Is it ethical to put human brain cells in a rat?

Researchers have successfully transplanted human neurons into the
brains of rats. The recent, groundbreaking study described how the
human cells took root inside the rat brains, hooked up to their
blood supplies and tapped into neural circuitry. Rather than create
a kind of super-rat, the ultimate aim is to better understand
neuropsychiatric disorders such as epilepsy and schizophrenia, and
examine the effects of drugs in real time. But do the potential
benefits outweigh the ethical questions that come with combining
human cells with other animals? Ian Sample speaks to Prof Julian
Savulescu about how the scientists managed to transplant the
neurons, what this means, and how we decide where to draw the line
in such an ethically complex field of research. Help support our
independent journalism at theguardian.com/sciencepod