Thanks to Flies, Doctors May Now Believe Your Chronic Pain

Renee Fabian
Fly under a magnifying glass

It may be the last place you’d expect to find validation for your chronic pain, but you might want to think twice before you swat at another fly. We now know, for the very first time, flies experience chronic pain — a breakthrough that might make doctors think twice before questioning your pain.

The new study, published in the journal Science Advances, examined how and why the common fruit fly experiences chronic pain. Fruit flies with nerve damage in one leg were allowed to heal completely. Afterward, researchers measured for neuropathic pain resulting from nerve damage and found flies were hypersensitive to stimuli that are normally non-painful. Sound familiar?

Chronic pain, unlike acute pain right after an injury, persists often without any obvious cause. Chronic pain can be classified as either inflammatory or neuropathic pain. Neuropathic pain is caused by nerve damage and occurs most commonly in people who have conditions like diabetes, Ehlers-Danlos syndrome (EDS), complex regional pain syndrome, cancer and multiple sclerosis (MS).

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The study also offers a fascinating history of pain through the ages — 500 million years or so in fact. Researchers point out a lot of data exists about acute pain immediately after an injury. Acute pain is adaptive because it teaches animals to avoid certain stimuli that could be life-threatening. However, according to this study’s authors, almost nothing is known about the origins of chronic pain. At least in fruit flies.

One theory behind the cause of chronic pain in all creatures is damage to what study co-author Greg Neely, Ph.D., associate professor at the University of Sydney in Australia, called “pain brakes.” Neely’s research found nerve damage stopped the pain brakes on the fly’s spinal cord-like nerve from preventing pain. Researchers theorized this is protective — the fly thought its leg injury was life-threatening and it became hypersensitive to all pain later to avoid a repeat injury. Neely said a similar process may occur in humans.

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“After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives,” Neely said in a news release. “So we knew that insects could sense ‘pain’, but what we didn’t know is that an injury could lead to long-lasting hypersensitivity to normally non-painful stimuli in a similar way to human patients’ experiences.”

Unlike flies who face greater threats to their lives, losing your pain brakes can cause debilitating chronic pain. For humans, chronic pain isn’t adaptive. According to Neely, who described adaptive chronic pain in flies as “cool and intuitive,” looking at the mechanisms underlying chronic pain in flies may help inform treatments in people.

“Now we know the critical step causing neuropathic ‘pain’ in flies, mice and probably humans, is the loss of the pain brakes in the central nervous system,” Neely said. “We are focused on making new stem cell therapies or drugs that target the underlying cause and stop pain for good.”

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Though the results of this study are interesting, often it’s not possible to generalize animal studies to humans, so take these findings with a grain of salt. This research also doesn’t get us any closer to finding better treatments or a cure for chronic pain yet. But it’s probably safe to say the fact even fruit flies experience chronic pain provides evidence it’s not just “all in your head.”

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