A unified platform to manage, share, and archive morphological and functional data in insect neuroscience

Insect neuroscience generates vast amounts of highly diverse data, of which only a small fraction are findable, accessible and reusable. To promote an open data culture, we have therefore developed the InsectBrainDatabase (IBdb), a free online platform for insect neuroanatomical and functional data. The IBdb facilitates biological insight by enabling effective cross-species comparisons, by linking neural structure with function, and by serving as general information hub for insect neuroscience. The IBdb allows users to not only effectively locate and visualize data, but to make them widely available for easy, automated reuse via an application programming interface. A unique private mode of the database expands the IBdb functionality beyond public data deposition, additionally providing the means for managing, visualizing, and sharing of unpublished data. This dual function creates an incentive for data contribution early in data management workflows and eliminates the additional effort normally associated with publicly depositing research data

Anatomical and functional characterization of the orientation network in the central and lateral complex of the desert locust Schistocerca gregaria

Spatial orientation is an indispensable basis of many behaviors that ensure the survival of an individual or a species. Foraging, finding mating partners, avoiding predators or developing new habitats rely on this ability. Insects show sophisticated skills for spatial orientation and navigation. These abilities require integration of external and internal stimuli that provide information about the animal’s own position in space or relative to an object. Under the open sky the sun is – even for humans – a prominent orientation cue that can be utilized for orientation by many insect species. Additionally, other celestial cues - that are not perceptible by humans - can be detected and used by insects. One of these is the polarization pattern of the sky that results from scattering of unpolarized sunlight in the earth’s atmosphere. It is characterized by the systematic arrangement of the prevailing plane of oscillation of polarized light (angle of polarization, AoP) and depends on the position of the sun. The degree of polarization (DoP) that indicates the percentage of polarized light within a light beam also depends on the sun’s position. In the insect brain, the AoP is encoded by the activity of polarization-sensitive neurons that transmit this information from the compound eyes into the central brain, where it is used to generate an internal compass. The internal compass is represented by the activity of neuronal populations of the central complex (CX), a navigation center that processes orientation-relevant information and is involved in the generation of appropriate locomotor responses. The CX comprises four midline spanning neuropils in the center of the brain; the protocerebral bridge (PB), the lower division of the central body (CBL; also known as ellipsoid body, EB, in flies) the upper division of the central body (CBU; also known as fan-shaped body, FB, in flies) and the paired noduli (NO). The neuropils are characterized by vertical columns (or slices) and horizontal layers that result from the neuronal projections of the neuron systems that constitute the CX. Arborizations of tangential neurons establish distinct layers and arborizations of columnar and pontine neurons result in distinct columns. Beside polarization information the neuronal network of the CX also integrates other information that underlies context- and experience dependent behavior. Another brain region, the lateral complex (LX) plays a major role in mediating information flow to and from the CX. The LX is located in both hemispheres laterally from the CX and consists of the lateral accessory lobe (LAL) with the associated gall and the bulb. A variety of neuron types connects the LX and the CX and provides connections between the LX and other brain regions as well as the thoracic ganglia. The present thesis investigates the physiology of polarization-sensitive neurons of the CX and the anatomical organization of the CX and the LX of the desert locust Schistocerca gregaria (Figure I). Electrophysiological experiments were performed to investigate the influence of the DoP on the coding of the AoP by polarization-sensitive neurons of the CX (Chapter I). They revealed that even low DoPs allow a reliable coding of AoPs in the locust brain. However, DoPs under a certain threshold result in a strong modulation of the activity of neurons at the input stage of the CX. Neuron types within the CX are characterized in addition to their physiology and morphology by the expression of neurotransmitters and neuropeptides. Immunocytochemical stainings revealed the expression pattern of myoinhibitory peptide (MIP) in the CX (Chapter II). We identified and characterized five MIP-expressing neuronal systems comprising cell types that have so far been identified mainly based on single-cell labeling. The combination of single-cell labelings and immunocytochemical stainings revealed potential feedback loops between cell types of the CX and the LX and were used to identify and describe novel cell types of the LAL (Chapter III)

Neuroarchitecture of the central complex in the brain of the honeybee: Neuronal cell types

The central complex (CX) in the insect brain is a higher order integration center that controls a number of behaviors, most prominently goal directed locomotion. The CX comprises the protocerebral bridge (PB), the upper division of the central body (CBU), the lower division of the central body (CBL), and the paired noduli (NO). Although spatial orientation has been extensively studied in honeybees at the behavioral level, most electrophysiological and anatomical analyses have been carried out in other insect species, leaving the morphology and physiology of neurons that constitute the CX in the honeybee mostly enigmatic. The goal of this study was to morphologically identify neuronal cell types of the CX in the honeybee Apis mellifera. By performing iontophoretic dye injections into the CX, we traced 16 subtypes of neuron that connect a subdivision of the CX with other regions in the bee's central brain, and eight subtypes that mainly interconnect different subdivisions of the CX. They establish extensive connections between the CX and the lateral complex, the superior protocerebrum and the posterior protocerebrum. Characterized neuron classes and subtypes are morphologically similar to those described in other insects, suggesting considerable conservation in the neural network relevant for orientation

Microglomerular Synaptic Complexes in the Sky-Compass Network of the Honeybee Connect Parallel Pathways from the Anterior Optic Tubercle to the Central Complex

While the ability of honeybees to navigate relying on sky-compass information has been investigated in a large number of behavioral studies, the underlying neuronal system has so far received less attention. The sky-compass pathway has recently been described from its input region, the dorsal rim area (DRA) of the compound eye, to the anterior optic tubercle (AOTU). The aim of this study is to reveal the connection from the AOTU to the central complex (CX). For this purpose, we investigated the anatomy of large microglomerular synaptic complexes in the medial and lateral bulbs (MBUs/LBUs) of the lateral complex (LX). The synaptic complexes are formed by tubercle-lateral accessory lobe neuron 1 (TuLAL1) neurons of the AOTU and GABAergic tangential neurons of the central body’s (CB) lower division (TL neurons). Both TuLAL1 and TL neurons strongly resemble neurons forming these complexes in other insect species. We further investigated the ultrastructure of these synaptic complexes using transmission electron microscopy. We found that single large presynaptic terminals of TuLAL1 neurons enclose many small profiles (SPs) of TL neurons. The synaptic connections between these neurons are established by two types of synapses: divergent dyads and divergent tetrads. Our data support the assumption that these complexes are a highly conserved feature in the insect brain and play an important role in reliable signal transmission within the sky-compass pathway

Parallel motion vision pathways in the brain of a tropical bee

Spatial orientation is a prerequisite for most behaviors. In insects, the underlying neural computations take place in the central complex (CX), the brain’s navigational center. In this region different streams of sensory information converge to enable context-dependent navigational decisions. Accordingly, a variety of CX input neurons deliver information about different navigation-relevant cues. In bees, direction encoding polarized light signals converge with translational optic flow signals that are suited to encode the flight speed of the animals. The continuous integration of speed and directions in the CX can be used to generate a vector memory of the bee’s current position in space in relation to its nest, i.e., perform path integration. This process depends on specific, complex features of the optic flow encoding CX input neurons, but it is unknown how this information is derived from the visual periphery. Here, we thus aimed at gaining insight into how simple motion signals are reshaped upstream of the speed encoding CX input neurons to generate their complex features. Using electrophysiology and anatomical analyses of the halictic bees Megalopta genalis and Megalopta centralis, we identified a wide range of motion-sensitive neurons connecting the optic lobes with the central brain. While most neurons formed pathways with characteristics incompatible with CX speed neurons, we showed that one group of lobula projection neurons possess some physiological and anatomical features required to generate the visual responses of CX optic-flow encoding neurons. However, as these neurons cannot explain all features of CX speed cells, local interneurons of the central brain or alternative input cells from the optic lobe are additionally required to construct inputs with sufficient complexity to deliver speed signals suited for path integration in bees

InsectBrainDatabase - A unified platform to manage, share, and archive morphological and functional data

Insect neuroscience generates vast amounts of highly diverse data, of which only a small fraction are findable, accessible and reusable. To promote an open data culture, we have therefore developed the InsectBrainDatabase (IBdb), a free online platform for insect neuroanatomical and functional data. The IBdb facilitates biological insight by enabling effective cross-species comparisons, by linking neural structure with function, and by serving as general information hub for insect neuroscience. The IBdb allows users to not only effectively locate and visualize data, but to make them widely available for easy, automated reuse via an application programming interface. A unique private mode of the database expands the IBdb functionality beyond public data deposition, additionally providing the means for managing, visualizing, and sharing of unpublished data. This dual function creates an incentive for data contribution early in data management workflows and eliminates the additional effort normally associated with publicly depositing research data