Scientists have created a hybrid brain

Scientists have created a human-rat hybrid brain to try to better understand diseases like autism and epilepsy.

Putting human cells in the brains of animals is a morally gray area due to concerns that animals might start to think like humans as a result.

But scientists say the best way to learn about neurological and psychiatric diseases is by watching what happens to human cells in a living brain, not in a lab. Stanford scientists used human stem cells, which can become any type of cell in the body, to create brain cells. These cells joined together to form clusters called “organelles”. The researchers placed these organelles in the brains of rat pups so that the cells grow and function normally, and they can learn about a genetic disorder called Timothy’s syndrome, which causes a form of autism and is associated with serious heart problems. It worked so well that when the researchers tickled the rats’ whiskers, about 70 percent of the human cells placed in the creatures’ brains responded to the sensation. It was possible to control the behavior of rats using human brain cells that were made light-sensitive. Whenever the rats quenched their thirst with a sip of water from their spout, the scientists used blue light to activate human cells in their brains. Two weeks later, a simple activation of the brain cells made the rats go and lick their spouts of water. The idea that hybrid-brain rats can be manipulated in this way raises other ethical issues as well. But the researchers say the breakthrough could also help test drugs for brain diseases.

Sergiu Pasca, Professor of Psychiatry and Behavioral Sciences at Stanford Medical School and senior author of the rat study: “Now we can study healthy brain development, as well as brain disorders that are thought to take root during development, in unprecedented detail, without the need to excise tissue from the human brain. We can also use this new platform to test new drugs and gene therapy for neuropsychiatric disorders.”

Researchers have drawn a line under the introduction of human brain tissue into the body of primates, such as chimpanzees or macaques, which have a brain more like a human.

Professor Pasca said that using primates for such research would be wrong.

Rats, which live much shorter than humans, develop brains about 20 times faster than ours, limiting the degree to which human brain cells integrate with rat brain cells.

Prof. Pasca says that primates would have much more integration: “I think we should first use the technology we have developed, put it to use, see what it can actually teach us about human brain development, about evolution, about diseases, about whether we can systematically use it for drug testing.”

The scientists grew the “organoids” for two months in the lab until they began to resemble the human cerebral cortex. They were then transplanted into the brains of rat pups that were only two or three days old, the time when most brain connections are established. Incredibly, human brain cells evolved similarly to how they would in humans, fusing with rat blood vessels and growing to about six times their size. Modified, harmless rabies, which tends to move from cell to cell in the brain, showed that human brain cells connected with rat cells, partially integrating with rodent brain circuits.

So far, scientists have transplanted cells from three patients with Timothy syndrome into hybrid rat-human brains. While the cells of people with this brain disorder looked fairly normal in the lab, they were found to shrink in the real brain, shedding new light on the disease.

The work, published in the journal Nature, could similarly advance research into mental disorders such as schizophrenia or autism without the need for invasive procedures such as extracting tissue from the brain. The scientists transplanted up to three million human brain cells into the somatosensory cortex of newborn rats, the area responsible for receiving and processing sensory information such as touch.

Professor Tara Spiers-Jones, Associate Director of the Discovery Center for Brain Research at the University of Edinburgh, said: “This study has the potential to improve what we know about human brain development and neurodevelopmental disorders, but more work remains to be done to make sure that this type of graft is a reliable way.”

Christina DENISYUK.

Source www.dailymail.co.uk

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