What A Fruit Fly's Chronic Pain Tells Us About Humans

In a bid to better understand chronic pain in humans and potential treatment options, researchers have turned their attention to an unlikely six-legged subject.

Scientists have known our tiny garden inhabitants experience something like pain since 2003, but to what degree they feel the sensation -- which is ultimately an emotional response -- is harder to determine.

"The old understanding was basically just that insects can sense dangerous situations and then respond and avoid them, which makes sense," University of Sydney's Associate Professor Greg Neely told 10 daily.

"If an insect couldn't tell they were in a fire then they would just die."

This ability is called 'nociception', and is what allows animals to detect potentially harmful stimuli like heat, cold or physical injury and work to avoid them.

"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," Neely said.

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In a study published in the journal Science Advances on Thursday, Neely and his colleagues believe they have proven -- for the first time -- fruit flies can not only feel pain, but also experience chronic pain that lasts long after an initial injury has healed.

Researchers looked at neuropathic 'pain' in fruit flies -- which occurs after damage to the nervous system -- by damaging a nerve in one leg of a fruit fly.

In humans, neuropathic pain is usually described as burning or shooting pain.

After the fly's injury healed seven days later, Neely said the insect's other legs became hypersensitive.

"So basically non-painful temperature now causes them to react like its painful," he said.

“After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives. That’s kind of cool and intuitive.”

While this might only seem relevant if you're advocating for the safety and rights of fruit flies, understanding this process on a genetic level may unlock doors to treating chronic pain conditions in humans in the future.

Attempts to understand chronic pain in humans typically splits into two camps, Neely said -- with focus on the central nervous system (your brain and spinal cord) on one side, and the peripheral nervous system (nerves outside the brain and spinal cord) the other.

"From our genetic dissection of pain and chronic pain in fruit flies, what we find is the central component is the fly's equivalent of a spinal cord that's the critical change," Neely explained.

"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."

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Neely hopes the discovery will help develop better, nonaddictive pain therapies that can reverse, or even resolve, chronic pain in humans.

"We've got a huge number of people who are living this daily, and we have very limited treatment options," PainAustralia CEO Carol Bennett told 10 daily.

According to PainAustralia, there are 3.24 million Australians living with chronic pain conditions.

The country's estimated annual cost of managing pain is almost $140 billion, and the "go-to" treatment option is currently medication.

"And yet we know that this is not recommended for long term chronic pain, particularly opioids," Bennett said.

Though there's no guarantee Neely's findings will successfully translate to human treatment, Bennett said any and all research into the issue is deeply important and that "we need more of it".

"I think the biggest problem is that we don't yet have chronic pain as a high priority health policy issue in Australia. It's not yet on the radar in terms of governments and decision makers understanding, or even health professionals to be honest."

"So we have some real challenges when it comes to accessing cost-effective treatments for chronic pain."

Last month, PainAustralia launched its new National Strategic Plan For Pain Management, providing the government with a blueprint for addressing the issue today.

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