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Brain's Painkiller System Seen in Action

A study that looked at chemical activity in the brains of human volunteers while they experienced sustained pain and reported how they felt is providing new insights into the importance of the body's natural painkiller system — and the reasons why each of us experiences pain differently.

The results confirm long-suspected connections between pain-dampening changes in brain chemistry and the senses and emotions experienced by people in pain. The findings may help researchers better understand prolonged pain and find more effective ways to relieve it.

Results from the brain imaging study were published in the July 13 issue of Science by NIDCR-supported researchers from the University of Michigan Health System and School of Dentistry. It is the first study to combine sustained, induced pain with simultaneous brain scan monitoring of a key neurochemical system and the self-reported pain ratings of human participants.

The research cements the critical role of the mu opioid system, in which naturally produced chemicals called endogenous opioids, or endorphins, match up with receptors on the surface of brain cells and reduce or block the spread of pain messages from the body through the brain. The mu opioid receptor in particular has been found to be a major target for both the body's own painkillers, as well as for drugs such as heroin, morphine, methadone, synthetic pain medications and anesthetics, which also numb pain.

The study found that the onset and slow release of jaw muscle pain — induced by the injection of high-concentration salt water directly into each volunteer's jaw muscle, which mimics the chronic condition of temporomandibular joint disorder — over 20 minutes caused a surge in the release of the chemicals. It also found that the flood of those chemicals coincided with a reduction in the amount of pain and pain-related emotions the volunteers said they felt. Specific brain regions, especially those already known to play a role in affective, or emotional, responses, and those known to help process signals from the body's sensory systems, had the biggest increase in the level of opioids when pain was introduced. The research also revealed major variation among volunteers in the baseline and pain-induced levels of opioids.


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