Elucidating the olfactory pathways within and beyond the antennal lobe in Drosophila melanogaster

The vinegar fly Drosophila melanogaster is confronted with various odors while exploring the environment. Some odors elicit innately the approach or avoidance of the odor source, e.g. pheromones cause the approach and contaminated food causes the avoidance. How does the fly evaluate the perceived odors and how is the innate preference accomplished? The information of perceived odors is processed in a complex neural circuitry consisting of sever-al neuron populations distributed throughout distinct brain areas. This thesis aimed at elucidat-ing the neuronal interplay within and beyond the primary olfactory processing center, the an-tennal lobe (AL), on a morphological and a functional level. To characterize morphologically the AL subunits, the so-called glomeruli, we generated a transgenic fly with an endogenous labeling of neuropil structures that enabled to establish an in vivo 3D-atlas of the AL. Furthermore, we correlated the glomerular volume with the num-bers of different neuron types innervating distinct glomeruli. This revealed a dependence of the glomerular volume to the number of sensory and projection neurons. In addition, consider-ing the functional properties of all odor processing channels emphasizes a dependence of the glomerular wiring to the odor tuning profile. To investigate how odor information is transferred from the primary to the higher processing centers the morphological and functional properties of inhibitory and excitatory projection neu-rons were analyzed. This revealed that the morphological topography of the AL is retained in the lateral horn (LH), a higher brain center which is assumed to mediate innate odor-guided behavior. Furthermore, in the LH odors are represented due to their hedonic valence and in-tensity in separate, global odor response domains. Characterizing the odor processing channels in the AL and the odor coding strategies in the LH is a step further to understand the neural circuitry of innate odor-guided behavior.