Role of postsynaptic synaptotagmins in synaptic plasticity

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Center PI: Malenka, Robert C. Principal Investigator (Project 1): Malenka, Robert C./Südhof, Thomas Project Summary The ability of the mammalian brain to undergo long-lasting, activity-dependent changes in synaptic function and structure importantly contributes to the neural circuit modifications that underlie many forms of adaptive and pathological experience-dependent plasticity, including learning and memory. A leading model for such synaptic plasticity is NMDA receptor-dependent long-term potentiation (LTP). Although progress has been made in understanding the mechanisms underlying LTP, much remains unknown. This project will perform experiments that for the first time examine the novel hypothesis that postsynaptic synaptotagmins (Syts) are critical for the trafficking of AMPA receptors to the plasma membrane during LTP and also in the growth of dendritic spines that accompanies LTP. Syts are known to trigger the presynaptic release of neurotransmitter in response to calcium but their potential postsynaptic functions are largely unknown. The experiments will use a “molecular replacement” strategy, which incorporates the simultaneous knockdown or genetic deletion of Syts with expression of a “replacement” version of wildtype or mutant Syt in single hippocampal pyramidal cells in vivo or in vitro. Electrophysiological assays in acute hippocampal slices and cell biological assays in cultured neurons will be performed to determine the consequences of Syt manipulations on basal synaptic responses, LTP, long-term depression and AMPA receptor exocytosis and endocytosis. The role of postsynaptic Syts on the spine growth that accompanies LTP will also be examined. Preliminary evidence supports a role specifically for postsynaptic Syt1 and 7 in LTP. We will focus on molecular manipulations of these proteins for which conditional knockout mice are already available. These experiments will elucidate novel molecular mechanisms by which excitatory synapses in the mammalian brain are likely modified during various forms of experience-dependent plasticity, including learning and memory. The results will also open up new, innovative areas of research on the postsynaptic membrane trafficking underlying synaptic plasticity. In addition, this research will provide information that is critical for the development of agents that modify synaptic transmission in ways that promote cognitive function and alleviate psychiatric symptoms. Relevance Learning and memory involve long-lasting modification of the communication between nerve cells at their physical connections, which are termed synapses. This project will use sophisticated experimental techniques to elucidate some of the key molecular mechanisms underlying how this modification happens. The information that will be collected is essential for developing more effective treatments for the deterioration of cognitive function that accompanies many forms of mental illness.