Thwack! Insects feel chronic pain after injury
Associate Professor Greg Neely and his team of pain researchers in the Charles Perkins Centre have found compelling evidence that insects feel persistent pain after injury.
Dr Thang Khuong and Associate Professor Greg Neely in the Charles Perkins Centre.聽
Scientists have known insects experience something like pain , but new research published today from and colleagues at the University of Sydney proves for the first time that insects also experience chronic pain that lasts long after an initial injury has healed.
The study in the peer-reviewed journal 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. Ongoing research into these mechanisms could lead to the development of treatments that, for the first time, target the cause and not just the symptoms of chronic pain.
鈥淚f 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,鈥� said Associate Professor Neely, whose team of researchers is studying pain at the with the goal of developing non-opioid solutions for pain management.
Do insects feel pain?聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽 聽Photo: Pixabay, main photo above, iStock.
Pain and insects
鈥淧eople don鈥檛 really think of insects as feeling any kind of pain,鈥� said Associate Professor Neely. 鈥淏ut it鈥檚 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 鈥榥ociception鈥�, the sense that detects potentially harmful stimuli like heat, cold, or physical injury, but for simplicity we can refer to what insects experience as 鈥榩ain鈥�.鈥�
鈥淪o we knew that insects could sense 鈥榩ain鈥�, but what we didn鈥檛 know is that an injury could lead to long lasting hypersensitivity to normally non-painful stimuli in a similar way to human patients鈥� experiences.鈥�
What is chronic pain?
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 study of fruit flies looked at neuropathic 鈥榩ain鈥�, 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.
Testing pain in fruit flies
In the study, Associate Professor Neely and lead author from the University鈥檚 Charles Perkins Centre, 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鈥檚 other legs had become hypersensitive. 鈥淎fter the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives,鈥� said Associate Professor Neely. 鈥淭hat鈥檚 kind of cool and intuitive.鈥�
Next, the team genetically dissected exactly how that works.
鈥淭he fly is receiving 鈥榩ain鈥� messages from its body that then go through sensory neurons to the ventral nerve cord, the fly鈥檚 version of our spinal cord. In this nerve cord are inhibitory neurons that act like a 鈥榞ate鈥� to allow or block pain perception based on the context,鈥� Associate Professor Neely said. 鈥淎fter 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鈥檛 have brakes on its 鈥榩ain鈥�. The 鈥榩ain鈥� threshold changes and now they are hypervigilant.鈥�
Brain and ventral nerve cord (resembling the spinal cord in human) of an uninjured fly showing nociceptive sensory neurons (green), stained with anti-GABA, an inhibitory neurotransmitter (red) and neuronal synaptic marker nc82 (blue).
鈥淎nimals need to lose the 鈥榩ain鈥� 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.鈥�
In humans, chronic pain is presumed to develop through either peripheral sensitisation or central disinhibition, said Associate Professor Neely. 鈥淔rom our unbiased genomic dissection of neuropathic 鈥榩ain鈥� in the fly, all our data points to central disinhibition as the critical and underlying cause for chronic neuropathic pain.鈥�
鈥淚mportantly now we know the critical step causing neuropathic 鈥榩ain鈥� 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.鈥澛�
Declaration: This research was funded by the .
