[ad_1]
The pigs came directly from the slaughterhouse, where workers had sliced their jugular vein and carotid artery and then decapitated them. But from four hours after the animals' brains stabilized and for the next six hours, the brain became … well, a little less dead, scientists from Yale University reported Wednesday. .
By attaching the brains to a specially constructed device and circulating artificial blood, the researchers claimed that they were able to restore certain molecular and cellular functions of the brain, including spontaneous electrical activity in the neurons and functions metabolic characteristics such as consumption. oxygen and glucose.
Although pork brains showed no organized electrical activity throughout the cortex associated with consciousness, sensory perception, pain, distress or other functions of the order Higher, the experience challenges a long-standing medical dogma and is likely to revive a heated debate on the subject. What is brain death, especially for the purpose of giving organs? Less controversial, the restoration system, called BrainEx, promises to give neuroscientists a better way to study brain wiring and function.
Scientists not involved in the study, who had heard the principal investigator present his preliminary results at closed meetings in 2017 and 2018, have described it with almost astonished terms, calling him " incredible "," very impressive "and" extremely significant ". Yale's team "showed that, at least at the cellular and molecular level, things are not so irreversible [after the brain is deprived of blood and oxygen] as we thought, "said neurologist James Bernat of Dartmouth College. I find that remarkable. They were able to restore brain activity a few hours after death and cessation of [blood] circulation, which was supposed to cause irreversible damage and loss of function ".
The potential of neuro-resuscitation
Like all scientists familiar with the study, Bernat quickly added that "there is a major difference between the restoration of cellular and molecular activity in the brain and the resuscitation of global brain function, what they could not do ". Or, as told journalist Nenad Sestan, a neuroscientist at Yale, who led the study, during a conference call, "This is not a living brain. C & # 39; Is a cell-active brain. "
Nevertheless, Andrea Beckel-Mitchener of the National Institute of Mental Health has described technology as a "breakthrough for brain research". Restoring a cellular function "has never been done before" in a large brain supposed to have died of mammals, she said. Keeping the cells alive and active, she added, the system promises scientists to study the complex circuit connections "and functions that are lost when the specimens are kept from another way". For example, neither cultured cultured brain cells nor slices of post-mortem brain tissue reveal much of the neural circuits and activity underlying thought.
The further development of BrainEx may one day support "neuroresuscitation", reversing the damage caused by stroke and other brain damage. "If it turns out that the system is safe in a living person, it is possible to improve the recovery of brain function," said Bernat.
Beyond any scientific or medical application, the work raises profound philosophical questions. In an essay accompanying the article, published in Nature, three bioethicists wrote that it "challenges long-standing assumptions about what makes an animal – or a human – alive." ".
Scientists have restored some cellular functions in the brains of pigs, but not their consciousness
For their experience, Sestan and his colleagues bought nearly 300 pork heads at a slaughterhouse near the Yale New Haven Campus for nearly 10 years while working on the BrainEx optimization – "ex Means ex vivo or "on the living." Eventually, the team connected 32 brains of pigs to the system – a blur of software, mixers, fluid tanks, pumps, heaters, filters, etc. for Rube Goldberg – whose role was to mimic pulsed blood flow with a special carotid artery blood four hours after killing the animals.They kept the brains connected for six hours and at normal, not cryogenic temperatures.
Other brains were connected to BrainEx but did not receive the infusion solution, or were not connected at all. In comparison, brains connected to BrainEx and infused showed "dramatic differences," said Sestan. Brain cells metabolized oxygen and glucose in the same way as living cells. Neurons have triggered electrical gusts carrying information, called action potentials, both spontaneously and in response to an electrical stimulus, as do living brains. The blood vessels have dilated in response to the drugs that cause this reaction in living brains. Glia, the immune cells of the brain, caused an inflammatory reaction of life when provoked. Mitochondria, which provide energy to cells, were intact inside neurons, as was myelin, the fatty sheath that insulates neurons so that they can conduct electrical signals.
Overall, many more cells remained alive, the circulatory system functioned, and the size, shape, and disposition of neurons and other cells appeared normal compared to brains that did not receive BrainEx treatment.
In a scientific underestimation model, the authors write that the brains of large mammals have "an underestimated ability to restore microcirculation and molecular and cellular activity after a prolonged post-mortem interval". In other words, in some cases, the death of a brain can be neither permanent nor irreversible.
"We never imagined we would get to that point, … restaurant cells at this level" of functionality, said Sestan. Neurological dogma has long held that brain cells die irreversibly and minutes after the blood stops flowing, just as pigs do. "But we were able to restore some cellular and molecular functions" after four hours of oxygen loss, he said. "We were really surprised."
Although he insisted that the lack of electrical activity on the brain scale meant that the pig brain had not regained consciousness and so could not feeling pain or distress, it was not won in advance. Scientists were sufficiently concerned about this possibility that they were ready to administer anesthesia to the brain or to cool it down drastically to stop such activity.
"It's the elephant in the room: the consciousness," said philosopher Jonathan Moreno of the University of Pennsylvania, who reviewed the paper for Nature and heard Sestan describe his findings as "the most important thing in the world." last year at a meeting at the National Institutes of Health, whose BRAIN initiative was funded in part. the research. "Neuroscience is a big fight to understand what people mean by conscience and what criteria should be used. [electrical activity in the dead pig brains] a small piece of consciousness? A small degree of consciousness? "
To complicate the question of whether consciousness can be restored in a dead brain, BrainEx liquid contains a chemical that inhibits neuronal activity. Without this, could the brains of pigs have shown the type of brain electrical activity associated with consciousness? "They could have," said Moreno. "This must make you ask, what would be the moral status" of a brain once dead but (partly) "restored"?
Beyond the philosophical and ethical concerns, BrainEx could complicate the already charged debate on brain death and organ donation, experts said.
Stuart, a bioethicist, questions the hypothesis that the brains of large mammals will irretrievably lose neural activity and consciousness within minutes of stopping blood flow. Youngner and Insoo Hyun of Case Western Reserve University wrote in a comment on the study. If the results continue, they "could exacerbate the tension between efforts to save the lives of individuals and those to get organs to give to others." As the science of resuscitation As the brain progresses, some efforts to save or restore the brains of people may seem more and more reasonable – and some decisions to forgo such attempts to procure organs for transplantation may seem less obvious. "
The study raises new questions about what it really means to be "brain dead"
The meaning of brain death is controversial enough for ethicists, transplant surgeons, other doctors and first-aiders to wonder whether to abandon efforts to save someone's life, but rather to save his organs. Most of the organs to be transplanted come from people who have been declared brain dead. But if BrainEx is improved and effective on human brains, people who have been declared brain dead may be eligible for brain resuscitation, not organ donation.
When asked if United Network for Organ Sharing, the private group that manages organ donations in the United States, had comments to make on the study, a spokeswoman said "We do not do it, it's far from being a gift of organs."
The experts were not in agreement. The study "further specifies that the brain is actually dead under certain circumstances," said Dr. Kathleen Fenton, a bioethicist and pediatric cardiologist surgeon in Maryland. "It should enlighten the discussion around brain death, [since it] shows that some loss of life and cellular functions that we all thought were irreversible do not seem irreversible. It's important. "
In another comment, Nita Farahany, an ethicist at Duke University, and two co-authors said in another replica of the 1987 movie "The Princess Bride": "There is a big difference between most deaths and deaths. Most of the dead are slightly alive.
[ad_2]
Source link