Introduction: Scientists want to use tiny brain-like structures grown from human stem cells, brain organoids, to study neurodegenerative and neuropsychiatric diseases that humans develop.

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Author: Sophia

Introduction: Scientists want to use tiny brain-like structures grown from human stem cells , to study neurodegenerative and neuropsychiatric diseases developed by humans. But so far, organoids have only mimicked the human brain. They do not develop blood vessels and therefore cannot obtain nutrients, which means they do not thrive for a long time. And they do not get the nutrients needed to grow adequately: In the brain of human babies, the growth of neurons and the development of connections with other neurons comes from sensory input.

A new study shows that tiny human brain structures transplanted into mice can send signals and respond to environmental cues picked up by mice’s beards. , a proven that human stem cell-grown neurons can interact with the nerve cells of living rodents, which may lead to a way to test treatments for human brain diseases. The study was published in the journal Nature.

https://www.nature.com/articles/d41586-022-03238-x

Major discovery

01

To provide this stimulation and support to brain organoids, Sergiu Pasca, a neuroscientist at Stanford University in California, and his colleagues cultivated these structures from human stem cells and injected them into the brains of newborn teenage mice, hoping that human cells would grow as the mouse’s own cells grow . The team placed organoids in a brain region called the somatosensory cerebral cortex, which receives signals from rat beards and other sensory organs, and then passes them to other brain regions that interpret the signals domain .

Human brain cells mature much slower than rat cells, so researchers have to wait more than six months for the organoids to be fully integrated into the rat brain. But when they examined the animal's brain at the end of that time, they found the integration to be very successful, almost like adding "another transistor " to the circuit.

Paola Arlotta excitedly said, “This is an important step for organoids to tell us more complex characteristics of the brain, although transplant procedures may still be too expensive and complex to be a standard research tool.” Arlotta added, “The next step in will be to study how individual human neurons, not just how fully developed organoids are integrated into in rat brains.”

behavioral trigger

02

researchers described how they genetically engineered neurons in organoids, and the team trained mice to lick their mouths to receive water when they turned on the light. Later, when the researchers shine light onto the mixed brain, the mice are prompted to lick their mouths, meaning that the human cells have been integrated well enough to help drive some of the animal's behavior. Additionally, when researchers adjusted the mice’s beards, they found that human cells in the sensory cortex responded, suggesting that these cells were able to obtain sensory information .

human neurons produced by stem cells and transplanted into rat brains (right) grow more fully than those cultured in Petri dishes (left).

To demonstrate their prospects for their work in studying brain diseases, Pasca and his colleagues also created brain organoids from stem cells of three people with Timothy syndrome, a condition that may cause symptoms similar to autism. These tiny structures look the same as any other brain organoids cultivated in in dishes, but when the researchers transplanted them into rats, they didn't look as big as others, and their neurons wouldn't fire in the same way.

Rusty Gage I'm glad to see these results. In 2018, he and a team of researchers discovered that human brain organoids transplanted by can be integrated into the brains of adult mice. Mice live less than rats, but the brains of neonatal young mice are more malleable than those of adult animals because they are able to better receive new cells .

Moral Challenge

03

"We are facing challenges," Gage said."But I do believe that porting programs will be a valuable tool." Some of the challenges of

are ethical. There are concerns that creating hybrids of rodents and humans may harm animals, or create animals with human brains. Last year, a team organized by National Academy of Sciences , the School of Engineering and the School of Medicine published a report that concluded that human brain organoids are still too primitive to become conscious, unable to obtain human-like intelligence or other capabilities that may require legal supervision. Pascal said his team's organoid transplants do not cause problems such as seizures or memory loss in rats, and it also does not appear to significantly change the animal's behavior.

But Alota, a member of the National Academy of Sciences team, said that with the advancement of science, problems may arise. We cannot discuss it once and let it develop. We need to weigh future medical concerns about human organoids with the needs of patients with neurological and mental illnesses. brain organoids and human-animal hybrid brains can reveal the underlying mechanisms of these diseases and allow researchers to test treatments for diseases such as schizophrenia and bipolar disorder .

Reference materials:

https://www.nature.com/articles/d41586-022-03238-x

Note: This article aims to introduce the progress of medical research and cannot be used as a reference for treatment plans. If you need health guidance, please go to a regular hospital for treatment.

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