ST. LOUIS - A substantial reduction in serotonin, the frontal lobe binding neurotransmitter that regulates impulsive behavior, could be linked to suicidal actions, according to a Belgian study. Using a highly specific radio-iodinated receptor antagonist and SPECT, the group from Ghent University studied the 5-HT-2A serotonin receptor system in attempted-suicide patients.
"The involvement of serotonin in suicide has been the target of considerable research in the past decades," said presenter Dr. Koenraad Van Laere at the Society of Nuclear Medicine meeting on June 7. However, many of these studies had to rely on suboptimal data, such as post-mortem research, when there is a limited amount of serotonin left to sample in the brain, he explained.
"SPECT and PET have made it possible to study the receptor in vivo in patients with mood disorders," he added.
The low activity of serotonin in the brain can lead to aggressive behavior, impulsiveness, insensitivity to future consequences, and most dramatically, attempted suicide, according to the Society for Neuroscience.
In this study sample, nine patients, ranging from age 18 to 60 and who had tried to kill themselves within a one-week period, received 185 MBq of the radio-iodinated receptor antagonist I-5-I-R91150, or 4-amino-N-[1-[3-(4-fluorophenoxy)propyl]-4-methyl-4-piperidinyl]-5-iodo-2-methoxybenzamide.
The group suffered from a variety of psychological disorders, ranging from depression to non-specific psychosis. Patients who had undergone electrotherapy, been placed on a lithium regimen, or had other kinds of treatment six months prior to the suicide attempt were excluded from the study, Van Laere said.
A control group of a dozen healthy patients also received the SPECT ligand. Individuals in the study group were scanned three days after a suicide attempt with a triple-head Toshiba GCA9300 camera with SHR fan-beam collimators and sequential transmission CT. The same scanning protocol was used on the volunteer control group.
In addition, the SPECT results were correlated with the Temperament and Character Inventory (TCI), a psycho-biological personality test that evaluates such traits as recklessness, competence, and feelings of hopelessness. The study group consisted of six deliberate self-poisoners and three deliberate self-injurers, Van Laere said.
The 5-HT-2A binding potential was expressed as the ratio of specific to non-specific activity, with the cerebellum used as a measure for the latter, he said. In a separate SNM poster presentation, researchers from the Institute of Psychiatry in London determined that the "very little specific binding in the cerebellum...[makes] it a suitable reference tissue...[and removes] subjective inaccuracies generally associated with equilibrium analysis."
According to the Ghent results, attempted suicide patients had a marked reduction in binding potential in the frontal lobe compared to the control group, with a p value of 0.002. The reduction was particularly pronounced (p < 0.001) among patients who turned to self-injury such as wrist slashing or strangulation.
A higher binding potential was associated with a better outcome on the TCI test, such as the desire to avoid harm and a greater aptitude for self-direction, he said.
Van Laere concluded that further tests on a larger population would be necessary. Knowing more about how the 5-HT-2A operates could determine the exact efficacy of drugs that regulate serotonin, particularly in preventing recurrent suicide attempts, he added.
By Shalmali Pal
AuntMinnie.com staff writer
June 8, 2000
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