Analysis of structural plasticity in microglomerular synaptic circuits of the honeybee mushroom-bodies after sensory experience
Sensory and Behavioural Biology
Final Report Abstract
The European honeybee, Apis mellifera, is an important model organism exhibiting exceptional neuronal plasticity evident in high-order sensory integration centres such as the mushroom bodies (MBs). The MB intrinsic neurons, the Kenyon cells (KCs), receive information from primary olfactory and visual centers. Within the MB calyx, olfactory and visual projection neurons (PNs) form synaptic complexes (microglomeruli, MG) with dendritic specializations from class I (spiny) and class II (clawed) KCs. Earlier studies mainly based on 3D quantitative imaging of synapsin-labeled PN boutons demonstrated that MG are an important site for synaptic and neuronal plasticity, most significantly during a honeybee’s transition from in-hive to outside tasks. The transition is reflected in a reduction in the number and density of MG. At the same time, an increase in MB calyx volume indicates extensive that KC dendritic branching and outgrowth, and an increase in the number of MG postsynaptic partners. In this project we focused on the cellular and subcellular architecture and plasticity of individual MG in the calyx at both pre- and postsynaptic sites. Fluorescent dye pressure injections into the vertical lobes of the MBs combined with immunohistochemical approaches were conducted to stain small KC populations in the MB calyx in the context of age-related plasticity. Our analyses show that individual dendrites of both KC classes extend only one dendritic specialization - that is either a spine or a claw - to an individual PN bouton. Spine type and frequency are independent of age in class I KCs, indicating that spine morphology is very dynamic throughout a honeybee’s adult life. Class II KCs exhibit a wide range of claw morphologies, indicating plasticity in post-synaptic contact areas. Using combinations of antibody staining and neuronal tracing followed by isotropic tissue expansion, we demonstrate that expansion microscopy (ExM) enables qualitative and quantitative analyses of structural plasticity in calycal MG with conventional confocal laser scanning microscopy at high resolution in a social insect brain. Based 3D tomograms using scanning transmission electron (STEM) tomography, we provide a first approach to visualize and quantify the ultrastructural presynaptic architecture and light-induced plasticity in visual PN boutons in the MB calyx. We did not find age-related or light-induced effects on clear-core vesicle density and active zone numbers which suggests that PN boutons retain a steady state even in dark conditions. To conclude, our findings in this funded project revealed important insights into the structural plasticity of neuronal circuits that accompany age- and sensory experience-related changes in sensory processing in the honeybee.
Publications
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Analysis of Synaptic Microcircuits in the Mushroom Bodies of the Honeybee. Insects, 11(1), 43.
Groh, Claudia & Rössler, Wolfgang
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Bigger brains are better: Shedding new light on neuroplasticity in the honeybee using expansion microscopy. 113th annual meeting of the German Zoological Society – online (poster)
Kraft N., Muenz T.S., Werner C., Sauer M., Groh C. & Rössler W.
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Expansion microscopy in honeybee brains: a new attempt to push the limits of neuroanatomical analyses in social insects. 14th Göttingen meeting of the German Neuroscience Society – online (poster)
Kraft N., Muenz T.S., Werner C., Sauer M., Groh C. & Rössler W.
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Adult neuronal plasticity of olfactory mushroom body microcircuits in the honeybee Apis mellifera. 18th European Symposium for Insect Taste and Olfaction (talk)
Groh C.
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Developmental and adult neuronal plasticity of mushroom body microcircuits in Hymenoptera. Mushroom body meeting (talk)
Groh C.
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Expansion microscopy in honeybee brains for high-resolution neuroanatomical analyses in social insects. Cell and Tissue Research, 393(3), 489-506.
Kraft, Nadine; Muenz, Thomas S.; Reinhard, Sebastian; Werner, Christian; Sauer, Markus; Groh, Claudia & Rössler, Wolfgang
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Light-induced ultrastructural synaptic plasticity in the mushroom body calyces of honeybees using STEM tomography. 15th Göttingen meeting of the German Neuroscience Society (poster)
Kraft N., Stigloher C., Rössler W. & Groh C.
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Analysis of mushroom body synaptic circuits in the adult Apis mellifera brain. 15th Internat. Congress of Neuroethology (poster)
Nicolaidou A.R,. el Jundi B., Rössler W. & Groh C.
