Excitatory neurotransmission in the mammalian central nervous system is mediated largely by the neurotransmitter glutamate acting on specific glutamate receptors (GluRs). It is well known that the efficiency of transmission at these glutamatergic synapses can be modulated for prolonged periods of time. This synaptic plasticity, thought to underlie basic mechanisms for learning and memory, is regulated by postsynaptic calcium ion. We, and others, have previously shown that the Ca2+ signaling pathway responsible for synaptic strengthening in region CA1 of the hippocampus involves members of the Ca2+/calmodin (Ca2+/CaM)-dependent protein kinase family (CaM-Ks), particularly CaM-KII and CaM-KIV. CaM-KII phosphorylates and potentiates current through the AMPA-type GluR (AMPA-Rs) in dendritic spines, and CaM-KIV stimulates gene expression through phosphorylation of nuclear transcription factors. ? Although molecular mechanisms of synaptic plasticity are beginning to be identified, detailed correlation of biochemical changes with electrophysiological responses in hippocampal neurons is lacking. In this grant application we will use glycine-induced synaptic potentiation of AMPA-Rs in cultured hippocampal neurons which enhances mEPSC amplitude and frequency. Potentiation at individual synapses will be subjected to nonstationary fluctuation analysis to determine mechanisms of synapses will be subjected to nonstationary fluctuation analysis to determine mechanisms of synaptic plasticity. We will identify biochemical modulations of key proteins that regulate AMPA-R properties including channel conductance, open probability, channel number and synaptic localization. Proteins to be investigated include CaM-KII, CaM-KIV, the GluR1 subunit of AMPA-R, transcription factors CREB and CBP and the translational regulatory protein CPEB. The phosphorylation states of these proteins and their regulatory consequences in terms of synaptic plasticity will be determined. ? The results of this study will provide biochemical details of multiple mechanisms of synaptic plasticity including modulation of AMPA-Rs, regulation of gene transcription and modulation of dendritic protein synthesis. ? ?
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