The results of an experiment in which human neurons have been transplanted into the brains of newborn rats – which had been genetically modified so that they did not have an immune system and prevented them from rejecting the graft – could revolutionize the knowledge and treatment of psychiatric diseases and neurodegenerative, since it has been proven that the behavior of rodents in which this brain tissue was implanted has undergone a change.
The research has been carried out by scientists from Stanford University, in the United States, led by the Romanian doctor Sergiu Pasca, who are specialists in producing “brain organoids”, a type of artificial organoids that consist of little balls a few millimeters in diameter with a few million cells, which are used in the laboratory to study the functioning of a real organ, which can be as complex as a human brain, which weighs one and a half kilos and has some 86,000 million neurons.
The researchers take cells from a person’s skin and return them to their embryonic state with a chemical process, so that they can become any organ in the body and transform them into brain cells. The authors of the new study, which has been published in Nature, have transplanted these cells into the brain of rat pups, where they have been successfully integrated, and have observed that touching the rodents’ whiskers activates the human cells, that are involved in their senses.
Touching the rat pups’ whiskers activates the transplanted human cells in their brains, meaning they have successfully integrated and influenced their behavior
This does not mean, as Pasca himself has clarified, that these animals have developed anything that resembles a human consciousness, considering the type of cells involved and their imperfect integration. “To understand psychiatric disorders we need better models. And, the more human these models are, the more we will have to address these ethical issues”, explains the scientist, who does not consider it convenient to use this strategy with monkeys or apes. “We need to strike a balance between the potential benefits of avoiding some of the suffering caused by these devastating brain disorders and the risks of generating models that are too human-like,” he stresses.
A mouse model to investigate brain diseases
Dr. Pasca believes that the main application of the mouse models he has developed will be in disease research, and in fact his team has already started with Timothy syndrome, a rare disease that causes serious neurological and cardiac problems in children. The researchers have transplanted cells from three patients into the brains of rats and have detected neuronal defects that were previously unknown. In addition, they are investigating more than 20 brain disorders, including autism and schizophrenia. “Now we can test new drugs in animals and study their effects on transplanted human neurons,” says Pasca.
Speaking to SMC Spain, Núria Montserrat, ICREA Research Professor at the Institute of Bioengineering of Catalonia, gave her opinion on this scientific milestone: “The study represents a very important advance in the field of brain organoids, it is of a quality excellent, and incorporates new methodological approaches to overcome certain limitations when it comes to conferring complex characteristics in these farming systems”.
According to the expert, “it is conceivable that the methodology used in this study could be applied in future studies that aim to study neural circuits that are involved in different human pathologies. In fact, in this study the authors have been able to identify that, after transplantation, the neurons of the organoids present more complex intrinsic functional and morphological characteristics, which has made it possible to identify defects related to Timothy syndrome”
And concludes: “Although the study has important implications regarding the possibility of developing strategies to overcome the current limitations when it comes to maturing and conferring physiologically relevant characteristics in these cell cultures, the study also shows that the methodological approach carried out This study has important limitations, since the differences between the human and rat nervous systems can lead to misinterpretations (as the researchers point out in the conclusions of their study)”.
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