Synapses are arguably the most elaborate signaling machine of cells. This complex intercellular junction is specialized for rapid (millisecond) directional signaling. In addition, synapses change in response to patterns of neural activity and these changes can endure, modifying neuronal circuitry. These competing properties of persistence and plasticity must be encoded by the precise content and arrangement of molecules that comprise the presynaptic and postsynaptic specializations. The objective of this project is to uncover the internal organization and dynamics of the postsynaptic specialization at excitatory glutamatergic synapses of the mammalian brain at an unprecedented nano-scale resolution. For this aim, neurobiologists, physicists and chemists join forces in a team with proven track record of collaboration. We will combine cellular and molecular neurobiology approaches with development of novel optical technologies, biosensors and combined quantitative light and electron microscopic imaging techniques. This will provide a new level of analysis to the fundamental problem of molecular information storage. Photothermal imaging of nano-gold particles will allow unprecedented quantitative histochemistry and tracking of protein trafficking up to the level of intact tissue. Development of Cryo-Photoactivated Light Microscopy will allow the correlative localization of synaptic elements at the light and electron-microscopic level. Novel biosensors and chemical tools will be developed for the investigation of the dynamic macromolecular events underlying synaptic plasticity. We will identify new mechanisms that control fast synaptic transmission and its long term activity dependent modification. We will unravel how fast receptor diffusion controls frequency dependent synaptic transmission and how regulation of receptor trafficking participates in synaptic plasticity.