Scientists just brought light-sensing cells in human eyes back to life

Death is perhaps the strangest subject for human beings to discuss. Even thinking about it is uncomfortable for some people.

To unravel the mystery behind it, researchers around the world are conducting scientific studies on death and getting startling results, like when researchers captured brainwaves during an individual’s death and found a semblance of high cognitive activities.

And now a team of American scientists may have found a way to rekindle a glow of activity in human eyes after death. According to a study published yesterday (May 11, 2022) in the journal Nature, the team managed to rekindle the connections between light-sensitive neurons in the eyes of organ donors.

Overcome oxygen deprivation

The research team measured retinal cell activity in mice and humans shortly after death. Early experiments indicated that oxygen deprivation is the critical factor leading to loss of photoreceptor communication with other retinal cells.

To get their results, Anne Hanneken, an associate professor at Scripps Research, obtained the eyes of an organ donor within 20 minutes of death. On the other hand, Frans Vinberg, an assistant professor at the John A. Moran Eye Center, has developed a transport unit to restore oxygenation and other nutrients to the eyes of organ donors. Vinberg also built a device that stimulates the retina and measures its electrical activity.

Using these devices, the team restored a specific electrical signal seen in living eyes, also known as the ‘b wave’ in post-mortem retinas. After being triggered by light, post-mortem retinas emitted peculiar b waves.

“We were able to awaken 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,” said Fatima Abbas, biomedical scientist and lead author of the study. study.

Questioning the irreversible character of death

Reviving photoreceptors also offers hope for future transplants that could help restore vision in people with eye disease. However, cells and patches transplanted from a donor retina should be seamlessly integrated into existing retinal circuitry. This is already a difficult problem that scientists are working on.

The study provides the first example of donated eyes responding to light. It therefore raises questions about the irreversibility of death, partly linked to the permanent loss of neuronal activity.

Death is defined as the irreversible arrest of circulatory, respiratory or cerebral activity. Many peripheral human organs can be transplanted from deceased donors using protocols to optimize viability. However, central nervous system tissues rapidly lose viability following cessation of circulation1,2, hampering their potential for transplantation. The time course and mechanisms causing neuronal death and reactivation potential remain poorly defined. Here, using the retina as a model of the central nervous system, we systematically examine the kinetics of neuronal death and rebirth. We demonstrate the rapid decline of neuronal signaling and identify conditions for reviving in vivo-like synchronous trans-synaptic transmission in postmortem mouse and human retina. We measure light-evoked responses in human macular photoreceptors in removed eyes up to 5 h after death and identify modifiable factors that lead to reversible and irreversible loss of light signaling after death. Finally, we quantify the rate-limiting silencing reaction of phototransduction, a model G-protein signaling cascade, in human and macaque peripheral and macular retina. Our approach will have broad applications and impact by enabling transformative studies in the human central nervous system, raising questions about the irreversibility of neuronal cell death, and offering new avenues for visual rehabilitation.

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