A new study has found a link between a stress-induced hormone in adolescence and genetic changes that can cause severe mental illness. The study, published recently in the journal Science, could lead to new treatments for schizophrenia, severe depression, or other mental illnesses.
"We have discovered a mechanism for how environmental factors, such as stress hormones, can affect the brain's physiology and bring about mental illness," said Dr. Akira Sawa, lead author of the study and a professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine. "We've shown in mice that stress in adolescence can affect the expression of a gene that codes for a key neurotransmitter related to mental function and psychiatric illness. While many genes are believed to be involved in the development of mental illness, my gut feeling is environmental factors are critically important to the process."
Researchers used mice to simulate social isolation during human adolescence. Mice were isolated from others during their three-week equivalent of adolescence. Though the behavior of healthy mice did not change, those with a genetic predisposition for mental illness began exhibiting behaviors associated with rodent mental illness, such as hyperactivity. They also failed to swim in water, which the researchers correlate with human depression. When the mentally ill mice were placed back with other mice they continued to display their abnormal behaviors.
"Genetic risk factors in these experiments were necessary, but not sufficient, to cause behaviors associated with mental illness in mice," said Sawa. "Only the addition of the external stressor - in this case, excess cortisol related to social isolation - was enough to bring about dramatic behavior changes."
In addition to raised cortisol levels, researchers also found the mice had lower levels of dopamine in brain regions involved in emotional control and cognition. Similar changes in dopamine have been found in patients with schizophrenia, depression, and mood disorders.