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Neuronal organization of the olfactory bulb in adult zebrafish

Moenig, Nila Rebecca. Neuronal organization of the olfactory bulb in adult zebrafish. 2024, Doctoral Thesis, University of Basel, Faculty of Science.

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Abstract

From an evolutionary perspective the brain can be considered as an organ that serves to control the state of an organism within its environment. Through selective pressure that optimizes the interaction of organisms with their particular environment, a rich diversity of nervous systems has evolved across the Eumetazoa. These nervous systems vary in structure, complexity, versatility, and – particularly noteworthy for their potential to broaden an organism’s behavioral spectrum, and thus the ability to adapt to various and varying environments – neuronal plasticity. Evolution can act through modifications of the nervous system on different levels. These adaptations may occur as alterations on the molecular level (e.g., odorant receptors), at the ultrastructural level as specializations of neuronal subcompartments (e.g., the specialization of apical and basal dendrites in pyramidal neurons), and through the emergence of novel neuron types up to transformations affecting the brain architecture. The impact of these adaptations unfolds on the behavioral level, changing the potential to control the organisms state or interact with the environment. Notably, complex cognitive behaviors have emerged from fundamentally different brain structures in different taxa such as cephalopods, birds, and primates. Conversely, similar circuits can be due to a similar solution, optimized to meet common environmental and functional demands imposed onto diverse organisms, rather than a common origin.
The olfactory system of invertebrates and vertebrates is such a case of convergent evolution. In arthropods, fish and mammals, similar principles have been identified with respect to the expression and turnover of odorant receptors in olfactory sensory neurons (OSNs) and the morphology of OSNs. Likewise, OSN projections show an equivalent organization into glomeruli within the respective first olfactory relay centers, the antennal or olfactory lobe of insects and crustaceans, respectively, or the olfactory bulb (OB) in vertebrates. These centers exhibit a comparable neuronal circuit organization and have been shown to perform the same types of computations and transformations on their inputs. Odorants carry diverse information vital for an organism’s survival and species continuity: Odors help locating and identifying desirable objects, like food, mating partners, home territory or mating grounds and can warn of dangers, e.g., predators, fire, inedible foods, etc. Moreover, odorants represent an important means for communication with conspecifics, they can signal e.g., territorial boundaries, kinship, hierarchy, and many more. Whether airborne or aquatic, these odorants are usually complex mixtures of multiple different molecules and little variation in composition can alter identity and meaning of the signal. The challenge of correctly parsing these complicated, but crucial signals in order to execute the appropriate behavioral response is comparable for all species, which may be the reason for the organizational similarity of the olfactory system across taxa.
The work presented here focuses on evolution’s substrate and objective in an olfactory system, namely the neuroanatomy of the olfactory bulb and olfactory behavior in adult zebrafish.
Section 2 covers the neuroanatomical part of this thesis, a comprehensive study of neuronal diversity in the OB of adult zebrafish. Single neuron reconstructions from the same animal are based on volumetric neurite segmentation in an EM volume. I developed a software tool to proofread this segmentation and reconstructed more than 200 neurons from all layers of OB. Based on these reconstructions, I extracted a detailed description of neuron morphology and defined neuron classes based upon this analysis. Further, I provide a qualitative investigation of the connectivity between defined interneuron classes and principal neurons in adult zebrafish OB.
The second project of my thesis is described in section 3. This study aimed at providing a tool which permits neuroscientists to functionally explore components of the olfactory system in adult zebrafish by means of a reproducible and scalable behavioral assay. I developed an olfactory discrimination paradigm for adult zebrafish in collaboration with Iori Namekawa. This study has been published with equal contribution first authorship. I contributed to the design of the behavioral setup and developed the software and apparatus for automating the stimulation procedure, which allowed to scale up the number of animals per training. Further, I developed and optimized the discrimination training and control procedures, trained more than 85% of fish, determined the optimal set of behavioral features, analyzed all behavioral data and together with Rainer Friedrich developed a behavioral population score. Iori Namekawa designed the training apparatus, designed, and developed the software for movie recording, offline fish tracking and feature extraction and trained the remaining fish. Rainer Friedrich wrote the manuscript with minor contributions from the other authors.
This olfactory discrimination paradigm has been used in a study led by Thomas Frank, who showed that a major target of the OB contains a low-dimensional representations of odor valence that can be modified by conditioning and relies on inhibition. I trained fish for this study together with Chie Satou and analyzed all behavioral data. I am a co-author of this publication, but I did not include it in my thesis because the main contribution to the study was made by Thomas Frank.
Advisors:Friedrich, Rainer
Committee Members:Neuhauss, Stephan
Faculties and Departments:05 Faculty of Science
09 Associated Institutions > Friedrich Miescher Institut FMI > Neurobiology > Neuronal circuits and computations (Friedrich)
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:15382
Thesis status:Complete
Number of Pages:203
Language:English
Identification Number:
  • urn: urn:nbn:ch:bel-bau-diss153824
edoc DOI:
Last Modified:08 Aug 2024 09:45
Deposited On:08 Aug 2024 09:45

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