Human brain cells have been successfully transplanted into rats, which may pave the way for a better understanding of brain development and mental disorders.

The human brain cells were grown in the lab, in clumps known as organoids, but for the first time researchers at Stanford University, in California, USA, have managed to inject the organoids into the brains of new-born rats.

The organoids were delivered to the brain region that processes sensory information, and the scientists observed that the human and rat brain cells became integrated.

The study showed that the human brain cells could drive the rats’ behaviour when activated, and that they also fired with electrical activity when the rats’ whiskers were stimulated.

Professor Sergiu Pasca, who led the research, said: “We can now study healthy brain development as well as brain disorders understood to take root in development in unprecedented detail, without needing to excise tissue from a human brain.”

However, ethical concerns have been raised in a recent article in Nature, asking whether the behaviour of the rodent-human hybrids could be significantly changed or possibly cause harm.

Another study, led by the University of Pennsylvania, also managed to integrate brain organoids with rats, and showed that this part of the rats’ brains could respond to visual stimuli, such as flashing lights, after three months.

H. Isaac Chen at Pennsylvania said: “We were not expecting to see this degree of functional integration so early.”

END