TY - THES A1 - Schmalz, Fabian Dominik T1 - Processing of behaviorally relevant stimuli at different levels in the bee brain T1 - Die Verarbeitung verhaltensrelevanter Stimuli auf unterschiedlichen Ebenen im Bienengehirn N2 - The behavior of honeybees and bumblebees relies on a constant sensory integration of abiotic or biotic stimuli. As eusocial insects, a sophisticated intraspecific communication as well as the processing of multisensory cues during foraging is of utter importance. To tackle the arising challenges, both honeybees and bumblebees have evolved a sophisticated olfactory and visual processing system. In both organisms, olfactory reception starts at the antennae, where olfactory sensilla cover the antennal surface in a sex-specific manner. These sensilla house olfactory receptor neurons (ORN) that express olfactory receptors. ORNs send their axons via four tracts to the antennal lobe (AL), the prime olfactory processing center in the bee brain. Here, ORNs specifically innervate spheroidal structures, so-called glomeruli, in which they form synapses with local interneurons and projection neurons (PN). PNs subsequently project the olfactory information via two distinct tracts, the medial and the lateral antennal-lobe tract, to the mushroom body (MB), the main center of sensory integration and memory formation. In the honeybee calyx, the sensory input region of the MB, PNs synapse on Kenyon cells (KC), the principal neuron type of the MB. Olfactory PNs mainly innervate the lip and basal ring layer of the calyx. In addition, the basal ring receives input from visual PNs, making it the first site of integration of visual and olfactory information. Visual PNs, carrying sensory information from the optic lobes, send their terminals not only to the to the basal ring compartment but also to the collar of the calyx. Receiving olfactory or visual input, KCs send their axons along the MB peduncle and terminate in the main output regions of the MB, the medial and the vertical lobe (VL) in a layer-specific manner. In the MB lobes, KCs synapse onto mushroom body output neurons (MBON). In so far barely understood processes, multimodal information is integrated by the MBONs and then relayed further into the protocerebral lobes, the contralateral brain hemisphere, or the central brain among others. This dissertation comprises a dichotomous structure that (i) aims to gain more insight into the olfactory processing in bumblebees and (ii) sets out to broaden our understanding of visual processing in honeybee MBONs. The first manuscript examines the olfactory processing of Bombus terrestris and specifically investigates sex-specific differences. We used behavioral (absolute conditioning) and electrophysiological approaches to elaborate the processing of ecologically relevant odors (components of plant odors and pheromones) at three distinct levels, in the periphery, in the AL and during olfactory conditioning. We found both sexes to form robust memories after absolute conditioning and to generalize towards the carbon chain length of the presented odors. On the contrary, electroantennographic (EAG) activity showed distinct stimulus and sex-specific activity, e.g. reduced activity towards citronellol in drones. Interestingly, extracellular multi-unit recordings in the AL confirmed stimulus and sex-specific differences in olfactory processing, but did not reflect the differences previously found in the EAG. Here, farnesol and 2,3-dihydrofarnesol, components of sex-specific pheromones, show a distinct representation, especially in workers, corroborating the results of a previous study. This explicitly different representation suggests that the peripheral stimulus representation is an imperfect indication for neuronal representation in high-order neuropils and ecological importance of a specific odor. The second manuscript investigates MBONs in honeybees to gain more insights into visual processing in the VL. Honeybee MBONs can be categorized into visually responsive, olfactory responsive and multimodal. To clarify which visual features are represented at this high-order integration center, we used extracellular multi-unit recordings in combination with visual and olfactory stimulation. We show for the first time that information about brightness and wavelength is preserved in the VL. Furthermore, we defined three specific classes of visual MBONs that distinctly encode the intensity, identity or simply the onset of a stimulus. The identity-subgroup exhibits a specific tuning towards UV light. These results support the view of the MB as the center of multimodal integration that categorizes sensory input and subsequently channels this information into specific MBON populations. Finally, I discuss differences between the peripheral representations of stimuli and their distinct processing in high-order neuropils. The unique activity of farnesol in manuscript 1 or the representation of UV light in manuscript 2 suggest that the peripheral representation of a stimulus is insufficient as a sole indicator for its neural activity in subsequent neuropils or its putative behavioral importance. In addition, I discuss the influence of hard-wired concepts or plasticity induced changes in the sensory pathways on the processing of such key stimuli in the peripheral reception as well as in high-order centers like the AL or the MB. The MB as the center of multisensory integration has been broadly examined for its olfactory processing capabilities and receives increasing interest about its visual coding properties. To further unravel its role of sensory integration and to include neglected modalities, future studies need to combine additional approaches and gain more insights on the multimodal aspects in both the input and output region. N2 - Honigbienen und Hummeln sind aufgrund ihrer Lebensweise auf die ständige Verarbeitung sensorischer Eindrücke abiotischen und biotischen Ursprungs angewiesen. Als eusoziale Insekten ist hierbei für beide Arten die Wahrnehmung innerartlicher Kommunikation wie auch die Verarbeitung multisensorischer Einflüsse während der Nahrungssuche von essenzieller Bedeutung. Um die daraus resultierenden vielfältigen Herausforderungen erfolgreich bewältigen zu können, verfügen Honigbienen und Hummeln über eine fortschrittliche Verarbeitung olfaktorischer und visueller Reize. In beiden Arten beginnt die Geruchsrezeption an den Antennen, welche geschlechtsspezifisch von zahlreichen olfaktorischen Sensillen besetzt sind. Diese beinhalten olfaktorische Rezeptorneurone (ORN), in welchen die Expression der Geruchsrezeptoren stattfindet. Axone der ORNs laufen dabei gebündelt über vier verschiedene Trakte in den Antennallobus (AL), das erste olfaktorische Verarbeitungszentrum im Bienengehirn. Im AL verschalten ORNs mit lokalen Interneuronen und Projektionsneuronen (PN) in kugelförmigen Strukturen, den sogenannten Glomeruli. PNs leiten die olfaktorische Information daraufhin über zwei charakteristische Trakte, den medialen und lateralen Antennallobustrakt, in den Pilzkörper (MB), das Verarbeitungszentrum für die Integration sensorischer Eindrücke und Gedächtnisbildung. Im Calyx der Honigbiene, der sensorischen Eingangsregion des MB, bilden die Endköpfchen der PNs synaptische Verbindungen mit Kenyonzellen (KC), den primären Nervenzellen im MB. Die Innervation des Calyx durch die PNs ist dabei spezifisch in drei verschiedenen Zonen organisiert, nämlich in Lippe, Hals und basalen Ring. Während die Lippe vornehmlich olfaktorische Information von PNs aus dem AL erhält, wird der basale Ring zusätzlich auch von visuellen PNs, welche Informationen aus dem optischen Lobus einbringen, angesteuert. Der basale Ring der Honigbiene wird dabei Ort der ersten räumlichen Integration visuellen und olfaktorischen Eingangs. Wiederum ähnlich zum unimodalen Eingang der Lippe, bezieht auch der Hals des Calyx grundsätzlich nur sensorischen Eingang einer Modalität, nämlich visuelle Information von PNs aus dem optischen Lobus. KCs verschalten im weiteren Verlauf die olfaktorischen und visuellen Informationen an Pilzkörperausgangsneurone (MBON). In einem bisher kaum erforschten Vorgang wird diese multimodale Information dabei verarbeitet und dann mithilfe der MBONs in verschiedene Bereiche des Gehirns geleitet, z.B. in die protocerebralen Loben, die kontralaterale Gehirnhemisphäre oder das Zentralgehirn. Diese Dissertation ist zweigeteilt und behandelt zuerst (i) die geschlechtsspezifische Verarbeitung olfaktorischer Reize in Hummeln und bespricht im zweiten Teil (ii) neue Einblicke in die neuronale Weiterverarbeitung visueller Reize durch MBONs in der Honigbiene. Manuskript 1 untersucht die Abläufe der Geruchsverarbeitung von Bombus terrestris und beschreibt geschlechtsspezifische Unterschiede. Hierbei wurden sowohl verhaltensbasierte als auch elektrophysiologische Methoden genutzt um die Wahrnehmung ökologisch relevanter Duftstoffe (Komponenten unterschiedlicher Pflanzendüfte oder Pheromone) auf drei verschiedene Weisen zu untersuchen, nämlich in der Peripherie, im AL und mittels olfaktorischer Konditionierung. Wir fanden in beiden Geschlechtern eine robuste Gedächtnisbildung nach absoluter Konditionierung und eine ausgeprägte Generalisierung anhand der Kohlenstoffkettenlänge der präsentierten Duftstoffe. Anders stellten sich die Ergebnisse der elektroantennographischen (EAG) Untersuchungen dar. Hier zeigten sowohl Drohnen als auch Arbeiterinnen neuronale Aktivität mit spezifischen Unterschieden zwischen den Stimuli, aber auch zwischen den Geschlechtern auf, z.B. löste die Applikation von Citronellol eine deutliche verringerte Reaktion in der EAG Aktivität der Drohnen aus. Interessanterweise zeigten auch extrazelluläre Ableitungen im AL stimulus- und geschlechtsspezifische Unterschiede, jedoch in unterschiedlicher Konstellation als in den EAG-Experimenten. Besonders Farnesol und 2,3-Dihydrofarnesol wiesen vor allem bei Arbeiterinnen eine deutliche Repräsentation in der neuronalen Aktivität auf; ein Alleinstellungsmerkmal welches für Farnesol bereits in einer früheren Studie beschrieben wurde. Diese explizit unterschiedliche neuronale Darstellung von Farnesol und 2,3-Dihydrofarnesol in der Peripherie und im AL führt zu der Annahme, dass die rezeptive Darstellung eines Stimulus in der Peripherie keine zuverlässigen Rückschlüsse über die neuronale Repräsentation in höheren Zentren oder die ökologische Relevanz zulässt. Im zweiten Manuskript stehen MBONs der Honigbiene im Fokus, um mehr Einblicke in die visuelle Verarbeitung im VL zu erlangen. Bisher können MBONs in folgende Klassen unterteilt werden: Visuelle, olfaktorische und multimodale MBONs, welche sensitiv für beide Modalitäten sind. Kern dieser Arbeit ist, mittels extrazellulärer Ableitungen festzustellen, welche zusätzlichen Aspekte eines visuellen Stimulus in diesem zentralen Verarbeitungszentrum repräsentiert sind. Dabei konnte zum ersten Mal gezeigt werden, dass Informationen über die Wellenlänge und die Intensität des Lichtstimulus im VL erhalten sind. Im weiteren Verlauf konnte eine Spezifizierung der bisherigen Kategorisierung visueller und multimodaler MBONs in drei weitere Untergruppen vollzogen werden: MBONs die spezifisch die Intensität, die Identität und dein Eingang eines Stimulus kodieren. Des Weiteren zeigte vor allem die Gruppe der Identitäts-MBONs eine bemerkenswerte Kategorisierung von UV-Licht. Diese neuen Erkenntnisse bestätigen die Ansicht, dass der MB, als Zentrum für sensorische Integration, eine Kategorisierung der verarbeiteten Eindrücke vornimmt und diese daraufhin auf die MBONs verschalten wird. Abschließend diskutiere ich Unterschiede in der peripheren Repräsentation von Stimuli und ihrer späteren neuronalen Verarbeitung. Hier zeige ich, die Aktivität von Farnesol in MS1 und UV-Licht MS2 als Beispiel nehmend, dass die periphere Repräsentation eines Stimulus keine sicheren Schlussfolgerungen über die nachfolgend induzierte neurale Aktivität oder die verhaltensrelevante Bedeutung zulässt. Im weiteren Verlauf werden dabei die Einflüsse konservierter Strukturen und plastischer Änderungen auf die Abläufe der sensorischen Peripherie oder der höheren Verarbeitungszentren, wie dem AL oder dem MB gezeigt. Obwohl der MB, das Zentrum für multimodale Integration und Gedächtnis, hinsichtlich seiner Rolle in der Geruchswahrnehmung ausgiebig erforscht ist, gibt es bezüglich der visuellen Verarbeitung oder dem Einfluss anderer Modalitäten noch ungeklärte Abläufe und Fragen. Wenngleich auch hier die Kenntnis speziell über die visuelle Verarbeitung im MB stetig zunimmt, sollten zukünftige Arbeiten mithilfe weiterer Methoden den MB Eingang und Ausgang explizit auf den Einfluss weiterer Modalitäten untersuchen, um so ein umfassenderes Bild über die Abläufe multimodaler Integration zu erhalten. KW - Biene KW - Elektrophysiologie KW - bee KW - electrophysiology KW - olfaction KW - vision KW - multi-unit recording KW - Olfaktorik KW - Sehen KW - Multi-Unit Aufnahmen Y1 - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-288824 ER - TY - JOUR A1 - Stieb, Sara Mae A1 - Kelber, Christina A1 - Wehner, Rüdiger A1 - Rössler, Wolfgang T1 - Antennal-Lobe Organization in Desert Ants of the Genus Cataglyphis JF - Brain, Behavior and Evolution N2 - Desert ants of the genus Cataglyphis possess remarkable visual navigation capabilities. Although Cataglyphis species lack a trail pheromone system, Cataglyphis fortis employs olfactory cues for detecting nest and food sites. To investigate potential adaptations in primary olfactory centers of the brain of C. fortis, we analyzed olfactory glomeruli (odor processing units) in their antennal lobes and compared them to glomeruli in different Cataglyphis species. Using confocal imaging and 3D reconstruction, we analyzed the number, size and spatial arrangement of olfactory glomeruli in C. fortis, C.albicans, C.bicolor, C.rubra, and C.noda. Workers of all Cataglyphis species have smaller numbers of glomeruli (198–249) compared to those previously found in olfactory-guided ants. Analyses in 2 species of Formica – a genus closely related to Cataglyphis – revealed substantially higher numbers of olfactory glomeruli (c. 370), which is likely to reflect the importance of olfaction in these wood ant species. Comparisons between Cataglyphis species revealed 2 special features in C. fortis. First, with c. 198 C. fortis has the lowest number of glomeruli compared to all other species. Second, a conspicuously enlarged glomerulus is located close to the antennal nerve entrance. Males of C. fortis possess a significantly smaller number of glomeruli (c. 150) compared to female workers and queens. A prominent male-specific macroglomerulus likely to be involved in sex pheromone communication occupies a position different from that of the enlarged glomerulus in females. The behavioral significance of the enlarged glomerulus in female workers remains elusive. The fact that C. fortis inhabits microhabitats (salt pans) that are avoided by all other Cataglyphis species suggests that extreme ecological conditions may not only have resulted in adaptations of visual capabilities, but also in specializations of the olfactory system. KW - olfactory glomeruli KW - plasticity KW - ant KW - antennal lobe KW - glomerulus KW - insects KW - interspecific comparison KW - macroglomerulus KW - olfaction Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-196815 SN - 0006-8977 SN - 1421-9743 N1 - This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively. VL - 77 IS - 3 ER - TY - JOUR A1 - Groh, Claudia A1 - Rössler, Wolfgang T1 - Analysis of Synaptic Microcircuits in the Mushroom Bodies of the Honeybee JF - Insects N2 - Mushroom bodies (MBs) are multisensory integration centers in the insect brain involved in learning and memory formation. In the honeybee, the main sensory input region (calyx) of MBs is comparatively large and receives input from mainly olfactory and visual senses, but also from gustatory/tactile modalities. Behavioral plasticity following differential brood care, changes in sensory exposure or the formation of associative long-term memory (LTM) was shown to be associated with structural plasticity in synaptic microcircuits (microglomeruli) within olfactory and visual compartments of the MB calyx. In the same line, physiological studies have demonstrated that MB-calyx microcircuits change response properties after associative learning. The aim of this review is to provide an update and synthesis of recent research on the plasticity of microcircuits in the MB calyx of the honeybee, specifically looking at the synaptic connectivity between sensory projection neurons (PNs) and MB intrinsic neurons (Kenyon cells). We focus on the honeybee as a favorable experimental insect for studying neuronal mechanisms underlying complex social behavior, but also compare it with other insect species for certain aspects. This review concludes by highlighting open questions and promising routes for future research aimed at understanding the causal relationships between neuronal and behavioral plasticity in this charismatic social insect. KW - mushroom body KW - microglomeruli KW - projection neurons KW - Kenyon cells KW - dendritic specializations KW - structural synaptic plasticity KW - behavioral plasticity KW - vision KW - olfaction Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-200774 SN - 2075-4450 VL - 11 IS - 1 ER - TY - JOUR A1 - Kropf, Jan A1 - Rössler, Wolfgang T1 - In-situ recording of ionic currents in projection neurons and Kenyon cells in the olfactory pathway of the honeybee JF - PLoS ONE N2 - The honeybee olfactory pathway comprises an intriguing pattern of convergence and divergence: ~60.000 olfactory sensory neurons (OSN) convey olfactory information on ~900 projection neurons (PN) in the antennal lobe (AL). To transmit this information reliably, PNs employ relatively high spiking frequencies with complex patterns. PNs project via a dual olfactory pathway to the mushroom bodies (MB). This pathway comprises the medial (m-ALT) and the lateral antennal lobe tract (l-ALT). PNs from both tracts transmit information from a wide range of similar odors, but with distinct differences in coding properties. In the MBs, PNs form synapses with many Kenyon cells (KC) that encode odors in a spatially and temporally sparse way. The transformation from complex information coding to sparse coding is a well-known phenomenon in insect olfactory coding. Intrinsic neuronal properties as well as GABAergic inhibition are thought to contribute to this change in odor representation. In the present study, we identified intrinsic neuronal properties promoting coding differences between PNs and KCs using in-situ patch-clamp recordings in the intact brain. We found very prominent K+ currents in KCs clearly differing from the PN currents. This suggests that odor coding differences between PNs and KCs may be caused by differences in their specific ion channel properties. Comparison of ionic currents of m- and l-ALT PNs did not reveal any differences at a qualitative level. KW - action potentials KW - olfaction KW - honeybee Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-175869 VL - 13 IS - 1 ER - TY - JOUR A1 - Falibene, Augustina A1 - Roces, Flavio A1 - Rössler, Wolfgang T1 - Long-term avoidance memory formation is associated with a transient increase in mushroom body synaptic complexes in leaf-cutting ants JF - Frontiers in Behavioural Neuroscience N2 - Long-term behavioral changes related to learning and experience have been shown to be associated with structural remodeling in the brain. Leaf-cutting ants learn to avoid previously preferred plants after they have proved harmful for their symbiotic fungus, a process that involves long-term olfactory memory. We studied the dynamics of brain microarchitectural changes after long-term olfactory memory formation following avoidance learning in Acromyrmex ambiguus. After performing experiments to control for possible neuronal changes related to age and body size, we quantified synaptic complexes (microglomeruli, MG) in olfactory regions of the mushroom bodies (MB) at different times after learning. Long-term avoidance memory formation was associated with a transient change in MG densities. Two days after learning, MG density was higher than before learning. At days 4 and 15 after learning when ants still showed plant avoidance MG densities had decreased to the initial state. The structural reorganization of MG triggered by long-term avoidance memory formation clearly differed from changes promoted by pure exposure to and collection of novel plants with distinct odors. Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip. We hypothesize that while sensory exposure leads to MG pruning in the MB olfactory lip, the formation of long-term avoidance memory involves an initial growth of new MG followed by subsequent pruning. KW - Acromyrmex ambiguus KW - leaf-cutting ants KW - avoidance learning KW - olfaction KW - honeybee KW - microglomeruli KW - mushroom body KW - synaptic plasticity Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148763 VL - 9 IS - 84 ER - TY - JOUR A1 - Falibene, Augustine A1 - Roces, Flavio A1 - Rössler, Wolfgang A1 - Groh, Claudia T1 - Daily Thermal Fluctuations Experienced by Pupae via Rhythmic Nursing Behavior Increase Numbers of Mushroom Body Microglomeruli in the Adult Ant Brain JF - Frontiers in Behavioral Neuroscience N2 - Social insects control brood development by using different thermoregulatory strategies. Camponotus mus ants expose their brood to daily temperature fluctuations by translocating them inside the nest following a circadian rhythm of thermal preferences. At the middle of the photophase brood is moved to locations at 30.8°C; 8 h later, during the night, the brood is transferred back to locations at 27.5°C. We investigated whether daily thermal fluctuations experienced by developing pupae affect the neuroarchitecture in the adult brain, in particular in sensory input regions of the mushroom bodies (MB calyces). The complexity of synaptic microcircuits was estimated by quantifying MB-calyx volumes together with densities of presynaptic boutons of microglomeruli (MG) in the olfactory lip and visual collar regions. We compared young adult workers that were reared either under controlled daily thermal fluctuations of different amplitudes, or at different constant temperatures. Thermal regimes significantly affected the large (non-dense) olfactory lip region of the adult MB calyx, while changes in the dense lip and the visual collar were less evident. Thermal fluctuations mimicking the amplitudes of natural temperature fluctuations via circadian rhythmic translocation of pupae by nurses (amplitude 3.3°C) lead to higher numbers of MG in the MB calyces compared to those in pupae reared at smaller or larger thermal amplitudes (0.0, 1.5, 9.6°C), or at constant temperatures (25.4, 35.0°C). We conclude that rhythmic control of brood temperature by nursing ants optimizes brain development by increasing MG densities and numbers in specific brain areas. Resulting differences in synaptic microcircuits are expected to affect sensory processing and learning abilities in adult ants, and may also promote interindividual behavioral variability within colonies. KW - microglomeruli KW - temperature KW - broodtranslocation KW - camponotus ants KW - olfaction KW - vision KW - synapticplasticity KW - mushroom body Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-146711 VL - 10 IS - 73 ER - TY - JOUR A1 - Chen, Yi-chun A1 - Gerber, Bertram T1 - Generalization and discrimination tasks yield concordant measures of perceived distance between odours and their binary mixtures in larval Drosophila JF - The Journal of Experimental Biology N2 - Similarity between odours is notoriously difficult to measure. Widely used behavioural approaches in insect olfaction research are cross-adaptation, masking, as well as associative tasks based on olfactory learning and the subsequent testing for how specific the established memory is. A concern with such memory-based approaches is that the learning process required to establish an odour memory may alter the way the odour is processed, such that measures of perception taken at the test are distorted. The present study was therefore designed to see whether behavioural judgements of perceptual distance are different for two different memory-based tasks, namely generalization and discrimination. We used odour-reward learning in larval Drosophila as a study case. In order to challenge the larvae's olfactory system, we chose to work with binary mixtures and their elements (1-octanol, n-amyl acetate, 3-octanol, benzaldehyde and hexyl acetate). We determined the perceptual distance between each mixture and its elements, first in a generalization task, and then in a discrimination task. It turns out that scores of perceptual distance are correlated between both tasks. A re-analysis of published studies looking at element-to-element perceptual distances in larval reward learning and in adult punishment learning confirms this result. We therefore suggest that across a given set of olfactory stimuli, associative training does not grossly alter the pattern of perceptual distances. KW - discrimination KW - drosophila melanogaster KW - generalization KW - memory KW - olfaction KW - perception Y1 - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-121625 VL - 217 IS - 12 ER - TY - JOUR A1 - Brill, Martin F. A1 - Meyer, Anneke A1 - Roessler, Wolfgang T1 - It takes two—coincidence coding within the dual olfactory pathway of the honeybee JF - Frontiers in Physiology N2 - To rapidly process biologically relevant stimuli, sensory systems have developed a broad variety of coding mechanisms like parallel processing and coincidence detection. Parallel processing (e.g., in the visual system), increases both computational capacity and processing speed by simultaneously coding different aspects of the same stimulus. Coincidence detection is an efficient way to integrate information from different sources. Coincidence has been shown to promote associative learning and memory or stimulus feature detection (e.g., in auditory delay lines). Within the dual olfactory pathway of the honeybee both of these mechanisms might be implemented by uniglomerular projection neurons (PNs) that transfer information from the primary olfactory centers, the antennal lobe (AL), to a multimodal integration center, the mushroom body (MB). PNs from anatomically distinct tracts respond to the same stimulus space, but have different physiological properties, characteristics that are prerequisites for parallel processing of different stimulus aspects. However, the PN pathways also display mirror-imaged like anatomical trajectories that resemble neuronal coincidence detectors as known from auditory delay lines. To investigate temporal processing of olfactory information, we recorded PN odor responses simultaneously from both tracts and measured coincident activity of PNs within and between tracts. Our results show that coincidence levels are different within each of the two tracts. Coincidence also occurs between tracts, but to a minor extent compared to coincidence within tracts. Taken together our findings support the relevance of spike timing in coding of olfactory information (temporal code). KW - olfaction KW - mushroom body KW - insect KW - coincidence KW - multi-electrode-recording KW - antennal lobe Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-126179 VL - 6 IS - 208 ER - TY - JOUR A1 - Falibene, Agustina A1 - Roces, Flavio A1 - Rössler, Wolfgang T1 - Long-term avoidance memory formation is associated with a transient increase in mushroom body synaptic complexes in leaf-cutting ants JF - Frontiers in Behavioral Neuroscience N2 - Long-term behavioral changes related to learning and experience have been shown to be associated with structural remodeling in the brain. Leaf-cutting ants learn to avoid previously preferred plants after they have proved harmful for their symbiotic fungus, a process that involves long-term olfactory memory. We studied the dynamics of brain microarchitectural changes after long-term olfactory memory formation following avoidance learning in Acromyrmex ambiguus. After performing experiments to control for possible neuronal changes related to age and body size, we quantified synaptic complexes (microglomeruli, MG) in olfactory regions of the mushroom bodies (MBs) at different times after learning. Long-term avoidance memory formation was associated with a transient change in MG densities. Two days after learning, MG density was higher than before learning. At days 4 and 15 after learning—when ants still showed plant avoidance—MG densities had decreased to the initial state. The structural reorganization of MG triggered by long-term avoidance memory formation clearly differed from changes promoted by pure exposure to and collection of novel plants with distinct odors. Sensory exposure by the simultaneous collection of several, instead of one, non-harmful plant species resulted in a decrease in MG densities in the olfactory lip. We hypothesize that while sensory exposure leads to MG pruning in the MB olfactory lip, the formation of long-term avoidance memory involves an initial growth of new MG followed by subsequent pruning. KW - microglomeruli KW - olfaction KW - avoidance learning KW - leaf-cutting ants KW - acromyrmex ambiguus KW - synaptic plasticity KW - mushroom body Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-125522 VL - 9 IS - 84 ER - TY - THES A1 - Brill, Martin Fritz T1 - Processing and plasticity within the dual olfactory pathway in the honeybee brain T1 - Verarbeitung und Plastizität in der dualen olfaktorischen Bahn im Gehirn der Honigbiene N2 - In their natural environment animals face complex and highly dynamic olfactory input. This requires fast and reliable processing of olfactory information, in vertebrates as well as invertebrates. Parallel processing has been shown to improve processing speed and power in other sensory systems like auditory or visual. In the olfactory system less is known about olfactory coding in general and parallel processing in particular. With its elaborated olfactory system and due to their specialized neuroanatomy, honeybees are well-suited model organism to study parallel olfactory processing. The honeybee possesses a unique neuronal architecture - a dual olfactory pathway. Two mirror-imaged output projection neuron (PN) pathways connect the first olfactory processing stage, the antennal lobe (analog to the vertebrates olfactory bulb, OB), with the second, the mushroom body (MB) known to be involved in orientation and learning and memory, and the lateral horn (LH). The medial antennal lobe-protocerebral tract (m-APT) first innervates the MB and thereafter the LH, while the other, the lateral-APT (l-APT) projects in opposite direction. The neuroanatomy and evolution of these pathways has been analyzed, yet little is known about its physiology. To analyze the function of the dual olfactory pathway a new established recording method was designed and is described in the first chapter of this thesis (multi-unit-recordings). This is now the first time where odor response from several PNs of both tracts is recorded simultaneously and with high temporal precision. In the second chapter the PN odor responses are analyzed. The major findings are: both tracts responded to all tested odors but with differing characteristics. Since recent studies describe the input to the two tracts being rather similar, the results now indicate differential odor processing along the tracts, therefore this is a good indicator for parallel processing. PNs of the m-APT process odors in a sparse manner with delayed response latencies, but with high odor-specificity. PNs of the l-APT in contrast respond to several odor stimuli and respond in general faster. In some PN originating from both tracts, characteristics of odor-identity coding via response latencies were found. Analyzing the over-all dynamic range of the PNs both l- and m-APT PNs were tested over a large odor concentration range (10-6 to 10-2) (3. chapter). The PNs responded with linear and non-linear correlation of the response strength to the odor concentration. In most cases the l-APT is comparatively more sensitive to low odor concentrations. Response latency decreases with increasing odor concentration in both tracts. Alternative coding principles and elaboration on the hypothesis whether the dual olfactory pathway may contribute coincidental innervation to the next higher-order neurons, the Kenyon cells (KC), is subject of the 4. chapter. Cross-correlations and synchronous responses of both tracts show that in principle odors may be coded via temporal coding. Results suggest that odor processing is enhanced if both tracts contribute to olfactory coding together. In another project the distribution of the inhibitory neurotransmitter GABA (gamma-aminobutyric acid) was measured in the bee’s MB during adult maturation (5. chapter). GABAergic inhibition is of high importance in odor coding. An almost threefold decrease in the total amount of GABAergic innervation was found during adult maturation in the l- and m-APT target region, in particular at the change in division of labor during the transition from a young nurse bee to an older forager bee. The results fit well into the current understanding of brain development in the honeybee and other social insects during adult maturation, which was described as presynaptic pruning and KC dendritic outgrowth. Combining anatomical and functional properties of the bee’s dual olfactory pathway suggests that both rate and temporal coding are implemented along two parallel streams. Comparison with recent work on analog output pathways of the vertebrate’s OB indicates that parallel processing of olfactory information may be a common principle across distant taxa. N2 - In ihrem natürlichen Lebensraum sind Lebewesen mit komplexen und hoch dynamischen olfaktorischen Reizen konfrontiert, was eine schnelle und zuverlässige Duft-Verarbeitung sowohl bei Insekten als auch bei Wirbeltieren erfordert. Im visuellen oder auditorischen System wird sensorischer Eingang durch Parallel-Verarbeitung schneller und effektiver an höhere Gehirnzentren übertragen und verarbeitet. Im olfaktorischen System ist generell und im speziellen über Parallel-Verarbeitung noch wenig bekannt. Die Honigbiene stellt jedoch mit ihrer hoch spezialisierten Duftwahrnehmung und ihrem Duft und Pheromon gesteuerten Verhalten aufgrund ihrer Neuroanatomie einen besonderen Modelorganismus für die Erforschung der Duftverarbeitung und insbesondere der olfaktorischen Parallel-Verarbeitung dar. Honigbienen besitzen „duale olfaktorische Bahnen“, die ausschließlich in Hymenopteren (Bienen, Ameisen, Wespen) als Merkmal ausgeprägt sind. Gebildet werden sie aus zwei spiegelbildlichen Projektions-Neuronen (PN) Ausgangs-Trakten, die das erste olfaktorische Verarbeitungs-Zentrum, den Antennal-Lobus (vergleichbar mit dem Olfaktorischen Bulbus der Wirbeltiere, OB) mit sekundären Verarbeitungszentren, dem Pilzkörper (MB) und dem lateralen Horn (LH) verbinden. Der mediale Antennal-Lobusprotocerebrale Trakt (m-APT) innerviert erst den MB und dann das LH, der laterale Trakt (l-APT) projiziert in umgekehrter Reihenfolge. Der MB ist bei Orientierung, Lernen und Gedächtnis involviert, über die Funktion des LH ist in der Biene noch wenig bekannt. Über die Neuroanatomie und Evolution dieser dualen Bahnen wurde viel geforscht, die Funktion und damit ihre Physiologie sind allerdings noch unzureichend aufgeklärt. Die vorliegende Dissertation beschäftigt sich deshalb mit der Duftverarbeitung im Bienengehirn und im Speziellen mit Parallelverarbeitung in der Olfaktorik. Für die Aufklärung wurde eine neu entwickelte und in dieser Dissertation beschriebene Messmethode etabliert (1. Kapitel). Mit Hilfe dieser Messapparatur (Multi-Unit Recordings) ist es jetzt das erste Mal möglich, hoch-zeitaufgelöst simultan aus beiden Trakten mehrere PNs auf unterschiedliche Düfte hin zu untersuchen. Das 2. Kapitel beschäftigt sich eingehender mit der Analyse von Duftanworten der PN. Die Hauptergebnisse sind, dass beide Trakte auf alle getesteten Düfte regieren, dies aber mit unterschiedlichen Charakteristiken tun. Da gezeigt wurde, dass beide Trakte ähnlichen olfaktorischen Eingang erhalten, die Trakte aber Düfte unterschiedlich verarbeiten, stellen diese Ergebnisse ein erstes Indiz für Parallelverarbeitung im olfaktorischen System der Biene dar. M-APT PN reagieren mit Zeitverzögerung und duftspezifisch, d.h. selektiver auf Düfte. Dagegen reagieren l-APT PN vergleichsweise schneller und duft-unspezifischer auf die in dieser Arbeit verwendeten Düfte. In einigen PN beider Trakte wurde gefunden, dass die PN Duft-Identitäten über duftspezifische Antwort-Latenzen abgebildet werden können. Um Aufschluss über die Gesamtdynamik der PN zu gewinnen, wurden l- und m-APT PN Antworten über weite Duftkonzentrationen (10-6 bis 10-2) hin untersucht (3. Kapitel). Die PN reagierten mit linearen und nicht-linearen Korrelationen. Zudem sind in den meisten Fällen l-APT PN bei schwachen Duftkonzentrationen sensitiver. Die Antwort-Latenz ist zur Duftkonzentration in beiden Trakten negativ-proportional. Alternative Kodierungsmöglichkeiten und die Ausarbeitung der Hypothese, dass die dualen Bahnen eine Koinzidenzverschaltung auf die nächst höheren Neurone, die Kenyon Zellen (KC), bilden könnten, wird im 4. Kapitel behandelt. Dazu zeigen Kreuz-Korrelationsanalysen und synchrone Antwortmuster aus beiden Trakten, dass prinzipiell Düfte auch über Zeit-Kodierung verarbeitet werden können. Generell zeigt sich, dass die dualen olfaktorischen Bahnen eine verbesserte Duftkodierung gegenüber einem Trakt gewährleisten. In einem weiteren Ansatz wurde die alterskorrelierte Plastizität der inhibitorischen GABAergen (gamma-Aminobuttersäure) Innervation im Pilzkörper der Biene während der Adult-Reifung bestimmt (5. Kapitel). Inhibition ist für olfaktorische Kodierung sehr wichtig. Eine fast dreifache Reduktion in der Gesamtmenge von GABA wurde während der Adult-Reifung in beiden Zielregionen der dualen olfaktorischen Bahn gleichermaßen gefunden. Dieser Effekt wurde mit einer insgesamt halbierten GABA Innervierung ebenfalls im visuellen Innervationsgebiet des MB gefunden. Die Ergebnisse passen gut in das derzeitige Verständnis von Adultplastizität der Pilzkörper in der Honigbiene, in denen eine Ausdünnung (Pruning) präsynaptischer Endigungen von PN und ein Auswachsen von KC-Dendriten beschrieben wurde. Aus den neuroanatomischen und physiologischen Eigenschaften der dualen olfaktorischen Bahnen lässt sich schlussfolgern, dass Düfte sowohl über Raten- als auch Zeit-Kodierung bis hin zu Koinzidenz-Verschaltungen verarbeitet werden können. Zudem zeigen derzeitige Arbeiten über analoge Ausgangs-Trakte im OB von Wirbeltieren, dass Parallelverarbeitung im olfaktorischen System ein allgemeines Kodierungsprinzip über weit entfernte Taxa zu sein scheint. KW - Tierphysiologie KW - Geruchssinn KW - Nervennetz KW - Nervenzelle KW - Biene KW - Antennallobus KW - antennal lobe KW - olfaction KW - multi-unit recording KW - Insekten KW - Geruch KW - Physiologie Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-85600 ER -