MAY 27, 2018 1:15 PM PDT

Why Opioids Can't Always Reduce Chronic Pain

WRITTEN BY: Carmen Leitch

While opioids have been in use in North America since at least the time of the Civil War, we still don’t know everything about how they work. New research has indicated that chronic pain alters receptors in the brain that attach to opioids. This alteration may reduce the effectiveness of opioids. The study also provided insight into how opioids can cause depression. The work, by a team of scientists at the National Institutes of Health (NIH) and McGill University, Montreal, was reported in the journal Pain.

“We know that people with chronic pain have reduced availability of opioid receptors — the molecules opioid drugs bind to — in the brain,” said study co-author Mark Pitcher, Ph.D., a visiting fellow in the Division of Intramural Research at the National Center for Complementary and Integrative Health (NCCIH). “What we haven’t known, until now, is why. Are there preexisting brain differences that might predispose some people to develop chronic pain? Or might chronic pain cause these differences? Our findings suggest that chronic pain itself is responsible.”

An imaging technique that allows researchers to see disease or injury, positron emission tomography (PET), was performed on cross-sections of rat brains. The scientists had mimicked chronic pain by making a surgical nerve injury on one group of those rats; another group was a control that had a surgery that did not cause injury. The scientists found that within three months, opioid receptor availability had gone down in several parts of the brain in the rats with the chronic pain injury; the other group was unaffected.

Other experiments explored the link between depression and chronic pain. Typically, rats will drink sugar water instead of regular water if given the option. When such animals have a symptom of depression called anhedonia, a reduced experience of pleasure, their interest in the sugar water decreases. In this work, after the injury, the rats experiencing chronic pain also had a reduced interest in the sugar water. These animals demonstrated a link between the availability of opioid receptors and their interest in sugar water.

Credit: Pxhere

“It’s well known that there’s a link between chronic pain and depression. The results of this study indicate that pain-induced changes in the brain’s opioid system may play a role in this association. Animals with the greatest decrease in opioid receptor availability showed the greatest increase in depression-like symptoms after experiencing chronic pain,” explained study co-author M. Catherine Bushnell, Ph.D., scientific director of NCCIH’s Division of Intramural Research. 

“These results provide insights into why we see limited effectiveness of opioid therapy in chronic pain and the mechanism of the depression that may accompany it,” said NCCIH Acting Director Dr. David Shurtleff. “These basic research findings support NIH’s efforts to better understand chronic pain and comorbid symptoms and to develop better ways to help chronic pain patients effectively manage their pain.”

Studies in humans will, of course, be needed to confirm that people experience the same effects. Chronic pain is known to cause neurological changes, however.


Sources: NIH, American Battlefield Trust, Scientific Reports, Physiology & BehaviorPain

About the Author
  • Experienced research scientist and technical expert with authorships on over 30 peer-reviewed publications, traveler to over 70 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
MAR 01, 2021
Microbiology
New Therapeutic Potential for a 'Miracle Poison'
MAR 01, 2021
New Therapeutic Potential for a 'Miracle Poison'
Most people know botulism as a nasty disease and botox as a wrinkle reducer that may cause a 'frozen' look if it's overu ...
MAR 03, 2021
Microbiology
Study May Explain Higher Flu Risk in Adults That Were Premature Babies
MAR 03, 2021
Study May Explain Higher Flu Risk in Adults That Were Premature Babies
Medical treatments for the care of premature babies have allowed many individuals to get through that challenge and lead ...
MAR 08, 2021
Microbiology
Researchers Discover a New Symbiosis
MAR 08, 2021
Researchers Discover a New Symbiosis
A new type of endosymbiosis has been discovered; the organisms are shown in this image by S. Ahmerkamp, Max Planck Insti ...
MAR 19, 2021
Cell & Molecular Biology
These Cells Can Cry Tears
MAR 19, 2021
These Cells Can Cry Tears
Reporting in Cell Stem Cell, scientists have engineered miniature versions of human tear glands that actually emit tears ...
APR 05, 2021
Neuroscience
Could a Keto Diet Treat Alzheimer's Disease?
APR 05, 2021
Could a Keto Diet Treat Alzheimer's Disease?
  Researchers from Brigham Young University have found evidence that eating a ketogenic diet- which is a diet that ...
APR 06, 2021
Microbiology
A Bacterial Protein That Causes Nausea
APR 06, 2021
A Bacterial Protein That Causes Nausea
The bacterium Campylobacter is thought to cause more cases of food poisoning than any other microbial pathogen. Scientis ...
Loading Comments...