MAY 27, 2018 01:15 PM PDT
Why Opioids Can't Always Reduce Chronic Pain
WRITTEN BY: Carmen Leitch
2 1 140

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...
You May Also Like
APR 25, 2018
Genetics & Genomics
APR 25, 2018
Advances in Cancer Research Through Organoids
Researchers have been using a new tool in biomedical research to more closely mimic human biology - mini models of human organs, called organoids.
MAY 07, 2018
Immunology
MAY 07, 2018
Breast Milk: An Important Source of Protective Immune Cells
For the first time, scientists have identified innate lymphoid cells (ILCs) among the arsenal of protective cells transferred to newborn babies via breast
MAY 08, 2018
Genetics & Genomics
MAY 08, 2018
A Genetic Assessment of a Drug-resistant Pathogen
Drug resistance is a growing threat to public health and is responsible for the death of around 23,000 people every year in the US alone.
MAY 09, 2018
Cell & Molecular Biology
MAY 09, 2018
Valuable insights into better protein expression
Pharmaceutical companies, biotech, and academia all have a hand in accelerating our understanding of proteins, whether through wide-ranging proteomics stud
MAY 28, 2018
Neuroscience
MAY 28, 2018
How Lab-Grown Brains Advance Research
The human brain has a big job. It runs every system of the body, 24/7/365 and it does so better than any supercomputer on the planet. There is a great deal
JUN 08, 2018
Genetics & Genomics
JUN 08, 2018
Visualizing Gene Activity in Single Cells
Updates to a technique that labels genes with fluorescent tags has enabled the simultaneous visualization of over 10,000 genes in one cell.
Loading Comments...