A research team from Duke University has found a small area of the brain in mice that can profoundly shut down pain. “It’s located in an area where few people would have thought to look for an anti-pain center, the amygdala, which is often considered the home of negative emotions and responses, like the fight or flight response and general anxiety,” reports ScienceDaily. From the report: The researchers found that general anesthesia also activates a specific subset of inhibitory neurons in the central amygdala, which they have called the CeAga neurons (CeA stands for central amygdala; ga indicates activation by general anesthesia). Mice have a relatively larger central amygdala than humans, but [senior author Fan Wang, the Morris N. Broad Distinguished Professor of neurobiology in the School of Medicine] said she had no reason to think we have a different system for controlling pain. Using technologies that Wang’s lab has pioneered to track the paths of activated neurons in mice, the team found the CeAga was connected to many different areas of the brain, “which was a surprise,” Wang said.
By giving mice a mild pain stimulus, the researchers could map all of the pain-activated brain regions. They discovered that at least 16 brain centers known to process the sensory or emotional aspects of pain were receiving inhibitory input from the CeAga. Using a technology called optogenetics, which uses light to activate a small population of cells in the brain, the researchers found they could turn off the self-caring behaviors a mouse exhibits when it feels uncomfortable by activating the CeAga neurons. Paw-licking or face-wiping behaviors were “completely abolished” the moment the light was switched on to activate the anti-pain center.
When the scientists dampened the activity of these CeAga neurons, the mice responded as if a temporary insult had become intense or painful again. They also found that low-dose ketamine, an anesthetic drug that allows sensation but blocks pain, activated the CeAga center and wouldn’t work without it. Now the researchers are going to look for drugs that can activate only these cells to suppress pain as potential future pain killers, Wang said. The study has been published in the journal Nature Neuroscience.