Long-term Effects of Neonatal Pain on Adulthood Stress Behavior and Neuroendocrinology

Each year, thousands of premature babies are treated in neonatal intensive care units and are exposed to invasive noxious procedures, the long term effects of which are unclear. It was once believed that premature babies undergoing invasive treatments did not feel pain because they lacked pain perception circuitry. However, research has shown that early life is a very critical time period for development. Studies utilizing laparotomy, a simple abdominal surgery in rodents to mimic surgeries undergone by humans has shown that when administered to mice early in life, there is a decrease in adulthood pain sensitivity (Sternberg et al. 2005). Furthermore, previous research has consistently found that stress pathways undergo sensitive periods of development during early life. Rat pups separated from their mother for 180 minutes each day for the first two weeks of life showed a significantly increased response in levels of the stress hormone corticosterone in adulthood compared with those in control groups (Plotsky et al. 1993). The “StressInduced Analgesia” (SIA) theory has united the pain and stress biological. Endogenous opioid compounds are known to be the compounds responsible for inhibiting pain. They are commonly found along brain and spinal cord regions of the descending pain pathways. Similar to a fight or flight response, the SIA theory postulates that stress prompts an increase in the circulation of stress hormones. In turn, an increase in stimulation of opiate receptors occurs via increased secretion of endogenous opioid compounds. This results in a temporary relief in pain. Given that neonatal pain sensations have been shown to decrease adulthood pain behavior, and furthermore neonatal stress has been shown to increase the amounts of circulating stress hormone, it is hypothesized