Synapsin I is believed to be involved in regulating
neurotransmitter release and in synapse formation. Its interactions with the actin filaments and synaptic vesicles are regulated by phosphorylation. Because exocytosis and
synapsin I phosphorylation are a Ca(2+)-dependent process, it is possible that an ischemic insult modifies the presynaptic
proteins. However, the neuronal damage and the changes in
synapsin I as well as its phosphorylation level as a result of
glucose/
oxygen deprivation (GOD) and reperfusion in organotypic hippocampal slice cultures have not been established. In this study, the level of
synapsin I and phosphosynapsin was measured in organotypic hippocampal slice cultures in order to determine the role of
synapsin I in the presynaptic nerve terminals during GOD/reperfusion.
Propidium iodide fluorescence was observed in the CA1 area after GOD for 30 min, which could be detected in the whole pyramidal cell layer during reperfusion for 24 h. The immunofluorescence of the neuron specific
nuclear protein, NeuN, showed a negative correlation with the PI fluorescence. During GOD/reperfusion, the immunofluorescence of
synapsin I increased in the stratum radiatum and the stratum oriens of the CA1 area and the stratum lucidum and the stratum oriens of the CA3 area. The phosphosynapsin level evidently increased in the stratum lucidum of the CA3 area after GOD for 30 min, which was reduced to the control level after reperfusion. These results suggested that the neuronal damage and degenerations were observed as a result of GOD/reperfusion and the increase in
synapsin I and its phosphorylation might play a role in modulating the release of
neurotransmitters via exocytosis and in the formation of new synapses after
brain ischemia.