Scientists used a laser to "fill" a rat's brain with blue light. The rodent, true to its previous two weeks of training, went through its glass box to find a tiny spigot, where it was rewarded – it drank water.
To all of us this would appear to be a very simple neuroscience experiment, except that the neurons that directed the rat to the water to quench its thirst contained no rat DNA.
Instead, they came from a human “mini brain” – a ball of human tissue called an organoid. Researchers at Stanford University School of Medicine had grown it in a lab and implanted it into the rodent's cortex months earlier.
The experiment – part of a study that was published Wednesday in Nature – is the first to describe human neurons influencing the behavior of another species.
The advance opens the door to using such human-rodent monsters to better understand how the human brain develops and what goes wrong in neurological and psychiatric conditions such as schizophrenia, autism and epilepsy. When Stanford scientists implanted organoids grown from cells from patients with a severe genetic brain disorder, they saw neurons grow abnormally.
Neuroscientist Tomasz Nowakowski, of the University of California, San Francisco, who uses brain organoids in his research on neurodevelopmental disorders, said:
"What's really important about this study is that it shows that brain organoids can complete their maturation trajectory when transplanted. So it really expands our toolkit to ask more nuanced questions about how genetic mutations lead to behavioral disorders.”
"Performing the experiments in very young rats whose cortices are not yet saturated with synapses," the article states, the researchers "found that human neurons were easily integrated into the rapidly developing animal brain."