Derangements in synaptic transmission are part of the pathology of several neurological and mental diseases including epilepsy, schizophrenia, depression, and Alzheimer's disease. We are studying the molecular mechanisms underlying regulation of synaptic transmission. Here we propose to study regulatory pathways at glutamatergic synapses governed by Ca2+/calmodulin-dependent protein kinase II (CaMKII). CaMKII is concentrated in the postsynaptic density where it can be activated by Ca 2+ influx through NMDA receptors. The proposal focuses on two principal postsynaptic substrates of CaMKII, SynGAP, a Ras GTPase-activating protein that is concentrated in the postsynaptic density, and densin, a proposed docking site for CaMKII. In the First Aim, we will test the hypothesis that synGAP participates in regulation of the cytoskeleton at synapses in brain slices. We have previously shown that synGAP helps to regulate the spine cytoskeleton during synapse formation in cultured neurons, and that the location and activation of the kalirin/PAK kinase pathway is altered in hippocampal slices heterozygous for synGAP. We will use slices from wild type and synGAP deficient mutants to map the role of synGAP in this and related pathways following synaptic stimulation. In the Second Aim, we will use electrophysiological studies in hippocampal slices from wild type and conditional synGAP deficient mice to investigate whether the effects of synGAP deficiency on LTP are a result of developmental abnormalities or of acute loss of synGAP. We will also test the hypothesis that synGAP participates in regulation of the modulation of dendritic excitability by MAP kinase. In the Third Aim, we will examine recruitment of CaMKII to the PSD in neuronal cultures prepared from knock-in mice that are missing the carboxyl terminal tails of the NR2A and NR2B subunits of the NMDA receptor. We will also examine recruitment of CaMKII in these cultures after introducing recombinant forms of the intracellular tails of densin, or reducing the expression of densin by introduction of siRNA. In the Fourth Aim, we propose to determine the physiological importance of densin, and test the hypothesis that densin is a docking site for CaMKII in the PSD by constructing knockout and conditional knockout mutants of densin.