Scientists have succeeded in transplanting a type of human brain cell - known as "organoids" - into small mice. With the aim of improving the study of complex mental disorders, such as schizophrenia, and possibly trying more treatments, according to a study published yesterday, Wednesday, and quoted by Agence France-Presse.
It is very difficult to study mental disorders , because animals do not suffer from them in the same way that humans do, who, in turn, cannot be experimented with in vivo.
Scientists used to transplant human brain tissue from stem cells into "petri dishes" (a test dish), but in the lab, "neurons do not reach the size they would in a real human brain," says Sergio Pasca, a professor. Psychiatry and Behavioral Sciences at Stanford University, USA, and lead author of the study published in the journal Nature .
Since the tissues are implanted outside the human body, they do not allow the study of symptoms resulting from any malfunction.
The solution is to transplant human brain tissue into the brains of young mice, and the age factor in this case is important, because the brain of an adult animal stops developing, which may affect the integrity of human cells.
Professor Pasca explains that by transplanting human brain cells into a small animal, "we found that the organelles can become very large and vascularized" and thus can be supplied to the mouse's blood network, to the point of "occupying about a third of the brain's hemisphere".
The researchers tested the correct implantation of the organelles by sending a burst of air into the whiskers of mice, which triggered electrical activity in the human-derived neurons, a sign that they were playing their role as receptors well when a stimulus was present.
Then they wanted to see if these neurons could transmit a signal to the rat's body. To do so, they implanted organoids that had been pre-modified in the lab to react to blue light. They then trained the rats to drink from a bottle of water when that blue light stimulated the organelles via a wire attached to their brains. The process proved effective within two weeks.
**For internal use only*** Depression is one of the world's leading causes of disability, and a major contributor to the overall global burden of disease. Source: WHO official Twitter account
Ethical questions
The team of researchers recently used its new technology with organisms from patients suffering from a genetic disease known as "Timothy syndrome", and they noticed that in the mice's brain, these organisms grew more slowly, and their activity was less than that of organisms from healthy patients.
This technology could eventually be used to test new drugs, according to two scientists who were not involved in the study, but who commented on the results published in the journal Nature.
Gray Camp, from the Swiss Roche Institute for Translational Bioengineering, and Barbara Treutlin, from the Zurich Polytechnic, wrote that these findings "transport our ability to study the evolution and pathology of the human brain into unknown territory."
Mice shell
The technique raises ethical questions, particularly about how much human brain tissue transplantation into an animal can alter its deep nature.
Pasca, for his part, ruled out such a danger to the rat, due to the greater speed with which its brain develops compared to the human brain. He described the action of the rat's cortex as a "natural barrier", noting that this cortex would not have time to deeply integrate neurons of human origin.
Such a barrier could not exist in species anatomically close to humans, says Pasca, who opposes using this method in primates.
The term primate in zoology is applied to any mammal from the group that includes lemurs, lorises, carpals, monkeys, monkeys and humans, according to the Encyclopedia Britannica.
Pasca concludes that "human mental disorders are largely unique to humans, which is why we have to think carefully how much we want to work on some of these models."
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