A half- dead brain
Scientists restored pig brain function four hours after death
Andrey Ukrainsky, N+1
Scientists have created a system that connects the brain of large mammals to restore individual functions of the organ and preserves its structural integrity. A successful experiment that lasted six hours was conducted with pig brains four hours after death. The technology provides a previously inaccessible opportunity to study a number of brain functions on a whole isolated organ. Article by Vrselja et al. Restoration of brain circulation and cellular functions hours post-mortem is published in the journal Nature. The authors reported their experiments at a meeting of the ethics committee of the National Institutes of Health in April 2018, but the details were not disclosed at that time.
The brain of many mammals is highly sensitive to the lack of oxygen. After the cessation of circulation (perfusion) of blood within a few minutes, the process of cell death and damage to nerve fibers begins in it. This, as well as the formation of blood clots in small vessels, prevents the study of brain functions in ex vivo dynamics, on an isolated organ. Freezing and preservation allow only static research.
A number of observations call into question the inevitability of the death of nerve cells within minutes and even hours after the cessation of blood circulation and suggests that these limitations for research can potentially be circumvented. Thus, scientists have already managed to obtain samples of viable cells and tissues of both animals and humans, as well as to record electrophysiological activity long after death. It is known that the mitochondria of the human cerebral cortex can function 10 hours after death. Also, after an hour of complete ischemia, the monkeys were able to restore electrical activity and the work of neurons. A case of complete restoration of human brain functions in conditions of low temperature after prolonged cardiac arrest is described. And finally, recent data show that removing a blood clot within 16 hours increases the chances of a good outcome of an ischemic stroke.
A group of scientists led by Nenad Sestan from Yale University has developed a high-tech system to protect the isolated brain from rapid destruction, as well as a solution to nourish the brain and a special surgical procedure to isolate it. Researchers have shown that certain brain functions can persist for a long time after death and there is at least a partial possibility of their recovery.
The system, which the authors called BrainEx (BEx), can support the circulation of a special perfusion solution in the brain, which is similar in parameters to the physiological one. With the help of the device, perfusion can be performed with a pressure of 20-140 millimeters of mercury, a frequency of 40-180 beats per minute and a temperature of 3-42 degrees Celsius. The system is equipped with mechanisms for enriching the solution with oxygen and purifying it from toxins. The brain is placed in a spherical chamber in which a relative humidity of 95 percent is maintained so that the organ does not dry out and does not "bathe in liquid". Scientists have created a solution for perfusion based on hemoglobin, without cellular elements. To facilitate research, echogenic substances were added to it. The surgical procedure that the authors developed was to isolate the brain and its vessels at a level above the medulla oblongata.
Diagram of the BrainEx system device. Drawings from an article in Nature.
For the experiments, the scientists used about three hundred pigs aged six to eight months, which they received from meat processing plants. After setting up the technology, 32 pig brains were used in the study. The scientists identified four experimental groups: perfusion with control fluid, perfusion with BEx fluid, without perfusion, and brains examined an hour after death. The brains were connected to the BEx system four hours after death, the observation time was six hours, respectively, the brain lived 10 hours after death.
Examining the pig's brain before connecting to the system, scientists found that specific cellular functions were preserved: tissues reacted to pharmacological and immunological tests, spontaneous synapse activity and active metabolism were noted in the absence of brain activity. Based on this, the scientists noted that the ability to restore the functions of the brain of large mammals under certain conditions is underestimated.
In the brains connected to the system with BEx perfusion solution, the anatomical and cellular structure was preserved, the vessels provided circulation of the nutrient solution, the function of the neuroglia was restored, tissue metabolism and the electrical activity of neurons were maintained. Scientists found that the preservation of cells and fibers in different parts of the brain differed. Thus, in the hippocampal CA1 field, especially sensitive to the lack of oxygen, signs of vacuolization, membrane damage and cytoplasmic lysis were observed even when examined an hour after death. In the brain tissues through which the control solution was passed, rapid destruction was observed.
Immunofluorescence staining of neurons (green), astrocytes (red) and cell nuclei (blue) in the hippocampal CA3 field in the brain that remained without perfusion (left) and received perfusion using BrainEx technology. In the brain that did not receive the perfusion solution, astrocytes and neurons were destroyed.
Scientists point out that with the help of intracranial electroencephalography, it was not possible to detect global electrical activity in the brain, which indicates a lack of consciousness and perception.
"This line of research could lead to the emergence of a new method of post-mortem examination of the brain. The new technology opens up opportunities to study the complex interactions of cells and networks of neurons that are lost in other ways of preserving tissues. It could also stimulate research on the development of methods for restoring the brain after the cessation of blood supply to the brain, for example, in myocardial infarction," she said Andrea Beckel-Mitchener, head of the Brain Research project by Promoting Innovative Neurotechnologies (BRAIN Initiative) of the US National Institutes of Health in a press release of the organization.
In their conclusions, the scientists write that their technology can potentially help build bridges between clinical research and theoretical neurology. They also note that new opportunities raise new ethical questions: clear standards are required that will prevent the possibility of restoring consciousness and other brain functions, the maintenance of which may inadvertently cause suffering.
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