@phdthesis{Mrestani2022,
  author    = {Mrestani, Achmed},
  title     = {Strukturelle Differenzierung und Plastizit{\"a}t pr{\"a}synaptischer Aktiver Zonen},
  doi       = {10.25972/OPUS-23578},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-235787},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Ziel der vorliegenden Arbeit war die nanoskopische Analyse struktureller Differenzierung und Plastizit{\"a}t pr{\"a}synaptischer aktiver Zonen (AZs) an der NMJ von Drosophila melanogaster mittels hochaufl{\"o}sender, lichtmikroskopischer Bildgebung von Bruchpilot (Brp). In erster Linie wurde das lokalisationsmikroskopische Verfahren dSTORM angewendet. Es wurden neue Analyse-Algorithmen auf der Basis von HDBSCAN entwickelt, um eine objektive, in weiten Teilen automatisierte Quantifizierung bis auf Ebene der Substruktur der AZ zu erm{\"o}glichen. Die Differenzierung wurde am Beispiel phasischer und tonischer Synapsen, die an dieser NMJ durch Is- und Ib-Neurone gebildet werden, untersucht. Phasische Is-Synapsen mit hoher Freisetzungswahrscheinlichkeit zeigten kleinere, kompaktere AZs mit weniger Molek{\"u}len und h{\"o}herer molekularer Dichte mit ebenfalls kleineren, kompakteren Brp-Subclustern. Akute strukturelle Plastizit{\"a}t wurde am Beispiel pr{\"a}synaptischer Hom{\"o}ostase, bei der es zu einer kompensatorisch erh{\"o}hten Neurotransmitterfreisetzung kommt, analysiert. Interessanterweise zeigte sich hier ebenfalls eine kompaktere Konfiguration der AZ, die sich auch auf Ebene der Subcluster widerspiegelte, ohne Rekrutierung von Molek{\"u}len. Es konnte demonstriert werden, dass sich eine h{\"o}here Molek{\"u}ldichte in der Lokalisationsmikroskopie in eine h{\"o}here Intensit{\"a}t und gr{\"o}ßere Fl{\"a}che in der konfokalen Mikroskopie {\"u}bersetzt, und damit der Zusammenhang zu scheinbar gegens{\"a}tzlichen Vorbefunden hergestellt werden. Die Verdichtung bzw. Kompaktierung erscheint im Zusammenhang mit der Kopplungsdistanz zwischen VGCCs und pr{\"a}synaptischen Vesikeln als plausibles Muster der effizienten Anordnung molekularer Komponenten der AZ. Die hier eingef{\"u}hrten Analysewerkzeuge und molekularbiologischen Strategien, basierend auf dem CRISPR/Cas9-System, zur Markierung von AZ-Komponenten k{\"o}nnen zuk{\"u}nftig zur weiteren Kl{\"a}rung der Bedeutung der molekularen Verdichtung als allgemeines Konzept der AZ-Differenzierung beitragen.},
  subject      = {Synapse},
  language  = {de}
}
@phdthesis{Grotemeyer2019,
  author    = {Grotemeyer, Alexander},
  title     = {Characterisation and application of new optogenetic tools in \(Drosophila\) \(melanogaster\)},
  doi       = {10.25972/OPUS-17879},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178793},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2019},
  abstract  = {Since Channelrhodopsins has been described first and introduced successfully in freely moving animals (Nagel et al., 2003 and 2005), tremendous impact has been made in this interesting field of neuroscience. Subsequently, many different optogenetic tools have been described and used to address long-lasting scientific issues. Furthermore, beside the 'classical' Channelrhodopsin-2 (ChR2), basically a cation-selective ion channel, also altered ChR2 descendants, anion selective channels and light-sensitive metabotropic proteins have expanded the optogenetic toolbox. However, in spite of this variety of different tools most researches still pick Channelrhodopsin-2 for their optogenetic approaches due to its well-known kinetics. In this thesis, an improved Channelrhodopsin, Channelrhodopsin2-XXM (ChR2XXM), is described, which might become an useful tool to provide ambitious neuroscientific approaches by dint of its characteristics. Here, ChR2XXM was chosen to investigate the functional consequences of Drosophila larvae lacking latrophilin in their chordotonal organs. Finally, the functionality of GtACR, was checked at the Drosophila NMJ. For a in-depth characterisation, electrophysiology along with behavioural setups was employed. In detail, ChR2XXM was found to have a better cellular expression pattern, high spatiotemporal precision, substantial increased light sensitivity and improved affinity to its chromophore retinal, as compared to ChR2. Employing ChR2XXM, effects of latrophilin (dCIRL) on signal transmission in the chordotonal organ could be clarified with a minimum of side effects, e.g. possible heat response of the chordotonal organ, due to high light sensitivity. Moreover, optogenetic activation of the chordotonal organ, in vivo, led to behavioural changes. Additionally, GtACR1 was found to be effective to inhibit motoneuronal excitation but is accompanied by unexpected side effects. These results demonstrate that further improvement and research of optogenetic tools is highly valuable and required to enable researchers to choose the best fitting optogenetic tool to address their scientific questions.},
  subject      = {Optogenetik},
  language  = {en}
}
@phdthesis{Guan2016,
  author    = {Guan, Chonglin},
  title     = {Functional and genetic dissection of mechanosensory organs of \(Drosophila\) \(melanogaster\)},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-146220},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2016},
  abstract  = {In Drosophila larvae and adults, chordotonal organs (chos) are highly versatile mechanosensors that are essential for proprioception, touch sensation and hearing. Chos share molecular, anatomical and functional properties with the inner ear hair cells of mammals. These multiple similarities make chos powerful models for the molecular study of mechanosensation. In the present study, I have developed a preparation to directly record from the sensory neurons of larval chos (from the lateral chos or lch5) and managed to correlate defined mechanical inputs with the corresponding electrical outputs. The findings of this setup are described in several case studies. (1) The basal functional lch5 parameters, including the time course of response during continuous mechanical stimulation and the recovery time between successive bouts of stimulation, was characterized. (2) The calcium-independent receptor of α-latrotoxin (dCIRL/Latrophilin), an Adhesion class G protein-coupled receptor (aGPCR), is identified as a modulator of the mechanical signals perceived by lch5 neurons. The results indicate that dCIRL/Latrophilin is required for the perception of external and internal mechanical stimuli and shapes the sensitivity of neuronal mechanosensation. (3) By combining this setup with optogenetics, I have confirmed that dCIRL modulates lch5 neuronal activity at the level of their receptor current (sensory encoding) rather than their ability to generate action potentials. (4) dCIRL´s structural properties (e.g. ectodomain length) are essential for the mechanosensitive properties of chordotonal neurons. (5) The versatility of chos also provides an opportunity to study multimodalities at multiple levels. In this context, I performed an experiment to directly record neuronal activities at different temperatures. The results show that both spontaneous and mechanically evoked activity increase in proportion to temperature, suggesting that dCIRL is not required for thermosensation in chos. These findings, from the development of an assay of sound/vibration sensation, to neuronal signal processing, to molecular aspects of mechanosensory transduction, have provided the first insights into the mechanosensitivity of dCIRL. In addition to the functional screening of peripheral sensory neurons, another electrophysiological approach was applied in the central nervous system: dCIRL may impact the excitability of the motor neurons in the ventral nerve cord (VNC). In the second part of my work, whole-cell patch clamp recordings of motor neuron somata demonstrated that action potential firing in the dCirl\(^K\)\(^O\) did not differ from control samples, indicating comparable membrane excitability.},
  subject      = {Taufliege},
  language  = {en}
}
@phdthesis{Ljaschenko2013,
  author    = {Ljaschenko, Dmitrij},
  title     = {Hebbian plasticity at neuromuscular synapses of Drosophila},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-90465},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {Synaptic plasticity determines the development of functional neural circuits. It is widely accepted as the mechanism behind learning and memory. Among different forms of synaptic plasticity, Hebbian plasticity describes an activity-induced change in synaptic strength, caused by correlated pre- and postsynaptic activity. Additionally, Hebbian plasticity is characterised by input specificity, which means it takes place only at synapses, which participate in activity. Because of its correlative nature, Hebbian plasticity suggests itself as a mechanism behind associative learning. Although it is commonly assumed that synaptic plasticity is closely linked to synaptic activity during development, the mechanistic understanding of this coupling is far from complete. In the present study channelrhodopsin-2 was used to evoke activity in vivo, at the glutamatergic Drosophila neuromuscular junction. Remarkably, correlated pre- and postsynaptic stimulation led to increased incorporation of GluR-IIA-type glutamate receptors into postsynaptic receptor fields, thus boosting postsynaptic sensitivity. This phenomenon is input-specific. Conversely, GluR-IIA was rapidly removed from synapses at which neurotransmitter release failed to evoke substantial postsynaptic depolarisation. This mechanism might be responsible to tame uncontrolled receptor field growth. Combining these results with developmental GluR-IIA dynamics leads to a comprehensive physiological concept, where Hebbian plasticity guides growth of postsynaptic receptor fields and sparse transmitter release stabilises receptor fields by preventing overgrowth. Additionally, a novel mechanism of retrograde signaling was discovered, where direct postsynaptic channelrhodopsin-2 based stimulation, without involvement of presynaptic neurotransmitter release, leads to presynaptic depression. This phenomenon is reminiscent of a known retrograde homeostatic mechanism, of inverted polarity, where neurotransmitter release is upregulated, upon reduction of postsynaptic sensitivity.},
  subject      = {Synapse},
  language  = {en}
}