In a recently published study in Nature, researchers have reported that circulation and cellular activity were restored in a pig’s brain for 4 hours after its death – a finding that not only raises ethical and legal questions about the nature of death and consciousness, but also challenges the long-held assumptions about the irreversible nature of the cessation of some brain functions after death.
The research team obtained the brain of a post-mortem pig from a meatpacking plant, where it was then isolated and circulated with a specially designed chemical solution. Many of the basic cellular functions that scientists once thought to cease seconds or minutes after oxygen and blood flow cease, were observed, according to the investigators.
“The intact brain of a large mammal retains a previously under-appreciated capacity for restoration of circulation and certain molecular and cellular activities multiple hours after circulatory arrest,” commented Nenad Sestan (Yale School of Medicine, CT, USA), senior author of the paper.
However, the researchers have stressed that the treated brain lacked any recognizable global electrical signals associated with normal brain function. “At no point did we observe the kind of organized electrical activity associated with perception, awareness, or consciousness. Clinically defined, this is not a living brain, but it is a cellularly active brain,” stated Zvonimir Vrselja (Yale School of Medicine).
In addition to this, the researchers reported that the small tissue samples they worked with routinely demonstrated signs of cellular viability, even when it was harvested multiple hours post mortem. Moreover, 4 hours after the pig’s death, they were able to connect the vasculature of the brain to circulate a uniquely formulated solution that they developed to preserve brain tissue (referred to as BrainEx).
The team found that neural integrity was preserved, and certain neuronal, glial and vascular cell functionality was restored.
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While the research has no immediate clinical application, the investigators anticipate that the platform may one day be able to help clinicians find ways to salvage brain function in stroke patients, or alternatively, test the efficacy of novel therapies targeting recovery after injury.
It remains unclear whether this approach can be applied to a recently deceased human brain, as the chemical solution used lacks many components natively found in human blood (e.g., immune system and other blood cells). This makes the experimental system significantly different from normal living conditions.
However, the researchers stressed that any future study involving human tissue or possible revival of global electrical activity in post-mortem animal tissue should be done under strict ethical oversight.
“Restoration of consciousness was never a goal of this research,” explained Stephen Latham (Yale University), co-author of the study. “The researchers were prepared to intervene with the use of anesthetics and temperature-reduction to stop organized global electrical activity if it were to emerge.”
“Everyone agreed in advance that experiments involving revived global activity couldn’t go forward without clear ethical standards and institutional oversight mechanisms,” Latham concluded.
Sources: Vrselja Z, Daniele SG, Silbereis J et al. Restoration of brain circulation and cellular functions hours post-mortemhttps://www.nature.com/articles/s41586-019-1099-1. Nature doi:10.1038/s41586-019-1099-1 (2019) (Epub ahead of print); https://news.yale.edu/2019/04/17/scientists-restore-some-functions-pigs-brain-hours-after-death