Coding of sky-compass information in neurons of the anterior optic tubercle of the desert locust Schistocerca gregaria

The primary aim of my Doctoral thesis project was to test through intracellular recordings the hypothesis that the lower unit of the AOTu participates in polar- ization vision. Four types of interneurons with ramifications in the lower unit of the AOTu were characterized in multiple recordings. All of these neurons were sensitive to polarized light, sub- stantiating our hypothesis (Chapter I, -> page 19). Two types of neuron, called lobula tuber- cle neuron (LoTu1) and tubercle tubercle neuron (TuTu1), were especially amenable to intracel- lular recordings, due to their large axon diam- eters. In the first set of experiments, we found that all polarization-sensitive neurons were also responsive to unpolarized light (Chapter I, -> page 19). To investigate the significance of this finding, we extended the stimulation with un- polarized light in a second set of experiments. The responses of both LoTu1 and TuTu1 to UV and green light spots from different directions suggest that these neurons signal the horizontal direction of the sun (solar azimuth), by exploit- ing both intensity- and color-gradients as well as the sky-polarization pattern (Chapter II, -> page 35). The use of both unpolarized and po- larized light information to detect the solar az- imuth can result in conflicting information pro- vided by the different cues. One way to reduce this conflict of information is to exclude certain areas of polarized skylight from being analyzed by the polarization-vision system. By stimulat- ing with different degrees of polarization (d), we showed that the threshold for E-vector detec- tion lies around d-values of 0.3. This means that an area of around 100 degrees around the sun con- tains no visible E-vector information for these neurons (Chapter III, -> page 51). Recent be- havioral experiments further confirmed that the pathway described above is vital for polarotaxis in locusts. Tethered locusts that are flown under a slowly rotating polarizer show periodic changes in yaw torque with a period of 180 degrees (Mappes & Homberg, 2004). When the anterior optic tract is unilaterally transected, the locusts are still able to respond to the rotating E-vector in the same manner as intact animals. However, when the DRA that is contralateral to the transection site is occluded, the animals become disoriented (Mappes and Homberg, in revison)

Magnetic field simulation of pinch mode magnetorheological fluid valve

This thesis presents the magnetic field simulation of magnetorheological fluid using finite element method. Magnetorheological fluid (MRF) is a smart material fluid carrying small magnetic particles. There are four operational mode of MRF that is squeeze mode, valve mode, shear mode and pinch mode. This thesis will focus on pinch mode which is named as magnetic gradient pinch mode (MGP). The objective of this thesis is to develop a design concept of a magnetic gradient pinch mode valve. It is very important to develop a concept design because it can help in finding the possible design configuration in producing a magnetic gradient pinch shape inside the valve from the reaction of the electromagnetic. From the concept design, simulation was conducted using Finite Element Method Magnetics (FEMM) software to get the magnetic flux density, B and magnetic field intensity, H produced by MGP valve. By getting the magnetic flux density from the finite element analysis, magnetic saturation was prevented in the valve. Magnetic saturation happened when the magnetic flux density at the valve gap is more than the maximum magnetic flux density of the MRF at 0.78 T. Magnetic field intensity, H, determine the generated maximum yield stress. One of the proposed design which is the third design, was exhibit highest magnetic flux density, B than other two design. Therefore, the thrird design is suitable for MGP valve due to abality to produce highest yield stress, thus, can withstand higher pressure when applied

Spectral properties of identified polarized-light sensitive interneurons in the brain of the desert locust Schistocerca gregaria

Many migrating animals employ a celestial compass mechanism for spatial navigation. Behavioral experimentsin bees and ants have shown that sun compass navigation may rely on the spectral gradient in the sky as well as onthe pattern of sky polarization. While polarized-light sensitive interneurons (POL neurons) have been identifiedin the brain of several insect species, there are at present no data on the neural basis of coding the spectral gradientof the sky. In the present study we have analyzed the chromatic properties of two identified POL neurons in thebrain of the desert locust. Both neurons, termed TuTu1 and LoTu1, arborize in the anterior optic tubercle andrespond to unpolarized light as well as to polarized light. We show here that the polarized-light response of both types of neuron relies on blue-sensitive photoreceptors. Responses to unpolarized light depended on stimulus position and wavelength. Dorsal unpolarized blue light inhibited the neurons, while stimulation from the ipsilateral side resulted in opponent responses to UV light and green light. While LoTu1 was inhibited by UV light and was excited by green light, one subtype of TuTu1 was excited by UV and inhibited by green light. In LoTu1 the sensitivity to polarized light was at least 2 log units higher than the response to unpolarized light stimuli. Taken together, the spatial and chromatic properties of the neurons may be suited to signal azimuthal directions based on a combination of the spectral gradient and thepolarization pattern of the sky

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

A Distinct Layer of the Medulla Integrates Sky Compass Signals in the Brain of an Insect

Mass migration of desert locusts is a common phenomenon in North Africa and the Middle East but how these insects navigate is still poorly understood. Laboratory studies suggest that locusts are able to exploit the sky polarization pattern as a navigational cue. Like other insects locusts detect polarized light through a specialized dorsal rim area (DRA) of the eye. Polarization signals are transmitted through the optic lobe to the anterior optic tubercle (AOTu) and, finally, to the central complex in the brain. Whereas neurons of the AOTu integrate sky polarization and chromatic cues in a daytime dependent manner, the central complex holds a topographic representation of azimuthal directions suggesting a role as an internal sky compass. To understand further the integration of sky compass cues we studied polarization-sensitive (POL) neurons in the medulla that may be intercalated between DRA photoreceptors and AOTu neurons. Five types of POL-neuron were characterized and four of these in multiple recordings. All neurons had wide arborizations in medulla layer 4 and most, additionally, in the dorsal rim area of the medulla and in the accessory medulla, the presumed circadian clock. The neurons showed type-specific orientational tuning to zenithal polarized light and azimuth tuning to unpolarized green and UV light spots. In contrast to neurons of the AOTu, we found no evidence for color opponency and daytime dependent adjustment of sky compass signals. Therefore, medulla layer 4 is a distinct stage in the integration of sky compass signals that precedes the time-compensated integration of celestial cues in the AOTu

Segregation of visual inputs from different regions of the compound eye in two parallel pathways through the anterior optic tubercle of the bumblebee (Bombus ignitus).

Visually guided behaviors require the brain to extract features of the visual world and to integrate them in a context-specific manner. Hymenopteran insects have been prime models for ethological research into visual behaviors for decades but knowledge about the underlying central processing is very limited. This is particularly the case for sky-compass navigation. To learn more about central processing of visual information in general and specifically to reveal a possible polarization vision pathway in the bee brain, we used tracer injections to investigate the pathways through the anterior optic tubercle, a prominent output target of the insect optic lobe, in the bumblebee Bombus ignitus. The anterior optic tubercle of the bumblebee is a small neuropil of 200 μm width and is located dorsolateral to the antennal lobe at the anterior surface of the brain. It is divided into a larger upper and a smaller lower subunit, both of which receive input from the optic lobe and connect to the lateral accessory lobe, and the contralateral tubercle, via two parallel pathways. The lower subunit receives input from the dorsal rim area (DRA) of the compound eye. The bumblebee DRA shares structural similarities with polarization-sensitive DRAs of other insects and looks similar to that of honeybees. We identified several neurons within this pathway that could be homologous to identified polarization-sensitive neurons in the locust brain. We therefore conclude that the pathway through the lower subunit of the anterior optic tubercle could carry polarization information from the periphery to the central brain

Investigation of visual pathways in honeybees (Apis mellifera) and desert locusts (Schistocerca gregaria): anatomical, ultrastructural, and physiological approaches

Many insect species demonstrate sophisticated abilities regarding spatial orientation and navigation, despite their small brain size. The behaviors that are based on spatial orientation differ dramatically between individual insect species according to their lifestyle and habitat. Central place foragers like bees and ants, for example, orient themselves in their surrounding and navigate back to the nest after foraging for food or water. Insects like some locust and butterfly species, on the other hand, use spatial orientation during migratory phases to keep a stable heading into a certain direction over a long period of time. In both scenarios, homing and long-distance migration, vision is the primary source for orientation cues even though additional features like wind direction, the earth’s magnetic field, and olfactory cues can be taken into account as well. Visual cues that are used for orientational purposes range from landmarks and the panorama to celestial cues. The latter consists in diurnal insects of the position of the sun itself, the sun-based polarization pattern and intensity and spectral gradient, and is summarized as sky-compass system. For a reliable sky-compass orientation, the animal needs, in addition to the perception of celestial cues, to compensate for the daily movement of the sun across the sky. It is likely that a connection from the circadian pacemaker system to the sky-compass network could provide the necessary circuitry for this time compensation. The present thesis focuses on the sky-compass system of honeybees and locusts. There is a large body of work on the navigational abilities of honeybees from a behavioral perspective but the underlying neuronal anatomy and physiology has received less attention so far. Therefore, the first two chapters of this thesis reveals a large part of the anatomy of the anterior sky-compass pathway in the bee brain. To this end, dye injections, immunohistochemical stainings, and ultrastructural examinations were conducted. The third chapter describes a novel methodical protocol for physiological investigations of neurons involved in the sky-compass system using calcium imaging in behaving animals. The fourth chapter of this thesis deals with the anatomical basis of time compensation in the sky-compass system of locusts. Therefore, the ultrastructure of synaptic connections in a brain region of the desert locust where the contact of both systems could be feasible has been investigated

Coding of sky-compass information in neurons of the anterior optic tubercle of the desert locust Schistocerca gregaria

The primary aim of my Doctoral thesis project was to test through intracellular recordings the hypothesis that the lower unit of the AOTu participates in polar- ization vision. Four types of interneurons with ramifications in the lower unit of the AOTu were characterized in multiple recordings. All of these neurons were sensitive to polarized light, sub- stantiating our hypothesis (Chapter I, -> page 19). Two types of neuron, called lobula tuber- cle neuron (LoTu1) and tubercle tubercle neuron (TuTu1), were especially amenable to intracel- lular recordings, due to their large axon diam- eters. In the first set of experiments, we found that all polarization-sensitive neurons were also responsive to unpolarized light (Chapter I, -> page 19). To investigate the significance of this finding, we extended the stimulation with un- polarized light in a second set of experiments. The responses of both LoTu1 and TuTu1 to UV and green light spots from different directions suggest that these neurons signal the horizontal direction of the sun (solar azimuth), by exploit- ing both intensity- and color-gradients as well as the sky-polarization pattern (Chapter II, -> page 35). The use of both unpolarized and po- larized light information to detect the solar az- imuth can result in conflicting information pro- vided by the different cues. One way to reduce this conflict of information is to exclude certain areas of polarized skylight from being analyzed by the polarization-vision system. By stimulat- ing with different degrees of polarization (d), we showed that the threshold for E-vector detec- tion lies around d-values of 0.3. This means that an area of around 100 degrees around the sun con- tains no visible E-vector information for these neurons (Chapter III, -> page 51). Recent be- havioral experiments further confirmed that the pathway described above is vital for polarotaxis in locusts. Tethered locusts that are flown under a slowly rotating polarizer show periodic changes in yaw torque with a period of 180 degrees (Mappes & Homberg, 2004). When the anterior optic tract is unilaterally transected, the locusts are still able to respond to the rotating E-vector in the same manner as intact animals. However, when the DRA that is contralateral to the transection site is occluded, the animals become disoriented (Mappes and Homberg, in revison)