ABSTRACT
OBJECTIVE: It has been suggested that the occurrence of persistent pain signal during the early postnatal period may alter an individual's response to pain later in life. The aim of this study is to assess whether neonatal nerve injury resulted in long-lasting consequences on nociceptive system in the rat. METHODS: We examined whether neuropathic pain behaviors and the changes of spinal neuropeptides (SP, CGRP, VIP and VIP) induced by peripheral nerve injury within 1 day after birth (Neonate group) were different from those at 8 weeks after birth (Mature group). RESULTS: The Neonate group showed more robust and long-lasting pain behaviors than the Mature group. Immunohistochemical findings demonstrated that spinal SP- & CGRP-immunoreactivities(ir) of the ipsilateral to the contralateral side increased in the Neonate group, whereas those decreased in the Mature group. In addition, increase in spinal VIP- & NPY-ir of the ipsilateral to the contralateral side was more robust in the Mature group than in the Neonate group. CONCLUSION: These results suggest that peripheral nerve injury in the early postnatal period may result in long-lasting and potentially detrimental alterations in nociceptive pathways.