@article{HeckmannPauli2022,
  author    = {Heckmann, Manfred and Pauli, Martin},
  title     = {Visualizing presynaptic active zones and synaptic vesicles},
  series = {Frontiers in Synaptic Neuroscience},
  volume    = {14},
  journal   = {Frontiers in Synaptic Neuroscience},
  issn      = {1663-3563},
  doi       = {10.3389/fnsyn.2022.901341},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-274687},
  year      = {2022},
  abstract  = {The presynaptic active zone (AZ) of chemical synapses is a highly dynamic compartment where synaptic vesicle fusion and neurotransmitter release take place. During evolution the AZ was optimized for speed, accuracy, and reliability of chemical synaptic transmission in combination with miniaturization and plasticity. Single-molecule localization microscopy (SMLM) offers nanometer spatial resolution as well as information about copy number, localization, and orientation of proteins of interest in AZs. This type of imaging allows quantifications of activity dependent AZ reorganizations, e.g., in the context of presynaptic homeostatic potentiation. In combination with high-pressure freezing and optogenetic or electrical stimulation AZs can be imaged with millisecond temporal resolution during synaptic activity. Therefore SMLM allows the determination of key parameters in the complex spatial environment of AZs, necessary for next generation simulations of chemical synapses with realistic protein arrangements.},
  language  = {en}
}
@article{CapetianMuellerVolkmannetal.2020,
  author    = {Capetian, Philipp and M{\"u}ller, Lorenz and Volkmann, Jens and Heckmann, Manfred and Erg{\"u}n, S{\"u}leyman and Wagner, Nicole},
  title     = {Visualizing the synaptic and cellular ultrastructure in neurons differentiated from human induced neural stem cells - an optimized protocol},
  series = {International Journal of Molecular Sciences},
  volume    = {21},
  journal   = {International Journal of Molecular Sciences},
  number    = {5},
  issn      = {1422-0067},
  doi       = {10.3390/ijms21051708},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-236053},
  year      = {2020},
  abstract  = {The size of the synaptic subcomponents falls below the limits of visible light microscopy. Despite new developments in advanced microscopy techniques, the resolution of transmission electron microscopy (TEM) remains unsurpassed. The requirements of tissue preservation are very high, and human post mortem material often does not offer adequate quality. However, new reprogramming techniques that generate human neurons in vitro provide samples that can easily fulfill these requirements. The objective of this study was to identify the culture technique with the best ultrastructural preservation in combination with the best embedding and contrasting technique for visualizing neuronal elements. Two induced neural stem cell lines derived from healthy control subjects underwent differentiation either adherent on glass coverslips, embedded in a droplet of highly concentrated Matrigel, or as a compact neurosphere. Afterward, they were fixed using a combination of glutaraldehyde (GA) and paraformaldehyde (PFA) followed by three approaches (standard stain, Ruthenium red stain, high contrast en-bloc stain) using different combinations of membrane enhancing and contrasting steps before ultrathin sectioning and imaging by TEM. The compact free-floating neurospheres exhibited the best ultrastructural preservation. High-contrast en-bloc stain offered particularly sharp staining of membrane structures and the highest quality visualization of neuronal structures. In conclusion, compact neurospheres growing under free-floating conditions in combination with a high contrast en-bloc staining protocol, offer the optimal preservation and contrast with a particular focus on visualizing membrane structures as required for analyzing synaptic structures.},
  language  = {en}
}
@article{BeckEhmannAndlaueretal.2015,
  author    = {Beck, Katherina and Ehmann, Nadine and Andlauer, Till F. M. and Ljaschenko, Dmitrij and Strecker, Katrin and Fischer, Matthias and Kittel, Robert J. and Raabe, Thomas},
  title     = {Loss of the Coffin-Lowry syndrome-associated gene RSK2 alters ERK activity, synaptic function and axonal transport in Drosophila motoneurons},
  series = {Disease Models \& Mechanisms},
  volume    = {8},
  journal   = {Disease Models \& Mechanisms},
  doi       = {10.1242/dmm.021246},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-145185},
  pages     = {1389-1400},
  year      = {2015},
  abstract  = {Plastic changes in synaptic properties are considered as fundamental for adaptive behaviors. Extracellular-signal-regulated kinase (ERK)-mediated signaling has been implicated in regulation of synaptic plasticity. Ribosomal S6 kinase 2 (RSK2) acts as a regulator and downstream effector of ERK. In the brain, RSK2 is predominantly expressed in regions required for learning and memory. Loss-of-function mutations in human RSK2 cause Coffin-Lowry syndrome, which is characterized by severe mental retardation and low IQ scores in affected males. Knockout of RSK2 in mice or the RSK ortholog in Drosophila results in a variety of learning and memory defects. However, overall brain structure in these animals is not affected, leaving open the question of the pathophysiological consequences. Using the fly neuromuscular system as a model for excitatory glutamatergic synapses, we show that removal of RSK function causes distinct defects in motoneurons and at the neuromuscular junction. Based on histochemical and electrophysiological analyses, we conclude that RSK is required for normal synaptic morphology and function. Furthermore, loss of RSK function interferes with ERK signaling at different levels. Elevated ERK activity was evident in the somata of motoneurons, whereas decreased ERK activity was observed in axons and the presynapse. In addition, we uncovered a novel function of RSK in anterograde axonal transport. Our results emphasize the importance of fine-tuning ERK activity in neuronal processes underlying higher brain functions. In this context, RSK acts as a modulator of ERK signaling.},
  language  = {en}
}
@phdthesis{Paul2014,
  author    = {Paul, Mila Marie},
  title     = {Vesikelverkehr in Aktiven Zonen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-110791},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Aktive Zonen (AZs) sind hoch spezialisierte, subzellul{\"a}re Kompartimente von Neuronen, die der synaptischen {\"U}bertragung dienen. Sie enthalten Ger{\"u}stproteine wie RIM (Rab3 interacting molecule) sowie elektronendichte Projektionen bestehend aus Bruchpilot bei Drosophila melanogaster oder Bassoon im S{\"a}uger, welche Schl{\"u}sselkomponenten des Vesikelverkehrs darstellen. Bei der Fliege sind Anzahl und Verteilung von Bruchpilot-Molek{\"u}len in AZs relevant f{\"u}r die funktionelle Differenzierung. Ihre Anordnung wird im Abstand von weniger als einem Mikrometer innerhalb einer pr{\"a}synaptischen Endigung reguliert. Im Rahmen der vorliegenden Arbeit wurden elektrophysiologische Ableitungen und konfokale sowie h{\"o}chstaufl{\"o}sende, immunhistochemische Bildgebung mit dem dSTORM (direct Stochastic Optical Reconstruction Microscopy) Verfahren an larvalen, neuromuskul{\"a}ren Synapsen von Drosophila durchgef{\"u}hrt. Dabei wurde das genetische Potenzial des Modellorganismus genutzt, um relevante Proteinfunktionen und -interaktionen zu analysieren. RIM als zentrale Komponente Aktiver Zonen ist relevant f{\"u}r synaptische Plastizit{\"a}t. Eine als CORD7 (cone-rod dystrophy type 7) bezeichnete Punktmutation (Arginin zu Histidin) innerhalb der 310 Helix der C2A-Dom{\"a}ne von RIM wurde mit erh{\"o}hten kognitiven F{\"a}higkeiten einer Patientengruppe in Verbindung gebracht. Weil die Drosophila C2A-Dom{\"a}ne eine hohe Homologie zur S{\"a}ugerdom{\"a}ne aufweist, konnte der Einfluss dieser Mutation auf Struktur und Funktion von Synapsen untersucht werden. Es zeigte sich, dass der Aminos{\"a}ureaustausch der CORD7-Position und des benachbarten Arginin-Restes die synaptische Organisation und Transmission beeinflussen. In einer Reihe weiterer Experimente wurde das Zusammenspiel von Bruchpilot und Synaptotagmin, dem Calciumsensor der evozierten Transmitterfreisetzung, analysiert. W{\"a}hrend AZs ohne Bruchpilot auch ohne Synaptotagmin funktionieren, f{\"u}hrt dessen Reduktion zu einer Umverteilung von Bruchpilot-Molek{\"u}len innerhalb von AZs und zu dramatischen {\"A}nderungen in ihrer Anzahl. Abschließend wurde so ein Beitrag zum Verst{\"a}ndnis der molekularen Organisation synaptischer Informationsverarbeitung und Plastizit{\"a}t geleistet, wobei zu kl{\"a}ren bleibt, wie die zuverl{\"a}ssige Speicherung von Informationen an AZs erreicht werden kann.},
  subject      = {Aktive Zonen},
  language  = {de}
}
@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}
}