Back in 2003, scientists discovered that insects can feel pain. However, a new study suggests that they can also experience chronic pain that lasts long after the initial injury has healed.
WebMD defined chronic pain as a persistent pain that continues weeks, months, or even years after the injury. And it exists in two forms: neuropathic pain and inflammatory pain.
For their study, the researchers analyzed neuropathic pain in fruit flies. In humans, the pain occurs after damage to the nervous system and is characterized by a burning or shooting pain.
Conditions that could cause this form of persistent pain in humans include diabetic neuropathy, postherpetic neuralgia, sciatica, spinal cord injuries, and pinched nerve. While these conditions may not be present in insects, the neuropathic pain that follows is.
According to the co-author of the study and associate professor at the University of Sidney, Greg Neely:
“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 ordinarily non-painful stimuli in a similar way to human patients’ experiences.”
Testing For Chronic Pain in Fruit Flies
To test for pain in insects, Neely, and lead author of the study, Dr. Thang Khuong damaged a nerve in a fruit fly’s leg. Then, they waited for the injury to heal.
After the injury healed, the researchers noted that the fruit fly had developed a sort of reaction to the injury. In order to protect itself better, the fly’s other leg had become hypersensitive.
Next, the team decided to explore the genetic basis of this reaction.
Think of pain as a message that the fly receives through its body. The message moves through the sensory neurons to the ventral cord – the insect’s version of the spinal cord.
The ventral cord consists of inhibitory neurons that act as a brake. It could either allow or block the perception of pain based on a concept.
When the fruit fly got injured, the damaged nerve sent all its pain through the nerve cord, removing the “brake” in the process. As a result, the insect could no longer block the perception of pain. Its threshold for pain changes and the fruit fly ultimately becomes hyper-vigilant.
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While this is not necessarily a bad thing in animals, we can’t say the same for humans.
Associate Professor Neely noted:
“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.”
The previous belief was that either central disinhibition or peripheral sensitizations cause chronic pain. Data from the study suggest that neuropathic pain is caused by the latter.
Now researchers can figure out how to finally treat chronic pain.
“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,” Neely concluded.
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