
"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 looked in these types of neurons for changes in the levels of two enzymes that are needed for the production of allopregnanolone, a brain hormone that acts to reduce stress through regulation of GABA, an important neurotransmitter. They found that the level of one of the enzymes, called 5-alpha-reductase type I, was reduced nearly 50 percent in the lonesome mice. Levels of the other enzyme did not change.
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.