“复苏”大脑| Nature Podcast

来源：Nature自然科研

又到了每周一次的 Nature Podcast 时间了！欢迎收听本周由Benjamin Thompson和 Shamini Bundell 带来的一周科学故事，本期播客片段讨论离体数小时的猪脑“复苏”。欢迎前往iTunes或你喜欢的其他播客平台下载完整版，随时随地收听一周科研新鲜事。

音频文本：

Host: Benjamin Thompson

First up in the show, we’re talking about neuroscience. For obvious reasons, whole brains are difficult things to work with in a lab, and most lab-based neuroscience is done on tissue samples or small cultures of brain cells. But this week in Nature, a paper presents a new way to study brains, by plugging them into a machine that partially restores their function. Reporter Nick Howe has been talking to the researchers involved to find out more. 

Interviewee: Nenad Sestan

The idea for this study came about from a very routine observation. We and other scientists have observed that viable cells can be harvested from post-mortem brains and cultured in a dish. This indicates that cells in the post-mortem brain still have the capacity to be revived. 

Interviewer: Nick Howe

This is Nenad Sestan, a professor of neuroscience at Yale School of Medicine. The idea he’s talking about is whether it’s possible to restore brains after death. When the heart stops beating, brains lose oxygen and begin to deteriorate rapidly. This deterioration was thought to be irreversible. 

Interviewee: Nenad Sestan

We were very surprised by this finding, and that’s why it took us five years before we submitted the paper. We just wanted to be sure that this is what we are seeing. 

Interviewer: Nick Howe

The team took brains from pigs that had been slaughtered for food production. Four hours after death, they hooked up the brains up to a machine called BrainEx. BrainEx pumped, or perfused, a blood-like substance into and out of the removed brains and simulated the function of the heart, lungs, kidneys and liver. The artificial blood had chemicals in it that the team hoped would encourage the recovery of the brains, such as compounds that prevent cell death. And indeed, by hooking up the brains to BrainEx, they were able to revive the cells and restore some functions for around six hours. 

Interviewee: Nenad Sestan

What we can show is that basically the brain – and that means the cells – is consuming oxygen and glucose, which are two major nutrients and it’s producing CO2 and other metabolites that are clear signs that cells are viable.

Interviewer: Nick Howe

What’s more, Nenad and his team showed that the brains retained some of their functions. They demonstrated inflammatory responses similar to living brains, their synapses were able to fire, and the brains responded to certain drugs. 

Interviewee: Nenad Sestan

And we show that basically the cells in our perfused brains have all the signs that are associated with normal functioning cells. 

Interviewer: Nick Howe

This is a striking result says Simone Di Giovanni, a professor of neuroscience at Imperial College London, who wasn’t associated with this study. 

Interviewee: Simone Di Giovanni

I think the extent to which they were able to preserve the survival of many cells into the brain and the extent to which they were able also to show that there was some function at the cellular level, also preserved for many hours. So, this was quite surprising and very interesting. 

Interviewer: Nick Howe

Having restored functions to cells, Nenad and his team believe that isolated brains could be a useful model system for answering neuroscience questions. Simone agrees. 

Interviewee: Simone Di Giovanni

This can be something that we could exploit in the future to understand cellular and molecular mechanisms of disease or physiology. 

Interviewer: Nick Howe

So, the brains could be useful models for testing drugs or answering neurological questions. They wouldn’t be able to answer every question though, as the brains were not fully functioning. But, this was by design. If at any point activity associated with consciousness or sensation was detected, Nenad and his team would have stopped the experiment immediately, on ethical grounds. The brains were not alive, but they weren’t exactly dead either. 

Interviewee: Simone Di Giovanni

At the cellular level, these brains are very close to being alive, but if we consider life of a brain as the expression of the functionality of the brain, then they are very, very far from being alive. 

Interviewer: Nick Howe

In other words, the isolated brains didn’t show the organised activity that we see in living brains – they would be unable to learn, remember or perceive the world. But the individual cells within them showed signs of being alive. Because these brains sit in an in-between zone, being neither alive nor exactly dead, they challenge our assumptions about death itself. Our current understanding is that death means irreversible loss of brain function. 

Interviewee: Nita Farahany

This new research study suggests that that may not be the case. 

Interviewer: Nick Howe

This is Nita Farahany, a professor of philosophy and law at Duke University. 

Interviewee: Nita Farahany

The irreversibility that we thought existed with the loss of brain function from oxygen deprivation may in fact at least partly be reversible. And if that’s the case, our existing definition of death, which is so important to things like being able to declare a human legally dead, so important for us to be able to have that person qualify for organ donation, for example, those things are now fundamentally challenged by the possibility of being able to reverse the damage from loss of oxygen to the brain. 

Interviewer: Nick Howe

Another consideration is that restoring function to a brain after death could lead to consciousness and sensation. Whilst in this study there was no EEG activity, which is a marker of consciousness, the study used neuronal activity blockers and anaesthetic. It’s possible that these prevented any form of consciousness arising. 

Interviewee: Nita Farahany

There’s still a gap between this study and achieving any kind of consciousness or any kind of sentience-like capabilities, but that doesn’t mean it’s impossible. It just means that there may be more work to do before it could get there. 

Interviewer: Nick Howe

This study raises many questions, both scientific and ethical. The study will need to be replicated and attempts made to understand whether consciousness could occur and if it did, how scientists and society should respond to that possibility. Despite the challenging ethical questions, Nita and her colleagues think it’s important that this research continues. 

Interviewee: Nita Farahany

We are enthusiastic about this research and think that it’s really important that this research be allowed to proceed. So, we’re excited about the possibilities that this offers, to offer insights into studying the brain, and we also recognise that this research team really is a model for trying to address the ethical questions that research raises, particularly when ethics hasn’t caught up with the science. 

Host: Benjamin Thompson

That was Nita Farahany from Duke University. She and group of other ethicists have written Comment pieces in this week’s Nature about this study, which you can find over at nature.com/opinion. You also heard Simone Di Giovanni from Imperial College London and Nenad Sestan from Yale School of Medicine. You can read Nenad’s paper over at nature.com.ⓝ

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