A Stanford-led research team connected human neurons to a rat's brain

Scientists put human cells into baby rat brains and watched them grow.

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A team of researchers led by Stanford University's Sergiu Paşca, Felicity Gore, Kevin Kelley and Omer Revah from the Hebrew University of Jerusalem reported their breakthrough research in Nature today.

Scientists have worked for years on ways to study neurological and psychological disorders in the lab by growing human brain cells in petri dishes, but their efforts have been met with limited success. It is possible to grow the brain cells, but they don't form the same types of connections that are found inside of the brain.

Starting about 15 years ago, scientists also learned that it was possible to coax human stem cells into so-called organoids - three dimensional clusters of tissue that can be crafted to demonstrate much of the complexity of complex biological organs.

The Stanford team created such organoids out of stem cells that were harvested from stem cells in the human skin. Having done so, the organoids were transplanted into the brains of days-old rat pups whose brains were still in the process of forming. After the transplants, the researchers monitored how the cells grew and connected to the rats' own biological systems.

What they found was that the tiny organoid grew inside the rats' bodies and reached a size that occupied roughly ¹/₃ of one hemisphere of the rats' brains. They also found that the cells inside the rats' bodies grew to a size that was approximately six times bigger than similar organoids grown in a dish. In addition to the size advantage, the cells in the rats' brains also formed stronger communications pathways than the cells in the dish. It is suggested that these benefits came from being nourished by the rats' blood by way of an organic connection to the rats' vascular systems.

Although the cells in the rats' brains duplicated many of the functions that are found in human brains, they did not achieve all of the characteristics of human or rat brain cells. For example, they neither organized themselves into multilayered structures that resemble the human cortex, nor organized themselves into barrel-like columns that would be found in a rat's somatosensory cortex. Additionally, the human neuron growth was not accompanied by emergence of other human brain-like tissues such as microglia or astrocytes.

Still, experts in the field say that this research indicates a potential path for future research that could be helpful in identifying neurological causes and treatments for things like autism, epilepsy, and a variety of psychiatric conditions. For example, Cambridge's Madeline Lancaster said, "This approach is a step forward for the field and offers a new way to understand disorders of neuronal functioning." Similarly, USC's Giorgia Quadrato said, "This is a much needed and elegant study that steers the field in the right direction of looking for approaches to advance the physiological relevance of human brain organoids to model later stages of human brain development."

It's probably obvious, however, that there would be ethical concerns associated with this type of work, too. One concern has to do with the well-being of the animals, and the other concern has to do with creating some sort of hybrid organism that has human-like qualities, especially qualities pertaining to consciousness and intelligence. Harvard's bio-ethicist, Insoo Hyun said that he's not concerned about this particular research because no enhanced capabilities were observed in the rats and because it followed the guidelines of the International Society for Stem Cell Research. He expressed concerns about a potential slippery slope, though, suggesting that things will get trickier if other research teams are tempted to perform similar experiments with higher order animals like primates. Another Harvard bio-ethicist, Jeantine E Lunshof expressed similar sentiments saying of the experiment, "It increases the usefulness of cerebral organoids for human brain disease.," and also noted that the human brain is far more complex than just a rat brain holding a clump of human brain cells.

References

• Human brain cells transplanted into baby rats’ brains grow and form connections
• Lab-Grown Human Brain Tissue Works in Rats
• Lab-Grown Human Cells Form Working Circuits in Rat Brains
• Maturation and circuit integration of transplanted human cortical organoids

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Thank you for your time and attention.

As a general rule, I up-vote comments that demonstrate "proof of reading".

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Steve Palmer is an IT professional with three decades of professional experience in data communications and information systems. He holds a bachelor's degree in mathematics, a master's degree in computer science, and a master's degree in information systems and technology management. He has been awarded 3 US patents.

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^{Pixabay license, source}

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