The brains of dead pigs have been somewhat revived by scientists hours after the animals were killed in a slaughterhouse.

The Yale University research team is careful to say that none of the brains regained the kind of organized electrical activity associated with consciousness or awareness. Still, the experiment described Wednesday in the journal Nature showed that a surprising amount of cellular function was either preserved or restored.

The implications of this study have staggered ethicists, as they contemplate how this research should move forward and how it fits into the current understanding of what separates the living from the dead.

"It was mind-blowing," says Nita Farahany, who studies the ethics of emerging technologies at Duke Law School. "My initial reaction was pretty shocked. It's a groundbreaking discovery, but it also really fundamentally changes a lot of what the existing beliefs are in neuroscience about the irreversible loss of brain function once there is deprivation of oxygen to the brain."

The brain is extremely sensitive to a lack of oxygen and shuts down quickly. But researchers have long known that viable cells can be removed from post-mortem brains hours after death, says Nenad Sestan, a neuroscientist at the Yale School of Medicine in New Haven, Conn.

Such cells can be studied in a lab dish, Sestan says, "but the problem is, once you do that, you are losing the 3D organization of the brain."

He and some colleagues wondered whether it might be possible to study brain cells while leaving them in an intact organ. Doing so meant somehow supplying them with oxygen, nutrients and various other cell-protective chemicals.

The scientists have spent the past six years developing a technique to do that, testing their methods on around 300 pig heads they obtained from a local pork processing center.

"This really was a shot-in-the-dark project," says team member Stefano Daniele. "We had no preconceived notion of whether or not this could work."

After deciding on the final version of their technology, which they call BrainEx, they did a detailed study using 32 pig heads. Daniele says that while at the slaughterhouse, he and fellow researcher Zvonimir Vrselja flushed the brains to clear out residual blood and to cool down the tissue.

Back at the lab, they removed the brains from the pigs' heads and placed the isolated brains in an experimental chamber. The researchers hooked key blood vessels up to a device that pumped in a specially formulated chemical cocktail for six hours, starting about four hours after the pigs had been killed.

These brains ended up looking dramatically different from pig brains that were left alone to deteriorate. "We found that tissue and cellular structure is preserved and cell death is reduced. In addition, some molecular and cellular functions were restored," Sestan says. "This is not a living brain, but it is a cellularly active brain."

The researchers' approach offers a new way to study brain diseases or injuries in the lab and to explore the basic biology of the brain. "We could actually answer questions that we can't now," Vrselja says.

"This is a real breakthrough for brain research. It's a new tool that bridges the gap between basic neuroscience and clinical research," agrees Andrea Beckel-Mitchener of the National Institute of Mental Health who works with the BRAIN Initiative. The BRAIN Initiative, which started in 2013 to accelerate neuroscience research, provided funding for the work.

The researchers emphasize that the goal was definitely not to restore consciousness in these pig brains. "It was something that the researchers were actively worried about," says Stephen Latham, a Yale bioethicist who worked with the team.

The scientists constantly monitored the pig brains' electrical activity, Latham says. If they had seen any evidence that signals associated with consciousness had emerged, they would have used anesthesia and cooling to shut that down immediately.

"And the reason is that they didn't want to do an experiment that raises the ethical questions that would be raised if consciousness were being evoked in this brain," Latham says, "without first getting some kind of serious ethical guidance."

The special solution pumped into the brains included the anti-seizure drug lamotrigine, which is known to block or dampen neuronal activity. That's because "the researchers thought that brain cells might be better preserved and their function might be better restored if they were not active," Latham says.

But tests done on single cells taken from the pig brains, which involved washing off the solution, showed that individual cells were capable of electrochemical responses. So it's unclear whether the team would have seen global electrical activity linked to consciousness in the pig brains if the neuronal-activity blocker had been left out of the treatment or if the blocker had been removed after cells had partly revived.

"That's a very important question, and one that we have discussed at length," Daniele says. "We cannot speak with any scientific certainty to that point since we did not run those experiments."

The potential ethical questions raised by this research range from how to protect animal welfare to how it might affect organ donation from people declared brain-dead.

"The science is so new that we all need to work together to think proactively about its ethical implications so that we can responsibly shape how this science moves forward," says Khara Ramos, director of the neuroethics program at the National Institute of Neurological Disorders and Stroke.

A few years ago, the Yale researchers consulted with a neuroethics working group convened by the National Institutes of Health's BRAIN Initiative. That's how Farahany learned of the research. She says these results need to be replicated in other labs to see whether they hold up.

But if they do, the findings challenge a lot of assumptions that underlie legal and ethical controls on experiments.

"If it's a dead animal, it's not subject to any research protections because you wouldn't expect that it would suffer from any pain or distress or need to be thought about in terms of humane care," Farahany says. But if that animal's brain can be even partially revived, she asks, then "what do we need to do immediately, today, in order to ensure that there's adequate protections in place for animal research subjects?"

What's more, she adds, "immediately people are going to recognize the potential of this research. If, in fact, it is possible to restore cellular activity to brain tissue that we thought was irreversibly lost in the past, of course people are going to want to apply this eventually in humans."

While there are protections in place for human research subjects, that's not so much the case for dead human tissue, says Christine Grady, chief of the department of bioethics at the NIH Clinical Center.

"Once a human dies and their tissue is in a laboratory, there are many fewer restrictions on what can be done," Grady says. "It is interesting to think about this issue in light of this experiment."

In a commentary that accompanied the research paper in Nature, Farahany and her colleagues Henry Greely and Charles Giattino say the work reminds them of a line from the 1987 movie The Princess Bride: "There's a big difference between mostly dead and all dead. Mostly dead is slightly alive."

Research like this could complicate the effort to secure organs for transplant from people who have been declared brain-dead, according to another commentary written by Case Western Reserve University bioethicists Stuart Youngner and Insoo Hyun.

If people who are declared brain-dead could become candidates for attempts at brain resuscitation, they write, "it could become harder for physicians or family members to be convinced that further medical intervention is futile."

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