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Insects may enter a state similar to neuropathic pain after nerve injury, according to a new fruit fly study (Drosophila melanogaster).
Khuong et al offer the first genetic evidence of what causes chronic pain in Drosophila melanogaster. Image credit: Virvoreanu Laurentiu.
Chronic pain is defined as persistent pain that persists after healing from the initial injury. It comes in two forms: inflammatory pain and neuropathic pain.
The study examined neuropathic pain, which occurs after an injury to the nervous system and which, in humans, is usually described as burning or throbbing pain.
"People do not really think that insects feel any pain," said Dr. Greg Neely, a researcher at Sydney University, lead author of the study.
"But it has already been shown in many invertebrate animals that they can detect and avoid the dangerous stimuli we perceive as painful."
"In non-humans, we call it the nociception of meaning, the sense that detects potentially harmful stimuli such as heat, cold, or physical injury, but for simplicity we can talk about the pain felt by insects. "
"We knew that insects could feel the pain, but what we did not know was that an injury could lead to long-lasting hypersensitivity to normally pain-free stimuli, just like patient experiences."
In the study, Dr. Neely and his colleagues damaged a nerve in a fly. The injury was then allowed to heal completely.
After healing the injury, the scientists discovered that the other legs of the fly had become hypersensitive.
"After being hurt once, the animal is hypersensitive and tries to protect itself for the rest of his life. It's pretty cool and intuitive, "said Dr. Neely.
Then the authors of the study genetically dissected exactly how it works.
"The fly receives messages of pain from his body that then pass through sensory neurons to the ventral nerve cord, the version of our spinal cord by the fly. In this nerve cord, inhibitory neurons act as a door to allow or block the perception of pain depending on the context, "said Dr. Neely.
"After the injury, the injured nerve throws all its cargo into the nerve cord and kills all the brakes, forever. Then the rest of the animal is not braked. The threshold of pain changes and they are now hypervigilant. "
"Animals have to lose the painkillers to survive in dangerous situations, but when humans lose those brakes, our lives are miserable. We must recover the brakes to lead a comfortable and painless existence. "
In humans, chronic pain is thought to develop through peripheral sensitization or central disinhibition.
"From our unbiased genomic dissection of neuropathic pain in the fly, all our data suggest that central disinhibition is the underlying and underlying cause of chronic neuropathic pain," said Dr. Neely.
"It is important to note that now we are experiencing the crucial stage of neuropathic pain in flies, mice and probably humans; it is the loss of pain brakes in the central nervous system. We focus on creating new stem cell treatments or pain-targeting drugs for the good. "
The study was published in the journal Progress of science.
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Thang M. Khuong et al. 2019. Nerve damage leads to an increased state of alertness and neuropathic sensitization in Drosophila. Progress of science 5 (7): eaaw4099; doi: 10.1126 / sciadv.aaw4099
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