Imaging activity-dependent signaling dynamics at the neuronal synapse using FRET-based biosensors

In this chapter, we introduce the combined use of FRET-based biosensors and synaptic markers as an effective tool for studying intracellular signaling pathways in small synaptic terminals of neuronal cells. The approach is based on the unmixing of excitation/emission spectral fingerprints of a FRET donor and acceptor pair, as well as a lipophilic styryl dye, FM1-43, loaded into presynaptic terminals. The destaining of FM1-43 during evoked release provides a map to guide the sampling of fluorescence for FRET analysis. In the example presented here, we measure the temporal dynamics of cAMP at the presynaptic terminal using an intramolecular CFP/YFP-based FRET sensor. However, this methodology can be applied to investigate the spatial and temporal regulation of a variety of signaling processes, as well as dynamic changes in protein-protein interaction.