Do you believe it? The human and mouse mixed brain appeared, and the human neurons received stimulation and the mice responded quickly! A recent study showed that the microhuman brain transplanted into mice could send signals and direct mice to respond (Figure 1). For example, if you touch the mouse’s beard, your brain cells can provide corresponding feedback normally. This research result proves that the neurons grown in human stem cells can interact with the nerve cells of living rodents, which can not be underestimated in promoting the process of human brain disease therapy .
Figure 1 The human brain organoid (bright green) was transplanted into the brain of newborn rats, creating a hybrid brain with neuronal interfaces (Photo source: Nature)
Seven years ago, researchers at Stanford University in the United States cultivated human brain tissue with human stem cells in the laboratory, and then injected the tissue into the brain of newborn rats. The results, published on Nature on October 12, show that brain-like human tissue binds to the brain tissue of mice and then continues to grow, and that these brain cells appear to affect the behavior of mice.
The human "mini brain" was transplanted into rats
grows to 6 times larger
Researchers inject human tissue cultured with human stem cells into the rat's somatosensory cortex, that is, the area where the mice receive and process sensory information such as touch or pain (Figure 2). After about two weeks of training, whenever the researchers stimulate human neurons in mice with blue light lasers, the mice will start licking their mouths and looking for water sources. This means that human cells interact well enough to help drive animal behavior. Additionally, when researchers poked mice’s beards, they found that human cells in the cortex responded, suggesting that these cells were able to obtain sensory information.
Figure 2 Transplant human cortical organoids in the developing rat cortex (Photo source: Nature)
One of the researchers said: "After we stimulate our beard, the response of human neurons becomes very fast. In fact, more than 70% of human neurons start some form of activity around one second after being stimulated, which proves that they interact." Human neurons have become part of the mouse brain circuit, and under the microscope, these neurons flash with "light".
After the human "mini brain" was transplanted into rats, human neurons grew to 6 times larger in about 8 months, accounting for about one-third of the single hemisphere of the rat brain. These transplanted rats did not experience health problems such as epilepsy that researchers were very worried about. One year after transplantation, more than 70% of the rats were still alive.
Research exploration began decades ago, and
can help treat autism
This study is the latest case of trying to transplant human cells into animals. The scientific exploration of human cell transplantation into animals began decades ago, with a series of explorations succeeding (Figure 3).
Figure 3 Process of human cell transplantation into animals | Mapmaking: Biological exploration editorial team
Brivanlow said that Stanford University research is novel and landmark. This study can cultivate complex 3D structures representing the human cerebral cortex. The cerebral cortex is the most important part of the brain and the place where the cognitive center is located. The researchers hope that the ability of human-mouse transplants can help humans better understand how gene mutations affect brain circuits and how they can affect how humans think and behave.
This type of rat model can also be used to study neurodegenerative diseases such as mental illness, autism, Parkinson's disease or Alzheimer's disease, and can even be used to determine new treatments or test their effectiveness .
Rusty Gage, a neuroscientist at the Solk Institute for Biology in La Jolla, California, is pleased to see the results of the Stanford University trial. In the experiment, because the brains of newborn infant mice are more plastic than those of adult animals, they are able to better receive new cells. But Gage said: There are still challenges, but what is certain is that the prospects for human brain transplantation programs are limitless.
The challenge currently faces is moral ethics, and researchers worry that creating a “hybrid” of rodents and human brains may harm animals, or create animals with human brains. Last year, a report released by National Academy of Sciences , the School of Engineering and the School of Medicine showed that human brain organoids are still too primitive to gain awareness and ability similar to artificial intelligence and need to be regulated by law. Pascal said that his team's organoid transplants did not cause problems such as seizures in rats or memory loss, and did not appear to significantly change animal behavior.
But Alota, a member of the National Academy of Sciences team, said that with the advancement of science, problems may arise. “It can’t be discussed only once and let it develop,” Alotta added, adding that needs to weigh concerns about human organoids with the needs of patients with neurological and mental illnesses. The brain organoids and human-animal hybrid brain can reveal the underlying mechanisms of many diseases and provide researchers with treatments for diseases such as schizophrenia and bipolar disorder .
Written by | Qiao Weijun
Typesetting | Qiao Weijun
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Reference materials:
[1]https://www.nature.com/articles/s41586-022-05277-w#author-information
[2]https://tech.creaders.net/2022/10/13/2535641.html
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