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Abstract
Complex external stimuli such as odorants are believed to be internally represented
in the brain by spatiotemporal activity patterns of extensive neuronal ensembles.
These activity patterns can be recorded by optical imaging techniques. However, optical
imaging with conventional fluorescence dyes usually does not allow for resolving the
activity of biologically defined groups of neurons. Therefore, specifically targeting
reporter molecules to neuron populations of common genetic identity is an important
goal. We report the use of the genetically encoded calcium-sensitive fluorescence
protein cameleon 2.1 in the Drosophila brain. We visualized odorant-evoked intracellular
calcium concentration changes in selectively labeled olfactory projection neurons
both postsynaptically in the antennal lobe, the primary olfactory neuropil, and presynaptically
in the mushroom body calyx, a structure involved in olfactory learning and memory.
As a technical achievement, we show that calcium imaging with a genetically encoded
fluorescence probe is feasible in a brain in vivo. This will allow one to combine
Drosophila's advanced genetic tools with the physiological analysis of brain function.
Moreover, we report for the first time optical imaging recordings in synaptic regions
of the Drosophila mushroom body calyx and antennal lobe. This provides an important
step for the use of Drosophila as a model system in olfaction.