"We have discovered a mechanism for how environmental factors, such as stress hormones, can affect the brain's physiology and bring about mental illness," says study leader Akira Sawa, M.D., Ph.D., 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."
Sawa, director of the Johns Hopkins Schizophrenia Center, and his team set out to simulate social isolation associated with the difficult years of adolescents in human teens. They found that isolating healthy mice from other mice for three weeks during the equivalent of rodent adolescence had no effect on their behavior. But, when mice known to have a genetic predisposition to characteristics of mental illness were similarly isolated, they exhibited behaviors associated with mental illness, such as hyperactivity. They also failed to swim when put in a pool, an indirect correlate of human depression. When the isolated mice with genetic risk factors for mental illness were returned to group housing with other mice, they continued to exhibit these abnormal behaviors, a finding that suggests the effects of isolation lasted into the equivalent of adulthood.