To Study Disease, Scientists Put Human Brain Cells into Rats

Scientists have transplanted human brain cells into the brains of baby rats, where the cells grew and formed connections.

The research is part of an effort to study human brain development and diseases affecting this most complex of organs.

Dr. Sergiu Pasca of Stanford University in California was the lead writer of a study describing the work. It appeared recently in the publication Nature.

"Many disorders such as autism and schizophrenia are likely uniquely human," Pasca said. But the human brain has not been very easy to study. Research that does not involve taking tissue out of the human brain is a "promising" area for trying to deal with these conditions, Pasca added.

The research builds upon the team's earlier work creating brain "organoids." These organoids are very small structures similar to human organs. Organoids have been made to represent organs such as the liver, kidneys and prostate.

To make the brain organoids, Stanford University scientists changed human skin cells into stem cells. They then caused the stem cells to become several kinds of brain cells. Those cells then grew in number to form organoids that resemble the cerebral cortex, the human brain's outermost layer. The cerebral cortex is linked to memory, thinking, learning, reasoning and emotions.

Scientists transplanted those organoids into baby rats that were two to three days old. At that age, brain connections are still forming. The organoids grew so that they eventually occupied a third of the hemisphere of the rat's brain where they were implanted. Neurons from the organoids formed working connections with the brain.

Human neurons have been transplanted into rodents before, but in adult animals, usually mice. Pasca, who is a professor at the Stanford School of Medicine, said this is the first time these organoids have been placed into the brains of baby rats.

To examine how the idea might be useful for studying human health, scientists transplanted organoids into both sides of a rat's brain. One side had organoids created from a healthy person's cells and the other side had cells of a person with Timothy syndrome, a rare genetic condition linked with heart problems and autism.

Five to six months later, they saw effects of the disease in the activity of the neurons. There were differences in the two sides' electrical activity, and the neurons from the person with Timothy syndrome were much smaller and did not grow as many extensions that pick up signals from nearby neurons.

The researchers, whose study was paid for partly by the National Institutes of Health, said they could do the same kinds of experiments using organoids made from the cells of people with disorders such as autism or schizophrenia. Such studies could help them learn new things about how these conditions affect the brain.

Dr. Flora Vaccarino of Yale University said the study moves the field forward.

"It's extremely impressive what they do here in terms of what these cells can actually show us in terms of their advanced development ... in the rat," said Vaccarino, who was not involved with the study.

I'm John Russell.

Laura Ungar reported on this story for the Associated Press. John Russell adapted it for VOA Learning English.

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transplant – v. medical : to move an organ or other part (such as a cell) from something and put it into something else

disorder – n. medical : a physical or mental condition that is not normal or healthy

uniquely – adv. belonging to or connected with only one particular thing

stem cell – n. a simple cell in the body that is able to develop into any one of various kinds of cells (such as blood cells, skin cells, etc.)

impressive – adj. deserving attention, admiration, or respect : making a good impression

advanced -- adj. far along in a course of progress or development