Activity-regulated changes in synapse function lie at the heart of molecular theories of learning and neural development, and are the targets of diseases and disorders including Alzheimer's Disease, schizophrenia, and epilepsy. At glutamatergic synapses of the brain, multi-domain proteins establish the core of the postsynaptic density (PSD), the structure which links neurotransmitter receptors to the actin cytoskeleton and to intracellular signaling pathways. It has been proposed that such PSD proteins control synaptic strength by controlling the anchoring or mobility of synaptic receptors, but direct evidence regarding how this might be accomplished within the PSD has been lacking. Furthermore, though PSD size and shape correlate with synaptic receptor levels when assayed as a population at single time points, it is not known whether single PSDs transition among various morphologies, or whether such transformations mediate weakening of synapses during long-term depression. We have established a novel fluorescence morphometry approach for examining single, living PSDs, and have developed two high-resolution photobleaching assays for monitoring the movement of proteins within them. We have found that PSDs undergo a large degree of continuous morphological change, contrary to expectations for a simple scaffold. However, mobility of core protein within the complex is extremely limited, indicating that internal structure is nevertheless maintained. We therefore hypothesize that dynamic adjustment of PSD form continuously alters synapse function, and that long-term synaptic depression requires the disruption of this structure to accommodate the removal of receptors. In this proposal, we will clarify the role of PSD internal dynamics in synaptic function and plasticity. In cultured neurons from rat hippocampus, we will use quantitative fluorescence microscopy along with patch-clamp electrophysiology, photolysis, and time-resolved electron microscopy to address the following specific aims. First, is PSD morphological change coordinated with presynaptic structure? Second, do these changes dynamically alter synaptic strength? Third, does actin control the internal stability of the postsynaptic scaffold? Fourth, does the PSD undergo regulated changes in morphology or dynamics before or after receptor loss in long-term depression? The answers to these questions will fill large gaps in our understanding of the synaptic structure-function relationship. Further, they will provide an important platform on which to test hypotheses regarding the molecular basis of disorders that disrupt synaptic transmission.

National Institute of Health (NIH)
National Institute of Mental Health (NIMH)
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Synapses, Cytoskeleton and Trafficking Study Section (SYN)
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Asanuma, Chiiko
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University of Maryland Baltimore
Schools of Medicine
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Lu, Hsiangmin E; MacGillavry, Harold D; Frost, Nicholas A et al. (2014) Multiple spatial and kinetic subpopulations of CaMKII in spines and dendrites as resolved by single-molecule tracking PALM. J Neurosci 34:7600-10
MacGillavry, Harold D; Song, Yu; Raghavachari, Sridhar et al. (2013) Nanoscale scaffolding domains within the postsynaptic density concentrate synaptic AMPA receptors. Neuron 78:615-22
Lieberman, Joshua A; Frost, Nicholas A; Hoppert, Michael et al. (2012) Outer membrane targeting, ultrastructure, and single molecule localization of the enteropathogenic Escherichia coli type IV pilus secretin BfpB. J Bacteriol 194:1646-58
Kerr, Justin M; Blanpied, Thomas A (2012) Subsynaptic AMPA receptor distribution is acutely regulated by actin-driven reorganization of the postsynaptic density. J Neurosci 32:658-73
Weinman, Edward J; Steplock, Deborah; Shenolikar, Shirish et al. (2011) Dynamics of PTH-induced disassembly of Npt2a/NHERF-1 complexes in living OK cells. Am J Physiol Renal Physiol 300:F231-5
MacGillavry, Harold D; Kerr, Justin M; Blanpied, Thomas A (2011) Lateral organization of the postsynaptic density. Mol Cell Neurosci 48:321-31
Frost, Nicholas A; Shroff, Hari; Kong, Huihui et al. (2010) Single-molecule discrimination of discrete perisynaptic and distributed sites of actin filament assembly within dendritic spines. Neuron 67:86-99
Frost, Nicholas A; Kerr, Justin M; Lu, Hsiangmin E et al. (2010) A network of networks: cytoskeletal control of compartmentalized function within dendritic spines. Curr Opin Neurobiol 20:578-87
Weinman, Edward J; Steplock, Deborah; Cha, Boyoung et al. (2009) PTH transiently increases the percent mobile fraction of Npt2a in OK cells as determined by FRAP. Am J Physiol Renal Physiol 297:F1560-5
Blanpied, Thomas A; Kerr, Justin M; Ehlers, Michael D (2008) Structural plasticity with preserved topology in the postsynaptic protein network. Proc Natl Acad Sci U S A 105:12587-92