Pain in infancy is capable of altering the brain's ability to process pain in adulthood, researchers at Georgia State University have explained.
The study has now indicated that infants who spent time in the neonatal intensive care unit (NICU) show altered pain sensitivity in adolescence.
The results have profound implications, and highlight the need for pre-emptive and post-operative pain medicine for newborn infants.
For the study, graduate student Jamie LaPrairie and professor Anne Murphy used Sprague-Dawley rats to examine 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 and they are also the 'feel good' substances that are released following high levels of exercise or love.
As these peptides are released following injury and act like morphine to dampen the experience of pain, the researchers tested to see if the rats, who were injured at birth, had unusually high levels of endogenous opioids in adulthood.
Thus, they gave adult animals that were injured at the time of birth a drug called naloxone, which blocks the actions of endogenous opioids.
The researchers observed that after animals received an injection of naloxone, they behaved just like an uninjured animal.
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.
Interestingly, while there is an increase in endorphin and enkephalin proteins in adults, there is also a big decrease in the availability of mu and delta opioid receptors, which are necessary in order for pain medications, such as morphine, to work.
This means that it takes more pain-relieving medications in order to provide relief as there are fewer available receptors in the brain. Studies in humans are reporting the same phenomenon.
The number of invasive procedures an infant experienced in the NICU is negatively correlated with how responsive the child is to morphine later in life.
Thus, the researchers concluded that the more painful procedures an infant experienced, the less effective morphine is in alleviating pain.
he study has been published online in the journal Frontiers in Behavioral Neuroscience.