But simply having low levels of serotonin is insufficient as a
predictor.
"It has more to do with the predisposition to suicide than
to generating suicidal behavior," said Mann. "Serotonin
is detectable and independent of timing. So by evaluating the
function of the serotonin system, we can identify who is vulnerable
and plan more specific pharmacological intervention."
Mann said serotonin indexes which have been employed in the lab
include the cerebrospinal fluid level of 5-hydroxyindoleacetic
acid, prolactin response to serotonin agonists-such as fenfluramine
hydrochloride (Pondimin)-and platelet serotonin-related proteins
or serotonin content (Mann and others, 1992).
Said Mann, "Three different measures of serotonin function-completely
unrelated approaches-all show the same thing, mainly a deficiency
in patients with a history for more lethal suicide attempts."
Now, Mann and his group are looking at imaging of serotonin responses
in the brains of patients, using positron emission tomography
(PET).
Deficiency Factors
So what causes serotonin deficiency?
"Genetics are an important area, but there are some environmental
factors that increase or decrease serotonergic activity,"
he said, listing factors such as genetics, diet, drugs
and alcohol, gender and age.
For instance, lowering and raising cholesterol levels in monkeys
significantly lowers and raises serotonin activity. So although
lowering levels in humans does reduce heart attacks, it may raise
the risk of dying from other causes, including suicide.
