title: Anatomical and functional characterization of the orientation network in the central and lateral complex of the desert locust Schistocerca gregaria
title: Anatomische und funktionelle Charakterisierung des Orientierungsnetzwerkes im Zentralkomplex und lateralen Komplex der Wüstenheuschrecke Schistocerca gregaria
titleType: AlternativeTitle
Creators: name: Hensgen, Ronja Melanie
Publisher: name: Philipps-Universität Marburg
Year: 2022
Subjects: Polarisationsmuster
Neurobiologie
Life sciences
Biowissenschaften, Biologie
sky compass
Orientation
insects
Orientierung
Zentralkomplex
polarisation pattern
neurobiology
sky polarisation
navigation
Navigation
Himmelskompass
Insekten
central complex

description: Spatial orientation is an indispensable basis of many behaviors that ensure the survival of an individual or a species. Foraging, finding mating partners, avoiding predators or developing new habitats rely on this ability. Insects show sophisticated skills for spatial orientation and navigation. These abilities require integration of external and internal stimuli that provide information about the animal’s own position in space or relative to an object. Under the open sky the sun is – even for humans – a prominent orientation cue that can be utilized for orientation by many insect species. Additionally, other celestial cues - that are not perceptible by humans - can be detected and used by insects. One of these is the polarization pattern of the sky that results from scattering of unpolarized sunlight in the earth’s atmosphere. It is characterized by the systematic arrangement of the prevailing plane of oscillation of polarized light (angle of polarization, AoP) and depends on the position of the sun. The degree of polarization (DoP) that indicates the percentage of polarized light within a light beam also depends on the sun’s position. In the insect brain, the AoP is encoded by the activity of polarization-sensitive neurons that transmit this information from the compound eyes into the central brain, where it is used to generate an internal compass. The internal compass is represented by the activity of neuronal populations of the central complex (CX), a navigation center that processes orientation-relevant information and is involved in the generation of appropriate locomotor responses. The CX comprises four midline spanning neuropils in the center of the brain; the protocerebral bridge (PB), the lower division of the central body (CBL; also known as ellipsoid body, EB, in flies) the upper division of the central body (CBU; also known as fan-shaped body, FB, in flies) and the paired noduli (NO). The neuropils are characterized by vertical columns (or slices) and horizontal layers that result from the neuronal projections of the neuron systems that constitute the CX. Arborizations of tangential neurons establish distinct layers and arborizations of columnar and pontine neurons result in distinct columns. Beside polarization information the neuronal network of the CX also integrates other information that underlies context- and experience dependent behavior. Another brain region, the lateral complex (LX) plays a major role in mediating information flow to and from the CX. The LX is located in both hemispheres laterally from the CX and consists of the lateral accessory lobe (LAL) with the associated gall and the bulb. A variety of neuron types connects the LX and the CX and provides connections between the LX and other brain regions as well as the thoracic ganglia. The present thesis investigates the physiology of polarization-sensitive neurons of the CX and the anatomical organization of the CX and the LX of the desert locust Schistocerca gregaria (Figure I). Electrophysiological experiments were performed to investigate the influence of the DoP on the coding of the AoP by polarization-sensitive neurons of the CX (Chapter I). They revealed that even low DoPs allow a reliable coding of AoPs in the locust brain. However, DoPs under a certain threshold result in a strong modulation of the activity of neurons at the input stage of the CX. Neuron types within the CX are characterized in addition to their physiology and morphology by the expression of neurotransmitters and neuropeptides. Immunocytochemical stainings revealed the expression pattern of myoinhibitory peptide (MIP) in the CX (Chapter II). We identified and characterized five MIP-expressing neuronal systems comprising cell types that have so far been identified mainly based on single-cell labeling. The combination of single-cell labelings and immunocytochemical stainings revealed potential feedback loops between cell types of the CX and the LX and were used to identify and describe novel cell types of the LAL (Chapter III).