Trauma primes brain to overreact to stress – a study in mice

Scientists in Canada have discovered how previously traumatised mice became overly sensitive to stress and pain long after healing. 

The vital ability to detect pain or other danger cues allows animals to recognise, learn and remember threats, allowing rapid and coordinated responses to danger.  However, in chronic pain conditions, the nervous system can stay hypersensitive long after the original injury has healed.

A research team at EARA member University of Toronto injected mice with a bacterial toxin (CFA) that caused temporary inflammation and pain in one of the hind paws. After recovery, the mice were exposed to the scent of a predator. Previously injured mice displayed exaggerated fear responses and developed long-lasting pain in both hind paws, including the uninjured side, for over six months. 

The team found that corticosterone, a stress hormone, intensifies pain signals by activating a protein known as “wasabi receptor” (TRPA1). Blocking either one reduced both pain and fear, however long-lasting pain was caused by stress hormones alone, suggesting that future treatments might need different approaches for fear and pain.

 “Our research gives us new insight into how past injuries can shape the brain's response to future challenges and could open the door to better treatments for chronic pain and anxiety disorders," said Loren Martin, professor at the University of Toronto and senior author of the study published in Current Biology.