These results are somewhat counter-intuitive because normally, vasopressin facilitates aggression and serotonin inhibits it. In these hamsters, however, the balance of the two neurotransmitters is upset, for reasons as yet unknown, and causes unusual behavior in a specific context, he believes. The hamsters behave no differently than nontraumatized hamsters until they're threatened. Part of the difference between his hamsters and the low serotonin monkeys is the hamsters' lack of impulsivity, which indicates the complex nature of the neurotransmitter system, he added. Ferris suspects that any changes in the serotonin system lower an animal's threshold for handling stress.
Environmental triggers can then stimulate behaviors.
This is similar to mental illness, where symptoms seem to worsen when patients are under stress from their environments, said Ferris. A similar cascade seems to occur in suicidal people, according to J. John Mann, PhD, of Columbia University and the New York State Psychiatric Institute. People who commit suicide almost always have some form of mental illness, studies find. But mental illness alone doesn't provoke people to kill themselves, and the severity of a person's illness does not increase the likelihood of an attempt, studies find. Instead, people who commit suicide tend to be impulsive, aggressive and less able to handle the pain of their mental illness.