Abstract: AIM: To investigate the mechanism of blocking visceral hyperalgesia by Fentanyl analgesia in neonatal period through observeing the Fos expression of lumbosacral spinal dorsal horn in visceral hyperalgesia rats. METHODS: Colorectal irritation (CI) stimulation in neonatal period was used to establish the model of visceral hypersensitivity in young rats.32 neonatal rats were divided into four groups by 2×2 factorial design with each 8. Group A₁B₁ was imposed on CI at neonatal period and imposed on fentanyl intraperitoneal injection before CI stimulation; Group A₁B₂ was imposed on CI at neonatal period and administration saline before CI; Group A₂B₁ was not imposed on CI at neonatal period and imposed on fentanyl intraperitoneal injection; Group A₂B₂ was not imposed on CI at neonatal period and not imposed on fentanyl intraperitoneal injection. Then, conventionally breeding till the young period (6-week age), rats were sampled the spinal cord from L6 to S2, the semi-quantity analysis of staining density and the cell numbers of Fos-like immunoreactivity(FLI) of spinal cord were made through immunohisrochemical coloration and computer image analyzing system. RESULTS: The number of FLI and integral opticaldensity of FLI significantly decreased in lumbosacral spinal dorsal horn by neonatal Fentanyl analgesia. The spinal Fos expression in young rats were affected both by CI at neonatal period and neonatal fentanyl analgesia. Futhermore, there were interaction effects between the two factors. CONCLUSION: Neonatal fentanyl analgesia before CI can decrease spinal Fos expression and visceral hypersensitivity in young rats.

Key words: neonatal, fentanyl analgesia, Fos, young rats