Scientists create hybrid brain fusing human neurons into baby rat brains

Scientists create hybrid brain fusing human neurons into baby rat brains

Indeed, brain connections are largely formed early in development, making young rats ideal candidates for transplantation (Photo: Sergiu PASCA / Stanford University / AFP)

Scientists have succeeded in transplanting human brain tissue into the brains of newborn rats.

Stanford University researchers created these hybrid rat brains where human and rodent nerve cells connected, grew and matured to form functional circuits.

These brains serve as “living labs,” allowing the team to grow and manipulate human brain tissue and see how it influences animal behavior.

The experts said their work, published in the journal Nature, could advance research into mental disorders such as schizophrenia or autism, without the need for invasive procedures such as the extraction of brain tissue.

“We can now study healthy brain development as well as brain disorders believed to have roots in development in unprecedented detail, without the need to excise tissue from a human brain,” said Sergiu Pasca, professor of psychiatry. and behavioral sciences at the Stanford School of Medicine. , and lead author of the study.

Scientists have succeeded in transplanting human brain tissue into the brains of newborn rats (Credits: PA)

“We can also use this new platform to test new drugs and gene therapies for neuropsychiatric disorders,”

Researchers have created mini-brains in the lab – using stem cells – to study brain development.

However, they said these mini-brains, also known as organoids, lack the connectivity that exists in real people, limiting the ability to study them for advanced research.

For the study, the scientists used two- to three-day-old pups – the equivalent of a human newborn.

This is because brain connections are largely formed early in development, making young rats ideal candidates for transplantation.

The team cultured human brain organoids in the lab, and two months later, when they began to resemble human cerebral cortex, the organoids were transferred into the brains of rat pups.

Close-up of two white lab rats sniffing each other in a glassy box on a pharmaceutical scientist's desk

These brains serve as ‘living laboratories’, allowing the team to grow and manipulate human brain tissue and see how it influences animal behavior (Credit: Getty Images/iStockphoto)

Organoid neurons “settle” into rat brains, the scientists said, forging connections with rodent brain tissue to form hybrid working circuits.

Six months later, individual neurons from the human cells occupied a full third of the rat brain’s hemisphere, the team said.

The neurons also showed more complex branching patterns and were at least six times larger than lab-grown organoids, they added.

Experiments with rodent whiskers showed that when transplanted into rat brains, human neurons were able to respond to sensory stimulation.

The researchers then transplanted cells from three patients with Timothy syndrome, a rare genetic condition associated with serious heart problems.

Cute white lab rat in the hands of a researcher in a lab (in blue tones)

Scientists are creating a hybrid brain fusing human neurons into the brains of baby rats (Photo: Getty Images/iStockphoto)

They found that, compared to rat brains with normal neuron cells, rodent brains with Timothy syndrome neurons were much smaller and lacked sophisticated branching patterns.

“We learned a lot about Timothy syndrome by studying organoids preserved in a dish,” Professor Pasca said.

“But it was only with transplantation that we were able to see these differences related to neuronal activity,”

The scientists said bioethicists were involved in reviewing the ethical aspects of their research.

‘This is the most advanced human brain circuit ever built from human skin cells and a demonstration that implanted human neurons can influence an animal’s behavior,’ Professor Pasca said.

“Our platform provides, for the first time, behavioral readouts for human cells and could hopefully accelerate our understanding of complex psychiatric conditions,”

Commenting on the research in Nature’s News & Views, J Gray Camp, of the Roche Innovation Center in Switzerland, and Barbara Treutlein, of ETH Zurich, also in Switzerland, wrote: “An active discourse between researchers, bioethicists, regulators and the public is needed to develop frameworks and boundaries for research that uses organoids to model human brain circuitry,”

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