Scientists have momentarily restored a faint flaw of life to dying cells in the human eye.
A team of US researchers analyzed activity in mouse and human retinal cells as well as their ability to digest the way nerve cells lose weight due to a lack of oxygen.
Amazingly, with a few tweaks to the tissue''s environment, they were able to revive the cells'' ability to communicate hours later.
The postmortem retinas were observed to emit specific electrical signals, referred to as b-waves, when stimulated by light.
These waves are also seen in living retinas, and they indicate communication between all the layers of macular cells that enable us to see.
It''s the first time that deceased human donor eyes have ever responded to light in this manner, and it has some experts worried about the irreversible nature of death in the central nervous system.
"We were able to recognize photoreceptor cells in the human macula, which is the part of the retina responsible for our central vision and our ability to see fine detail and color," says biomedical scientist Fatima Abbas of the University of Utah.
"They responded to bright light, colored lights, and even severe dim flashes of light as a result of the surgery," said the scientist.
After death, it''s possible to save some organs in the human body for transplantation. However, the central nervous system as a whole has stopped responding far too quickly for any form of long-term recovery.
Despite the fact that not all types of neuron fail at the same rate, a variety of regions and different forms of cell have different survival mechanisms, making the whole brain-death issue a lot complicated.
Learning how select tissues in the nervous system cope with a loss of oxygen might imply that we may learn a little bit about repurposing lost brain functions.
Researchers have already had some success. In 2018, researchers at Yale University made headlines when they kept pig brains alive for as long as 36 hours after their deaths.
They were even able to resurgence a small response after a four-hour postmortem, although nothing was organized or global that could be measured with an electroencephalogram.
By stalling the rapid breakdown of mammalian neurons, using artificial blood, heaters, and pumps to restore circulation of oxygen and nutrients, these feats were achieved.
A similar technique appears to be possible in mice and humans eyes, which is the only extruding component of the nervous system.
After his death, researchers at the University of Utah and Scripps Research were able to initiate synchronous activity among neurons by restoring oxygenation and some nutrients to the organ donor eyes.
"We were able to make retinal cells talk to each other, the way they do in the living eye, to assist in human vision," says visual scientist Frans Vinberg of the University of Utah.
"Past studies have restored very limited electrical activity in organ donor eyes, but this has never been achieved in the macula, and never to the extent we have now demonstrated."
Initially, retinal cells continued to react to light for up to five hours following death. However, crucial inter-cellular b-wave signals quickly dropped off, apparently due to the loss of oxygen.
Even if retinal tissue is carefully protected from oxygen deprivation, the researchers were unable to completely restore robust b-waves.
Besides, the reintroduction of the retinal cells does not mean the donor eyeballs might''see''. Higher visual areas in the brain are required to increase full visual sensation and perception.
Despite this, some definitions of ''brain death'' require a loss of synchronous activity among neurons. If this definition is accepted, then the human retinas in the present study were not yet completely dead.
"Since the retina is a member of the CNS, our treatment of the b-wave in this study raises the question of whether brain death, as it is currently defined, is irreversible," the authors say.
If special neurons, known as photoreceptors, may be revived in some ways, then this indicates hope for future transplantations that may assist restore vision in people with eye disease.
That day, however, is still a long way away. Unlike previously mentioned cells and patches of a donor retina would need to somehow be seamlessly integrated into existing retinal circuits, which is a daunting challenge that scientists are already investigating.
In the meantime, donors and animal models will need to do so, and testing for b-waves might be beneficial to determine if a retinal graft is feasible or not.
"The scientific community can now study human perception in ways that are just not possible with laboratory animals," Vinberg said.
"We hope this will help organ donor organizations, organ donors, and eye banks by facilitating them to understand the exciting new possibilities this type of research offers."
The research was published in Nature.