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Die aktuellen Veränderungen der Arbeitswelt erfordern eine stetige Anpassung an immer neue Herausforderungen seitens der Arbeitgeber und Arbeitnehmer. Lebenslanges Lernen und damit eine kontinuierliche Weiterbildung der Mitarbeiter ist essentiell für Unternehmen, um auf dem schnelllebigen Arbeitsmarkt wettbewerbsfähig zu sein. Die Bereitschaft und die Motivation von Menschen, dazuzulernen, ist jedoch sehr unterschiedlich. Eine mögliche Erklärung dafür liefert die dispositionelle Zielorientierung, welche der Achievement-Goal-Theorie entstammt. Das Konstrukt beschreibt, ob Menschen eine individuelle Präferenz für Lernziele (z.B. Kompetenzzuwachs) oder Leistungsziele (z.B. gute Beurteilungen bekommen oder schlechte Beurteilungen vermeiden) haben. Neben den Persönlichkeitsaspekten konzentriert sich die Forschung im Rahmen der Achievement-Goal-Theorie auch auf den Einfluss der Umgebung auf Lern- und Leistungsprozesse. Die sogenannte arbeitsplatzbezogene Zielorientierung beschreibt die wahrgenommene Zielstruktur der Arbeitsumgebung und stellt das situationsbedingte Gegenstück der Dispositionen dar. Zahlreiche Befunde aus dem Bereich der pädagogischen Psychologie zu Zielstrukturen der Umgebung zeigen einen Einfluss auf beispielsweise Lernerfolg, Motivation, Selbstregulationsprozesse oder Leistung. Zielstrukturen im Arbeitskontext stellen hingegen ein bisher wenig beachtetes Konstrukt dar. Ausgehend von den aktuellen Befunden zu Zielstrukturen, könnte die arbeitsplatzbezogene Zielorientierung jedoch einen wichtigen Beitrag leisten, wenn es um die Frage geht, wie Mitarbeiter unterstützt und zu Lernprozessen angeregt werden können. Die Identifizierung von lern- und leistungsförderlichen Zielstrukturen der Arbeitsumgebung würde wertvolle Ansatzpunkte für die Mitarbeiterentwicklung in der betrieblichen Praxis liefern.
Im Rahmen von drei empirischen Studien wird der Relevanz der Zielorientierung im Arbeits-kontext nachgegangen. Neben der Überprüfung eines ins Deutsche übertragenen und angepassten Mess-instruments zur Erhebung der arbeitsplatzbezogenen Zielorientierung (Studie 1) steht vor allem die Untersuchung möglicher Einflüsse des Konstrukts auf arbeitsrelevante Variablen im Vordergrund, um förderliche Zielstrukturen zu identifizieren (Studie 1 & 2). Darüber hinaus werden erstmalig mögliche Person-Situation-Interaktionen in diesem Zusammenhang untersucht (Studie 2). Abschließend erfolgt eine Untersuchung möglicher Antezedenten der arbeitsplatzbezogenen Zielorientierung, woraus sich erste wichtige Anhaltspunkte für Interventionsmaßnahmen am Arbeitsplatz ableiten lassen (Studie 3).
Die Ergebnisse der Studien zeigen, dass insbesondere ein lernzielorientierter Arbeitsplatz förderlich für die untersuchten Variablen wie Lernerfolg, Leistung oder auch berufliche Selbstwirksamkeit ist. In Bezug auf die Interaktion von Person und Situation ergaben sich gemischte Befunde, die kein eindeutiges Interaktionsmuster aufweisen. Bei der Frage, wie ein lernzielorientierter Arbeitsplatz gefördert werden kann, erwies sich vor allem die Art und Weise, wie Führungskräfte mit Fehlern umgehen, als relevant. Die Studien liefern demnach wichtige erste Ansätze für theoretische und praktische Implikationen, wie Mitarbeiter in Lern- und Leistungsprozessen unterstützt werden können.
No abstract available.
Ciliary neurotrophic factor (Cntf) acts as a differentiation and survival factor for different types of neurons and glial cells. It is expressed by peripheral Schwann cells and astrocytes in the central nervous system and mediates its effects via a receptor complex involving CntfRα, LifRß and gp130, leading to downstream activation of Stat3. Recent studies by our group have shown that Cntf modulates neuronal microtubule dynamics via Stat3/stathmin interaction. In a mouse model for motor neuron disease, i.e. pmn, Cntf is able to rescue axonal degeneration through Stat3/stathmin signaling. While these findings suggest a role of Cntf in controlling axonal functions in the neuromuscular system, additional data indicate that Cntf might also play a role in synaptic plasticity in the hippocampus. Electrophysiological recordings in hippocampal organotypic cultures and acute slices revealed a deficit in long-term potentiation (LTP) in Cntf -/- mice. This deficit was rescued by 24 h stimulation with Cntf, combined with an acute application of Cntf during LTP-measurements indicating that Cntf is both necessary and sufficient for hippocampal LTP, and possibly synaptic plasticity. Therefore, Cntf knockout mice were investigated to elucidate this possible role of Cntf in hippocampal LTP and synaptic plasticity.
First, we validated the presence of Cntf in the target tissue: in the hippocampus, Cntf was localized in Gfap-positive astrocytes surrounding small blood vessels in the fissure and in meningeal areas close to the dentate gyrus. Laser micro-dissection and qPCR analysis showed a similar distribution of Cntf-coding mRNA validating the obtained immunofluorescent results. Despite the strong LTP deficit in organotypic cultures, in vivo behavior of Cntf -/- mice regarding hippocampus-dependent learning and anxiety-related paradigms was largely inconspicuous. However, western blot analysis of hippocampal organotypic cultures revealed a significant reduction of pStat3 levels in Cntf -/- cultures under baseline conditions, which in turn were elevated upon Cntf stimulation. In order to resolve and examine synaptic structures we turned to in vitro analysis of cultured hippocampal neurons which indicated that pStat3 is predominantly located in the presynapse. In line with these findings, presynapses of Cntf -/- cultures were reduced in size and when in contact to astrocytes, contained less pStat3 immunoreactivity compared to presynapses in wildtype cultures.
In conclusion, our findings hypothesize that despite of a largely inconspicuous behavioral phenotype of Cntf -/- mice, Cntf appears to have an influence on pStat3 levels at hippocampal synapses. In a next step these two key questions need to be addressed experimentally: 1) is there a compensatory mechanism by members of the Cntf family, possibly downstream of pStat3, which explains the in vivo behavioral results of Cntf -/- mice and can likewise account for the largely inconspicuous phenotype in CNTF-deficient humans? 2) How exactly does Cntf influence LTP through Stat3 signaling? To unravel the underlying mechanism further experiments should therefore investigate whether microtubule dynamics downstream of Stat3 and stathmin signaling are involved in the Cntf-induced modulation of hippocampal synaptic plasticity, similar to as it was shown in motoneurons.
Foraging behavior is a particularly fascinating topic within the studies of social insects. Decisions made by individuals have effects not only on the individual level, but on the colony level as well. Social information available through foraging in a group modulates individual preferences and shapes the foraging pattern of a colony. Identifying parameters influencing foraging behavior in leaf-cutting ants is especially intriguing because they do not harvest for themselves, but for their symbiotic fungus which in turn influences their plant preferences after the incorporation of the substrate. To learn about the substrates’ unsuitability for the fungus, ants need to be able to identify the incorporated substrate and associate it with detrimental effects on the fungus. Odor is an important plant characteristic known to be used as recognition key outside the nest in the context of foraging. Chapter 1 shows that foragers are able to recall information about the unsuitability of a substrate through odor alone and consequently reject the substrate, which leads to the conclusion that inside the nest, odor might be enough to indentify incorporated substrate. Identification of plant species is a key factor in the foraging success of leaf-cutting ants as they harvest a multitude of different plant species in a diverse environment and host plant availability and suitability changes throughout the year. Fixed plant preferences of individuals through innate tendencies are therefore only one factor influencing foraging decisions. On the individual as well as the colony level, foraging patterns are flexible and a result of an intricate interplay between the different members involved in the harvesting process: foragers, gardeners and the symbiotic fungus. In chapter 2 I identified several conditions necessary for naïve foragers to learn about the unsuitability of substrate inside the nest. In order to exchange of information about the unsuitability of a substrate, the plant in question must be present in the fungus garden. Foragers can learn without own foraging experience and even without experiencing the effects of the substrate on the fungus, solely through the presence of experienced gardeners. The presence of experienced foragers alone on the other hand is not enough to lower the acceptance of substrate by naïve foragers in the presence of naïve gardeners, even if experienced foragers make up the majority of the workforce inside the nest. Experienced foragers are also able to reverse their previous negative experience and start accepting the substrate again. The individual behavior of foragers and gardeners with different experiential backgrounds in the presence of suitable or unsuitable substrate inside the fungus chamber was investigated in chapter 3 to shed some light on possible mechanisms involved in the flow of information about substrate suitability from the fungus to the ants. Gardeners as well as foragers are involved in the leaf processing and treatment of the applied leaf patches on the fungus. If the plant material is unsuitable, significantly more ants treat the plant patches, but foragers are less active overall. Contacts between workers initiated by either gardeners or foragers occur significantly more frequent and last longer if the substrate is unsuitable. Even though experienced gardeners increase naïve foragers’ contact rates and duration with other workers in the presence of suitable plant patches, naïve foragers show no differences in the handling of the plant patches. This suggests that foragers gain information about plant suitability not only indirectly through the gardening workers, but might also be able to directly evaluate the effects of the substrate on the fungus themselves. Outside the nest, foragers influence each other the trail (chapter 4). Foraging in a group and the presence of social information is a decisive factor in the substrate choice of the individual and leads to a distinct and consentaneous colony response when encountering unfamiliar or unsuitable substrates. As leaf-cutting ants harvest different plant species simultaneously on several trails, foragers gain individual experiences concerning potential host plants. Preferences might vary among individuals of the same colony to the degree that foragers on the same trail perceive a certain substrate as either suitable or unsuitable. If the majority of foragers on the trail perceives one of the currently harvested substrates as unsuitable, naïve foragers lower their acceptance within 4 hours. In the absence of a cue in the fungus, naïve foragers harvesting by themselves still eventually (within 6 hours) reject the substrate as they encounter experienced gardeners during visits to the nest within foraging bouts. As foraging trails can be up to 100 m long and foragers spend a considerable amount of time away from the nest, learning indirectly from experienced foragers on the trail accelerates the distribution of information about substrate suitability. The level of rejection of a formerly unsuitable substrate after eight hours of foraging by naïve foragers correlates with the average percentage of unladen experienced foragers active on the trail. This suggests that unladen experienced foragers might actively contact laden naïve workers transmitting information about the unsuitability of the load they carry. Results from experiments were I observed individual laden foragers on their way back to the nest backed up this assumption as individuals were antennated and received bites into the leaf disk they carried. Individuals were contacted significantly more often by nestmates that perceived the carried leaf disk as unsuitable due to previous experience than by nestmates without this experience (chapter 6). Leaf-cutting ants constantly evaluate, learn and re-evaluate the suitability of harvested substrate and adjust their foraging activity accordingly. The importance of the different sources of information within the colony and their effect on the foraging pattern of the colony depend on the presence or absence of each of them as e.g. experienced foragers have a bigger influence on the plant preferences of naïve foragers in the absence of a cue in the fungus garden.
An animal depends heavily on its sense of smell and its ability to form olfactory associations as this is crucial for its survival. This thesis studies in two parts about such associative olfactory learning in larval Drosophila. The first part deals with different aspects of odour processing while the second part is concerned with aspects related to memory and learning. Chapter I.1 highlights how odour intensities could be integrated into the olfactory percept of larval Drosophila. I first describe the dose-effect curves of learnability across odour intensities for different odours and then choose odour intensities from these curves such that larvae are trained at intermediate odour intensity, but are tested for retention with either that trained intermediate odour intensity, or with respectively HIGHer or LOWer intensities. I observe a specificity of retention for the trained intensity for all the odours used. Further I compare these findings with the case of adult Drosophila and propose a circuit level model of how such intensity coding comes about. Such intensity specificity of learning adds to appreciate the richness in 'content' of olfactory memory traces, and to define the demands on computational models of olfaction and olfactory learning. Chapter I.2 provides a behaviour-based estimate of odour similarity using four different types of experiments to yield a combined, task-independent estimate of perceived difference between odour-pairs. Further comparison of these perceived differences to published measures of physico- chemical difference reveals a weak correlation. Notable exceptions to this correlation are 3-octanol and benzaldehyde. Chapter I.3 shows for two odours (3-octanol and 1-octene-3-ol) that perceptual differences between these odours can either be ignored after non-discriminative training (generalization), or accentuated by odour-specific reinforcement (discrimination). Anosmic Or83b1 mutants have lost these faculties, indicating that this adaptive adjustment is taking place downstream of Or83b expressing sensory neurons. Chapter II.1 of this thesis deals with food supplementation with dried roots of Rhodiola rosea. This dose-dependently improves odour- reward associative function in larval Drosophila. Supplementing fly food with commercially available tablets or extracts, however, does not have a 'cognitive enhancing' effect, potentially enabling us to differentiate between the effective substances in the root versus these preparations. Thus Drosophila as a genetically tractable study case should now allow accelerated analyses of the molecular mechanism(s) that underlie this 'cognitive enhancement' conveyed by Rhodiola rosea. Chapter II.2 describes the role of Synapsin, an evolutionarily conserved presynaptic phosphoprotein using a combined behavioural and genetic approach and asks where and how, this protein affects functions in associative plasticity of larval Drosophila. This study shows that a Synapsin-dependent memory trace can be pinpointed to the mushroom bodies, a 'cortical' brain region of the insects. On the molecular level, data in this study assign Synapsin as a behaviourally- relevant effector of the AC-cAMP-PKA cascade.
Learning and memory is considered to require synaptic plasticity at presynaptic specializations of neurons. Kenyon cells are the intrinsic neurons of the primary olfactory learning center in the brain of arthropods – the mushroom body neuropils. An olfactory mushroom body memory trace is supposed to be located at the presynapses of Kenyon cells. In the calyx, a sub-compartment of the mushroom bodies, Kenyon cell dendrites receive olfactory input provided via projection neurons. Their output synapses, however, were thought to reside exclusively along their axonal projections outside the calyx, in the mushroom body lobes. By means of high-resolution imaging and with novel transgenic tools, we showed that the calyx of the fruit fly Drosophila melanogaster also comprised Kenyon cell presynapses. At these presynapses, synaptic vesicles were present, which were capable of neurotransmitter release upon stimulation. In addition, the newly identified Kenyon cell presynapses shared similarities with most other presynapses: their active zones, the sites of vesicle fusion, contained the proteins Bruchpilot and Syd-1. These proteins are part of the cytomatrix at the active zone, a scaffold controlling synaptic vesicle endo- and exocytosis. Kenyon cell presynapses were present in γ- and α/β-type KCs but not in α/β-type Kenyon cells.
The newly identified Kenyon cell derived presynapses in the calyx are candidate sites for an olfactory associative memory trace. We hypothesize that, as in mammals, recurrent neuronal activity might operate for memory retrieval in the fly olfactory system.
Moreover, we present evidence for structural synaptic plasticity in the mushroom body calyx. This is the first demonstration of synaptic plasticity in the central nervous system of Drosophila melanogaster. The volume of the mushroom body calyx can change according to changes in the environment. Also size and numbers of microglomeruli - sub-structures of the calyx, at which projection neurons contact Kenyon cells – can change. We investigated the synapses within the microglomeruli in detail by using new transgenic tools for visualizing presynaptic active zones and postsynaptic densities. Here, we could show, by disruption of the projection neuron - Kenyon cell circuit, that synapses of microglomeruli were subject to activity-dependent synaptic plasticity. Projection neurons that could not generate action potentials compensated their functional limitation by increasing the number of active zones per microglomerulus. Moreover, they built more and enlarged microglomeruli. Our data provide clear evidence for an activity-induced, structural synaptic plasticity as well as for the activity-induced reorganization of the olfactory circuitry in the mushroom body calyx.
Sugar reward learning in Drosophila : neuronal circuits in Drosophila associative olfactory learning
(2006)
Genetic intervention in the fly Drosophila melanogaster has provided strong evidence that the mushroom bodies of the insect brain act as the seat of memory traces for aversive and appetitive olfactory learning (reviewed in Heisenberg, 2003). In flies, electroshock is mainly used as negative reinforcer. Unfortunately this fact complicates a comparative consideration with other inscets as most studies use sugar as positive reinforcer. For example, several lines of evidence from honeybee and moth have suggested another site, the antennal lobe, to house neuronal plasticity underlying appetitive olfactory memory (reviewed in Menzel, 2001; Daly et al., 2004). Because of this I focused my work mainly on appetitive olfactory learning. In the first part of my thesis, I used a novel genetic tool, the TARGET system (McGuire et al., 2003), which allows the temporally controlled expression of a given effector gene in a defined set of cells. Comparing effector genes which either block neurotransmission or ablate cells showed important differences, revealing that selection of the appropriate effector gene is critical for evaluating the function of neural circuits. In the second part, a new engram of olfactory memory in the Drosophila projection neurons is described by restoring Rutabaga adenlylate cyclase (rut-AC) activity specifically in these cells. Expression of wild-type rutabaga in the projection neurons fully rescued the defect in sugar reward memory, but not in aversive electric shock memory. No difference was found in the stability of the appetitive memories rescued either in projection neurons or Kenyon cells. In the third part of the thesis I tried to understand how the reinforcing signals for sugar reward are internally represented. In the bee Hammer (1993) described a single octopaminergic neuron – called VUMmx1 – that mediates the sugar stimulus in associative olfactory reward learning. Analysis of single VUM neurons in the fly (Selcho, 2006) identified a neuron with a similar morphology as the VUMmx1 neuron. As there is a mutant in Drosophila lacking the last enzymatic step in octopamine synthesis (Monastirioti et al., 1996), Tyramine beta Hydroxylase, I was able to show that local Tyramine beta Hydroxylase expression successfully rescued sugar reward learning. This allows to conclude that about 250 cells including the VUM cluster are sufficient for mediating the sugar reinforcement signal in the fly. The description of a VUMmx1 similar neuron and the involvement of the VUM cluster in mediating the octopaminergic sugar stimulus are the first steps in establishing a neuronal map for US processing in Drosophila. Based on this work several experiments are contrivable to reach this ultimate goal in the fly. Taken together, the described similiarities between Drosophila and honeybee regarding the memory organisation in MBs and PNs and the proposed internal representation of the sugar reward suggest an evolutionarily conserved mechanism for appetitive olfactory learning in insects.
Service Learning ist eine Lehr-Lernform, bei der Studierende das in Lehrveranstaltungen erworbene Wissen in konkreten Praxisprojekten zum Nutzen sozialer Einrichtungen oder bedürftiger Menschen einsetzen. Das aus den USA stammende Konzept findet in Deutschland seit 2003 in der Schule und Hochschullehre Anwendung. Um die Wirkung auf die soziale Entwicklung und den Wissenserwerb von Studierenden zu prüfen, wurde eine Längsschnittstudie bei Studierenden verschiedener deutscher Hochschulen durchgeführt. Dieser Band berichtet die in dieser Studie verwendeten Fragebogenkonstrukte und gibt Auskunft über die Zuverlässigkeit der Skalen.
No abstract available.
Eine der größten Herausforderungen in der Neurobiologie ist es, die neuronalen Prozesse zu verstehen, die Lernen und Gedächtnis zugrundeliegen. Welche biochemischen Pfade liegen z.B. der Koinzidenzdetektion von Reizen (klassische Konditionierung) oder einer Handlung und ihren Konsequenzen (operante Konditionierung) zugrunde? In welchen neuronalen Unterstrukturen werden diese Informationen gespeichert? Wie ähnlich sind die Stoffwechselwege, die diese beiden Arten des assoziativen Lernens vermitteln und auf welchem Niveau divergieren sie? Drosophila melanogaster ist wegen der Verfügbarkeit von Lern-Paradigmen und neurogenetischen Werkzeugen ein geeigneter Modell-Organismus, zum diese Fragen zu adressieren. Er ermöglicht eine umfangreiche Studie der Funktion des Gens S6KII, das in der Taufliege in klassischer und operanter Konditionierung unterschiedlich involviert ist (Bertolucci, 2002; Putz et al., 2004). Rettungsexperimenten zeigen, dass die olfaktorische Konditionierung in der Tully Maschine (ein klassisches, Pawlow’sches Konditionierungsparadigma) von dem Vorhandensein eines intakten S6KII Gens abhängt. Die Rettung war sowohl mit einer vollständigen, als auch einer partiellen Deletion erfolgreich und dies zeigt, dass der Verlust der phosphorylierenden Untereinheit der Kinase die Hauptursache des Funktionsdefektes war. Das GAL4/UAS System wurde benutzt, um die S6KII Expression zeitlich und räumlich zu steuern. Es wurde gezeigt, dass die Expression der Kinase während des adulten Stadiums für die Rettung hinreichend war. Dieser Befund schließt eine Entwicklungsstörung als Ursache für den mutanten Phänotyp aus. Außerdem zeigte die gezielte räumliche Rettung von S6KII die Notwendigkeit der Pilzkörper und schloss Strukturen wie das mediane Bündel, die Antennalloben und den Zentralkomplex aus. Dieses Muster ist dem vorher mit der rutabaga Mutation identifizierten sehr ähnlich (Zars et al., 2000). Experimente mit der Doppelmutante rut, ign58-1 deuten an, dass rutabaga und S6KII im gleichen Signalweg aktiv sind. Vorhergehende Studien hatten bereits gezeigt, dass die unterschiedlichen Ergebnisse bei operanter und klassischer Konditionierung auf verschiedenen Rollen für S6KII in den zwei Arten des Lernens hindeuten (Bertolucci, 2002; Putz, 2002). Diese Schlussfolgerung wurde durch den mutanten Phänotyp der transgenen Linien in der Positionskonditionierung und ihr wildtypisches Verhalten in der klassischen Konditionierung zusätzlich bekräftigt. Eine neue Art von Lern-Experiment, genannt „Idle Experiment“, wurde entworfen. Es basiert auf der Konditionierung der Laufaktivität, stellt eine operante Aufgabenstellung dar und überwindet einige der Limitationen des „Standard“ Heat-Box Experimentes. Die neue Art des Idle Experimentes erlaubt es, „gelernte Hilflosigkeit“ in Fliegen zu erforschen, dabei zeigte sich eine erstaunliche Ähnlichkeit zu den Vorgängen in komplizierteren Organismen wie Ratten, Mäusen oder Menschen. Gelernte Hilflosigkeit in der Taufliege wurde nur in den Weibchen beobachtet und wird von Antidepressiva beeinflusst.