Researchers transplant human neurons into rats

Stanford University scientists transplanted human brain cells into baby rats in order to study developmental disorders like autism and schizophrenia. The study, published on Oct. 12 in Nature, adds to the team’s previous research on creating poppy seed-sized clusters of human brain cells called organoids. According to Dr. Sergiu Pasca, a senior author of the study and psychiatry professor at the Stanford School of Medicine, although human brain cells have been grown in adult rodents before, this is the first time organoids have been put into baby rat brains, creating the most realistic and complex model yet of how a human brain functions. The organoids grew new connections with the rats’ existing brain circuits, which allowed the human neurons to detect the rat’s feelings. For instance, when researchers blew air on the rats’ whiskers, their organoids responded to the stimuli. Because the organoids also wired themselves into the rats’ reward and motivation systems, the rats could be trained to drink water when they received this sensory information. The team utilized their new findings in a separate experiment, in which they took skin cells from volunteers and used chemicals that mimicked a developing brain environment to change them into neurons. They implanted these cells in both sides of the rat’s brain: one side had healthy brain cells, while the other had brain cells from a volunteer with Timothy syndrome, a heart condition that causes patients to exhibit  autistic spectrum disorders. Around half a year later, the results showed a contrast between the activity of the two sides. When compared to the healthy side, the Timothy syndrome neurons grew smaller and developed shorter extensions. However, this research also created an ethical dilemma — the team did not find evidence of the rats experiencing pain, nor were the rats any smarter compared to normal ones, but this may not be true if the same procedure were done on close relatives of humans, where the organoids could influence primates’ mental processes. Even so, according to University of Pennsylvania neurosurgeon Dr. Isaac Chen, who was not part of the study, these new findings potentially lead the way for future medical breakthroughs in which patients with brain injuries could be injected with organoids that grow to repair the damage.