Browsing by Subject "network activity"

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  • Alafuzoff, Aleksander (Helsingfors universitet, 2016)
    Background. Birth asphyxia is a pathological state that occurs if fetal gas exchange is disrupted for an extended period of time during delivery. Prolonged birth asphyxia causes brain damage and can even lead to death, but which in mild and moderate cases causes motor and cognitive disability. One of the brain regions often damaged is the hippocampus, which is known to play a major role in memory processing. Thus, damage to the hippocampus may in part explain the long-term cognitive consequences of birth asphyxia. In the neonatal brain hippocampal network activity is discontinuous, dominated by sharp waves and oscillatory bouts, of which the former are thought to be important for memory consolidation in the adult brain. Later in development sharp waves exhibit fast oscillations called ripples that organise hippocampal activity after learning. The aim of this thesis was to establish how sharp wave signalling in the neonatal hippocampus is affected by birth asphyxia. Methods. A rat model developed at the Laboratory of Neurobiology, University of Helsinki, was used to study birth asphyxia and a putative therapeutic strategy. Neonatal rat pups aged 5-8 days were used in the study. These animals were randomly assigned to one of four experimental groups: naive control, sham control, asphyxia, and graded restoration of normocapnia. Hippocampal network activity was measured in vivo under urethane anaesthesia using local field potential (LFP) recordings 24 hours after the asphyxic insult. Sharp waves were detected and analysed in terms of event counts, timing, size, shape and ripple properties. Results and conclusions. After asphyxia, sharp waves occurred more frequently within clusters than in isolation. In addition, sharp wave ripples were detected for the first time during early neonatal development. In asphyxiated animals, the number and magnitude of detected ripples was statistically significantly decreased. Interestingly, animals that underwent graded restoration of normocapnia after asphyxia were no different from controls, suggesting a protective effect of the treatment. The abnormal SPW development after birth asphyxia may form a mechanism contributing to the emergence of cognitive deficits.