Processes like learning and memory require functional modification of neuronal networks through reorganization of existing synapses, modification of their efficacy, or modulation of neuronal endogenous excitability. Synapses are particularly prone to dynamic alterations and thus are believed to play a major role in plasticity. We study structural and functional synaptic modifications regulated by posttranslational modifications including: i) protein-specific proteolysis by extracellular matrix proteolytic modifiers, ii) S-nitrosylation and S-palmitoylation i.e. addition of palmitate or nitric oxide that reversibly modifies numerous classes of neuronal proteins. We focus on the role of rapid posttranslational modifications of synaptic proteins in protein organization in the synapse under physiological stimuli as well as pathological conditions (such as chronic stress). We employ novel imaging based techniques and mass spectrometry methods to assess the reorganization of activity patterns accompanied by local volumetric and molecular changes at the synapses.