Researchers have long suspected that experiencing stress as a child may cause a person to experience chronic pain later in life. But now, new research suggests that this pain sensitivity could be increased if stress is experienced again as an adult.
This is according to a study published in the journal Biological Psychiatry.
The research team, from the University of California, San Francisco, says there is also an increasing concern that chronic pain syndromes could be a complication of post-traumatic stress disorder (PTSD).
But the researchers note that this connection is very difficult to study, since the majority of stressful events that cause PTSD lead to physical trauma, and previous animals studies analyzing this area have not “accurately reflected” the early life stress that humans experience.
In an attempt to better understand these links, the research team analyzed a group of female rats that had been stressed through restricted nesting and bedding material for 1 week while caring for their pups.
When rat mothers are stressed, the researchers explain, they do not provide consistent levels of nurturing to their pups, which in turn causes the pups to become stressed.
When the pups became adults, the researchers found they demonstrated increased reactivity to painful stimuli. They were then exposed to stress stimuli in the form of sound, and this was found to increase their reactivity to pain further.
The researchers explain that this increased pain reactivity was associated with catecholamines – an organic compound in the body involved in “fight-or-flight” reactions. The rats’ reactivity was also linked to cykotines – molecules that play a part in the body’s response to inflammation.
However, the researchers found that when they stopped the actions of both the cykotines and catecholamines, the stressed pups showed reduced pain sensitivity.
The study authors explain that their findings suggest the presence of a “two hit model” for the risk of chronic pain – that initial stress “predisposes” increased reactivity to stress that is experienced later on.
Dr. Jon Levine, of the University of California, San Francisco, and lead study author, says these findings may lead to new diagnostic tools for those at risk of chronic pain, as well as new treatment methods:
“While it has been recognized for some time that early life events can shift homeostatic balance, predisposing adults to the development of chronic pain, that this could be mediated by a peripheral mechanism, involving the interaction between immune and neuroendocrine stress axes suggests novel approaches to detecting individuals at risk as well as to treatment of chronic pain.”
Medical News Today recently reported on a study revealing that infants born to mothers who experience stressful life events show increased CRF1 expression at birth – a gene linked to anxiety and stress.