Brain inflammation caused by chronic nerve pain can impact parts of the brain involved in mood, leading to symptoms of depression and anxiety in patients with such pain. The findings of a new study could lead to new ways of treating chronic pain.
Catherine Cahill, PhD, an associate professor of anesthesiology and perioperative care at the University of Calfornia—Irvine and colleagues looked at the growth of certain immune cells, known as microglia, in the brains of rodents with chronic pain. They discovered that the pain lead to brain inflammation, which increased the rate at which the microglia became active and grew.
The reason why this rate increase may lead to depression and anxiety is that microglia set off chemical signals in the brain that block the release of the neurotransmitter dopamine, which regulates parts of the brain affiliated with reward and pleasure.
While opioid drugs are commonly used to treat pain — since they are designed stimulate the release of dopamine — the researchers found that no such response happened when the rodents were given opioids. However, when they were given a drug that inhibits the activation of microglia, dopamine release started again and reward-motivated behavior returned, the researchers reported in the Journal of Neuroscience.
“We have a drug compound that has the potential to normalize reward-like behavior and subsequent clinical research could then employ imaging studies to identify how the same disruption in reward circuitry found in rodents occurs in chronic pain patients,” Cahill said in a statement.
For the first time, scientists have discovered that braininflammation caused by chronic nerve pain can affect signaling in theregions of the brain associated with mood and motivation. This discoverysuggests there is a mechanism that connects chronic pain with symptomsof depression and anxiety that many patients experience.
The findings of the study, published in the Journal of Neuroscience,could lead to new methods of treatment for chronic pain, the mostcommon form of enduring illness for people aged below 60 in the US.
Researchers from the University of California-Irvine(UCI) and theUniversity of California-Los Angeles (UCLA) made their discovery afterexamining the growth of immune cells in the brains of mice and rats withchronic pain.