Lab mice whose brains were injected with cells from schizophrenia patients became afraid of strangers, slept fitfully, felt intense anxiety, struggled to remember new things, and showed other signs of the mental disorder, scientists reported on Thursday.

The latest advance in “chimeras,” animals created by transplanting cells from one species into another, demonstrated the value of the technique, scientists not involved in the study said, but is likely to draw renewed attention to a controversial field that opponents see as deeply immoral and undermining the natural order.

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That success represents a dilemma for neuroscience, said bioethicist Hank Greely of Stanford University: “When you make a chimera with human cells in its brain, the closer the resulting brain is to human” in structure and function and “the greater the ethical and public concern.” But because the mice had human glia but not human neurons, he said, “we would have fewer concerns about any conceivable ‘humanization’ of the mouse.”