The early postnatal period has been suggested to be the vulnerable time for structural and functional reorganization of sensory systems, and painful stimuli at this time may alter neuronal circuits, thereby leading to changes in an individual's response to pain later in life. In the present study, we examined whether inflammatory experience in the early life can affect pain responses to subsequent noxious insults later in life. The two groups of neonatal rats, treated with an inflammatory irritant and untreated, were subjected to inflammation and peripheral nerve injury in adulthood. Neonatal inflammation was induced by injection of complete Freund's adjuvant (CFA, 25 μl) into the hindpaw or tail of newborn rat pups. Adult rats which had suffered from neonatal paw inflammation at P0 were subjected to re-injection of CFA into the paw neonatally exposed to CFA or L5 spinal nerve ligation. Paw thickness and histology of inflamed paw were examined to assess the neonatal inflammation. Adult animals whose tail had been subjected to CFA injection on P3 received tail-innervating nerve injury. The results showed that the neonatal CFA-treated rats suffered from chronic inflammation, confirmed by persistent increase of paw thickness and histological result of inflamed paw. These animals showed enhanced pain responses to re-inflammatory challenge by injection of CFA (200 μl) into the neonatally inflamed paw 8 weeks after birth compared with the neonatally untreated animals. However, neuropathic pain on the hindpaw and the tail which had been induced by peripheral nerve injury in the neonatal CFA-treated group were not different from those of the untreated group. The present data suggest that early neonatal long-lasting inflammation differentially affects pain responses later in life, depending on the types of subsequent noxious insults.
|Number of pages||8|
|Journal||International Journal of Developmental Neuroscience|
|Publication status||Published - 2009 May|
Bibliographical noteFunding Information:
This research was supported by a grant (M103KV010015-08K2201-01510) from Brain Research Center of the 21st Century Frontier Research Program funded by the Ministry of Science and Technology of Republic of Korea.
- Inflammatory pain
- Neonatal inflammation
- Neuropathic pain
- Peripheral nerve injury
ASJC Scopus subject areas
- Developmental Neuroscience
- Developmental Biology