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Dissection of Drosophila Visual Circuits Implicative in Figure Motion
Get PDFThe Drosophila visual system offers a model to study the foundations of how motion signals are computed from raw visual input and transformed into behavioral output. My studies focus on how specific cells in the Drosophila nervous system implement this input-output transformation. The individual cell types are known from classical studies using Golgi impregnations, but the assembly of motion processing circuits and the behavioral outputs remain poorly understood. Using an electronic flight simulator for flies and a white-noise analysis developed by Aptekar et al., I screen specific neurons in the optic lobes for behavioral ramifications. This approach produces wing responses to both the spatial and temporal dynamics of motion signals. The results of these experiments give Spatiotemporal Action Fields (STAFs) across the entire visual panorama. Genetically inactivating a distinct grouping of cells in the third optic ganglion, the Lobula Plate, the Horizontal System (HS) cell group, produced a robust phenotype through STAF analysis. Using the Gal4-UAS transgene expression system, we selectively inactivated the HS cells by expressing in their membrane inward rectifying potassium channels (Kir2.1) to hyperpolarize these cells, preventing their role in synaptic signaling. The results of the experiments show mutants lose steering responses to several distinct categories of figure motion and reduced behavioral responses to figure motion set against a contrasting moving background, highlighting their role in figure tracking behavior. Finally, a synapse inactivating protein, tetanus toxin (TNT), expressed in the HS cell group, produces a different behavioral phenotype than overexpressing inward rectifier. TNT, a bacterial neurotoxin, cleaves SNARE proteins resulting in loss of synaptic output of the cell, but the dendrites are intact and signal normally, preserving dendro-dendritic interactions known to sculpt the visual receptive fields of these cells. The two distinct phenotypes to each genetically targeted silencer differentiate the functional role of dendritic integration versus axonal output in this important cell group
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Neural and Behavioral Analysis of Object Detection in Drosophila
Get PDFAs we move through the world, our visual system constantly detects and tracks objects around us, using cues such as movement, texture, brightness, color and shape. A solid mechanistic understanding of how an object is distinguished from its background has eluded researches examining this question across many model organisms. In this thesis, we describe a novel object-detecting neuron class in the fly optic lobe by characterizing its anatomy and physiology. We then show direct evidence that inhibitory currents play a major role in mediating object-selectivity. To find origins of inhibition, we screen publicly available libraries and identify candidate presynaptic input neurons. In addition, we examine the receptor expression profile of object-detecting neurons and identify receptor types that are likely to mediate inhibition and excitation. Our results provide insights into the only known object-detector neuron in Drosophila.To elucidate the possible behavioral contributions of object-detecting neurons, we investigate the object tracking behavior in flies. We show that luminance and motion cues contribute to object tracking behavior in distinct ways. Specifically, flies exhibit quantitatively and qualitatively distinct behavioral responses to luminance-defined and motion-defined objects. Our results complement previously published research and demonstrate the existence of parallel visual streams carrying different information (motion or luminance) that are relevant for object tracking behaviors
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Olfactory proteins mediating chemical communication in the navel orangeworm moth, Amyelois transitella.
Get PDFBACKGROUND:The navel orangeworm, Amyelois transitella Walker (Lepidoptera: Pyralidae), is the most serious insect pest of almonds and pistachios in California for which environmentally friendly alternative methods of control--like pheromone-based approaches--are highly desirable. Some constituents of the sex pheromone are unstable and could be replaced with parapheromones, which may be designed on the basis of molecular interaction of pheromones and pheromone-detecting olfactory proteins. METHODOLOGY:By analyzing extracts from olfactory and non-olfactory tissues, we identified putative olfactory proteins, obtained their N-terminal amino acid sequences by Edman degradation, and used degenerate primers to clone the corresponding cDNAs by SMART RACE. Additionally, we used degenerate primers based on conserved sequences of known proteins to fish out other candidate olfactory genes. We expressed the gene encoding a newly identified pheromone-binding protein, which was analyzed by circular dichroism, fluorescence, and nuclear magnetic resonance, and used in a binding assay to assess affinity to pheromone components. CONCLUSION:We have cloned nine cDNAs encoding olfactory proteins from the navel orangeworm, including two pheromone-binding proteins, two general odorant-binding proteins, one chemosensory protein, one glutathione S-transferase, one antennal binding protein X, one sensory neuron membrane protein, and one odorant receptor. Of these, AtraPBP1 is highly enriched in male antennae. Fluorescence, CD and NMR studies suggest a dramatic pH-dependent conformational change, with high affinity to pheromone constituents at neutral pH and no binding at low pH
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Multisensory functional and comparative analysis of object tracking in flying fruit flies
Get PDFThe survival and success of animals across phyla is critically dependent on generating appropriate behavioral responses to visual cues that are often complex and ambiguous. Visual objects can represent predators, conspecifics, obstacles and navigational goals, and must be discriminated from moving panoramas whose spatial features can vary greatly across environments. Due to its high-performance demands, insect flight is an excellent system used to study the behavioral algorithms governing the detection and responses to moving objects, and their underlying neural mechanisms. Yet, much of our understanding of the neurobiology of object discrimination comes from highly restrictive preparations that limit or severely compromise the multisensory feedback that modulates visual circuits in freely behaving animals. This dissertation probes how robust and well-characterized object tracking behaviors can be modulated by both multisensory context and visual-ecological adaptations. We demonstrate that the absence of naturalistic body movement cues in classical body-fixed virtual reality paradigms relegates smooth optomotor responses typically reserved for gaze stabilization to object pursuit tasks. We show that this occurs through a simple gain modulation mechanism and propose the gyroscopic haltere proprioceptive circuit that play a role in actively damping visual circuits. We generate novel genetic reagents in D. melanogaster that allow targeted manipulation of haltere feedback and propose experiments to test the integration of proprioceptive and visual feedback in vivo. Finally, through comparative studies across Drosophila species, we demonstrate that the same object pursuit strategies that we found to be highly dependent on multisensory context are also shaped by the properties of the visual ecology. This series of studies can inform the design and interpretation of neurophysiological assays where parameters are necessarily restricted to probe neural mechanisms. More importantly perhaps, these studies illuminate general principles that expand our understanding of how locomoting animals process visual cues in relevant naturalistic contexts
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Columnar visual pathways for smooth optomotor steering and saccadic object tracking in Drosophila
Get PDFAll visual animals stabilize their gaze by moving their eyes, head, or body. Humans, with camera type eyes, use a “fixate and saccade” strategy that combines smooth tracking movements and ballistic eye saccades to stabilize gaze. Drosophila melanogaster, having a radically different type of eye, nonetheless move their full body during flight to use these smooth optomotor steering and saccade maneuvers to stabilize visual gaze. Despite the ubiquitous expression of these two behaviors across different species, the neural mechanisms that differentially control these maneuvers remain unknown. In this paper, we utilize the Gal4-UAS system to express a potassium inward rectifier, known as Kir2.1, in T4/T5, T2 or T3 columnar cells to test for differences in a flying fly’s ability to perform smooth optomotor steering and saccade maneuvers. Our data confirm prior work showing that T4/T5 neurons contribute motion related information to the downstream circuitry responsible for computing the speed of a moving panorama across the fly retina and accurately matching it to smooth fixational optomotor gain. We extend these results to show that T4/T5 are largely dispensable for the control of object tracking saccades. Additionally, our results strongly suggest that T2/T3 neurons contribute to the downstream circuitry responsible for target acquisition mechanisms required for recognizing and initiating saccadic tracking bouts in response to a moving barlike stimulus
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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Olfactory modulation of visual object behaviors in Drosophila melanogaster
Get PDFVisual objects in the natural world convey many meanings to vinegar flies, signifying the presence of predators, food sources, or potential mates. How animals rapidly distinguish among these small objects remains unclear at the mechanistic level. It is thought that multimodal integration of sensory cues, likely via actions of neuromodulators, is one mechanism for this behavioral plasticity. In this thesis, we begin by reviewing the current understanding of neuromodulation of insect vision. Next, we describe innate object behaviors in a flight simulator paradigm in both freely rotating, magnetically-tethered and yaw-restricted, rigidly-tethered melanogaster. The experimental paradigm in rigidly-tethered flies is then modified to assess the effects of odor on object responses. In a paradigm in which visual stimuli positions were negatively coupled to the fly’s steering effort, we find that appetitive odor reduces the probability that flies engage in aversive behaviors in response to encountering small visual objects. In a complementary paradigm in which visual stimuli position were restricted to the visual periphery, we show that the presence of appetitive food odors reverses innate object avoidance to attraction, whereby flies begin to approach and track the small object. We term this behavior odor-induced visual valence reversal. Subsequently, we show through optogenetic activation studies that this modulation seems in part to be induced by the neuromodulator octopamine, the insect orthologs of norepinephrine, as well as small-field visual motion detectors, T4/T5 neurons. Efforts to assess whether octopamine and T4/T5 neurons mediate object valence reversal via the same neural circuit were inconclusive, likely due to off-target effects and genetic backgrounds. Separately, in vivo calcium imaging of T4/T5 responses to visual objects with pharmacological application of octopamine or its agonist, chlordimeform, suggest that variation in T4/T5 visual responses were likely due to the quiescent animal’s internal state. Our results identify neural components involved in olfactory modulation of object vision and highlight the importance to further assess the contributions of locomotion in understanding neuromodulatory mechanisms
A pair of dopamine neurons target the D1-like dopamine receptor DopR in the central complex to promote ethanol-stimulated locomotion in Drosophila.
Get PDFDopamine is a mediator of the stimulant properties of drugs of abuse, including ethanol, in mammals and in the fruit fly Drosophila. The neural substrates for the stimulant actions of ethanol in flies are not known. We show that a subset of dopamine neurons and their targets, through the action of the D1-like dopamine receptor DopR, promote locomotor activation in response to acute ethanol exposure. A bilateral pair of dopaminergic neurons in the fly brain mediates the enhanced locomotor activity induced by ethanol exposure, and promotes locomotion when directly activated. These neurons project to the central complex ellipsoid body, a structure implicated in regulating motor behaviors. Ellipsoid body neurons are required for ethanol-induced locomotor activity and they express DopR. Elimination of DopR blunts the locomotor activating effects of ethanol, and this behavior can be restored by selective expression of DopR in the ellipsoid body. These data tie the activity of defined dopamine neurons to D1-like DopR-expressing neurons to form a neural circuit that governs acute responding to ethanol
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