A research team at the Helmholtz Centre for Environmental Research (UFZ) has developed an innovative high-throughput screening method that tests the neurotoxic effect of chemicals without conventional animal experiments. The study, published in the journal Environmental Health Perspectives, uses the chemical chlorophene as an example to show how such tests can reveal neurotoxic effects and their molecular mechanisms.

Worldwide, about 350,000 chemicals are commercially available, but only about 200 have been tested for neurotoxic effects because conventional testing methods are time-consuming, costly and usually associated with animal experiments on rats or mice. The UFZ team used embryos of the zebrafish (Danio rerio), whose genes match around 70 percent of human genes, to develop a fast, ethically justifiable test procedure. This enables the investigation of chemicals for their effect on the nervous system, especially on learning and memory processes.

The method is based on the observation of the learning behavior of zebrafish embryos that react to recurring acoustic or visual stimuli. Neurotoxic substances can change these reactions, for example by preventing or accelerating habituation to stimuli. In tests with ten substances that influence the NMDAR receptor system , which is important for learning and memory, chlorophen showed a particularly strong effect: it completely blocked learning behavior and led to a so-called paradoxical excitation, in which the embryos reacted to acoustic but not to visual stimuli.

Further research revealed that chlorophen acts via GABAA receptors, which play a central role in the nervous system. This effect was confirmed by tests on mouse and human cell models as well as by computer models. Another mechanism of action that influences learning behavior could be mediated via special potassium channels, as comparisons with the painkiller flupirtin suggest.

The new screening procedure makes it possible to test chemicals for neurotoxic effects quickly, cost-effectively and without animal testing. It supports the goals of the EU Chemicals Strategy and the European Green Deal by identifying hazards at an early stage. The researchers emphasize that the findings could increase confidence in zebrafish-based tests to protect human health from harmful chemicals. Further studies are intended to deepen the molecular mechanisms in order to further refine the test methodology.

Original Paper:

Multi-behavioral phenotyping in early-life-stage zebrafish for identifying disruptors of non-associative learning | Environmental Health Perspectives | Vol. 0, No. 0