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Opioid connection?

Posted by SLS on May 23, 2002, at 7:40:36

From Medscape / Reuters:


Low Mu-Opioid Receptor Binding Linked to Response to Emotional Stimulus

NEW YORK (Reuters Health) May 14 - New research suggests that low levels of mu-opioid receptor binding in the limbic system are associated with a stronger than normal response to emotional stimulation.
According to investigators from the University of Michigan at Ann Arbor, this finding may explain the mechanism underlying such psychiatric conditions as posttraumatic stress disorder (PTSD) and depression, and could lead to new pharmacologic approaches to treat these disorders.

Dr. Israel Liberzon and colleagues describe in the May 14th issue of the Proceedings of the National Academy of Sciences a "marriage" of two techniques, both using positron emission tomography. To estimate regional cerebral blood flow, they assessed emission scans after intravenous injection of radioactive water. For mu-opioid receptor binding, they injected the radioactive ligand carfentanil and measured its uptake.

Dr. Liberzon's group first measured regional blood flow in 12 healthy male volunteers. They then measured mu-opioid receptor binding as the men were shown images from the standardized international affective picture system. These included aversive images, such as facial mutation, wounds, and dead bodies, while neutral images included faces with neutral expressions and benign scenes. Blank images consisted of a fixation mark on a field of gray.

There was a significant negative correlation between mu-opioid receptor availability in the inferior temporal pole at baseline and cerebral blood flow during the aversive and the nonaversive stimuli.

"This methodology delineates potential neurochemical mechanisms involved in the regulation of mood and activation of regions in the brain," Dr. Liberzon told Reuters Health. "Studying these mechanisms will be important in understanding how dysregulation of emotional responses can occur in psychiatric disorders."

He noted that "we find abnormal activity in PTSD in the same brain region in which we find this relationship between the mu-opioid system and activation in response to emotional stimuli." He speculated that PTSD might also involve abnormalities in the mu-opioid system.

Proc Natl Acad Sci USA 2002;99:7084-7089.


Receptors May Blunt Response to Disturbing Images
Last Updated: May 14, 2002 10:29 AM ET
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NEW YORK (Reuters Health) - New research suggests that levels of a particular brain receptor may influence the brain's response to unpleasant images.

People with low levels of the receptor, known as the mu-opioid receptor, tend to react more strongly to unpleasant images, according to researchers from the University of Michigan at Ann Arbor. The discovery could help explain some of the mechanisms of post-traumatic stress disorder, Dr. Israel Liberzon and colleagues suggest in the May 14th issue of the journal Proceedings of the National Academy of Sciences.

Mu-opioid receptors are present in a part of the brain called the limbic system. Among other things, the limbic system affects motivation and mood.

In previous research, Liberzon's team had uncovered evidence that a brain region called the amygdala, which is part of the limbic system, is involved in emotional responses including fear and disgust. Normally, mu-opioid receptors respond to the body's natural painkillers, called endorphins, or drugs such as morphine and heroin.

In experiments with 12 men, the researchers used an imaging test called a PET scan to investigate the relationship between mu-opioid receptors and limbic activity. The participants underwent one scan to measure their level of receptors, and then a second scan to measure brain activity while they viewed unpleasant and neutral images.

In all of the men, the limbic system became more active while they were looking at unpleasant images. The reaction to disturbing images was greatest in men who had the lowest levels of mu-opioid receptors.

The findings suggest that mu-opioid receptors play a role in inhibiting the brain's response to things that trigger an unpleasant emotional response. The connection between mu-opioid receptors and the response to unpleasant images "has direct relevance to psychiatric conditions, such as post-traumatic stress disorder (PTSD) or depression," Liberzon and colleagues report.

They note that at least two studies have suggested that PTSD patients have abnormalities in the limbic system. The present study may help explain how these abnormalities occur, as well as point the way toward new approaches for treating the disorder, the authors conclude.

SOURCE: Proceedings of the National Academy of Sciences 2002;99:7084-




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