Researchers explore mechanisms of how infant pain changes sensitivity in adults
Scientists at Georgia State University have uncovered the mechanisms of how pain in infancy alters how the brain processes pain in adulthood.
Research is now indicating that infants who spent time in the neonatal intensive care unit (NICU) show altered pain sensitivity in adolescence. These results have profound implications and highlight the need for pre-emptive and post-operative pain medicine for newborn infants.
The study, published online in the journal Frontiers in Behavioral Neuroscience, sheds light on how the mechanisms of pain are altered after infant injury in a region of the brain called the periaqueductal gray, which is involved in the perception of pain.
Using Sprague-Dawley rats, Jamie LaPrairie, a graduate student in associate professor Anne Murphy's laboratory, examined why the brief experience of pain at the time of birth permanently decreased pain sensitivity in adulthood.
Endogenous opioid peptides, such as beta-endorphin and enkephalin, function to inhibit pain. They're also the 'feel good' substances that are released following high levels of exercise or love. Since these peptides are released following injury and act like morphine to dampen the experience of pain, LaPrairie and Murphy tested to see if the rats, who were injured at birth, had unusually high levels of endogenous opioids in adulthood.
To test this hypothesis, LaPrairie and Murphy gave adult animals that were injured at the time of birth a drug called naloxone. This drug blocks the actions of endogenous opioids. After animals received an injection of naloxone, they behaved just like an uninjured animal.
The scientists then focused on the periaqueductal gray region to see if inflammation at birth altered the natural opioid protein expression in this brain region. Using a variety of anatomical techniques, the investigators showed that animals that were injured at birth had endogenous opioid levels that were two times higher than normal.
While it's beneficial to decrease pain sensitivity in some cases, it's not good to be completely resilient to pain.
"Pain is a warning sign that something is wrong," Murphy explained. "For example, if your hand is in water that's too hot, pain warns you to remove it before tissue damage occurs."