Anne Murphy, associate professor of neuroscience at George State University, is observing the relationship between pain felt as an infant and the related long-term effects.
Unalleviated pain during the perinatal period is associated with permanent decreases in pain sensitivity, blunted cortisol responses and higher rates of neuropsychiatric disorders.
To date, the mechanism(s) by which these long-term changes in stress and pain behavior occur, and whether such alterations can be prevented by appropriate analgesia at the time of injury, remains unclear.
We have previously reported in rats that inflammation experienced on the day of birth permanently upregulates central opioid tone, resulting in a significant reduction in adult pain sensitivity. However, the impact on early life pain on anxiety- and stress-related behavior is not known.
As adults, animals that experienced pain on the day of birth displayed blunted responses to anxiety- and stress-provoking stimuli. These animals also show decreased corticosterone release following stress.
The dampened behavioral responses to anxiety- and stress-provoking stimuli were accompanied by 2-fold changes in brain enkephalin expression, an endogenous opioid known to regulate stress and pain.
Changes in brain enkephalin levels were evident 24 hours after injury and persisted into adulthood, suggesting that early life pain permanently alters brain opioidergic circuits. These changes in stress responsiveness were completely reversed in animals that received morphine at the time of injury.
Together, our studies demonstrate the degree, severity and preventability of the long-term deficits in stress response associated with a single painful experience early in life.