Pain-Derived Brain Inflammation Associated with Depression

A recent study found that brain inflammation caused by chronic nerve pain alters activity in the mood-regulating regions of the brain, a discovery that points to a direct link between depression and longterm pain.

The study results, published online in the Journal of Neuroscience, revealed that brain inflammation triggered by chronic pain accelerates the growth and activation of microglia. In turn, these immune cells restrict the release of dopamine, a neurotransmitter that regulates the brain’s reward and pleasure centers.

The study authors suggested that these findings could explain why opioid drugs, such as morphine, are often ineffective in treating chronic pain. Whereas morphine typically triggers the release of dopamine, opioid drugs failed to stimulate a similar dopamine response in mice and rats experiencing chronic pain, leading to impaired reward-motivated behavior in these animals. However, the authors found that treating these animals with a drug compound that inhibits microglial activation restored the release of dopamine and reward-motivated behavior. The research team next plans to study whether pain-derived changes in human brain circuitry are also responsible for mood disorders.

“For over 20 years, scientists have been trying to unlock the mechanisms at work that connect opioid use, pain relief, depression, and addiction,” said lead author Catherine Cahill, PhD, in a press release. “Our findings represent a paradigm shift, which has broad implications that are not restricted to the problem of pain and may translate to other disorders.”