Neuronal parts list and wiring diagram for a visual system.

A catalogue of neuronal cell types has often been called a 'parts list' of the brain, and regarded as a prerequisite for understanding brain function. In the optic lobe of Drosophila, rules of connectivity between cell types have already proven to be essential for understanding fly vision. Here we analyse the fly connectome to complete the list of cell types intrinsic to the optic lobe, as well as the rules governing their connectivity.

Connectomic reconstruction predicts visual features used for navigation.

Many animals use visual information to navigate, but how such information is encoded and integrated by the navigation system remains incompletely understood. In Drosophila melanogaster, EPG neurons in the central complex compute the heading direction by integrating visual input from ER neurons, which are part of the anterior visual pathway (AVP). Here we densely reconstruct all neurons in the AVP using electron-microscopy data.

Connectomic reconstruction predicts the functional organization of visual inputs to the navigation center of the brain.

Many animals, including humans, navigate their surroundings by visual input, yet we understand little about how visual information is transformed and integrated by the navigation system. In , compass neurons in the donut-shaped ellipsoid body of the central complex generate a sense of direction by integrating visual input from ring neurons, a part of the anterior visual pathway (AVP). Here, we densely reconstruct all neurons in the AVP using FlyWire, an AI-assisted tool for analyzing electron-microscopy data.

Non-celestial polarization vision in arthropods.

Most insects can detect the pattern of polarized light in the sky with the dorsal rim area in their compound eyes and use this visual information to navigate in their environment by means of 'celestial' polarization vision. 'Non-celestial polarization vision', in contrast, refers to the ability of arthropods to analyze polarized light by means of the 'main' retina, excluding the dorsal rim area. The ability of using the main retina for polarization vision has been attracting sporadic, but steady attention during the last decade.

Neuronal "parts list" and wiring diagram for a visual system.

A catalog of neuronal cell types has often been called a "parts list" of the brain, and regarded as a prerequisite for understanding brain function. In the optic lobe of , rules of connectivity between cell types have already proven essential for understanding fly vision. Here we analyze the fly connectome to complete the list of cell types intrinsic to the optic lobe, as well as the rules governing their connectivity.

Behavioral responses of free-flying Drosophila melanogaster to shiny, reflecting surfaces.

Active locomotion plays an important role in the life of many animals, permitting them to explore the environment, find vital resources, and escape predators. Most insect species rely on a combination of visual cues such as celestial bodies, landmarks, or linearly polarized light to navigate or orient themselves in their surroundings. In nature, linearly polarized light can arise either from atmospheric scattering or from reflections off shiny non-metallic surfaces like water.

Tight Complex Formation of the Fumarate Sensing DcuS-DcuR Two-Component System at the Membrane and Target Promoter Search by Free DcuR Diffusion.

Signaling of two-component systems by phosphoryl transfer requires interaction of the sensor kinase with the response regulator. Interaction of the C4-dicarboxylate-responsive and membrane-integral sensor kinase DcuS with the response regulator DcuR was studied. , the cytoplasmic part of DcuS (PAS-Kin) was employed.

Synaptic targets of photoreceptors specialized to detect color and skylight polarization in .

Color and polarization provide complementary information about the world and are detected by specialized photoreceptors. However, the downstream neural circuits that process these distinct modalities are incompletely understood in any animal. Using electron microscopy, we have systematically reconstructed the synaptic targets of the photoreceptors specialized to detect color and skylight polarization in , and we have used light microscopy to confirm many of our findings.

Vision: Space and colour meet in the fly optic lobes.

Colour vision involves colour-opponent cells, which are excited and inhibited by different wavelengths. Synaptic interconnections between Drosophila Dm8 cells are required for forming spatio-chromatic receptive fields with a center and surround of opposing polarity which can invert, depending on the stimulus.

Colour opponency: Chromatic and achromatic circuits in the mix.

The molecular genetic dissection of Drosophila colour vision circuitry reveals converging pathways previously categorized as being chromatic versus achromatic. Amacrine-like Dm8 cells receive direct and indirect inputs with different spectral sensitivity tuning, thereby forming the second stage of colour-opponent processing.

The development and function of neuronal subtypes processing color and skylight polarization in the optic lobes of Drosophila melanogaster.

The retinal mosaics of many insects contain different ommatidial subtypes harboring photoreceptors that are both molecularly and morphologically specialized for comparing between different wavelengths versus detecting the orientation of skylight polarization. The neural circuits underlying these different inputs and the characterization of their specific cellular elements are the subject of intense research. Here we review recent progress on the description of both assembly and function of color and skylight polarization circuitry, by focusing on two cell types located in the distal portion of the medulla neuropil of the fruit fly Drosophila melanogaster's optic lobes, called Dm8 and Dm9.

Parallel Visual Pathways with Topographic versus Nontopographic Organization Connect the Eyes to the Central Brain.

One hallmark of the visual system is a strict retinotopic organization from the periphery toward the central brain, where functional imaging in revealed a spatially accurate representation of visual cues in the central complex. This raised the question how, on a circuit level, the topographic features are implemented, as the majority of visual neurons enter the central brain converge in optic glomeruli. We discovered a spatial segregation of topographic versus nontopographic projections of distinct classes of medullo-tubercular (MeTu) neurons into a specific visual glomerulus, the anterior optic tubercle (AOTU).

Modular assays for the quantitative study of visually guided navigation in both flying and walking flies.

Background: The quantitative study of behavioral responses to visual stimuli provides crucial information about the computations executed by neural circuits. Insects have long served as powerful model systems, either when walking on air suspended balls (spherical treadmill), or flying while glued to a needle (virtual flight arena).

New Method: Here we present detailed instructions for 3D-printing and assembly of arenas optimized for visually guided navigation, including codes for presenting both celestial and panorama cues.

Autophagy-dependent filopodial kinetics restrict synaptic partner choice during Drosophila brain wiring.

Brain wiring is remarkably precise, yet most neurons readily form synapses with incorrect partners when given the opportunity. Dynamic axon-dendritic positioning can restrict synaptogenic encounters, but the spatiotemporal interaction kinetics and their regulation remain essentially unknown inside developing brains. Here we show that the kinetics of axonal filopodia restrict synapse formation and partner choice for neurons that are not otherwise prevented from making incorrect synapses.

A neurodevelopmental origin of behavioral individuality in the visual system.

The genome versus experience dichotomy has dominated understanding of behavioral individuality. By contrast, the role of nonheritable noise during brain development in behavioral variation is understudied. Using , we demonstrate a link between stochastic variation in brain wiring and behavioral individuality.

Colour Vision: Self-Centered Fly Photoreceptors Communicate over Distances.

A new study shows that the synaptically interconnected axon terminals of colour-sensitive fly photoreceptors that sample the same point in visual space receive additional inhibition from surrounding units; the resulting additional chromatic comparisons result in an optimal decorrelation of photoreceptor inputs. There are striking parallels between newly identified horizontal interactions and those mediated by mammalian horizontal cells.

Cellular and synaptic adaptations of neural circuits processing skylight polarization in the fly.

Specialized ommatidia harboring polarization-sensitive photoreceptors exist in the 'dorsal rim area' (DRA) of virtually all insects. Although downstream elements have been described both anatomically and physiologically throughout the optic lobes and the central brain of different species, little is known about their cellular and synaptic adaptations and how these shape their functional role in polarization vision. We have previously shown that in the DRA of Drosophila melanogaster, two distinct types of modality-specific 'distal medulla' cell types (Dm-DRA1 and Dm-DRA2) are post-synaptic to long visual fiber photoreceptors R7 and R8, respectively.

Heading choices of flying Drosophila under changing angles of polarized light.

Many navigating insects include the celestial polarization pattern as an additional visual cue to orient their travels. Spontaneous orientation responses of both walking and flying fruit flies (Drosophila melanogaster) to linearly polarized light have previously been demonstrated. Using newly designed modular flight arenas consisting entirely of off-the-shelf parts and 3D-printed components we present individual flying flies with a slow and continuous rotational change in the incident angle of linear polarization.

Modality-Specific Circuits for Skylight Orientation in the Fly Visual System.

In the fly optic lobe, ∼800 highly stereotypical columnar microcircuits are arranged retinotopically to process visual information. Differences in cellular composition and synaptic connectivity within functionally specialized columns remain largely unknown. Here, we describe the cellular and synaptic architecture in medulla columns located downstream of photoreceptors in the dorsal rim area (DRA), where linearly polarized skylight is detected for guiding orientation responses.

Insect Responses to Linearly Polarized Reflections: Orphan Behaviors Without Neural Circuits.

The e-vector orientation of linearly polarized light represents an important visual stimulus for many insects. Especially the detection of polarized skylight by many navigating insect species is known to improve their orientation skills. While great progress has been made towards describing both the anatomy and function of neural circuit elements mediating behaviors related to navigation, relatively little is known about how insects perceive non-celestial polarized light stimuli, like reflections off water, leaves, or shiny body surfaces.

Brain Wiring in the Fourth Dimension.

In this issue of Cell, Langen et al. use time-lapse multiphoton microscopy to show how Drosophila photoreceptor growth cones find their targets. Based on the observed dynamics, they develop a simple developmental algorithm recapitulating the highly complex connectivity pattern of these neurons, suggesting a basic framework for establishing wiring specificity.

The evolutionary diversity of insect retinal mosaics: common design principles and emerging molecular logic.

Independent evolution has resulted in a vast diversity of eyes. Despite the lack of a common Bauplan or ancestral structure, similar developmental strategies are used. For instance, different classes of photoreceptor cells (PRs) are distributed stochastically and/or localized in different regions of the retina.

So many pieces, one puzzle: cell type specification and visual circuitry in flies and mice.

The visual system is a powerful model for probing the development, connectivity, and function of neural circuits. Two genetically tractable species, mice and flies, are together providing a great deal of understanding of these processes. Current efforts focus on integrating knowledge gained from three cross-fostering fields of research: (1) understanding how the fates of different cell types are specified during development, (2) revealing the synaptic connections between identified cell types ("connectomics") by high-resolution three-dimensional circuit anatomy, and (3) causal testing of how identified circuit elements contribute to visual perception and behavior.

A Drosophila toolkit for the visualization and quantification of viral replication launched from transgenic genomes.

Arthropod RNA viruses pose a serious threat to human health, yet many aspects of their replication cycle remain incompletely understood. Here we describe a versatile Drosophila toolkit of transgenic, self-replicating genomes ('replicons') from Sindbis virus that allow rapid visualization and quantification of viral replication in vivo. We generated replicons expressing Luciferase for the quantification of viral replication, serving as useful new tools for large-scale genetic screens for identifying cellular pathways that influence viral replication.

Quantification of 33 antidepressants by LC-MS/MS--comparative validation in whole blood, plasma, and serum.

In the present study, a liquid chromatography-mass spectrometry (LC-MS/MS) multi-analyte approach based on a simple liquid-liquid extraction was developed for fast target screening and quantification of 33 antidepressants in whole blood, plasma, and serum. The method was validated with respect to selectivity, matrix effects, recovery, process efficiency, accuracy and precision, stabilities, and limits. In addition, cross-calibration between the three biosamples was done to assess the impact of the different matrices on the calibration.