By Pat Anson, Editor

Scientists already know that chronic pain can change the way our brains work, but now there is new evidence that pain may also make lasting changes in our immune systems.

In studies on laboratory rats, researchers at McGill University in Montreal found that chronic pain alters the way genes work in the immune system. The discovery may help explain why pain can persist long after the initial injury.

"We found that chronic pain changes the way DNA is marked not only in the brain but also in T cells, a type of white blood cell essential for immunity,” said Moshe Szyf, a professor in the Faculty of Medicine at McGill. "Our findings highlight the devastating impact of chronic pain on other important parts of the body such as the immune system."

McGill researchers examined DNA from the brains and white blood cells of rats nine months after a nerve injury. They found a “stunning” number of changes in DNA methylation – which regulates how genes function. Chronic pain appeared to reprogram how the genes work.

"We were surprised by the sheer number of genes that were marked by the chronic pain -- hundreds to thousands of different genes were changed," adds Szyf. "We can now consider the implications that chronic pain might have on other systems in the body that we don't normally associate with pain."

Many of the genes that were altered are associated with depression, anxiety, and loss of cognition, which are some of the negative side effects of chronic pain.  The findings could open new avenues to diagnosing and treating chronic pain in humans, as some of the genes affected by chronic pain could represent new targets for pain medications.

“These findings reveal potential new avenues for the development of novel therapeutics directed at either the molecular regulation of methylation or at key genes or pathways dysregulated in chronic pain,” the study found.  “This work also provides a possible mechanistic explanation for commonly observed comorbidities observed in chronic pain (i.e anxiety, depression). Finally, the sheer magnitude of the impact of chronic pain, particularly in the prefrontal cortex, illustrates the profound impact that living with chronic pain exerts on an individual.”

The McGill study is published in the journal Scientific Reports.

A recent study at Northwestern University found that chronic pain “rewires” a part of the brain that controls whether we feel happy or sad.  Researchers found that a group of neurons thought to be responsible for negative emotions became hyper-excitable within days of an injury that triggers chronic pain.