A paper published this week (April 18, 2019) in Nature reports on a < strong > system that restores brain circulation and some cellular functions hours after brain death in pigs. However, there is no evidence of whole-brain electrical activity associated with consciousness, cognition or other higher-order brain functions. The approach may provide a platform for studying the whole brain, but further tests are needed to explore wider applications.
The mammalian brain is extremely sensitive to a drop in oxygen supply; short-term blood flow interruptions can cause rapid depletion of oxygen and energy storage, which is believed to cause neuronal death and irreparable brain damage. Some studies have questioned whether this cascade of injuries is unavoidable for a short time after bloodstream interruption.
Named Sestan of Yale University Medical School and colleagues assume that even after several hours of death, specific cellular brain activity may be partially restored. To test this hypothesis, they developed a Brain < EM > Ex system to simulate pulsatile blood flow (perfusion) at normal body temperature (37 degrees Celsius). In this study, 32 pig brains from food processing plants were connected to Brain < EM > Ex system hours after death. The authors observed a decrease in cell death during the 6-hour perfusion period and found evidence that some cell functions, including synaptic activity, were restored. However, no evidence of whole-network activity or whole-brain function was found during the experiment.
These findings suggest that the brain has stronger cellular recovery than previously expected, and that the deterioration of cellular function after interruption of blood flow may be a slow rather than rapid process. Whether the Brain < EM > Ex system can restore all normal brain functions remains unknown. The authors clarify that this effect is not obvious in the current study, and further experiments are needed to prolong the perfusion time in order to explore wider applications.
This week Nature also published two related reviews discussing the implications of this study for the field. In one commentary, Stuart Youngner and Insoo Hyun suggested that the study might intensify the debate about human organ transplantation. “As the science of brain resuscitation advances, some efforts to save or restore the human brain may seem more and more reasonable — giving up such attempts and tending to acquire transplanted organs may seem less reasonable,” they wrote.
In another commentary, Nita Farahany and his colleagues pointed out that the possibilities opened by the study highlighted “the potential limitations of current regulations on research animals”. They called for guidelines to help researchers cope with the ethical dilemmas posed by the study, which “questioned long-standing assumptions about how to determine whether animals or humans are alive or not”.
Related papers: https://www.nature.com/articles/s41586-019-1090-x