Methylnitrosourea (MNU)-induced Retinal Degeneration and Regeneration in the Zebrafish: Histological and Functional Characteristics

Abstract

Retinal degenerative diseases, e.g. retinitis pigmentosa, with resulting photoreceptor damage account for the majority of vision loss in the industrial world. Animal models are of pivotal importance to study such diseases. In this regard the photoreceptor-specific toxin N-methyl-Nnitrosourea (MNU) has been widely used in rodents to pharmacologically induce retinal degeneration. Previously, we have established a MNUinduced retinal degeneration model in the zebrafish, another popular model system in visual research.A fascinating difference to mammals is the persistent neurogenesis in the adult zebrafish retina and its regeneration after damage. To quantify this observation we have employed visual acuity measurements in the adult zebrafish. Thereby, the optokinetic reflex was used to follow functional changes in non-anesthetized fish. This was supplemented with histology as well as immunohistochemical staining for apoptosis (TUNEL) and proliferation (PCNA) to correlate the developing morphological changes.In summary, apoptosis of photoreceptors occurs three days after MNU treatment, which is followed by a marked reduction of cells in the outer nuclear layer (ONL). Thereafter, proliferation of cells in the inner nuclear layer (INL) and ONL is observed. Herein, we reveal that not only a complete histological but also a functional regeneration occurs over a time course of 30 days. Now we illustrate the methods to quantify and follow up zebrafish retinal de-and regeneration using MNU in a video-format.

An Evaluation of Zebrafish, an Emerging Model Analyzing the Effects of Toxicants on Cognitive and Neuromuscular Function

“…Zebrafish’s visual abilities, like humans, can be significantly affected by environmental toxicants. 59 For example, N -methyl- N -nitrosourea (MNU) causes retinal degeneration in zebrafish. 59 In humans, cannabis can hinder contrast sensitivity and motion discrimination.…”

“…59 For example, N -methyl- N -nitrosourea (MNU) causes retinal degeneration in zebrafish. 59 In humans, cannabis can hinder contrast sensitivity and motion discrimination. 60 Studying the effects of neurotoxicants on zebrafish could help us understand this relatively unexplored condition.…”