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Frozen brain region resumes electrical activity after thawing

Researchers at Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and Uniklinikum Erlangen have succeeded in preserving brain tissues by deep freezing.After melting, nerve cells start exchanging electrical signals again.The method can be used, for example, to preserve brain tissue removed during surgery so that it can be studied later.This can also facilitate drug development.The results of the research were published in the journal Proceedings of the National Academy of Sciences.

The Siberian salamander is an amazing animal.According to some reports, it can survive in temperatures of 50 degrees below zero in hibernation and for decades in permafrost.As soon as the outside temperature rises, the salamander returns to normal activity.

They do this in the liver: The liver can produce the alcohol glycerin, which acts as a kind of antifreeze in the animal's body.This reduces the freezing point and helps protect cells and tissues from damage during freezing and thawing.

"Crystal formation is the reason why extreme cold is often harmful to living beings," explains Alexander German from the Department of Molecular Neurology (head: Prof. Dr. Jürgen Winkler) at Uniklinikum Erlangen.

The tissue fluid solidifies into a glass-like state

Human embryos can also be preserved for several years by deep freezing.To do this, the cells are treated with chemicals that prevent the formation of ice crystals, such as glycerol."Tissues also become stronger when cooled below -130 degrees," says German."However, water moves between and within cells in a glass-like state."Arranged as - not regularly crystalline

This process is called "vitrification".However, it has not been possible to freeze nerve cells or whole parts of the brain in such a way that they start working again after thawing.One of the reasons for this is that the "antifreezes" used are toxic to the affected cells.In addition, brain tissue is very complex: it is made up of hundreds of millions of nerve cells that are connected to each other by many tiny particles called synapses.Neurons exchange information through these connections.

Optimize preservatives and freezing processes

Previous vitrification methods fragment this highly complex network and also damage synapses.Even if individual cells survive, the frozen structure is no longer functional."However, we have optimized the composition of the preservatives and the cooling process so that the nerve tissue remains intact," emphasizes German.

The team tested the success of their method on certain parts of the brain.The researchers used this method to cool the hippocampus, a part of the rat brain that plays a key role in storing memory content, to -130 degrees Celsius.

"We were able to use electron microscopy images to prove that the nanostructure of the tissue was not altered by the freezing process," says German."After the warm-up, electrical signals were spontaneously generated again in the hippocampus, which normally propagate through neural networks."

But the neurons didn't just start exchanging information again. Dr. Fang Zheng, brain researcher at FAU's Department of Physiology and Pathophysiology, showed that so-called long-term potentiation can also be triggered in the nerve cells' synapses.This refers to a central cellular process that ensures the strengthening of frequently used synapses, allowing them to transmit information particularly well.

"This machine is very important for the processes of learning and retaining new information," says German.

Can cures for incurable diseases be fixed in the future?

The method developed in the study seems to make it possible to keep brain tissue in a working state for a long time and then examine it again for work.For example, in some people with epilepsy, nerve cells are removed during surgery.The sample can be used for drug testing many years later.Cryopreservation of pathologically altered tissue is also important for research on neurodegenerative diseases.

Alexander German also hopes that in the future it will be possible to put all living organisms into a kind of artificial hibernation and revive after a long time."This could be an option for space travel, for example, or for people with incurable diseases," he said."Because later, there may be a treatment option that can help the affected person."

Alexander German et al., Functional Recovery of Aged Mouse Hippocampus after Cryopreservation by Vitrification, Proceedings of the National Academy of Sciences (2026).DOI: 10.1073/pnas.2516848123.

Journal information: Proceedings of the National Academy of Sciences