Up to now it has mostly been tested by animal experiments with mice or rats whether a chemical can damage the brain development of unborn children. Researchers have now developed an alternative method that could save many mammals from doing this. Eggs and embryos from grasshoppers serve as indicators of a possible harmful effect on the brain. Special imaging allows the scientists to observe the developing nerves in the insects.
When it comes to the possible harmful effects of chemicals, it is not only necessary to test whether they are toxic to adults. Because especially babies and especially unborn babies are far more sensitive to pollutants. Therefore, industrial chemicals, pesticides, ingredients in cosmetics or pharmaceuticals can damage the developing nervous system during pregnancy or even after birth, even if adults are not harmed.
Linking nerves in the grasshopper embryo
So far, however, the tests for prenatal damage have been very complex and require a large number of animal experiments with mice and rats. For this reason, not all chemicals have been tested for this effect. “Until 2017, only 13 substances with a developmental neurotoxic effect on humans were identified,” report Karsten Bode from the University of Veterinary Medicine Hanover and his colleagues. “In contrast, tens of thousands of industrial compounds have not yet been checked for this.” There are already some methods in development that are based on cell cultures instead of animals. However, these only insufficiently capture an essential aspect of brain development: the networking of brain cells.
Now Bode and his colleagues have developed a method that can also include this essential aspect of brain development in chemical tests without causing mammals to suffer and die. The starting point of this test system are the developing locust embryos. They are carefully prepared from the eggs of the clutch and then individually placed in the wells of a test plate. By adding fluorescent antibodies, the pioneer axons in the embryo are stained – the nerve cells that form the first cell processes (axons). Then the test chemical is added. In order to make their effects visible, the embryo is then examined with special laser imaging that detects the pioneer axons and their connection.
First tests successful
This method makes it possible to make chemical-related disorders of the neuronal circuit visible. In initial tests, the researchers have already checked the suitability of their system with two known neurotoxic pollutants, methyl mercury and sodium arsenite. In both cases, the test successfully identified the neurotoxic effects on developing brains – it came to the same result as common epidemiological and animal-based methods. In the next step, Bode and his team now want to extend this review of the test method: “Now we are validating the insect embryo test with a training set of known developmental neurotoxic and control substances for its reliable informative value,” explains Bode’s colleague Gerd Bicker.
If the new method continues to prove itself, it could in future be used as a replacement and supplementary method for previously used experiments in mammals. “If the system is established, it could replace numerous experiments on mammals,” says Bicker.
Source: Hanover University of Veterinary Medicine Foundation; Technical article: Scientific Reports, doi: 10.1038 / s41598-020-59562-7