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Published online: 16 October 2006; | doi:10.1038/news061016-1 Suicidal behaviour linked to serotonin receptors.
Depression: a condition in its own right? Corbis
There is growing evidence that suicidal behaviour is a condition is its own right and not just a consequence of other psychiatric disorders, say brain researchers.
People who commit suicide show distinct changes in their brain that are independent of any mental illness they may be suffering from, according to studies presented on 15 October at the annual meeting of the Society for Neuroscience in Atlanta, Georgia. Such work could lead to new tests for suicide risk, say some of those behind the research.
They speculate it may also help to explain why a small minority of patients on SSRIs, a common form of anti-depressant that boosts serotonin levels, are more likely to commit suicide.
“There is an assumption that people get depressed, get depressed, get depressed….and then finally end it,” says Mihran Bakalian of the New York State Psychiatric Institute. “But that is not borne out by the biochemical or psychiatric studies.” Bakalian says the idea is becoming firmly established among groups such as his that study suicide, but has yet to filter down to many medical doctors.
Data from researchers such as Stella Dracheva, who is based at the Bronx Veterans Affairs Medical Center in New York, are beginning to change that.
Dracheva and her colleagues examined cell-surface receptors for serotonin, a substance known to be linked to depression, in the brains of 22 people who had committed suicide and 82 who had died by other means.
The serotonin receptor they studied 5-HT2C is unusual in that it comes in 24 different forms. Dracheva found that in one area of the dorsolateral prefrontal cortex, a brain region involved in high-level functions such as planning, one of these forms was present in higher levels in the suicide cases regardless of which psychiatric condition the person had been suffering from, if any at all. Although most suicides happen among those with conditions such as bipolar disorder, depression or schizophrenia, a small number happens among people simply under stress.
Although they don’t know for sure that these brain changes are a cause rather than an effect of suicide, the work suggests that some people are at higher risk of committing suicide due a difference in their brain structure or chemistry, Dracheva says.
Bakalian thinks that the difference is most likely to lie in the systems that modulate aggression. Psychiatric studies have frequently linked aggression with suicide, and it may be that people who take their own lives are unable to reign in aggressive urges towards themselves.
In a study also presented in Atlanta, Bakalian found that suicide victims had a lower density of serotonin receptors in their amygdala, a brain region involved in controlled aggression and other emotions, than those who died by other means.
Bakalian says that psychiatrists should be made more aware of these results. But he adds that there is little they could do at present, because there is as yet no better way to focus treatment.
Dracheva’s work suggests that a test for types of serotonin receptor might be useful to identify those most at risk.
She adds that in some cases it might be better for psychiatrists not to prescribe SSRIs. Data from animals suggest that SSRIs can increase the number of serotonin receptors now linked to suicide. That could be why a small minority of patients are more likely to commit suicide once on this medication, Dracheva speculates.