Researchers at the University of Pennsylvania who study hunger, specifically how it can alter perception, have discovered that the brain suppresses chronic pain when an animal is hungry, allowing it to search for food while keeping its response to acute pain intact. Their findings were published in the journal Cell.
J. Nicholas Betley, assistant professor of biology, and his team of researchers observed that mice that hadn’t eaten for 24 hours responded to sources of acute pain, but appeared less responsive to longer-term inflammatory pain than mice who had been fed. In a subsequent conditioning experiment, they discovered that mice that were not hungry avoided a place where they were exposed to inflammatory pain, while hungry mice did not.
“We didn’t set out having this expectation that hunger would influence pain sensation so significantly,” said Amber Alhadeff, a postdoctoral researcher, “but when we saw these behaviors unfold before us, it made sense. If you’re an animal, it doesn’t matter if you have an injury, you need to be able to overcome that in order to go find the nutrients you need to survive.”
Of the billions of neurons in the brain, researchers were able to isolate just 300 neurons that have the unique ability to prioritize hunger over pain: agouti-related protein (AgRP) neurons. AgRP neurons are activated by hunger, and when activated, their responses to chronic pain subsides, while responses to acute pain remain intact.
“We’ve initiated a new way of thinking about how behavior is prioritized,” Betley said. “It’s not that all the information is funneled up to your higher thinking centers in the brain but that there’s a hierarchy, a competition that occurs between different drives, that occurs before something like pain is even perceived.”
Next, researchers plan on exploring how the brain processes inflammatory pain, which would ideally yield more ways to suppress that pain, as well as how the brain processes and prioritizes survival behaviors.
If these findings hold up in humans, they offer a clear target for alleviating chronic inflammatory pain that lingers after injuries–a type of pain currently treated with opioids, which also reduce acute pain. New medication could specifically target the brain receptors that control survival behavior.
With the United States in the grips of a devastating opioid epidemic, the development of non-addictive opioid alternatives to treat chronic pain is growing increasingly important. These findings could have critical implications on the future of pain management.
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