Suicide brains: naturally prone to pain?

Suicide brains: Naturally to pain?

Brain cells that mediate the perception of pleasure and pain in suicide victims differ markedly from the same cells in people who die of natural causes, a new study indicates. The finidngs support a hypothesis linking suicidal behavior with specific biochemical abnormalities in the brain.

Previous work showed that the brains of clinically depressed or suicidal individuals harbor abnormal levels of the brain chemicals serotonin and norepinephrine (SN: 10/14/89, p.248). The new work, by Ruth Gross-Isserof of the Weizmann Institute of Science in Rehovot, Israel, and Anat Biegon of the New York University School of Medicine in New York City, is the first to look at opioid receptors in suicide victims' brains. Opioid receptors reside on the surface of some brain cells and sop up tiny amounts of opium-like chemicals produced in the brain. They play critical roles in the sensations of well-being and physical and mental suffering.

The researchers mesured opioid-receptor concentrations in 12 drug-free and disease-free suicide victims presumed to have been depressed before death. They found a 100 to 800 percent increase in the concentration of mu receptors (a type of opioid receptor) and a 50 percent decrease in another opioid receptor type called delta, compared with concentrations of those receptors in 12 people who had died of other causes.

Scientists know little about opioid-receptor types or the specific brain opioids to which each type responds, but the findings appear "very interesting," says David A. Baron, deputy clinical director of intramural research at the National Institute of Mental Health. "It makes good sense that there would be or should be an abnormality in the opioid system. You often hear from suicide patients that 'I couldn't take the pain anymore,' referring to physical or emotional pain," he says.

Indeed, Biegon adds, "we know people suffering from depression have a very high incidence of chronic pain. This may indicate a defect in the opioid system." Similarly, she says, "the essence of depression is anhedonia -- an inability to experience pleasure. And opioid receptors are the primary targets of the brain's reward system."

Biegon says her study cannot answer the question of what causes the altered receptor concentrations in suicide victims' brains. Animal experiments indicate that opioid-receptor concentrations often increase in resonse to a lack of opioids, but environmental and genetic factors may affect receptor levels directly, she says. In upcoming experiments, Biegon hopes to use traceable antibodies directed against opioid proteins to directly measure opioid concentrations in brains of live people with and without depression.

For now, she concludes, "I wouldn't say that changes in the opioid system cause depression. But it's very possible that they contribute to the syndrome."

Biegon presented the new findings in St. Louis last week at the annual meeting of the Society for Neuroscience. Details will appear in an upcoming issue of BRAIN RESEARCH.