Biology subjects

Hartenstein, V.

Publications and source records attributed to Hartenstein, V..

11 recordsLinked to original sources

bioRxiv2025

Electrical synapses mediate visual approach behavior

Detecting salient visual objects and orienting toward them are commonplace tasks for animals, yet the underlying neural circuits remain poorly understood. The fruit fly is an ideal model for a comprehensive analysis of feature detection mechanisms given its complete synaptic wiring diagrams, robust behavioral assays, and cell-type-specific gene expression datasets. We previously showed that columnar T3 neurons are required for saccadic orientation toward landscape features during flight. Here, we examine how signals downstream of T3 are processed in the central brain. We identify LC17 visual projection neurons as key postsynaptic targets: they receive strong excitatory input from T3, project to premotor brain regions, and are thus positioned to support visual approach. Using in vivo optical physiology and virtual reality behavior, we demonstrate that LC17 neurons are indeed necessary for object tracking during flight. Furthermore, we find that electrical synapses in LC17 are also required for tracking behavior. We show that the innexin Shaking B (shakB) is highly expressed in LC17 and localized to its dendrites, and genetic perturbations confirm its essential role for electrical coupling in this circuit. Our findings reveal mechanisms underlying visual approach, and highlight the interplay between electrical and chemical neurotransmission for rapid object detection and action selection.

neuroscience↗

bioRxiv2023

A consensus cell type atlas from multiple connectomes reveals principles of circuit stereotypy and variation

The fruit fly Drosophila melanogaster combines surprisingly sophisticated behaviour with a highly tractable nervous system. A large part of the flys success as a model organism in modern neuroscience stems from the concentration of collaboratively generated molecular genetic and digital resources. As presented in our FlyWire companion paper1, this now includes the first full brain connectome of an adult animal. Here we report the systematic and hierarchical annotation of this [~]130,000-neuron connectome including neuronal classes, cell types and developmental units (hemilineages). This enables any researcher to navigate this huge dataset and find systems and neurons of interest, linked to the literature through the Virtual Fly Brain database2. Crucially, this resource includes 4,552 cell types. 3,094 are rigorous consensus validations of cell types previously proposed in the "hemibrain" connectome3. In addition, we propose 1,458 new cell types, arising mostly from the fact that the FlyWire connectome spans the whole brain, whereas the hemibrain derives from a subvolume. Comparison of FlyWire and the hemibrain showed that cell type counts and strong connections were largely stable, but connection weights were surprisingly variable within and across animals. Further analysis defined simple heuristics for connectome interpretation: connections stronger than 10 unitary synapses or providing >1% of the input to a target cell are highly conserved. Some cell types showed increased variability across connectomes: the most common cell type in the mushroom body, required for learning and memory, is almost twice as numerous in FlyWire as the hemibrain. We find evidence for functional homeostasis through adjustments of the absolute amount of excitatory input while maintaining the excitation-inhibition ratio. Finally, and surprisingly, about one third of the cell types proposed in the hemibrain connectome could not yet be reliably identified in the FlyWire connectome. We therefore suggest that cell types should be defined to be robust to inter-individual variation, namely as groups of cells that are quantitatively more similar to cells in a different brain than to any other cell in the same brain. Joint analysis of the FlyWire and hemibrain connectomes demonstrates the viability and utility of this new definition. Our work defines a consensus cell type atlas for the fly brain and provides both an intellectual framework and open source toolchain for brain-scale comparative connectomics.

neuroscience↗

bioRxiv2023

Evolution of the ribbon-like organization of the Golgi apparatus in animal cells

The Golgi ribbon is a structural organization formed by linked Golgi stacks that is believed to be exclusive to vertebrate cells. Its functional contribution to cellular processes is unclear, yet its disruption is associated with several human pathologies. In this study we address the evolutionary origin of the Golgi ribbon, describe a potential molecular mechanism for its emergence and identify a cellular process in which it may be involved. We observed the ribbon-like architecture in the cells of several metazoan taxa, suggesting its early appearance during animal evolution before the emergence of vertebrates. Supported by AlphaFold2 modelling, we propose that the evolution of the complex between two Golgi resident proteins, Golgin-45 and GRASP, led to the tethering of Golgi stacks into the ribbon-like configuration. Finally, we find that the ribbon is assembled during the early embryogenesis of deuterostome animals, a strong indication of its role in development. Overall, our study indicates that the Golgi ribbon is functionally relevant beyond vertebrates and calls for further investigations to decipher its elusive functions. O_FIG O_LINKSMALLFIG WIDTH=89 HEIGHT=200 SRC="FIGDIR/small/528797v2_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@17a404forg.highwire.dtl.DTLVardef@11413b4org.highwire.dtl.DTLVardef@119c036org.highwire.dtl.DTLVardef@19a512f_HPS_FORMAT_FIGEXP M_FIG Graphical abstract C_FIG

cell biology↗

bioRxiv2022

Rewarding capacity of optogenetically activating a giant GABAergic central-brain interneuron in larval Drosophila

Larvae of the fruit fly Drosophila melanogaster are a powerful study case for understanding the neural circuits underlying behavior. Indeed, the numerical simplicity of the larval brain has permitted the reconstruction of its synaptic connectome, and genetic tools for manipulating single, identified neurons allow neural circuit function to be investigated with relative ease and precision. We focus on one of the most complex neurons in the brain of the larva (of either sex), the GABAergic anterior paired lateral neuron (APL). Using behavioral and connectomic analyses, optogenetics, Ca2+ imaging and pharmacology, we study how APL affects associative olfactory memory. We first provide a detailed account of the structure, regional polarity, connectivity, and metamorphic development of APL, and further confirm that optogenetic activation of APL has an inhibiting effect on its main targets, the mushroom body Kenyon cells. All these findings are consistent with the previously identified function of APL in the sparsening of sensory representations. To our surprise, however, we found that optogenetically activating APL can also have a strong rewarding effect. Specifically, APL activation together with odor presentation establishes an odor-specific, appetitive, associative short-term memory, whereas naive olfactory behavior remains unaffected. An acute, systemic inhibition of dopamine synthesis as well as an ablation of the dopaminergic pPAM neurons impair reward learning through APL activation. Our findings provide a study case of complex circuit function in a numerically simple brain, and suggest a previously unrecognized capacity of central-brain GABAergic neurons to engage in dopaminergic reinforcement. Significance statementThe single, identified giant anterior paired lateral (APL) neuron is one of the most complex neurons in the insect brain. It is GABAergic and contributes to the sparsening of neuronal activity in the mushroom body, the memory center of insects. We provide the most detailed account yet of the structure of APL in larval Drosophila as a neurogenetically accessible study case. We further reveal that, contrary to expectations, the experimental activation of APL can exert a rewarding effect, likely via dopaminergic reward pathways. The present study both provides an example of unexpected circuit complexity in a numerically simple brain, and reports an unexpected effect of activity in central-brain GABAergic circuits.

neuroscience↗

bioRxiv2022

The connectome of an insect brain

Brains contain networks of interconnected neurons, so knowing the network architecture is essential for understanding brain function. We therefore mapped the synaptic-resolution connectome of an insect brain (Drosophila larva) with rich behavior, including learning, value-computation, and action-selection, comprising 3,013 neurons and 544,000 synapses. We characterized neuron-types, hubs, feedforward and feedback pathways, and cross-hemisphere and brain-nerve cord interactions. We found pervasive multisensory and interhemispheric integration, highly recurrent architecture, abundant feedback from descending neurons, and multiple novel circuit motifs. The brains most recurrent circuits comprised the input and output neurons of the learning center. Some structural features, including multilayer shortcuts and nested recurrent loops, resembled powerful machine learning architectures. The identified brain architecture provides a basis for future experimental and theoretical studies of neural circuits. One-Sentence SummaryWe generated a synaptic-resolution brain connectome and characterized its connection types, neuron types, and circuit motifs.

neuroscience↗

bioRxiv2021

An atlas of the developing Tribolium castaneum brain reveals conserved anatomy and divergent timing to Drosophila melanogaster

Insect brains are formed by conserved sets of neural lineages whose fibres form cohesive bundles with characteristic projection patterns. Within the brain neuropil these bundles establish a system of fascicles constituting the macrocircuitry of the brain. The overall architecture of the neuropils and the macrocircuitry appear to be conserved. However, variation is observed e.g., in size and shape and timing of development. Unfortunately, the developmental and genetic basis of this variation is poorly understood although the rise of new genetically tractable model organisms such as the red flour beetle Tribolium castaneum allows the possibility to gain mechanistic insights. To facilitate such work, we present an atlas of the developing brain of T. castaneum, covering the first larval instar, the prepupal stage and the adult, by combining wholemount immunohistochemical labelling of fibre bundles (acetylated tubulin) and neuropils (synapsin) with digital 3D reconstruction using the TrakEM2 software package. Upon comparing this anatomical dataset with the published work in D. melanogaster, we confirm an overall high degree of conservation. Fibre tracts and neuropil fascicles, which can be visualized by global neuronal antibodies like anti-acetylated tubulin in all invertebrate brains, create a rich anatomical framework to which individual neurons or other regions of interest can be referred to. The framework of a largely conserved pattern allowed us to describe differences between the two species with respect to parameters such as timing of neuron proliferation and maturation. These features likely reflect adaptive changes in developmental timing that govern the change from larval to adult brain.

neuroscience↗

bioRxiv2021

Opposing subclasses of Drosophila ellipsoid body neurons promote and suppress sleep

Recent work in Drosophila has uncovered several neighboring classes of sleep-regulatory neurons within the central complex. However, the logic of connectivity and network motifs remains limited by the incomplete examination of relevant cell types. Using a recent genetic-anatomical classification of ellipsoid body ring neurons, we conducted a thermogenetic screen to assess sleep/wake behavior and discovered two opposing populations: sleep-promoting R3m and wake-promoting R3d neurons. Activation of these neurons influences sleep duration and architecture by prolonging or shortening sleep bouts, suggesting a key role in sleep maintenance. R3m and R3d neurons are GABAergic and require GABA synthesis for their effects on sleep. Finally, we use a fluorescent reporter for putative synaptic partners to embed these neurons within the known sleep-regulatory network; R3m and R3d neurons lay downstream of wake-active Helicon cells, and R3m neurons likely inhibit R3d neurons. Together, the data presented herein suggest a neural mechanism by which previously uncharacterized circuit elements operate within the sleep homeostat to stabilize sleep-wake states.

neuroscience↗

bioRxiv2020

A visual pathway for skylight polarization processing in Drosophila

Many insects use patterns of polarized light in the sky to orient and navigate. Here we functionally characterize neural circuitry in the fruit fly, Drosophila melanogaster, that conveys polarized light signals from the eye to the central complex, a brain region essential for the flys sense of direction. Neurons tuned to the angle of polarization of ultraviolet light are found throughout the anterior visual pathway, connecting the optic lobes with the central complex via the anterior optic tubercle and bulb, in a homologous organization to the sky compass pathways described in other insects. We detail how a consistent, map-like organization of neural tunings in the peripheral visual system is transformed into a reduced representation suited to flexible processing in the central brain. This study identifies computational motifs of the transformation, enabling mechanistic comparisons of multisensory integration and central processing for navigation in the brains of insects.

neuroscience↗

bioRxiv2020

Neurotransmitter Classification from Electron Microscopy Images at Synaptic Sites in Drosophila

High-resolution electron microscopy of nervous systems enables the reconstruction of connectomes. A key piece of missing information from connectomes is the synaptic sign. We show that for D. melanogaster, artificial neural networks can predict the transmitter type released at synapses from electron micrographs and thus add putative signs to connections. Our network discriminates between six transmitters (acetylcholine, glutamate, GABA, serotonin, dopamine, octopamine) with an average accuracy of 87%/94% for synapses/entire neurons. We developed an explainability method to reveal which features our network is using and found significant ultrastructural differences between the classical transmitters. We predict transmitters in two connectomes and characterize morphological and connection properties of tens of thousands of neurons classed by predicted transmitter expression. We find that hemilineages in D. melanogaster largely express only one fastacting transmitter among their neurons. Furthermore, we show that neurons with different transmitters may differ in features like polarization and projection targets.

neuroscience↗

bioRxiv2018

Neuronal constituents and putative interactions within the Drosophila ellipsoid body neuropil

The central complex (CX) is a midline-situated collection of neuropil compartments in the arthropod central brain, implicated in higher-order processes such as goal-directed navigation. Here, we provide a systematic genetic-neuroanatomical analysis of the ellipsoid body (EB), a compartment which represents a major afferent portal of the Drosophila CX. The neuropil volume of the EB, along with its prominent input compartment, called the bulb, is subdivided into precisely tessellated domains, distinguishable based on intensity of the global marker DN-cadherin. EB tangential elements (so-called ring neurons), most of which are derived from the DALv2 neuroblast lineage, interconnect the bulb and EB domains in a topographically-organized fashion. Using the DN-cadherin domains as a framework, we first characterized the bulb-EB connectivity by Gal4 driver lines expressed in different DALv2 ring neuron (R-neuron) subclasses. We identified 11 subclasses, 6 of which correspond to previously described projection patterns, and 5 novel patterns. These subclasses both spatially (based on EB innervation pattern) and numerically (cell counts) summate to the total EB volume and R-neuron cell number, suggesting that our compilation of R-neuron subclasses approaches completion. EB columnar elements, as well as non-DALv2 derived extrinsic ring neurons (ExR-neurons), were also incorporated into this anatomical framework. Finally, we addressed the connectivity between R-neurons and their targets, using the anterograde trans-synaptic labeling method, trans-Tango. This study demonstrates putative interactions of R-neuron subclasses and reveals general principles of information flow within the EB network. Our work will facilitate the generation and testing of hypotheses regarding circuit interactions within the EB and the rest of the CX.

neuroscience↗

bioRxiv2018

Developmentally arrested precursors of pontine neurons establish an embryonic blueprint of the Drosophila central complex

Serial electron microscopic analysis shows that the Drosophila brain at hatching possesses a large fraction of developmentally arrested neurons with a small soma, heterochromatin-rich nucleus, and unbranched axon lacking synapses. We digitally reconstructed all 812 \" small undifferentiated\" (SU) neurons on both hemispheres and assigned them to the known brain lineages. 54 SU neurons belonging to the DM1-4 lineages, which generate all columnar neurons of the central complex, form an embryonic nucleus of the fan-shaped body (FB). These \" FB pioneers\" develop into a speci1c class of bi-columnar elements, the pontine neurons. Even though later born, unicolumnar DM1-4 neurons fasciculate with the FB pioneers, selective ablation of these cells did not result in gross abnormalities of the trajectories of unicolumnar neurons, indicating that axonal path1nding of the two systems is controlled independently. Our comprehensive spatial and developmental analysis of the SU neuron adds to our understanding of the establishment of neuronal circuitry.

neuroscience↗