Insects experience chronic pain after injuries

July 12 (UPI) -- Insects can feel chronic pain, too, according to a new study. Even after an injury is healed, researchers found insects continue to experience pain.

Chronic pain comes in two forms: inflammatory and neuropathic. For the study, scientists looked at neuropathic pain, caused by nerve damage, in fruit flies.

In the lab, scientists damaged a nerve in one of the legs of a fly. Researchers allowed the injury to fully heal before subjecting the fruit fly to a series of tests. The experiments showed the leg remained hypersensitive for some time, even though the injury had healed.

"After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives," Greg Neely, an associate professor of environmental sciences at the University of Sydney, said in a news release. "That's kind of cool and intuitive."

During the second part of the study, Neely and his colleagues examined the genetic mechanisms responsible for the chronic pain.

"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," Neely said.

Post-injury, the nerve no longer acts like a functioning gate. Its brakes are shot. Now, the pain arrives in large quantities.

"The 'pain' threshold changes and now they are hyper-vigilant," Neely said.

Researchers suggests similar genetic mechanisms control pain in humans.

"Animals need to lose the 'pain' brakes to survive in dangerous situations but when humans lose those brakes it makes our lives miserable," Neely said. "We need to get the brakes back to live a comfortable and non-painful existence."

Until now, scientists weren't sure whether chronic neuropathic pain in humans is caused by peripheral sensitization or a "central disinhibition" mechanism. The latest research -- published this week in the journal Science Advances -- suggests central disinhibition best explains 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," Neely said.