University of Manchester researchers found that the pain threshold of patients with arthritis can increase with alterations in their brain chemistry. The study, “Striatal opioid receptor availability is related to acute and chronic pain perception in arthritis: does opioid adaptation increase resilience to chronic pain?” was published in the journal Pain.
The brain is known to have receptors that respond to natural pain-killing opiates such as endorphins. Researchers now have shown these receptors increase in number to help cope with long-term, severe pain.
To find evidence for the relationship between chronic pain and opioid receptors (OpR), Christopher Brown and colleagues used positron emission tomography and the radiotracer C-diprenorphine to scan 17 patients with arthritis pain and nine healthy controls. All study participants underwent whole-brain positron emission tomography scanning to examine OpR availability.
The results revealed that among the patients with arthritis, more OpR availability was found in the striatum of patients who reported higher levels of recent chronic pain. This means that endorphins act as biological painkillers, but the opioid receptors can rise over time to both reduce and help patients cope with long-term and severe pain.
Researchers think that increasing opioid receptors in the brain is an adapted response to chronic pain. “As far as we are aware, this is the first time that these changes have been associated with increased resilience to pain and shown to be adaptive,” Dr. Brown, the lead investigator, said in a news release. “Although the mechanisms of these adaptive changes are unknown, if we can understand how we can enhance them, we may find ways of naturally increasing resilience to pain without the side effects associated with many pain killing drugs.”
The team also found that patients with arthritis pain had less OpR availability within the striatum, particularly compared with healthy controls, coherent with the greater endogenous opioid binding that would be expected in chronic pain states.
“This is very exciting because it changes the way we think about chronic pain,” said a study author, Professor Anthony Jones. “There is generally a rather negative and fatalistic view of chronic pain. This study shows that although the group as a whole are more physiologically vulnerable, the whole pain system is very flexible and that individuals can adaptively up-regulate their resilience to pain. It may be that some simple interventions can further enhance this natural process, and designing smart molecules or simple non drug interventions to do a similar thing is potentially attractive.”
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