Floating in a warm, nutritious bath, the slices of mouse brain buzzed with electrical activity. Researchers gave them a number of zaps, and parts of the hippocampus strengthened their wiring.
This sort of experiment is an especially common method to decipher how the brain works. The slices, not a lot. Preserved in a deep freeze for roughly every week, they restarted some basic processes after being thawed. Neurons lit up, boosted their metabolism, and adjusted connections in the identical way our brains do when forming recent memories and recalling old ones.
“While the brain is taken into account exceptionally sensitive, we show that the hippocampus can resume electrophysiological activity after being rendered completely immobile in a cryogenic glass,” wrote University of Erlangen‐Nuremberg scientists in a paper describing the work.
In traditional freezing techniques, ice crystals shred delicate neurons and the connections between them. There could be no probability of recovering memories stored inside. The brand new study used a way called vitrification, which rapidly cools tissue before crystals can form. An improved thawing process protected cells from toxic chemicals of their cryogenic bath.
Each pre-sliced and whole mouse brains recovered after warming, although some neural activity was barely off-kilter. To be clear, brains can’t be completely revived like in the films. However the approach pushes the known frontier of what brain tissue can tolerate, wrote the team.
Ice, Ice Baby
Suspended animation is considered one of science fiction’s oldest tropes. Whether characters are traveling between the celebs or awaiting future cures for untreatable diseases, cryogenics is the last word pause button they’ll use to speedrun a long time, if not centuries and beyond.
The concept was popularized within the Nineteen Sixties, when Robert Ettinger “the daddy of cryonics” argued that individuals could possibly be frozen and revived in the long run, with their memories, cognition, and physical capabilities intact. He took the perimeter idea and turned it right into a mainstream dream.
But cryosleep has earlier roots. Within the late 1800s, scientists realized that certain cells and easy living creatures could survive freezing, suggesting it’s possible to temporarily suspend life.
Liquid nitrogen and other chemical preservatives are actually used every day in labs to freeze individual cells—including brain cells—at extremely low temperatures. Many don’t survive, but people who do regain normal function upon thawing. Scientists use the technology to preserve various kinds of neurons to check theories and share with other labs.
Cryopreserving brain slices or whole brains is much tougher. These contain the fragile neural branches brain cells use to speak, that are easily destroyed throughout the freeze-thaw cycle. Ice is the predominant offender. Even with protective chemicals, liquids in cells rapidly solidify into sharp crystals that jab cells in and out like a thousand knives.
Still, scientists have kept frozen human fetal tissue intact, and cryopreserved rat cells have developed functional networks once thawed. One other effort kept a rodent’s heart structurally intact with a magnetic method that step by step brings the organ back to biological temperature. Techniques to preserve livers and kidneys can keep them in stasis for as much as 100 days, and the organs are still healthy enough for transplantation after warming up.
“Progress in cryopreservation of rodent organs has moved the theme of suspending technologies closer to plausibility,” wrote the team.
Structure determines function for every organ. However the brain presents unique challenges. Lots of of molecules zoom around neurons to accumulate or whittle down synapses. Others that dot the surfaces of those cells tweak electrical charges to strengthen or weaken activity. Even without tearing up the cell itself, damage to those processes renders neurons incapable of forming or retrieving memories.
Ice is just a part of the revival equation. As liquids freeze, they alter the pressure of the encircling environment, causing cells to lose water and shrink. This could collapse internal structures and wreck synaptic connections. Cryoprotectants, equivalent to a sugary liquid called glycerol, limit the damage but are toxic at high doses.
Looking Glass
The authors of the brand new study turned to vitrification. Here, rapid cooling with cryoprotectants limits damage by freezing cells in a disorganized, glass-like state without forming ice crystals.
They first tested cryoprotectant recipes on brain slices that included the hippocampus, a brain region related to the formation of memories. After soaking the slices within the chemical cocktails, the team bathed them in liquid nitrogen at a bone-chilling -196 degrees Celsius (−320.8 degrees Fahrenheit), which immediately froze the tissues. They then moved the slices to a −150 degrees Celsius (−238 degrees Fahrenheit) freezer and kept them there for as much as every week.
The team could visually see whether each cocktail worked, they wrote. Vitrified slices had a glossy, transparent look; people who failed were dull and opaque.
After slow thawing, the slices sprang back to life.
The cells’ mitochondria ramped up energy production. Neuron membranes and synapses remained intact. And though there have been some differences in comparison with fresh brain slices, the reawakened hippocampal cells mostly retained their usual patterns. Given a number of electrical zaps, they strengthened their connections, a mechanism underlying learning and memory.
The team also tried the tactic on whole mouse brains. They’d to repeatedly tweak the recipe to attenuate toxicity from the cryoprotectants and ward off severe brain dehydration. But once thawed, slices from the entire preserved brains had intact neural wiring, including complex circuits within the hippocampus. Some brain cells languished and were harder to activate, whereas others perked right up.
It seems some sorts of neurons are more tolerant to vitrification than others, wrote the team.
Because they recorded activity in brain slices, it’s unattainable to say whether the method would restore memory and learning. And the slices naturally deteriorated after 10 to fifteen hours, making it hard to say much about longer timescales. To get around this, they might test the tactic on mini brains, or brain organoids, which higher mimic whole brains and may be kept alive for years in culture.
The team is now expanding their work to incorporate human brain slices and preservation of other organs, equivalent to the guts. It’ll take loads of trial and error. Human organs are far larger and will easily crack from mechanical stress throughout the cryopreservation process.
However the study shows “the brain is remarkably robust…to near-complete shutdown” right into a glass-like state. “This reinforces the tenet of brain function being an emergent property of brain structure, and hints on the potential of life-suspending technologies,” wrote the team.