It is very difficult to study mental disorders because animals do not experience them in the same way as humans, who cannot be experienced in vivo.
This is why scientists have implanted a kind of human brain cells, organoids, in young rats to better study complex psychiatric disorders, such as schizophrenia, and perhaps even experiment with treatments, according to a study published on Wednesday.
Scientists are already practicing cultures, in Petri dishes, of human brain tissue from stem cells. But in the laboratory, “the neurons do not reach the size they would reach in a real human brain”, explains Sergiu Pasca, professor of psychiatry and behavioral sciences at the American University of Stanford, and lead author of the study published in Nature.
Moreover, since these tissues are cultured outside the human body, they do not allow the symptoms resulting from a defect in their functioning to be studied.
Testing new drugs?
The solution is to implant these human brain tissues, called organoids, into the brains of young rats. Age is important because the brain of an adult animal stops developing, which would have affected the integration of human cells.
By transplanting them into a young animal, “we found that the organoids can become quite large and vascular” and therefore be supplied by the blood network of the rat, to the point of “occupying about a third of the hemisphere of the brain” of the animal, explains Prof. Pasca.
The researchers tested the correct implantation of the organoids by sending a blast of air to the rat’s whiskers, which resulted in electrical activity in the human-derived neurons – a sign that they were playing their role as receivers well with a stimulus.
They then wanted to know if these neurons could transmit a signal to the rat’s body. To do this, they implanted organoids previously modified in the laboratory to react to blue light. They then trained the rats to drink from a cannula of water when this blue light stimulated the organoids via a cable connected to their brains. The maneuver proved effective in two weeks.
The team finally used their new technique with organoids from patients with a genetic disease, Timothy syndrome. She observed that in the brain of the rat, these organoids grew more slowly and had a lower activity than organoids from healthy patients.
This technique could eventually be used to test new drugs, according to two scientists who were not involved in the study, but who commented on its findings in Nature.