Scientists Successfully Transplanted Human Brain Cells Into Baby Rats. Now Other Scientists are Afraid of Creating Super Rats

The study has caused controversy. 

If inflation, the possibility of a nuclear conflict, or climate change is making you nervous, look at it this way: At least the world hasn't been overrun by Super Rats. Yet. Some scientists worry that a souped-up version of the vermin may be headed to trash cans and pizza places near you, after a group of researchers successfully transplanted human brain cells into baby rats. Read on to find out more about the experiment that's giving nightmares to some in the scientific community. 

What The Study Found


In a study published in the journal Nature on Wednesday, scientists injected human nerve cells into the brains of rats. They found that those neurons continued to grow, forming connections with their host's brain cells and guiding their behavior. In the experiment, clusters of human brain cells—circuits known as brain organoids—were grown in a lab, then transplanted into the brains of newborn rats. Those cells ultimately grew to comprise one-sixth of the animals' brains. The researchers' intent was to learn more about human neuropsychiatric disorders. "The ultimate goal of this work is to begin to understand features of complex diseases like schizophrenia, autism spectrum disorder, bipolar disorder," Paola Arlotta, a neuroscientist at Harvard, told NPR. But the study has caused controversy. 

Are Scientists Making Rats More Human?


​​"It's an important step forward in progress into [understanding and treating] brain diseases," Julian Savulescu, a bioethicist at the National University of Singapore, told MIT Technology Review. But the findings also raise an ethical conundrum, he said—what does it mean to "humanize" animals? "There is a tendency for people to assume that when you transfer the biomaterials from one species into another, you transfer the essence of that animal into the other," bioethicist Insoo Hyun told NPR, noting that even the most advanced brain organoids are still extremely basic versions of a human brain.

Ethical Questions Abound


Is a rat with human brain cells still a rat? "The question is: What would be the criteria for a species change?" Jeantine Lunshof, a philosopher and ethicist at the Wyss Institute for Biologically Inspired Engineering at Harvard University, told MIT. Scientists generally believe some change in cognition would be necessary; Lunshof points out that only a small number of brain cells were used in this study.

"Creating An Enhanced Rat"


But perhaps the more dramatic question is: Are scientists unwittingly creating a real-life version of an '80s horror movie (that was somehow never made)? "It raises the possibility that you're creating an enhanced rat that might have cognitive capacities greater than an ordinary rat," said Savulescu. 

Human Cells Don't Make Rats More Human, Yet


Giorgia Quadrato, a neurobiologist at the University of Southern California who was not involved in the study, told the New York Times that the transplanted human brain cells didn't make the rats more human: They scored the same on learning tests as other rats. "They are rats, and they stay rats," said Quadrato. "This should be reassuring from an ethical perspective."

Michael Martin
Michael Martin is a New York City-based writer and editor. Read more
Filed Under
 •  •