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Abstract:
Chemosensation, the sense of smell and taste, is an essential tool for most animals, including humans, for finding and evaluating possible food sources not only with respect to their edibility but also their nutritious value. Hence, odorants and tastants often have intrinsic valence which means that they are perceived as either positive or negative and can cause innate attraction or aversion. Using in vivo whole brain light field imaging in the adult fruit fly ( D. melanogaster). We have investigated how neurons respond to odor and taste of different valence on a brain wide level. The peripheral perception of this sensory inputs has been studied intensively, yet how these signals are encoded in higher brain centers, is still poorly understood, especially in gustation. How odor and taste is combined in the brain is even less understood. Since it has been demonstrated that the valence of a stimulus can be modulated by metabolic state of the animal, we further examined which brain regions are influenced in their odor or taste responses by starvation. In order to study this, we expressed the calcium-sensitive protein GCamp pan-neuronally in all neurona cells. We recorded the Ca2+ -dependent changes in fluorescence with high temporal resolution using a custom-build light field microscope (LFM) and reconstructed a three-dimensional image of neu responses to odors and tastes of the whole brain. With this approach, we analyzed valence-coding an integration of sensory stimuli on a global scale. We have imaged both fed and starved flies and exposed them to different odor and taste substances. We analyzed the peak responses in twelve major brain areas and found that depending on the se modality, the response is highly region-specific. Odors elicited high responses in the lateral horn (LH), the mushroom bodies (MB) as well as the superior neuropils (SNP), whereas tastants strongly activated th gnathal ganglia (GNG). Moreover, we found that starvation increases the response to appetitive odors and in contrast reduces the response to non-appetitive tastes in multiple brain regions. This suggests t metabolic state modulates olfactory and gustatory circuits in different ways. When pairing a taste with a odor stimulus, both odor and taste responsive regions were activated simultaneously. We found that pairing an appetitive odor with a bitter taste results in higher responses brain-wide, especially in fed flies. Th suggests that brain activity during multisensory integration of chemosensory stimuli is influenced by valence information and the internal state. In a second step, we are analyzing this data set, using independent component analysis (ICA) in order to identify functional subregions for multisensory and metabolic state integration that show highly correlated activity in response to the stimulus with the aim of mapping them to anatomical subregions, neural tracts or even individual neurons. We aim at creating a functional map across the whole fly brain that illustrates the neural circuits involved in integration of taste and odor as well as metabolic state, based on our in v experiments.
