<> "The repository administrator has not yet configured an RDF license."^^ . <> . . "NMDA receptor mediated contribution to neuronal cell death - an in vitro evaluation"^^ . "Brain ischemia is one of the leading causes of death and disability in the world with enormous socioeconomic consequences annually, however to date, despite multiple studies, the only clinically available remedy is the thrombolytic tissue plasminogen activator (tPa). The development of new therapeutic interventions/strategies requires a deeper insight into the pathology, which can only come from better characterization of ischemic models and usage of appropriate parameters to evaluate neuronal damage. The usage of a right model and cell death assay is essential for an effective translation to in vivo and clinical studies. Organotypical hippocampal slice cultures offer an in vitro model to study brain ischemia by induction of oxygen and glucose deprivation (OGD). In organotypic hippocampal slice cultures the interaction between neuronal and non-neuronal cells are well preserved and intrinsic connections of the hippocampal structure are largely maintained. However, there is scant data regarding the expression and functionality of N-Methyl-D-aspartate receptors (NMDARs) in such slice cultures. NMDARs, which are essential mediators of synaptic plasticity under normal physiological conditions, are during brain ischemia excessively activated due to glutamate overflow and mediate excitotoxic cell death. The aim of the first part of my thesis was thus to evaluate the expression of NR1, NR2A and NR2B and their contribution to excitotoxic cell death after exposure to NMDA or OGD in organotypical hippocampal slices cultures after 14 days in vitro (DIV14). OGD induced the typical ischemic injury damage as it is delayed and most pronounced in the hippocampus cornu ammonis (CA) 1 pyramidal neurons. This study revealed that NR1, NR2A and NR2B subunits were expressed at DIV14 and contributed to cell death, as shown by use of the NMDAR antagonist MK-801 (dizocilpine). Excitotoxic cell death induced by NMDA was antagonized by 10 μM MK-801, a dose that offered only partial protection against OGD-induced cell death. High concentrations of MK-801 (50–100 μM) were required to counteract delayed cell death (48–72 h) after OGD. The higher dose of MK-801 needed for protection against this delayed phase of OGD-induced death could not be attributed to down-regulation of NMDARs at the gene expression level. Additionally, I found that NR2B-subunits did not contribute to NMDA-or OGD-induced cell death at DIV14 and that NR2B possibly is post-translationally modified under normal physiological conditions. My data indicate that NMDAR signaling is just one of several mechanisms underlying ischemic cell death and that prospective cytoprotective therapies must be directed to multiple targets. Another important aspect to be taken in consideration in studies aimed to discover cytoprotective agents are the parameters used for evaluation. Most studies evaluate neuronal survival from nuclear damage, which reflects the final stage of cell death and lacks information about neuronal function. The aim of the second part of my thesis was to investigate more subtle changes in neurons prior to cell death by assessing dendritic damage and furthermore to characterize the functionality of these neurons using electrophysiological recordings. Dendritic damage, manifesting as focal swellings of dendrites (beadings), is an early morphological hallmark of neuronal damage and has been described in a variety of pathological conditions including brain ischemia. Protection against dendritic beading is likely to reduce later neuronal damage. NMDARs are involved in mediating also cell survival, not only cell death. Increased synaptic activity triggers Ca2+ influx via synaptic NMDAR receptors that activates a gene transcription dependent acquired neuroprotection program. Here I show that increased synaptic activity protects, in a transcription and partly nuclear calcium dependent manner, against dendritic damage. Increased synaptic activity induced gene program for acquired neuroprotection includes activating transcription factor 3 (ATF3). I show additionally that overexpression of ATF3 protects against NMDA-induced dendritic damage in line with its known protection against neuronal death. Furthermore, the protected dendrites are functional indicated by the restoration of synaptic transmission-dependent network activity within 48 h of an otherwise toxic NMDA insult. I conclude that ATF3 is a robust neuroprotective gene offering protection against acute neuronal injury and hence improving the functional outcome after neuronal damage. "^^ . "2012" . . . . . . . . "Hanna"^^ . "Ahlgren"^^ . 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