Serotonin
Over the past 30 years scientists have discovered that brain neurochemistry may have an important role to play in the risk for and expression of suicidal behavior. In the mid-1970’s it was discovered that patients who completed suicide had lower brain levels of the neurotransmitter serotonin, and also had lower levels of the breakdown product of serotonin called 5 hydroxyindole acetic acid (5-HIAA) which is found in cerebrospinal fluid (CSF). In the early 1980’s alterations were found in serotonin receptors in frontal brain areas of suicide victims. These frontal brain areas were known to be associated with the regulation of mood and also with modulating behavioral restraint. Studies in the mid-90’s using brain imaging technology found that similar serotonin abnormalities were found in live patients who had made severe suicide attempts. In summary, serotonin contributes to the regulation of mood and also behavioral restraint, and patients who express suicidal behavior including suicide have lower brain levels of serotonin and reduced serotonin responsivity. It is postulated therefore that patients in suicidal crisis will require behavioral restraint to suppress the urge to act on the suicidal impulses, and that brain serotonin function may be an important modulator of behavioral activity as to whether or not a suicidal act is completed as opposed to contemplated.
What influences serotonin function
Age and Sex
In the general population it is established that men have significantly lower function than women, and that serotonin function declines with age. Serotonin function fluctuates across the menstrual cycle and may be affected by estrogen levels, as serotonin responsivity is lowest in the luteal phase when estrogen is lowest. Several other factors may influence serotonin function.
Seasons
There are seasonal fluctuations, being lowest in Fall and late Spring.
Dietary factors
Serotonin responsivity may also be affected by diet. Diets high in cholesterol lead to higher levels of serotonin function. Serotonin levels may be artificially lowered in the research laboratory using a technique called tryptophan depletion. Serotonin is manufactured in the body from tryptophan, and essential amino-acid the must be taken in the diet. Tryptophan is taken up into the brain, but must compete with other essential amino-acids for its brain uptake. A brief diet without tryptophan but rich in other essential amino-acids leads to a transient brain tryptophan depletion which in turn causes a transient drop of up to 80% in brain serotonin levels. In research experiments with healthy controls blind to the dietary condition, many controls experienced transient depressive symptoms while undergoing the tryptophan depletion experiment compared with a control diet. In depressed patients some patients experienced a transient increase in their depressive symptoms, and in patients who had recovered from their depressive episode, the tryptophan depletion experiment caused a transient (6 hour) relapse. These experiments serve to demonstrate the significant mood and behavioral effects associated with even brief fluctuations in brain serotonin levels, and suggest further research should investigate other possible ways in which serotonin levels may be compromised such as following alcohol intake.
Stress and Cortisol
Studies with laboratory animals have suggested that stress early in life causes lower serotonin function in later adulthood. It is suggested that this may be mediated through chronic cortisol levels (stress hormone) released during the stress may influence the pathways to full development of a healthy serotonin system.
Genetics
Serotonin levels seem to be under significant genetic regulation, which may explain at least in part the biologic mode of transfer of suicide risk across generations.
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