In contrast to mammals, zebrafish possess a high regenerative capacity even within the central nervous system including the retina. In the retina, lesions result in a loss of neurons and the subsequent activation of Müller glia, the retinal stem cells. Müller glia-derived progenitors differentiate into all types of retinal neurons. Eventually the anatomical tissue architecture is restored within a few weeks or months depending on the degree of lesion. However, little is known about how retinal lesions impair vision functionally, as well as how and to what extent visual function is restored during the course of regeneration, in particular in adult animals.
Here, quantitative behavioral assays were applied to assess visual function during homeostasis and regeneration in adult zebrafish. While the dark-light preference test has been identified to be too variable to assess visual function, a novel visiondependent social preference test as well as an automated two level OKR-based vision test have proved to be more suitable. Two different lesion paradigms have been compared in this study: light-induced lesions that target photoreceptor cells and neurotoxin-mediated lesions that act in a concentration-dependent manner either affecting only inner retinal neurons or all retinal cell types. It could be shown that visual function was significantly impaired after light lesion but fully though gradually recovered within 28 days. Vision for easy conditions with high contrast and low level of detail, as well as color vision, was restored around 7–10 days post lesion while vision under more demanding conditions - with low contrast and high level of detailwas regained only from 14 days post lesion onwards. The corresponding retinal morphology was monitored in vivo using optical coherence tomography and revealed a close correlation between structure and function. Injection of neurotoxins resulted in a multitude of morphological changes that impeded the analysis of functional recovery. In general, restoration of visual function after neurotoxin-mediated lesion was limited and highly dependent on the initial degree of damage. As suggested by the behavioral studies, visual functions are, at least partially, restored after lesion. However, no conclusions can be drawn on the restoration of the underlying retinal circuitry. Hence, large-scale electrophysiological recordings using multielectrode arrays have been established for the adult zebrafish retina allowing the recording of spontaneous and light-driven activity. This technique can be exploited to analyze the restoration of signal processing of the retina in future studies. In addition, the established tools can be applied to characterize visual mutants and models of retinal degenerative diseases both morphologically and functionally as exemplarily demonstrated here for the blind atoh7 mutant. It was shown that the adult atoh7mutant largely resembles the larval phenotype and displays distinct alterations in optic tectum structure as well as impairments of social behavior. Altogether, the established vision-dependent behavioral assays suggest that the degree and kinetics of functional recovery are highly dependent on the lesion paradigm as well as quality of morphological restoration. In combination with the established multielectrode array recordings, the field is provided with new readouts to study functional recovery that can be used in addition to existing criteria to assess regeneration of the adult zebrafish retina. The established toolbox can furthermore be exploited to analyze retinal function not only in a regeneration context but also in visual mutants, disease models or ageing. Eventually, a deeper understanding of the regenerative processes in zebrafish will provide new perspectives for the development of therapies for retinal degenerative diseases.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:84376 |
| Date | 28 March 2023 |
| Creators | Hammer, Juliane |
| Contributors | Brand, Michael, Neuhauss, Stephan, Technische Universität Dresden |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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