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Leiss, Florian (2009): Dendritic spines and structural plasticity in Drosophila. Dissertation, LMU München: Faculty of Biology
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Abstract

The morphology of dendrites is important for neuronal function and for the proper connectivity within neuronal circuits. The often very complex shape of dendritic trees is brought about by the action of many different genes throughout development. Moreover, neuronal activity is often involved in refining synaptic connections and shaping dendrites. Aiming at a better understanding of the interplay between genes and neuronal activity during dendrite differentiation I was trying to identify suitable neurons in the Drosophila central nervous system. Describing the morphology and cytoskeletal organization of a group of visual interneurons involved in motion processing I provided evidence that the dendrites of these neurons do bear small protrusions that share essential characteristics with vertebrate spines. Vertebrate spines received a lot of recent attention because neuronal activity can induce lasting changes in their morphology even in the adult. These morphological changes are believed to be cellular correlates of learning and memory. The observation of similar structures in flies raised the possibility to study structural plasticity in a genetically accessible model organism. Experience-dependent alterations in the volume of a region in the insect brain, called mushroom body calyx, have been shown. The calyx is known to contain the dendrites of olfactory interneurons, Kenyon cells, which are known to be required for the retrieval of olfactory memories in flies. I wanted to address if morphological rearrangements of the dendrites of these cells could underlie the experience-dependent changes in calycal volume. Kenyon cell dendrites and their presynaptic partners are known to form synaptic complexes, called microglomeruli, throughout the calyx. My results help refining the anatomical description of these structures. These findings are important to understand how olfactory experience is represented in the fly brain and how olfactory memories might be formed. Moreover, I developed a computer algorithm to quantitatively describe the morphology of these microglomeruli in an automated manner. Thereby, I found indications for morphological rearrangements of calycal microglomeruli during the first days of the adult life of Drosophila. I could show that olfactory experience is not required for these morphological alterations. My findings provide the basis for ongoing attempts to study the influence of neuronal activity on the dendritic morphology of Kenyon cells in more detail.