In a feat with significant bioethical implications, a team of researchers has restored circulation and some cellular activity in the whole brains of pigs several hours after death.
The research team, led by neuroscientist Nenad Sestan of Yale School of Medicine, says that the goal is not to bring a dead creature back to life, but instead to create a more complete system for studying how the brain works. They also believe the system, once optimized, can be used to test potential drugs for diseases like stroke, in which parts of the brain die because of a lack of oxygen (Nature. 2019, DOI: 10.1038/s41586-019-1099-1).
“This could be a really powerful model to study one of the major obstacles for getting drugs and chemicals into the brain—penetrating the blood brain barrier,” says Yale neuroscientist Stefano Daniele, one of the main researchers on the project. He adds that pig brains are more akin to human brains in terms of complexity and composition compared with lab animals like mice. “Utilizing a more complex brain would, in fact, be more reliable and higher fidelity.”
The team used brains from pigs that had been slaughtered for food. After waiting four hours, which Sestan says was a precaution against working on something that might still be conscious, the team hooked up a perfusion system to the carotid artery, pumping what they called a “secret sauce” of oxygenated hemoglobin, glucose, cell-death inhibitors, protein destruction inhibitors, antibiotics, and neuroprotective compounds into the blood vessels of the isolated brain. In addition, they added lamotrigine, an epilepsy medication that quiets down overall neuronal activity, another step to possibly preclude consciousness.
After six hours of perfusion, the team observed that the brains could metabolize glucose and oxygen, a critical step in assessing viable cell activity. They used ultrasound to watch as the fluid moved through the vasculature of the brain, detecting hemoglobin in different areas. They added a blood pressure drug to the perfusion mix, and saw that blood vessels dilated in response. Immune cells in the brains responded to injected lipopolysaccharide, a highly inflammatory bacterial compound, and in experiments to test the electrical activity of cells, the team could detect electrical signals produced by sodium and potassium ions moving in and out of hippocampal neurons.
In control experiments, the team perfused a mixture of just salts and antibiotics into the brains, and found more profound degeneration and cell death than the ones given the full “secret sauce,” which the team calls BrainEx.
Ethicists have raised several concerns about the study, and its implications for reanimation, but Sestan says reanimation was “not the goal of the study.” He points out that at no time in their experiments did they see an electroencephalogram signal, a commonly accepted measure of the kind of global cell-to-cell communication associated with consciousness.
Neuroscientist Dennis Choi of Stony Brook University says that this pig system would be better suited for modeling cardiac arrest in drug development. Stroke, he says, affects only parts of the brain, but in cardiac arrest, oxygen deprivation damages the whole brain, which is more like what is happening with the pigs.
Neuroscientist Juan Pascual of the University of Texas Southwestern Medical Center thinks the method could be very useful for imaging studies that look at how one action affects different parts of the brain. But, for disease work, he agrees that stroke is a strong target.
He cites a recent World Health Organization report on the burden of brain disease. After heart disease, according to the report, stroke is a major cause of mortality all over the world.