Finish the Job: Scientists Discover Insects Experience Chronic Neuropathic Pain After Severe Injury

Tuesday, 16 July 2019 - 12:44PM
Science News
Tuesday, 16 July 2019 - 12:44PM
Finish the Job: Scientists Discover Insects Experience Chronic Neuropathic Pain After Severe Injury
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I don't hate insects. They can be a domestic nuisance, certainly, and some spread disease on a scale that exterminates human life in the hundreds of thousands, but they serve a purpose in nature. For the most part I remain indifferent to their existence until I spot one within striking range in my domicile, at which point I destroy it by whatever means are at my disposal. 

Throughout my insecticidal endeavors, I've never entertained the notion that these resilient, seemingly bloodless parasites might experience any pain in being crushed by a shoe or maimed by a rolled-up copy of The New Yorker. Surely a universe that made a creature as nearly indestructible as the New York City cockroach would have gifted them the superpower of being impervious to pain, right? Well, wrong. According to Science News, a team of researchers at the University of Sydney have discovered that at least some insects will suffer from chronic neuropathic pain for the rest of their lives if left with a survivable injury.

There are two types of chronic pain: inflammatory pain (think arthritis) and neuropathic pain (think sciatica). The researchers were interested in exploring nociception (the perception of pain) as it relates to neuropathy in fruit flies. They did this by amputating a leg on each of the said flies and then letting them heal up. Then they tested them for pain sensitivity in rooms of various temperatures. As it turns out, the poor buzzards suffered hypersensitivity and pain in their other legs. The results, which were published in a paper in Science Advances, were groundbreaking: the "first evidence that nerve injury leads to chronic neuropathic sensitization in insects." 

"People don't really think of insects as feeling any kind of pain," said researcher and lead author Greg Neely in a news release. "But it's already been shown in lots of different invertebrate animals that they can sense and avoid dangerous stimuli that we perceive as painful. In non-humans, we call this sense 'nociception', the sense that detects potentially harmful stimuli like heat, cold, or physical injury, but for simplicity we can refer to what insects experience as 'pain'." In other words, the reason that insects avoid the swatter and the shoe is because they know that even if they're not killed, they could be hurt. 

"After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives," Neely continued. "That's kind of cool and intuitive." 

The sacrifices of these flies were not in vain, however: they open a window of understanding into how chronic neuropathic pain "works," and, therefore, how it might be treated. "The fly is receiving pain messages from its body that then go through sensory neurons to the ventral nerve cord, the fly's version of our spinal cord. In this nerve cord are inhibitory neurons that act like a gate to allow or block pain perception based on the context," Neely said. "After the injury, the injured nerve dumps all its cargo in the nerve cord and kills all the brakes, forever. Then the rest of the animal doesn't have brakes on its pain. The pain threshold changes and now they are hypervigilant." 

Opening quote
Animals need to lose the pain brakes to survive in dangerous situations but when humans lose those brakes it makes our lives miserable. We need to get the brakes back to live a comfortable and non-painful existence.
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Finding therapies and treatments that re-engage or rebuild these "pain brakes" may be key to helping patients suffering from neuropathy.

"Importantly 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 continued, "we are focused on making new stem cell therapies or drugs that target the underlying cause and stop pain for good."

Final thoughts: if you take a swing at a fly with a swatter and succeed only in knocking off a wing or a leg, you've committed that fly to live out the rest of its days in searing agony. That they generally have a lifespan of 15 - 30 days is beside the point: it's no way to go. Finish them off.
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