Human brain cells implanted in rats to study psychiatric disorders

Hope: experimenting with treatments. Scientists have succeeded in implanting a kind of human brain cells, organoids, in young rats to better study complex psychiatric disorders, such as schizophrenia, according to a study published Wednesday, October 12. 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.

Scientists are already practicing human brain tissue culture 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 (California), and main 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. 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 organoids can become quite large and vascularized” and therefore be supplied by the blood network of the rat, to the point of“occupy about a third of the hemisphere of the brain” of the animal, details Sergio Not that .

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 neurons, a sign that they were playing their role as receivers 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 was effective within two weeks.