THURSDAY, July 14, 2005 (HealthDay News) -- Imagine this scenario: Sometime in the not-too-distant future, scientists decide to test a potentially lifesaving treatment for Alzheimer's disease in a chimpanzee. The treatment involves the transplant of human neural stem cells into the ape's brain.
As their experiment progresses, the researchers notice the chimpanzee is changing in ways they never expected -- displaying signs of a much richer emotional and intellectual life as the transplanted human cells take root.
The scientists begin to feel uneasy about continuing their research. Has the animal gained an inner life that now makes her use in medical experiments morally wrong? Is this even possible?
Perhaps, concludes a special panel of ethicists, legal experts and scientists whose report on the ethics of neural stem cell research in non-human primates appears in the July 15 issue of Science.
"There was consensus on the view that there was indeed something to worry about. Ethically speaking, we cannot rule this possibility out," said panel member Mark Greene, an assistant professor of philosophy (and former veterinary surgeon) at the University of Delaware.
Greene and the other experts stressed that no experiments have as yet triggered this kind of shift in the moral ground between animal and human. However, based on evidence from the cell biologists, neuroscientists and primatologists taking part in the discussion, the panel agreed that the potential effects of human neural stem cell transplants in primate brains remains largely unknown.
Neural stem cells are progenitor cells that can grow into any number of brain cell types. Laboratories around the world are already hard at work investigating whether these cells might be used to re-grow brain cells lost to Alzheimer's, Parkinson's and other neurodegenerative illnesses.
Because they are the nearest relatives to humans, other primates are a logical choice for neural stem cell research.
"But the problem is that we can't rule out the possibility that engrafting human neural stem cells into a non-human primate would alter the emotional or cognitive life of the creature," said panel member Ruth Faden, director of the Berman Bioethics Institute at Johns Hopkins University.
This type of neurological change might also alter the animal's "moral status," which Faden defined as "the extent to which something is entitled to moral protection and respect."
It's easy to draw moral lines in the sand between humans and stones, insects and (for many people) rats. But things get tricky when higher-level animals are involved. The panelists decided to set aside the larger moral problem of whether animal experimentation itself is moral, and concentrated instead on this new question, borne of a new technology.
"A lot of people believe that humans are morally special, just by virtue of being human," Greene said. But he pointed out that we often give moral equivalency to other species -- at least fictional ones. "Look at science fiction, Star Trek -- you'll see all the time encounters with other species with rich mental lives, and we have no problem according them humanlike moral status."
So, real-life dilemmas could arise if scientific tinkering brought primates closer to "humanlike" moral status, he said. Such a change might be difficult to spot. "It's certainly not going to be talking," Greene said. "It might be that we suspect the animal's social needs have somehow changed, something like that."
The panelists agreed that scientists still understand very little about the inner lives of even well-studied primates like chimps or gorillas, so gauging any cognitive or emotional change would be tough. "But just because that change is subtle doesn't mean it's morally ignorable," Greene said.
While the group did not expect to reach a consensus on whether or not human neural stem cell transplants in non-human primates was morally correct, they were able to agree on rough guidelines that might help researchers avoid ethical quandaries.
Ideally, very small amounts of human neural stem cells, transplanted into the brains of fully grown, lower-order primates (i.e., not great apes) probably pose the least risk of cognitive enhancement approaching the morally ambiguous, they said.
"At the other end of the spectrum, if we are talking about an embryonic or fetal chimpanzee or bonobo, or some other great ape that's still developing, we can't rule out the possibility," Faden said. "Those human neural cells might integrate into the construction and function of the animal's brain, altering its experience."
She stressed that the panel's work was not about coming to any certainties on this issue, but simply to start discussion and to alert researchers that changes in an animal's "moral status" could potentially occur.
In the end, Faden said, researchers simply need to learn much more about man's closest evolutionary cousins before any definite recommendations can be made.
"This is an extraordinary puzzle," Faden said. "How can we possibly know what the inner life of another species is when we aren't privileged to the inner life of even our fellow humans? With other species, we can't even ask the simple question 'How do you feel?' "
For an insight into how primates aid scientific research, head to the Yerkes National Primate Research Center.