Embryonalententwicklung des Zentralkomplexes im Gehirn der Wüstenheuschrecke Schistocerca gregaria

The central complex is a major neuropil in the protocerebral midbrain of insects. It is involved in multimodal information processing (polarized light, olfaction, etc.), in coordinating motor behaviour (such as locomotion, sound production), and in spatial orientation. Its modular neuroarchitecture is highly organized, and in hemimetabolous insects like the grasshopper it is composed of the following parts: protocerebral bridge (PB), ellipsoid (EB) and central body (CB), paired noduli (N) and the lateral accessory lobes (LAL). A prominent feature in the central complex is the w-, x-, yand z-tract system in which axons project from neuronal clusters in the pars intercerebralis (PI) via the protocerebral bridge to the central body. Also prominent are the chiasms of the columns directly anterior and posterior to the central body between the parts of the central complex. This study examines cellular and molecular aspects of the embryonic development of the central complex of the grasshopper Schistocerca gregaria. First, the development of the modular w-, x-, yand z-tracts of the central body in the grasshopper is examined. A new topological map of neuroblast distributions in the protocerebrum in which the central complex is developing is created using the expression pattern of genes like the segment polarity gene engrailed. In each hemisphere 95 neuronal stem cells, the so-called neuroblasts (NBs), delaminate from the epithelium and appear arranged in seven rows like in the thoracic and abdominal segments. NBs are named according to their row-number and position in the row or with letters. Four of the 95 neuroblasts namely 1-1 (also known as W), 2-1 (also known as X), 3-1 (also known as Y), 4-1 (also known as Z) generate cell clusters whose neurons give rise to one of the four w-, x-, y-, z-tracts respectively. Since all the tracts develop in an analogous manner, the development of the z-tract was selected as being representative and is investigated at the single cell level. Second, the embryonic development of identified cells in the median domain (MD) of the midbrain of the grasshopper is investigated using immunohistochemistry, histology, and dye labeling coupled with confocal, fluorescenceand interference-contrast microscopy. The socalled lateral cells occur singly and are positioned in the MD at the border to the protocerebral hemispheres. They can be identified through their co-expression of the neuronal label HRP, the mesectodermal label Mes-3, and the cell surface lipocalin Lazarillo. Further, the 16 Embryonalentwicklung des Zentralkomplexes im Gehirn der Wüstenheuschrecke Schistocerca gregaria Michaela Romy Güntner development of other HRP-/Mes-3-expressing pioneers of the protocerebral commissure (PCPs) is described. The axons of the LCs and the PCPs fasciculate with one another and together with a third set of pioneers, the HRP-positive secondary commissure pioneers (SCNs), build an axonal scaffold on which other neuropils orientate during their development. A model describes their delamination, migration to their target positions in the midbrain, and subsequent development. Third, the embryonic development of expression patterns of different neuromodulators are studied for the first time. With the newly developed matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-IMS) technique (Crecelius et al., 2005) it is possible to analyse peptide expression in individual brain slices for the first time. Several neuromodulators belonging to the following peptide families were found: tachykinin, allatostatin, periviscerokinin, pyrokinin, FLRFamide and neuropeptide F. The developing expression patterns of these peptides, as well as of the indolamine serotonin and the endogenous messenger nitric oxide (NO) via its NO-synthesizing enzyme diaphorase (NADPHd) are described. Tachykinin is first seen in central complex neurons at 50% of embryonic development, allatostatin at 65%, NADPHd at 70% and serotonin at 75%. Later in the embryonic development single neurons show periviscerokinin and FLRFamide expression. The whole expression pattern is developing postembryonically. Expression is seen in tangential neurons first and later in columnar neurons of the central complex. The neuromodulators are expressed in different layers of the central body consistent with these layers having different functions in behavior. Some functions of the different neuromodulators and messengers in the development of nervous systems and in the adult central complex are known. To get a deeper understanding further studies are necessary. Embryonalentwicklung des Zentralkomplexes im Gehirn der Wüstenheuschrecke Schistocerca gregaria 17 Michaela Romy Güntner 18 Embryonalentwicklung des Zentralkomplexes im Gehirn der Wüstenheuschrecke Schistocerca gregaria Michaela Romy Güntner