The above picture shows a rat brain that has been transplanted with human tissue (highlighted)
- Scientists at Stanford used human stem cells to create brain cells in laboratory
- These cells connected to form ‘organoids’ – which were transplanted in baby rats
- Such experiments are moral grey area due to fears animals will think like people
To comprehend disorders like autism and epilepsy better, scientists have developed hybrid human-rat brains.
Because of worries that animals might begin to think more like humans as a result, implanting human cells into animal brains is morally dubious.
However, experts contend that observing what goes wrong with human cells in a real brain as opposed to a lab is the greatest method to learn about neurological and mental illnesses.
Stanford researchers developed brain cells in the laboratory using human stem cells, which can differentiate into any type of cell in the body.
Organoids were created when these cells were joined to one another.
In order for the cells to develop and function normally and for the researchers to learn more about Timothy syndrome, a hereditary disorder that causes a form of autism and is associated with significant heart difficulties, the researchers implanted these organoids into the brains of newborn rats.
This was so successful that 70% of the human brain cells implanted in rats responded when researchers tickled their whiskers.
Human brain cells that had been modified to be light-sensitive may even be used to affect the behavior of the rats.
Blue light was utilized to stimulate the human cells in the brains of rats every time they drank water from a spout to relieve their thirst.
Just turning on the brain cells after two weeks of this had the rats lick the water spout.
Other moral questions can be raised by the notion that rats with hybrid brains can be managed in this manner.
The discovery, according to the researchers, will also aid in the testing of medications for brain illnesses.
Sergiu Pasca, professor of psychiatry and behavioral sciences at the Stanford School of Medicine, and senior author of the rat study, said: ‘We can now study healthy brain development as well as brain disorders understood to take root in development in unprecedented detail, without needing to excise tissue from a human brain.
‘We can also use this new platform to test new drugs and gene therapies for neuropsychiatric disorders.’
When it comes to using human brain tissue in primates with more human-like brains, such as chimpanzees or macaques, the researchers have said no.
Using monkeys for comparable study, according to Professor Pasca, would be “concerning.”
Rats have brains that develop around 20 times quicker than those of humans, who have far shorter lifespans. This limits the degree to which human brain cells may ingest rat brain cells.
According to Professor Pasca, there would be much better integration in primates: “I think we first have to leverage the technology that we’ve developed, put it into play, see what it can actually teach us about the development of the human brain, about evolution, about disease, and whether we can use it systematically to test drugs – and then see what the limitations are at that time and think whether any other species would be necessary.”
‘In my opinion, at this time transplantation into primate is it’s not something that we would do and that I would encourage doing.’
The researchers’ “organoids” were grown in the lab for two months until they began to resemble the human cerebral cortex.
Then, they were implanted into the brains of two to three day old rat pups, which is when the majority of brain connections are established.
Amazingly, the human brain cells connected to blood arteries in the rat and grew to nearly six times the size they would have in the lab. They also evolved similarly to how they would in a person.
The human brain cells have connected to the rat ones, partially integrating with the rodent brain circuits, as demonstrated by a modified harmless rabies virus that jumps from brain cell to brain cell.
In the rat brains, the researchers claimed to have “set up shop,” constructing “living laboratories.”
Three Timothy syndrome patients’ cells have so far been implanted into the hybrid rat-human brains by the researchers.
While the cells from patients with this brain ailment appeared quite normal in the lab, it was discovered that they shrank in a real brain, providing new insight into the disorder.
The research, which was published in the journal Nature, may similarly assist the study of mental illnesses like schizophrenia or autism without the use of intrusive techniques like brain tissue extraction.
The somatosensory cortex, which is responsible for receiving and processing sensory information such as touch, was implanted with up to three million human brain cells in newborn rats.
This research has the potential to advance our understanding of human brain development and neurodevelopmental disorders, but more research is needed to ensure that this type of graft is a reliable procedure, according to Professor Tara Spires-Jones, deputy director of the Centre for Discovery Brain Sciences at the University of Edinburgh.
‘I also agree with the experts who wrote a commentary accompanying the paper who point out that these experiments pose several ethical questions that should be considered moving forward, including whether these rats will have more human-like thinking and consciousness due to the implants.’
by: Miss Cherry May Timbol – Independent Reporter
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