Structural and functional analysis of the Drosphila antennal lobe
The antennal lobe (AL) of the vinegar fly Drosophila melanogaster ranks among the best investigated structures in neuroscience. Increasing knowledge of its detailed morphological properties is paralleled by an enlarging number of studies on precise chemosensory functions and their related ecology. These meanings, like hard-wired aversion to geosmin or attraction to cis-vaccenyl acetate, are often assigned to be coded by a single subunit of the AL, glomerulus, each. Despite their functional heterogeneity, glomeruli are usually thought to be uniform. Only exception is the macroglomerular complex, a cluster of enlarged glomeruli located at the sensory entrance of the AL in most insects, known to be responsible for pheromone perception. The aim of this thesis was to show if glomeruli are actually uniform regarding their anatomy and if their putative morphological variability allows a functional prediction. Therefore we generated the first ever in vivo atlas of the Drosophila AL from a novel transgenic fly line (END1-2), providing a least artificial anatomical foundation for the succeeding projects. Based on the in vivo atlas we characterized each glomerulus regarding its number of afferent olfactory sensory neurons, in vivo volume and efferent projection neurons as well as integrated an external data set on the local interneuron innervation patterns (Chou et al. 2010). In parallel we carried out two studies on the functional specificity of glomeruli regarding their connectivity between each other as well as their stereotypic neuronal output in higher brain centers. We could show that increased functional specificity of the AL glomeruli in Drosophila is accompanied by morphological specialization. This allows predicting the functional significance of a glomerulus from its anatomy.
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