In what the authors term a breakthrough finding, researchers from UC Irvine and UCLA report that brain inflammation caused by chronic nerve pain alters activity in regions that regulate mood and motivation. This in turn suggests the existence of a direct biophysical link between chronic pain and depression, anxiety, and propensity to substance abuse. In work with rodents, the researchers observed that pain-derived brain inflammation causes the accelerated growth and activation of immune cells called microglia. These cells trigger chemical signals within neurons that restrict the release of dopamine, a neurotransmitter that helps control the brain’s reward and pleasure centers.
The findings, published online in Journal of Neuroscience, additionally provide insight into why opioid analgesics can fail to provide relief from chronic pain. The team observed that, in the study subjects with chronic pain, opioids did not induce a dopamine release response, resulting in impaired reward-motivated behavior. By contrast, treating the subject animals with a drug that inhibits microglial activation restored dopamine release and reward-motivated behavior.
Read more about the findings, with link to the journal article, here.