Diffuse alterations in synaptic protein expression following focal traumatic brain injury in the immature rat

Abstract

The mechanisms responsible for cognitive decline after traumatic brain injury (TBI) in pediatric patients are poorly understood. The present study examined the potential role of synaptic alterations in this process by using an animal model of immature head injury to define the impact of TBI on expression of the synaptic protein, synaptophysin. After craniotomy, TBI was induced in postnatal day 17 (PND17) rats using controlled cortical impact delivered to the left hemisphere. NeuN, a neuronal marker, and synaptophysin expression were examined 1 day, 1 week, and 1 month after injury by immunohistochemistry and immunoblotting. There were significant decreases in both NeuN and synaptophysin after 1 day and 1 week but not 1 month after injury within the hippocampus and neocortex adjacent to the impact site compared to sham-injured controls. The decrease in synaptophysin and NeuN was also noted in the contralateral hippocampus by 1 day after injury and in the contralateral neocortex by 1 week, indicating that changes in protein expression were not solely localized to the injury site but occurred in more distant regions as well. In conclusion, the decrease and recovery in synaptophysin parallel the cognitive changes that occur after experimental TBI in the PND17 rat, which suggests that changes in this protein may contribute to cognitive declines after injury. The results also suggest that, in spite of the focal nature of the impact, diffuse alterations in protein expression can occur after immature TBI and may contribute to the subsequent cognitive dysfunction.