An all-optical activation and readout setup to investigate the insect olfactory system network

We present first results in adding optogenetic tools to our experimental two-photon imaging platform. The efforts are aiming at applying this technique first to the fruit fly Drosophila melanogaster and subsequently to the honeybee Apis mellifera, at the level of the primary olfactory processing brain centers, the antennal lobes. Insect brains are an important model in neurobiology, thanks to their small sizes, tight structures, but rich performances. We use two-photon calcium imaging to study morphology and functions of the insect olfactory system in order to investigate various aspects of information coding. Activating specific nodes of the antennal lobe will allow modulating neuronal activity with high selectivity and precision both in the temporal and spatial domain, permitting us to study deeper the connectivity and the mechanisms of stimuli elaboration within this neuronal network. The required hardware for optical activation was integrated in our two-photon microscope: a 473 nm laser for opsin activation, overlapped with the infrared imaging beam. In a first attempt to combine optogenetics with calcium imaging, reducing problems of activation and emission crosstalk, different combinations of proteins were tested; in particular we focused on ChR2, ChR2-XXL opsins and GCaMP6, RGECO1.2 sensors. We present initial optogenetic experiments in HEK cell lines, and the first results with transgenic flies expressing these proteins. We give an idea of the innovative efforts to engineer a genetically modified bee too.