Chronic pain following an injury can lead to disability and depression.
Pain is considered chronic when it lasts for 6 months or more. It is one of the most common causes of disability globally, and the physical and emotional effects can seriously impact the individual's quality of life.
There are no effective treatments for chronic pain, nor is there any way to know who will develop it following an injury. Being able to predict this would enable prevention strategies to be developed.
Peripheral nerve injury has been linked to persistent, functional changes in the brain, and various kinds of chronic pain have been associated with changes in the prefrontal cortex (PFC).
The PFC plays an important role in the emotional and sensory aspects of chronic pain. It has also been linked to conditions that accompany chronic pain, such as anxiety, depression and problems with cognition.
Previous mouse studies have indicated that cognitive and emotional deficits can persist many months after a nerve injury.
But how these long-term effects of injury contribute to chronic pain remains a mystery.
DNA changes in the brain and the T cells
A team of researchers from McGill University in Montreal, Canada, studied DNA from the brains and white blood cells of rats to investigate the possibility of a link between chronic pain and DNA, or epigenetic mechanisms in the brain.
They used a method that mapped DNA marking by a chemical called a methyl group. Chemical marking is an important concept in epigenetics, a growing field of study into how the expression of gene activity is regulated while the genetic structure remains the same.
Methyl marks are important in epigenetics because they can help to track how genes work.
Genetic modifications occur when genes can be turned "on" or "off," like a switch. This switching mechanism alters the working of the genes.
The scientists found a large number - somewhere between hundreds and thousands - of genes that were marked by chronic pain. They also discovered that chronic pain changes the marking of DNA in both the brain and in the T cells, a type of white blood cell with an important role in the immune system.
Moshe Szyf, a professor in the Faculty of Medicine at McGill, says:
"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. [...] The findings highlight the devastating impact of chronic pain on other important parts of the body such as the immune system."
The team hopes that these results could lead to new ways of diagnosing and treating chronic pain in humans. Some of the genes that are marked by chronic pain could become targets for pain medications.
Medical News Today has previously reported on findings suggesting that acupuncture can help to relieve chronic pain in children.