Humans are social beings by nature. Social isolation in humans has been connected to various mental and physical conditions. A new research carried on lab mice at the University of Illinois at Chicago College of Medicine and published in the Proceedings of the National Academy of Sciences has connected the anxiety and aggressiveness induced by social isolation to impaired amounts of an enzyme that tunes the synthesis 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 co-author Dr. Erminio Costa, director of the UIC Psychiatric Institute, professor of biochemistry.

Other researches had pointed out the fact that the neural pathways inducing aggression, anxiety and fear were linked to the activation of specific types of neural circuitry linked to the amygdala, an almond-shaped brain nucleus connected with the inducing of emotions.
The scientists focused on these brain cells for variation in the amounts of two enzymes synthesizing allopregnanolone, a brain hormone that tunes brain stress levels by controlling gamma aminobutyric acid (GABA), an essential neurotransmitter. Solitary mice had the levels of 5-alpha-reductase type I, one of these two enzymes, decreased by half, while the levels of the other enzyme were constant.

This was enough to plummet the allopregnanolone's production, impairing the GABA- amygdala interactions, boosting the anxiety-related aggressive behavior in socially isolated mice. "Humans respond to similar stress in very similar ways. By identifying the mechanism we may be able to identify drugs that can treat these effects of stress," said Dr. Alessandro Guidotti, UIC scientific director and professor of biochemistry in psychiatry.

GABA receptors has been connected by various researches to nicotine dependence in tobacco smoking. Haloperidol, a common antipsychotic chemical used in emergency rooms against methamphetamine overdose, kills brain cells in combination with the drug in those brain zones involved in regulating movement by overstimulating the synthesis of GABA.