According to a study1, rats with implanted miniature human brain-like structures can transmit signals and react to environmental cues detected by the rats’ whiskers. It may be possible to test treatments for illnesses of the human brain as a result of the finding that neurons developed from human stem cells may communicate with nerve cells in living animals.
Brain organoids, which are tiny, brain-like structures created from human stem cells, are being researched by scientists with the purpose of understanding human neurodegenerative and neuropsychiatric illnesses. But organoids can only imitate human brains so much. They won’t survive for very long because they don’t grow blood vessels, which prevents them from receiving nourishment.
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Additionally, they lack the stimulation required to develop fully. In a human infant’s developing brain, sensory input plays a factor in how neurons grow and form connections with one another.
Sergiu Pasca, a neuroscientist at Stanford University in California, and his colleagues grew the structures from human stem cells and then injected them into the brains of newborn rat pups in the hopes that the human cells would grow alongside the rats’ own cells to provide brain organoids with this stimulation and support.
The somatosensory cerebral cortex, which receives signals from the rats’ whiskers and other sensory organs and then transmits them to other brain regions that interpret the data, is where the scientists implanted the organoids.
The researchers had to wait longer than six months for the organoids to fully integrate into the rat brains because human brain cells mature considerably more slowly than rat cells do. However, when they later looked into the animals’ brains, they discovered that the integration had been so effective that it was almost like adding “another transistor to a circuit,” Pasca remarked at a press conference on 10 October.
Has none of these people ever watched a single sci-fi movie? This does NOT end well . . . https://t.co/hMEdawyScC
— Glynn Washington (@glynnwashington) October 12, 2022
The findings thrill Paola Arlotta, a molecular biologist at Harvard University in Cambridge, Massachusetts. Although she believes that the transplanting method is probably still too expensive and complex to become a common research tool, she argues that it is a significant step in allowing organoids to tell us more intricate aspects of the brain. The following stage, says Arlotta, will be to determine how specific human neurons, rather than just fully-fledged organoids, are incorporated into the rat brain.
Behaviour Trigger
The researchers describe how they genetically modified the neurons in the organoids to fire when triggered with light from a fibre-optic wire inserted into the rats’ brains in their article, which was published in Nature on October 1st. When the light was turned on, the team taught the rats to lick a spout to receive water.
The rats were then stimulated to lick the spout when the scientists shone a light on the hybrid brains, indicating that the human cells had successfully assimilated and were now driving the animals’ behaviour. In addition, scientists discovered that when they adjusted the rats’ whiskers, human sensory cortex cells fired in response, indicating that the cells could pick up sensory information.
Pasca and his colleagues also developed brain organoids from the stem cells of three patients with Timothy syndrome, a genetic illness that can manifest symptoms resembling those of autism. This was done to show the potential of their research for researching brain disorders.
The microscopic structures had the same appearance as other brain organoids generated in a dish, but when the researchers implanted them into rats, they did not develop as well and their neurons did not fire similarly to those of other rats.
WRATH came out yesterday.🐀
And this article came out today.😬https://t.co/eokXxvvEJS
— Daniel Kraus (@DanielDKraus) October 12, 2022
The Salk Institute for Biological Studies in La Jolla, California, is home to neuroscientist Rusty Gage, who is pleased with the findings. He and a group of researchers discovered in 2018 that adult mice’s brains could integrate transplanted human brain organoids2.
Rats live longer than mice, so Pasca and his colleagues reasoned that the newborn rat pups’ brains would be more receptive to the new cells because they are more pliable than those of adult animals. There are obstacles in our path, Gage says. However, I do think the transplantation process will be a useful tool.
The difficulties include some ethical ones. People worry that producing rodent-human hybrids could hurt the animals or result in creatures with brains similar to humans. In a report published last year, a panel of experts from the US National Academies of Sciences, Engineering, and Medicine came to the conclusion that human brain organoids are still too immature to develop consciousness, intelligence comparable to that of humans, or other abilities that might call for legal regulation.
According to Pasca, the rats’ organoid transplants did not result in issues like seizures or memory loss, nor did they appear to dramatically alter the animals’ behaviour. But according to Arlotta, a member of the National Academies group, issues can appear as research develops. We can’t just talk about it once and move on, she argues.
She continues by saying that worries about human organoids must be considered against the need of those who suffer from neurological and psychological conditions. Human-animal hybrid brains and brain organoids may help scientists understand the mechanisms underlying these diseases and test potential treatments for illnesses like schizophrenia and bipolar disorder. According to Arlotta, “I believe that it is our duty as a society to do everything we can.”
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