Insects experience chronic pain like humans do
Researchers at the University of Sydney have found that insects suffer from chronic pain like humans. While previous studies demonstrated that insects experience pain, this is the first study to provide evidence that the pain can last long after a wound has healed.
The research pinpoints the genetic cause of chronic pain in fruit flies and suggests that similar mechanisms drive chronic pain in humans. The findings may ultimately lead to the development of treatments that target the root of chronic pain instead of just the symptoms.
“If we can develop drugs or new stem cell therapies that can target and repair the underlying cause, instead of the symptoms, this might help a lot of people,” said study lead author Professor Gteg Neely. His team is studying pain in an effort to identify non-opioid solutions for pain management.
“People don’t really think of insects as feeling any kind of pain,” said Professor Neely. “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.'”
“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.”
The investigation was focused on neuropathic pain that occurs in fruit flies after damage to the nervous system. In humans, this is usually described as a burning or shooting pain that results from a pinched nerve, spinal cord injury, diabetic neuropathy, cancer bone pain, or an accidental injury.
To test for chronic pain in fruit flies, the researchers damaged a nerve in one leg of the fly and then allowed the injury to fully heal. At this point, the experts found the fly’s other legs had become hypersensitive.
“After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives,” said Professor Neely. “That’s kind of cool and intuitive.”
Next, the team investigated how this happens genetically.
“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,” said Professor Neely.
“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.”
“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.”
Professor Neely explained that chronic pain in humans is presumed to develop through either peripheral sensitisation or central disinhibition.
“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.”
The study is published in the journal Science Advances.
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