Visualizing the activity of nerve cells using genetically encoded indicator proteins has emerged to a widely used technique in the field of neuroscience. In particular, intracellular Ca 2+ dynamics represents a parameter that is closely correlated with neuronal excitation, and a variety of genetically encoded Ca 2+ sensors have been developed. The fruit fl y Drosophila melanogaster is an extremely useful model organism to use these indicators because of its sophisticated genetic tools to express an artificial genetic construct in a spatially and temporally controlled pattern within the nervous system. Binary expression systems, for which large amount of different fl y strains exist, enable a targeted expression in selective neuronal populations. Advanced fl uorescence microscopical visualization techniques (see Part 3) allow for real-time monitoring of neural activity patterns. In Drosophila, optical Ca 2+ imaging has been used to analyze basic principles of neuronal coding and processing, e.g., olfactory coding, visual stimulus processing, taste perception, mechanosensation, or learning and memory. In this chapter, we will review how genetic targeting methods can be used in Drosophila to monitor neural Ca 2+ activity in vivo in order to study how individual neurons or neuronal ensembles encode stimulus information.
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