Since 2003, scientists have identified that insects experience something like pain, but for the first time, insects also experience chronic pain that lasts long after an initial injury has healed. These findings were contained in new research published by Associate Professor Greg Neely and colleagues at the University of Sydney.
In the peer-reviewed journal Science Advances, the new research provides the first genetic evidence of what causes chronic pain in Drosophila, fruit flies, and there is good evidence that the same changes also drive chronic pain in humans. An ongoing study into these mechanisms could result in the development of treatments that, for the first time, target the cause and not just the symptoms of chronic pain.
According to Associate Professor Neely, if the scientists can develop drugs or new stem cell therapies that can target and repair the underlying cause, rather than the symptoms, this might help a lot of people.
He further explained that people don't quite think of insects as feeling pain. However, it is already revealed in a lot of different invertebrate animals that they can sense and avoid dangerous stimuli that humans perceive as painful. In non-humans, this sense is called 'nociception,' the sense that detects possible harmful stimuli like cold, heat, or physical injury, but for simplicity, what insects experience can be referred to as 'pain.'
The research on fruit flies examined 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 damages.
In the study, Associate Professor Neely and lead author of the study, Dr. Thang Khuong from the University's Charles Perkins Center, damaged a nerve in one leg of the fly. Then, they allowed the injury to heal fully. After that, they discovered that the other leg of the fly had become hypersensitive. Neely noted that after the animal is hurt once severely, they are neurotic and try to protect themselves for the rest of their lives.
Then, the team genetically dissected precisely how that works.
Associate Professor Neely noted that 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 a human's spinal cord. There are inhibitory neurons in this nerve cord that function as an entrance to allow or block pain perception based on the context. After the injury, the injured nerve kills all the brakes forever after dumping all its cargo in the nerve cord. After that, the rest of the animal doesn't have brakes on its pain. The pain threshold changes, and now they are hypervigilant.
