Zebrafish colour vision: a survey of spectral processing in the zebrafish visual system

The zebrafish possesses a highly complex and utilised visual system. Its input is comprised of four distinct cone types as well as one rod type. However, in larvae, rods are thought to be immature. Accordingly, in their larval form, all visual input to the retina and brain circuits comes from the four cones. These feed into morphologically and functionally distinct and highly diverse circuits to ultimately drive a wide array of visual behaviours. While spatio-temporal processing in larval zebrafish has been studied at considerable depth, comparatively much less is known about their spectral processing. The goal of this thesis was to systematically map the physiological responses of most visual neurons in larval zebrafish – from cones via bipolar and ganglion cells to brain neurons - to stimuli that vary in wavelength. Specifically, we used 2-photon Ca2+imaging of light-driven activity both in the retina and the brain (Chapters 3,4,5). We used an original 2-photon microscope modification to allow for fast multi-plane imaging (Janiak et al, 2019). Stimulation was carried out using a custom-built high-speed monochromator (Belusic et al, 2016) with a high spectral resolution (Chapter 2). Transgenic lines expressing Ca2+-sensors in specific cell populations were generated to selectively observe different neuron types. We imaged cones and bipolar cells in the eye, and ganglion cell terminals as well as the somata of central neurons in the brain. Together, this served to establish a large-scale overview of the spectral computations that are performed at each stage, and how they may aid zebrafish visual functions. In the six chapters of this thesis I: 1. Introduce colour vision in the zebrafish. 2. Describe the construction of the visual stimulator. 3. Describe and discuss the photoreceptor data. Cones transform chromatic signals in a Principal Component Analysis-like manner. This can be part-explained as an adaptation to the spectral characteristics of the visual world (Zimmermann et al, 2018). Previously, such a transformation was thought to occur first in downstream circuits. 4. Describe and discuss the bipolar cell data. Synaptic terminals form several functional clusters that are highly wavelength-dependent, enabling possibilities for complex spectral coding. Spectral opponency is observed in several clusters. Moreover, eye-wide regional specializations are observed, in agreement with prior reports (Zimmermann et al, 2018). I conclude by discussing the functional layering of the inner plexiform layer of the retina in the context of predicted functional wiring from cones. 5. Briefly describe the ganglion cell axonal and brain somatic data. Unlike bipolar cells, their responses are surprisingly uniform. I hypothesize that the response profile is uniquely sensitive to near objects based on data from hyperspectral imaging. 6. Summarise the findings in light of the wider literature. I speculate about the overarching goal of colour vision, relate the findings back to Wilkins & Osorio (2019) and certain logic-related considerations

Abenteuer regionale Bio-Gastronomie - Mit Frische und Herzblut neue Gäste gewinnen

Die Nachfrage nach biologischen und regionalen Lebensmittel steigt stetig an. Wer zu Hause Wert auf möglichst frisches, gesundes und nachhaltig produziertes Essen legt, der nimmt sicher auch dementsprechende Angebote in der Gastronomie begeistert an. Trotzdem gibt es bisher nur wenige Kooperationen zwischen der Biolandwirtschaft und der örtlichen Gastronomie. Um den Ursachen dafür auf den Grund zu gehen, hat das Institut für ökologischen Landbau an der Universität für Bodenkultur in Wien eine ausführliche Umfrage unter Gastronomen durchgeführt. Die Ergebnisse zeigen ein komplexes Zusammenspiel aus innerer Überzeugung, Küchenmanagement, Lieferantenbeziehungen und Kommunikation mit den Gästen auf - und machen all jenen Mut, die sich auf das Abenteuer "Bio-Gastronomie" einlassen wollen..

Regionale Bio-Lebensmittel in der Gastronomie – Stärken, Schwächen, Chancen, Risiken

In den letzten Jahren ist seitens der KonsumentInnen eine stetig steigende Nachfrage nach biologischen und regionalen Lebensmitteln zu verzeichnen. Trotzdem gibt es bisher nur wenige Kooperationen zwischen der Biolandwirtschaft und der örtlichen Gastronomie

Spikeling: A low-cost hardware implementation of a spiking neuron for neuroscience teaching and outreach

Understanding how neurons encode and compute information is fundamental to our study of the brain, but opportunities for hands-on experience with neurophysiological techniques on live neurons are scarce in science education. Here, we present Spikeling, an open source in silico implementation of a spiking neuron that costs £25 and mimics a wide range of neuronal behaviours for classroom education and public neuroscience outreach. Spikeling is based on an Arduino microcontroller running the computationally efficient Izhikevich model of a spiking neuron. The microcontroller is connected to input ports that simulate synaptic excitation or inhibition, to dials controlling current injection and noise levels, to a photodiode that makes Spikeling light sensitive, and to a light-emitting diode (LED) and speaker that allows spikes to be seen and heard. Output ports provide access to variables such as membrane potential for recording in experiments or digital signals that can be used to excite other connected Spikelings. These features allow for the intuitive exploration of the function of neurons and networks mimicking electrophysiological experiments. We also report our experience of using Spikeling as a teaching tool for undergraduate and graduate neuroscience education in Nigeria and the United Kingdom

Colourfulness as a possible measure of object proximity in the larval zebrafish brain

The encoding of light increments and decrements by separate On- and Off- systems is a fundamental ingredient of vision, which supports edge detection and makes efficient use of the limited dynamic range of visual neurons. Theory predicts that the neural representation of On- and Off-signals should be balanced, including across an animal’s visible spectrum. Here we find that larval zebrafish violate this textbook expectation: in the zebrafish brain, UV-stimulation near exclusively gives On-responses, blue/green stimulation mostly Off-responses, and red-light alone elicits approximately balanced On- and Off-responses (see also references2, 3, 4). We link these findings to zebrafish visual ecology, and suggest that the observed spectral tuning boosts the encoding of object ‘colourfulness’, which correlates with object proximity in their underwater world

Spectral inference reveals principal cone-integration rules of the zebrafish inner retina

Retinal bipolar cells integrate cone signals at dendritic and axonal sites. The axonal route, involving amacrine cells, remains largely uncharted. However, because cone types differ in their spectral sensitivities, insights into bipolar cells' cone integration might be gained based on their spectral tunings. We therefore recorded in vivo responses of bipolar cell presynaptic terminals in larval zebrafish to widefield but spectrally resolved flashes of light and mapped the results onto spectral responses of the four cones. This "spectral circuit mapping" allowed explaining ∼95% of the spectral and temporal variance of bipolar cell responses in a simple linear model, thereby revealing several notable integration rules of the inner retina. Bipolar cells were dominated by red-cone inputs, often alongside equal sign inputs from blue and green cones. In contrast, UV-cone inputs were uncorrelated with those of the remaining cones. This led to a new axis of spectral opponency where red-, green-, and blue-cone "Off" circuits connect to "natively-On" UV-cone circuits in the outermost fraction of the inner plexiform layer-much as how key color opponent circuits are established in mammals. Beyond this, and despite substantial temporal diversity that was not present in the cones, bipolar cell spectral tunings were surprisingly simple. They either approximately resembled both opponent and non-opponent spectral motifs already present in the cones or exhibited a stereotyped non-opponent broadband response. In this way, bipolar cells not only preserved the efficient spectral representations in the cones but also diversified them to set up a total of six dominant spectral motifs, which included three axes of spectral opponency

Ancestral circuits for vertebrate color vision emerge at the first retinal synapse

For color vision, retinal circuits separate information about intensity and wavelength. In vertebrates that use the full complement of four “ancestral” cone types, the nature and implementation of this computation remain poorly understood. Here, we establish the complete circuit architecture of outer retinal circuits underlying color processing in larval zebrafish. We find that the synaptic outputs of red and green cones efficiently rotate the encoding of natural daylight in a principal components analysis–like manner to yield primary achromatic and spectrally opponent axes, respectively. Blue cones are tuned to capture most remaining variance when opposed to green cones, while UV cone present a UV achromatic axis for prey capture. We note that fruitflies use essentially the same strategy. Therefore, rotating color space into primary achromatic and chromatic axes at the eye’s first synapse may thus be a fundamental principle of color vision when using more than two spectrally well-separated photoreceptor types

The insect nephrocyte is a podocyte-like cell with a filtration slit diaphragm.

The nephron is the basic structural and functional unit of the vertebrate kidney. It is composed of a glomerulus, the site of ultrafiltration, and a renal tubule, along which the filtrate is modified. Although widely regarded as a vertebrate adaptation, 'nephron-like' features can be found in the excretory systems of many invertebrates, raising the possibility that components of the vertebrate excretory system were inherited from their invertebrate ancestors. Here we show that the insect nephrocyte has remarkable anatomical, molecular and functional similarity to the glomerular podocyte, a cell in the vertebrate kidney that forms the main size-selective barrier as blood is ultrafiltered to make urine. In particular, both cell types possess a specialized filtration diaphragm, known as the slit diaphragm in podocytes or the nephrocyte diaphragm in nephrocytes. We find that fly (Drosophila melanogaster) orthologues of the major constituents of the slit diaphragm, including nephrin, NEPH1 (also known as KIRREL), CD2AP, ZO-1 (TJP1) and podocin, are expressed in the nephrocyte and form a complex of interacting proteins that closely mirrors the vertebrate slit diaphragm complex. Furthermore, we find that the nephrocyte diaphragm is completely lost in flies lacking the orthologues of nephrin or NEPH1-a phenotype resembling loss of the slit diaphragm in the absence of either nephrin (as in human congenital nephrotic syndrome of the Finnish type, NPHS1) or NEPH1. These changes markedly impair filtration function in the nephrocyte. The similarities we describe between invertebrate nephrocytes and vertebrate podocytes provide evidence suggesting that the two cell types are evolutionarily related, and establish the nephrocyte as a simple model in which to study podocyte biology and podocyte-associated diseases.This work was supported by Wellcome Trust grants awarded to H.S. (072441 and 079221, H.W., B.D., H.S.); Deutsche Forschungsgemeinschaft (SFB 590) awarded to Elisabeth Knust (F.G.), ARC 1242 (H.W., B.D., H.S., F.G.); MEC grant awarded to M.R-G. (BFU2007-62201, S.P-S., M.R-G.); Fundación Ramón Areces grant to the CBMSO (M.R-G.); EC grant LSHG-CT-2004-511978 to MYORES (M.R-G.); an FPU fellowship from the MEC awarded to A.G-L.Peer reviewe

The miR-155-PU.1 axis acts on Pax5 to enable efficient terminal B cell differentiation.

A single microRNA (miRNA) can regulate the expression of many genes, though the level of repression imparted on any given target is generally low. How then is the selective pressure for a single miRNA/target interaction maintained across long evolutionary distances? We addressed this problem by disrupting in vivo the interaction between miR-155 and PU.1 in mice. Remarkably, this interaction proved to be key to promoting optimal T cell-dependent B cell responses, a previously unrecognized role for PU.1. Mechanistically, miR-155 inhibits PU.1 expression, leading to Pax5 down-regulation and the initiation of the plasma cell differentiation pathway. Additional PU.1 targets include a network of genes whose products are involved in adhesion, with direct links to B-T cell interactions. We conclude that the evolutionary adaptive selection of the miR-155-PU.1 interaction is exercised through the effectiveness of terminal B cell differentiation

Design of an inertial mass actuator for active vibration control of a planetary gearbox using piezoelectric shear actuator

To achieve higher bypass ratios and thus increase efficiency, high-speed planetary gearboxes are applied to geared turbofan engines. The gear meshing inside the gearbox causes high-frequency vibration that can potentially be uncomfortable for passengers in terms of airborne noise. In this work, a system for active vibration control using inertial mass actuators is proposed. One of the key challenges in the design of the system is the high frequency range around 5 kHz of the gear mesh vibration. The system requirements regarding frequency range and force are identified experimentally using a planetary gearbox test rig. The choice, design and development of the inertial mass actuator is presented. Piezoelectric shear actuators are selected due to their comparatively small electric capacitance, which is advantageous for the power amplifier. A simulation allows the optimization of actuator and amplifier properties. Parameters of the used models are identified experimentally. The performance of the final actuator-amplifier-unit is tested using the test-rig. The achievable vibration reduction is presented and results are discussed