Researchers at Washington University School of Medicine in St. Louis have identified a brain-based mechanism that acts as a natural brake on chronic pain — a discovery that could one day lead to powerful pain relief treatments that avoid the risks of opioids.
Published August 17 in Current Biology, the study focuses on the locus coeruleus, a small region in the brain's alert and stress center already known to regulate pain. The team found that mu opioid receptors on cells in this region act as gatekeepers that restrain pain signaling.
The research began by confirming that nerve injury can transform the locus coeruleus into an active source of pain. When researchers temporarily silenced cells in this region in mice, animals with neuropathic pain became less sensitive to touch and heat compared with healthy mice.
The critical discovery came when the team removed mu opioid receptors specifically from locus coeruleus cells in mice with neuropathic pain. Without those receptors, the animals became even more sensitive to touch and heat — demonstrating that the receptors normally function as a brake on the pain circuit. When the researchers restored the receptors, the increased sensitivity was reversed, effectively switching off the heightened pain response.
"Millions of adults live with chronic neuropathic pain caused by nerve damage," said Jordan McCall, PhD, the study's senior author. "The pain is difficult to treat, and traditional opioid medications bind to receptors throughout the entire body and brain, often leading to side effects, tolerance and addiction risk. Understanding how localized receptors in the locus coeruleus act as gatekeepers could lead to more targeted, effective pain therapies with fewer risks."
Neuropathic pain develops when injured nerve fibers repeatedly send abnormal signals to the brain, producing shooting, stabbing, or burning sensations. It is caused by conditions including diabetes, viral infections, and nerve compression, and affects millions worldwide.
The researchers are now investigating ways to alter activity in the locus coeruleus without affecting opioid receptors throughout the rest of the nervous system. Their goal is to develop therapies that engage mu opioid receptors specifically within this brain region, potentially delivering strong relief from chronic neuropathic pain while reducing the risks associated with drugs that act broadly across the brain and body.
The study was funded by the National Institutes of Health, the National Science Foundation, the McDonnell Center for Systems Neuroscience, and the Rita Allen Foundation.
