@phdthesis{Muenz2015,
  author    = {M{\"u}nz, Thomas Sebastian},
  title     = {Aspects of neuronal plasticity in the mushroom body calyx during adult maturation in the honeybee Apis mellifera},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-111611},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {Division of labor represents a major advantage of social insect communities that accounts for their enormous ecological success. In colonies of the honeybee, Apis mellifera, division of labor comprises different tasks of fertile queens and drones (males) and, in general, sterile female workers. Division of labor also occurs among workers in form of an age-related polyethism. This helps them to deal with the great variety of tasks within the colony. After adult eclosion, workers spend around three weeks with various duties inside the hive such as tending the brood or cleaning and building cells. After this period workers switch to outdoor tasks and become foragers collecting nectar, pollen and water. With this behavioral transition, workers face tremendous changes in their sensory environment. In particular, visual sensory stimuli become important, but also the olfactory world changes. Foragers have to perform a completely new behavioral repertoire ranging from long distance navigation based on landmark orientation and polarized-skylight information to learning and memory tasks associated with finding profitable food sources. However, behavioral maturation is not a purely age-related internal program associated with a change, for example, in juvenile hormone titers. External factors such as primer pheromones like the brood pheromone or queen mandibular pheromone can modulate the timing of this transition. In this way colonies are able to flexibly adjust their work force distribution between indoor and outdoor tasks depending on the actual needs of the colony. Besides certain physiological changes, mainly affecting glandular tissue, the transition from indoor to outdoor tasks requires significant adaptations in sensory and higher-order integration centers of the brain. The mushroom bodies integrate olfactory, visual, gustatory and mechanosensory information. Furthermore, they play important roles in learning and memory processes. It is therefore not surprising that the mushroom bodies, in particular their main input region, the calyx, undergo volumetric neuronal plasticity. Similar to behavioral maturation, plastic changes of the mushroom bodies are associated with age, but are also to be affected by modulating factors such as task and experience. In my thesis, I analyzed in detail the neuronal processes underlying volumetric plasticity in the mushroom body. Immunohistochemical labeling of synaptic proteins combined with quantitative 3D confocal imaging revealed that the volume increase of the mushroom body calyx is largely caused by the growth of the Kenyon cell dendritic network. This outgrowth is accompanied by changes in the synaptic architecture of the mushroom body calyx, which is organized in a distinct pattern of synaptic complexes, so called microglomeruli. During the first week of natural adult maturation microglomeruli remain constant in total number. With subsequent behavioral transition from indoor duties to foraging, microglomeruli are pruned while the Kenyon cell dendritic network is still growing. As a result of these processes, the mushroom body calyx neuropil volume enlarges while the total number of microgloumeruli becomes reduced in foragers compared to indoor workers. In the visual subcompartments (calyx collar) this process is induced by visual sensory stimuli as the beginning of pruning correlates with the time window when workers start their first orientation flights. The high level of analysis of cellular and subcellular process underlying structural plasticity of the mushroom body calyx during natural maturation will serve as a framework for future investigations of behavioral plasticity in the honeybee. The transition to foraging is not purely age-dependent, but gets modulated, for example, by the presence of foragers. Ethyl oleate, a primer pheromone that is present only in foragers, was shown to delay the onset of foraging in nurse bees. Using artificial application of additional ethyl oleate in triple cohort colonies, I tested whether it directly affects adult neuronal plasticity in the visual input region of the mushroom body calyx. As the pheromonal treatment failed to induce a clear behavioral phenotype (delayed onset of foraging) it was not possible to show a direct link between the exposure to additional ethyl oleate and neuronal plasticity in mushroom body calyx. However, the general results on synaptic maturation confirmed my data of natural maturation processes in the mushroom body calyx. Given the result that dendritic plasticity is a major contributor to neuronal plasticity in the mushroom body calyx associated with division of labor, the question arose which proteins could be involved in mediating these effects. Calcium/calmodulin-dependent protein kinase II (CaMKII) especially in mammals, but also in insects (Drosophila, Cockroach), was shown to be involved in facilitating learning and memory processes like long-term synaptic potentiation. In addition to presynaptic effects, the protein was also revealed to directly interact with cytoskeleton elements in the postsynapse. It therefore is a likely candidate to mediate structural synaptic plasticity. As part of my thesis, the presence and distribution of CaMKII was analyzed, and the results showed that the protein is highly concentrated in a distinct subpopulation of the mushroom body intrinsic neurons, the noncompact Kenyon cells. The dendritic network of this population arborizes in two calyx subregions: one receiving mainly olfactory input - the lip - and the collar receiving visual input. This distribution pattern did not change with age or task. The high concentration of CaMKII in dendritic spines and its overlap with f-actin indicates that CaMKII could be a key player inducing structural neuronal plasticity associated with learning and memory formation and/or behavioral transitions related to division of labor. Interestingly CaMKII immunoreactivity was absent in the basal ring, another subregion of the mushroom body calyx formed almost exclusively by the inner compact Kenyon cells and known to receive combined visual and olfactory input. This indicates differences of this mushroom body subregion regarding the molecular mechanisms controlling plastic changes in corresponding Kenyon cells. How is timing of behavioral and neuronal plasticity regulated? The primer pheromone ethyl oleate was found in high concentrations on foragers and was shown to influence behavioral maturation by delaying the onset of foraging when artificially applied in elevated concentrations. But how is ethyl oleate transferred and how does it shift the work force distribution between indoor and outdoor tasks? Previous work showed that ethyl oleate concentrations are highest in the honeycrop of foragers and suggested that it is transferred and communicated inside the colony via trophallaxis. The results of this thesis however clearly show, that ethyl oleate was not present inside the honey crop or the regurgitate, but rather in the surrounding tissue of the honey crop. As additionally the second highest concentration of ethyl oleate was measured on the surface of the cuticle of forgers, trophallaxis was ruled out as a mode of transmission. Neurophysiological measurements at the level of the antennae (electroantennogram recordings) and the first olfactory neuropil (calcium imaging of activity in the antennal lobe) revealed that the primer pheromone ethyl oleate is received and processed as an olfactory stimulus. Appetitive olfactory conditioning using the proboscis extension response as a behavioral paradigm showed that ethyl oleate can be associated with a sugar reward. This indicates that workers are able to perceive, learn and memorize the presence of this pheromone. As ethyl oleate had to be presented by a heated stimulation device at close range, it can be concluded that this primer pheromone acts via close range/contact chemoreception through the olfactory system. This is also supported by previous behavioral observations. Taken together, the findings presented in this thesis revealed structural changes in the synaptic architecture of the mushroom body calyx associated with division of labor. For the primer pheromone ethyl oleate, which modulates the transition from nursing to foraging, the results clearly showed that it is received via the olfactory system and presumably acts via this pathway. However, manipulation experiments did not indicate a direct effect of ethyl oleate on synaptic plasticity. At the molecular level, CaMKII is a prime candidate to mediate structural synaptic plasticity in the mushroom body calyx. Future combined structural and functional experiments are needed to finally link the activity of primer pheromones like ethyl oleate to the molecular pathways mediating behavioral and synaptic plasticity associated with division of labor in Apis mellifera. The here identified underlying processes will serve as excellent models for a general understanding of fundamental mechanisms promoting behavioral plasticity.},
  subject      = {Biene},
  language  = {en}
}
@phdthesis{Zube2008,
  author    = {Zube, Christina},
  title     = {Neuronal representation and processing of chemosensory communication signals in the ant brain},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-30383},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {Ants heavily rely on olfaction for communication and orientation and ant societies are characterized by caste- and sex-specific division of labor. Olfaction plays a key role in mediating caste-specific behaviours. I investigated whether caste- and sex-specific differences in odor driven behavior are reflected in specific differences and/or adaptations in the ant olfactory system. In particular, I asked the question whether in the carpenter ant, Camponotus floridanus, the olfactory pathway exhibits structural and/or functional adaptations to processing of pheromonal and general odors. To analyze neuroanatomical specializations, the central olfactory pathway in the brain of large (major) workers, small (minor) workers, virgin queens, and males of the carpenter ant C. floridanus was investigated using fluorescent tracing, immunocytochemistry, confocal microscopy and 3D-analyzes. For physiological analyzes of processing of pheromonal and non-pheromonal odors in the first odor processing neuropil , the antennal lobe (AL), calcium imaging of olfactory projection neurons (PNs) was applied. Although different in total glomerular volumes, the numbers of olfactory glomeruli in the ALs were similar across the female worker caste and in virgin queens. Here the AL contains up to ~460 olfactory glomeruli organized in 7 distinct clusters innervated via 7 antennal sensory tracts. The AL is divided into two hemispheres regarding innervations of glomeruli by PNs with axons leaving via a dual output pathway. This pathway consists of the medial (m) and lateral (l) antenno-cerebral tract (ACT) and connects the AL with the higher integration areas in the mushroom bodies (MB) and the lateral horn (LH). M- and l-ACT PNs differ in their target areas in the MB calyx and the LH. Three additional ACTs (mediolateral - ml) project to the lateral protocerebrum only. Males had ~45\% fewer glomeruli compared to females and one of the seven sensory tracts was absent. Despite a substantially smaller number of glomeruli, males possess a dual PN output pathway to the MBs. In contrast to females, however, only a small number of glomeruli were innervated by projection neurons of the m-ACT. Whereas all glomeruli in males were densely innervated by serotonergic processes, glomeruli innervated by sensory tract six lacked serotonergic innervations in the female castes. It appears that differences in general glomerular organization are subtle among the female castes, but sex-specific differences in the number, connectivity and neuromodulatory innervations of glomeruli are substantial and likely to promote differences in olfactory behavior. Calcium imaging experiments to monitor pheromonal and non-pheromonal processing in the ant AL revealed that odor responses were reproducible and comparable across individuals. Calcium responses to both odor groups were very sensitive (10-11 dilution), and patterns from both groups were partly overlapping indicating that processing of both odor classes is not spatially segregated within the AL. Intensity response patterns to the pheromone components tested (trail pheromone: nerolic acid; alarm pheromone: n-undecane), in most cases, remained invariant over a wide range of intensities (7-8 log units), whereas patterns in response to general odors (heptanal, octanol) varied across intensities. Durations of calcium responses to stimulation with the trail pheromone component nerolic acid increased with increasing odor concentration indicating that odor quality is maintained by a stable pattern (concentration invariance) and intensity is mainly encoded in the response durations of calcium activities. For n-undecane and both general odors increasing response dynamics were only monitored in very few cases. In summary, this is the first detailed structure-function analyses within the ant's central olfactory system. The results contribute to a better understanding of important aspects of odor processing and olfactory adaptations in an insect's central olfactory system. Furthermore, this study serves as an excellent basis for future anatomical and/or physiological experiments.},
  subject      = {Gehirn},
  language  = {en}
}
@phdthesis{Porsche2006,
  author    = {Porsche, Christian},
  title     = {Neuronale Plastizit{\"a}t im Hippocampus der Maus : Die Rolle von Neurotrophine und Cytokinen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-21968},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2006},
  abstract  = {Neurotrophe Faktoren haben ein breites Aufgabenfeld und spielen eine wichtige Rolle als {\"U}berlebensfaktoren embryonaler Neurone, bei Proliferation und Differenzierung im Nervensystem sowie als Modulatoren synaptischer Plastizit{\"a}t. Im ersten Themenkomplex der vorliegenden Arbeit wurden neurotrophe Faktoren als Modulatoren synaptischer Plastizit{\"a}t und ihr Einfluß auf die BDNF-Regulation im Hippocampus untersucht. Dabei wurde zun{\"a}chst das selbsthergestellte polyclonale BDNF-Immunserum f{\"u}r die Anwendung in der Immunhistochemie und im Western Blot optimiert, doch es konnten bez{\"u}glich BDNF keine Ver{\"a}nderungen in Hippocampi CNTF-defizienter M{\"a}use gegen{\"u}ber Wildtyp-Tieren festgestellt werden. Die Ergebnisse der Voruntersuchungen, die im Hippocampus CNTF-defizienter Tiere verminderte BDNF-Level gezeigt hatten, konnten somit nicht verifiziert werden. Im Rahmen dieser Arbeit wurde an CNTF-defizienten M{\"a}usen eine eingeschr{\"a}nkte LTP und LTD nachgewiesen. Zum besseren Verst{\"a}ndnis der - laut LTP-Untersuchungen - ver{\"a}nderten Situation an der hippocampalen CA1-Synapse bei CNTF-defizienten Tieren wurden elektronenmikroskopische Bilder dieser Region angefertigt, deren Auswertung keine augenscheinlichen Unterschiede ergab. Im Stratum radiatum der CA1-Region war zudem keine spezifische CNTF-F{\"a}rbung nachweisbar. Zur Kl{\"a}rung der Frage, ob es IGF-vermittelt nach Training zu hippocampaler BDNF-Hochregulation kommt, wurden Laufradexperimente mit wildtypischen und konditionalen IGF1-Rezeptor-knockout M{\"a}usen durchgef{\"u}hrt und die jeweiligen BDNF-Level untersucht. Dabei wurde BDNF durch Laufradtraining in beiden Genotypen in {\"a}hnlichem Maße hochreguliert, was f{\"u}r alternative Wege der BDNF-Hochregulation spricht. Der zweite Themenkomplex befasste sich mit dem Einfluß neurotropher Faktoren auf die Proliferation und Differenzierung in Hippocampus und Cortex. BrdU-Inkorporationsexperimenten zeigten in der K{\"o}rnerzellschicht des Gyrus dentatus gesteigerte Proliferationsraten bei CNTF-defizienten und CNTF\&LIF-defizienten M{\"a}usen, wobei LIF-defiziente Tiere keine ver{\"a}nderten Proliferationsraten zeigten. Untersuchungen an Kulturen cortikaler Vorl{\"a}uferzellen best{\"a}tigten die Hypothese, wonach cortikale Vorl{\"a}uferzellen zun{\"a}chst Neurone bilden, die einen Faktor sezernieren, der auf die cortikalen Vorl{\"a}uferzellen wirkt und sie zur Bildung von Astrozyten veranlasst. Es konnte gezeigt werden, dass CT-1 der Hypothese folgend in vitro und in vivo f{\"u}r die Einleitung der Astrozytogenese im Cortex verantwortlich ist.},
  subject      = {Maus},
  language  = {de}
}