Neuroarchitecture and central regulation of peptidergic systems in the ventral ganglion of Drosophila melanogaster

Neuropeptides regulate multiple physiological processes such as learning, reproduction and growth, both in vertebrates and invertebrates. In my doctoral thesis, I aimed at gaining insights into the neuroarchitecture and the central regulation of peptidergic systems in the larval ventral ganglion (LVG) of the fruit fly Drosophila melanogaster. In particular, I focused on the central regulation of peptidergic neurons which are involved in the control of ecdysis, because ecdysis is a vital and highly conserved behavior under complex neuroendocrine and central regulation. My dissertation consists of six chapters that address three key aspects: 1) Chapter I contains a three-dimensional morphological description of peptidergic systems in the LVG that helps to identify the neural network connections between peptidergic neurons and their pre- and postsynaptic neurons. The ensuing Chapter II then deals with the neuroarchitecture of aminergic neurons in the LVG, because aminergic neurons are likely to interact with peptidergic neurons. 2) Chapter III focuses on the identification of neurotransmitters that are involved in the central regulation of the ecdysis-relevant CCAP-producing neurons. The subsequent chapters IV and V are concerned with the development of methods for the transient synaptic isolation of CCAP-producing neurons during calcium imaging experiments, and the cell-specific silencing of nicotinic ACh receptors, respectively. 3) Chapter VI finally describes the generation and characterization of fluorescent neuropeptide fusion proteins that have been developed to measure neuropeptide release from peptidergic neurons in the intact CNS

Neuroarchitecture of Peptidergic Systems in the Larval Ventral Ganglion of Drosophila melanogaster

Recent studies on Drosophila melanogaster and other insects have revealed important insights into the functions and evolution of neuropeptide signaling. In contrast, in- and output connections of insect peptidergic circuits are largely unexplored. Existing morphological descriptions typically do not determine the exact spatial location of peptidergic axonal pathways and arborizations within the neuropil, and do not identify peptidergic in- and output compartments. Such information is however fundamental to screen for possible peptidergic network connections, a prerequisite to understand how the CNS controls the activity of peptidergic neurons at the synaptic level. We provide a precise 3D morphological description of peptidergic neurons in the thoracic and abdominal neuromeres of the Drosophila larva based on fasciclin-2 (Fas2) immunopositive tracts as landmarks. Comparing the Fas2 “coordinates” of projections of sensory or other neurons with those of peptidergic neurons, it is possible to identify candidate in- and output connections of specific peptidergic systems. These connections can subsequently be more rigorously tested. By immunolabeling and GAL4-directed expression of marker proteins, we analyzed the projections and compartmentalization of neurons expressing 12 different peptide genes, encoding approximately 75% of the neuropeptides chemically identified within the Drosophila CNS. Results are assembled into standardized plates which provide a guide to identify candidate afferent or target neurons with overlapping projections. In general, we found that putative dendritic compartments of peptidergic neurons are concentrated around the median Fas2 tracts and the terminal plexus. Putative peptide release sites in the ventral nerve cord were also more laterally situated. Our results suggest that i) peptidergic neurons in the Drosophila ventral nerve cord have separated in- and output compartments in specific areas, and ii) volume transmission is a prevailing way of peptidergic communication within the CNS. The data can further be useful to identify colocalized transmitters and receptors, and develop peptidergic neurons as new landmarks

Neuroarchitecture of Aminergic Systems in the Larval Ventral Ganglion of Drosophila melanogaster

Biogenic amines are important signaling molecules in the central nervous system of both vertebrates and invertebrates. In the fruit fly Drosophila melanogaster, biogenic amines take part in the regulation of various vital physiological processes such as feeding, learning/memory, locomotion, sexual behavior, and sleep/arousal. Consequently, several morphological studies have analyzed the distribution of aminergic neurons in the CNS. Previous descriptions, however, did not determine the exact spatial location of aminergic neurite arborizations within the neuropil. The release sites and pre-/postsynaptic compartments of aminergic neurons also remained largely unidentified. We here used gal4-driven marker gene expression and immunocytochemistry to map presumed serotonergic (5-HT), dopaminergic, and tyraminergic/octopaminergic neurons in the thoracic and abdominal neuromeres of the Drosophila larval ventral ganglion relying on Fasciclin2-immunoreactive tracts as three-dimensional landmarks. With tyrosine hydroxylase- (TH) or tyrosine decarboxylase 2 (TDC2)-specific gal4-drivers, we also analyzed the distribution of ectopically expressed neuronal compartment markers in presumptive dopaminergic TH and tyraminergic/octopaminergic TDC2 neurons, respectively. Our results suggest that thoracic and abdominal 5-HT and TH neurons are exclusively interneurons whereas most TDC2 neurons are efferent. 5-HT and TH neurons are ideally positioned to integrate sensory information and to modulate neuronal transmission within the ventral ganglion, while most TDC2 neurons appear to act peripherally. In contrast to 5-HT neurons, TH and TDC2 neurons each comprise morphologically different neuron subsets with separated in- and output compartments in specific neuropil regions. The three-dimensional mapping of aminergic neurons now facilitates the identification of neuronal network contacts and co-localized signaling molecules, as exemplified for DOPA decarboxylase-synthesizing neurons that co-express crustacean cardioactive peptide and myoinhibiting peptides

Neuroarchitecture and central regulation of peptidergic systems in the ventral ganglion of Drosophila melanogaster

Neuropeptides regulate multiple physiological processes such as learning, reproduction and growth, both in vertebrates and invertebrates. In my doctoral thesis, I aimed at gaining insights into the neuroarchitecture and the central regulation of peptidergic systems in the larval ventral ganglion (LVG) of the fruit fly Drosophila melanogaster. In particular, I focused on the central regulation of peptidergic neurons which are involved in the control of ecdysis, because ecdysis is a vital and highly conserved behavior under complex neuroendocrine and central regulation. My dissertation consists of six chapters that address three key aspects: 1) Chapter I contains a three-dimensional morphological description of peptidergic systems in the LVG that helps to identify the neural network connections between peptidergic neurons and their pre- and postsynaptic neurons. The ensuing Chapter II then deals with the neuroarchitecture of aminergic neurons in the LVG, because aminergic neurons are likely to interact with peptidergic neurons. 2) Chapter III focuses on the identification of neurotransmitters that are involved in the central regulation of the ecdysis-relevant CCAP-producing neurons. The subsequent chapters IV and V are concerned with the development of methods for the transient synaptic isolation of CCAP-producing neurons during calcium imaging experiments, and the cell-specific silencing of nicotinic ACh receptors, respectively. 3) Chapter VI finally describes the generation and characterization of fluorescent neuropeptide fusion proteins that have been developed to measure neuropeptide release from peptidergic neurons in the intact CNS

Chemical depletion of Arctic ozone in winter 1999/2000

Large losses of Arctic ozone occur during winters with cold, stable stratospheric circulations that result in the extensive occurrence of polar stratospheric clouds (PSCs). Reactions on the surface of PSCs lead to elevated abundances of chlorine monoxide (ClO) that, in the presence of sunlight, destroys ozone. Here we show that PSCs were more widespread during the 1999/2000 Arctic winter than for any other winter in the past two decades. We have used three fundamentally different approaches to derive the degree of chemical ozone loss from ozone sonde, balloon, aircraft and satelite instruments. We show that the ozone losses derived from these different instruments and approaches agree very well, resulting in a high level of confidence in the results. Chemical processes led to a 70% reduction of ozone for a ~1 km thick region of the lower stratosphere, the largest degree of local loss ever reported for the Arctic. The chemical loss of ozone in the total column amounted to about 100 DU by the end of the winter. This total column loss was balanced by transport, resulting in relatively constant total ozone between early January and late March, which is in contrast to the climatological increase of the total ozone column during this period, that is observed during most years