Background: The perinatal brain shows both an increased tolerance to hypoxic ischemic injury and a faster and more complete recovery than the adult one. It is, therefore, important to understand the sequence of events following hypoxia and ischemia in young animals. This study aims to clarify the time-course of μ-calpain activation, and expressions of c-fos protein (c-Fos), c-jun protein (c-Jun), HSP70 and HSP27 during hypoxic-ischemic brain injury (HIBI) in neonatal rats.

Methods: The model of HIBI was made in 7-day-old SD rats by left carotid arterial ligation and hypoxia (8% oxygen). The protein concentration was determined using a modified Bradford assay. μ-calpain activation, and expressions of c-Fos, c-Jun, HSP70 and HSP27 were observed by Western blot in cortical and hippocampal samples at 0, 1, 2, 4, 12 and 24 hours after the development of lesion.

Results: The cleavage of cytosolic μ-calpain was demonstrated in both cortical and hippocampal samples in neonatal rats after hypoxic-ischemia (HI). The ratio of 76/80 kD of μ-calpain was increased significantly after HI and reached a maximum at 24 hours after HI. Compared with that observed in the control group, the expression of nuclear c-Fos and c-Jun in cortical and hippocampal samples increased significantly at 1, 2, 4, 12 and 24 hours after HI (P<0.05). But significant expressions of cytosolic HSP70 and HSP27 could only be seen at 12 or 24 hours after HI (P<0.05). The significant differences between the cerebral cortex and the hippocampus were observed in c-Fos expression at 2 and 4 hours, and in HSP70 and HSP27 expressions at 24 hours after HI (P<0.05).

Conclusion: The early activation of μ-calpain and increased expressions of c-Fos, c-Jun, HSP27 or HSP70 following HI may contribute to neuronal apoptosis as well as induction of a significant brain neuroprotection in neonatal hypoxic-ischemic rat brain.