Animated retina
In the retina taken from a dead donor, it was possible to stimulate the activity characteristic of living eyes
Death is often defined as the irreversible cessation of blood circulation, respiration, or brain activity. However, when a mammal (for example, a human) dies, many of its organs and tissues can still be transplanted into a living organism and continue to function. To preserve their viability while they are out of the body, it is necessary to apply certain protocols, but in general it is possible and practiced. However, today it is not possible to do this with all organs. The tissues of the central nervous system quickly lose their viability, which limits the possibility of their transplantation. The mechanisms that cause the rapid death of neurons remain insufficiently studied. To shed a little more light on the mechanisms of nerve cell death, a group of American researchers began measuring the activity of mouse and human retinal cells shortly after their death. Surprisingly, in the end, by changing something in the environment in which the studied tissues were placed, they were able to restore the ability of the macular cells of the retina to communicate with each other a few hours after the death of the organism.
The macula on the fundus image.
Using the retina of human eyes removed five hours after the donor's death as a model of the central nervous system, the researchers made a number of discoveries that, as they write, "will allow for revolutionary studies of the human central nervous system, raise questions about the irreversibility of neuronal cell death and open up new opportunities for restoring vision."
"Until now, it has not been possible to force cells in all the different layers of the central zone of the retina to interact with each other in the way that it usually happens in a living retina," explained the co—author of the study. Anne Hanneken, ophthalmologist and researcher at the Scripps Research Institute in San Diego.
The reason, as the authors of the work understood, was oxygen starvation. Therefore, they set out to find a way to overcome the damage caused to the retina by lack of oxygen. Frans Vinberg from the Moran Eye Center, co-author of the study, has developed a special device capable of restoring oxygen saturation and other nutrients to the eyes removed from donors posthumously. This was not the only invention that Vinberg brought to the experiment. He also came up with a device capable of stimulating the retina to produce electrical activity, as well as allowing this activity to be measured. Thanks to this technique, the team was able to overcome another barrier by recording the first-ever "b-wave" signal from the central area of the retina of human eyes posthumously removed from a donor.
In living eyes, b-waves are a type of electrical signals associated with the health of the inner layers of the retina, so it is really important to be able to stimulate them in "postmortem" eyes. The recording of b-waves in the latter means that the layers of the macula have interacted with each other again — just as it happens when we are alive and use vision.
"We were able to get the retinal cells to communicate with each other, as it happens in a living eye ... — explained Vinberg. "Previous studies have restored very limited electrical activity in the eyes of organ donors, but this has never been achieved in the macula and never to the extent that we have now demonstrated."
Perhaps this result is not particularly impressive — after all, the yellow spot is only about five millimeters in diameter — but it is of great importance. In its current form, death is a condition partially determined by the death of neurons, which until now was considered irreversible. If neurons can really be restored to the quality of living ones, perhaps this will force us to reconsider once again the question of what is considered "dead". Over time, this may allow doctors to resuscitate patients in conditions that today force them to admit defeat. And, in any case, it will certainly expand the possibilities of nerve tissue transplantation and treatment of eye diseases.
Article by Abbas et al. The Revival of light signaling in the postmortem mouse and human retina is published in the journal Nature.
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