Glutamate receptors have been documented to play an essential role for initiating synaptic potentiation. However, the question whether changes in glutamate receptors themselves account for the lasting increase in synaptic responses has not yet been adequately investigated. Major long-term goals of this project are to analyze mechanisms, role and developmental aspects of glutamate receptor regulation with main emphasis on NMDA and AMPA receptors and to evaluate the hypothesis that changes in number or characteristics of functional glutamate receptors may account for changes in synaptic efficacy after treatments leading to synaptic potentiation. To induce potentiation, hippocampal slices will be stimulated at multiple electrode positions with a theta patterned stimulation paradigm. Membranes will then be prepared from the excised CAl fields. Alternatively, since only a fraction of the synapses can be activated by electrical stimulation, hippocampal slices will be briefly exposed to glutamate receptor activators under conditions which have proven to induce stable and selective potentiation of the orthodromically evoked responses. It will be further tested whether degeneration of CAl cells of the gerbil hippocampus after controlled ischemia is associated with changes in glutamate binding sites. The binding studies will make use of recent insights into the complex characteristics of NMDA and AMPA sites and will attempt to monitor these sites in more detail than previously possible. NMDA receptors will be tested for changes in ligand binding and in receptor/channel coupling by measuring association and dissociation rates of TCP binding and the effect of glutamate and glycine on these binding rates. Binding of AMPA to quisqualate receptor sites will be resolved into high and low-affinity components and tested for changes in their number, ratio and possible interconversions. The screening will further include kainate binding sites and AP5 insensitive glutamate-aspartate binding sites.
