Over time, the injected human stem cells matured to reveal behavioral patterns not typically seen in normal rats.
A new study published in the journal Nature Wednesday by a team of researchers from Stanford University reveals that injecting human stem cells into the brains of rats revealed changes in the behavior of the rats after a specific period that allowed the brain cells to mature.
The study began seven years ago with the meticulous experiment of injecting simplified versions of human brain tissue from stem cells into the somatosensory cortices of the brains of newborn rats. These specific parts of the brain receive sensory information about pain and touch.
Over time, the cells matured to reveal behavioral patterns not typically seen in normal rats.
For example, rats started licking a beak for water whenever their brains were stimulated with the use of blue light lasers. The researchers also used a puff of air to grow the rats’ whiskers and then watched the reaction of human neurons.
Sergiu Pașca, one of the study’s authors and professor of psychiatry and behavioral sciences at Stanford, told sources “We found that human neurons respond very quickly after stimulating the whiskers. In fact, more 70% of human neurons are engaged in some form of activity within a second or two of this stimulation, which tells us they’re probably wired.”
Pașca added that human neurons had become “part of the rat circuit” and that when stimulated, they “twitch” under the microscope.
Over a period of eight months after the injection, the researchers noticed that the human neurons grew up to six times their original size, which occupies almost a third of a single hemisphere in the brains of rats.
Contrary to scientists’ expectations, none of the rats showed signs of seizures or epilepsy. More than 70% remained alive one year after the injection.
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This research is the latest in a series of studies and trials aimed at observing the development of human cells in animals.
For example, in 2006, developmental biologist Ali Brivanlou and a research team from Rockefeller University cultured human embryos in mouse tissue.
Then, in 2013, a Belgian research team implanted human neurons into newborn mice, which led to the creation of functional brain circuits.
Another researcher from the Salk Institute for Biological Studies conducted a similar study in 2018 by grafting human brain-like structures into adult mice.
According to Brivanlou, the innovation brought by the Stanford study lies in its ability to develop complex three-dimensional structures that represent the human cortex.
Brivanlou said culturing such a type of tissue “hasn’t been done very often; in fact, perhaps not to the level of precision described in this paper.”
But scientists have instead been scrambling to realize that such a study would give them a better understanding of how genetic mutations influence brain circuitry and alter behaviors.
It is hoped that the results can help certain studies on psychiatric disorders, autism or neurodegenerative diseases such as Parkinson’s or Alzheimer’s, as well as the development of new treatments.
Brivanlou added that it can “open the doors to a tremendous medical and fundamental understanding of how the brain works and, at the same time, what happens when things aren’t working quite well.”
For example, they used their research to study Timothy syndrome, a rare genetic condition in humans that can lead to life-threatening abnormal heartbeats and can also lead to autism.
Tissues from three carriers of the disease were transplanted into the brains of baby rats.
They observed that these specific cells did not grow as large inside rats and were not as structurally complex as other human cells. This proved that the genetic mutations responsible for Timothy syndrome in humans slowed brain development in rats.
But researchers have not yet understood why such mutations alter the behavior of rats.
According to Pașca, although scientists have a considerable amount of information about the types of genes that cause certain psychiatric disorders, they don’t have much knowledge about what these genes change in the brain, or what factors are not genetics that contribute to neurological disorders. .
Hence the interest in studying Timothy syndrome since it is caused by the mutation of a single gene responsible for helping the brain to process electrical signals.
Brivanlou has not ignored the ethical questions that accompany such research.
“How much of a human cell can you put in a mouse embryo for that embryo to still be called a mouse?” I think that’s a very legitimate question that needs to be addressed,” Brivanlou said.
However, the benefits could make the experiments worth pursuing.
“If you have a way to save someone’s life or cure someone’s illness, or at least provide some kind of therapy to minimize pain or extend the person’s life, you should be allowed to exercise it,” Brivanlou said.
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