So it turns out humans and animals are not the only creatures to experience chronic pain. According to a new scientific study insects also experience chronic pain. Scientists have known insects experience something like pain for over a decade and a half, but this new research provides compelling evidence suggesting that insects also experience chronic pain that lasts long after an initial injury has healed.
The study offers the first genetic evidence of what causes chronic pain in Drosophila (fruit flies) and there is good evidence that similar changes also drive chronic pain in humans.
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Backstory
Chronic pain is defined as persistent pain that continues after the original injury has healed. It comes in two forms: inflammatory pain and neuropathic pain.
The recent study of fruit flies looked at neuropathic ‘pain’, which occurs after damage to the nervous system and, in humans, is usually described as a burning or shooting pain. Neuropathic pain can occur in human conditions such as sciatica, a pinched nerve, spinal cord injuries, postherpetic neuralgia (shingles), diabetic neuropathy, cancer bone pain, and in accidental injuries.
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Study overview
Researchers damaged a nerve in one leg of the fly. The injury was then allowed to fully heal. After the injury healed, they found the fly’s other legs had become hypersensitive.
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“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. 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.”
-Associate Professor Greg Neely, researcher, University of Sydney
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How is knowing that insects experience chronic pain useful?
“From our unbiased genomic dissection of neuropathic ‘pain’ in the fly, all our data points to central disinhibition as the critical and underlying cause for chronic neuropathic pain.
“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, we are focused on making new stem cell therapies or drugs that target the underlying cause and stop pain for good.”
-Associate Professor Greg Neely, researcher, University of Sydney
Journal Reference: Thang M. Khuong, Qiao-Ping Wang, John Manion, Lisa J. Oyston, Man-Tat Lau, Harry Towler, Yong Qi Lin, G. Gregory Neely. Nerve injury drives a heightened state of vigilance and neuropathic sensitization in Drosophila. Science Advances, 2019; 5 (7): eaaw4099 DOI: 10.1126/sciadv.aaw4099 overview
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