Experiments on newborn animals suggest that chronic pain during the first days of life may result in permanent hypersensitivity to pain in adulthood, a finding that may have enormous implications for newborns undergoing rigorous medical procedures, scientists say.
M.A. Ruda and her colleagues at the National Institute of Dental and Craniofacial Research found that rat pups that received a painful stimulus that affected them for several days -- a toxin injected into the hind paw -- had a much more dramatic response to pain as adults. When the researcher looked at nerve fibers that extended from the once-injured paw to the spinal column, they found that the experimental animals had 20 percent more pain-fibers than the control animals, and that the fibers extended to areas along which pain fibers don't normally travel.
The fear is that in humans, similar changes occur in newborns exposed to chronic pain during medical procedures, or even religious circumcision sometimes done without local anesthesia.
"We have to pay attention to the amount of pain and tissue injury in the newborn," Ruda said. "These procedures may be creating a heightened sensitivity to pain that will last a lifetime."
The results of their work appear in the latest issue of Science.
"The nervous system is very plastic during development," Ruda said. "Atypical outside events (like chronic pain) can impact how the pain system is coming together."
"The potential exists to teach the central nervous system a different response to pain," Ruda said.
Dr. Clifford Woolf, professor of anesthesia research at Harvard Medical School, said he is impressed by the study.
"For a long time it was thought that newborns don't feel much pain, and the standard care was delivered without pain medicines. Things have changed somewhat. But this study suggests that pain during the newborn period can lead to lasting changes."